A GENETEC STUDY OF CHARACTERS OF THE CUCUMBER, CUCUMIS SATIVUS L; IMPORTANT TO MECHAHECAL HARVESTING Thai: for the Degree of Ph. D. MICHIGAN STATE UNIVEESITY Milo Burnham 1965 THESIS LIBRARY Michigan State University This is to certify that the thesis entitled A Genetic Study of Characters of the Cucumber, Cucumis Sativus L. , Important to Mechanical Harvesting presented by Milo Burnharn has been accepted towards fulfillment of the requirements for _Bh..D.._ degree in _Honicn1t.ure 55%“; ’ . Major professor Date May 18. 1965 0-169 \\‘\ (flu ‘ cJCJ J It. . . ' a: %k/ E % ABSTRACT A GENETIC STUDY OF CHARACTERS OF THE CUCUMBER, CUCUMIS SATIVUS L., IMPORTANT CHANICAL HARVESTING by Milo Burnham Four characters of importance to successful mechanical harvesting of cucumbers were studied. The characters of reduced lateral branching, sex reversal, concentrated fruit set and ease of separation of the fruit from the stem are considered important to the success of multiple-pick mechanical harvesting. Concen- trated fruit set and ease of separation of the Fruit from the stem are characters considered important to the success of once-over mechanical harvesting. Genetic control of lateral branching was studied through a program of inbreeding and selection of a reduced branching inbred in an attempt to establish a nonebranching line. The F6Sib] generation contained a high percentage of non-branching plants, and with the ensuing five generations of self-pollination the mean percent of non-branching decreased. It appears that in the plant material studied a polygenic system, in which a threshold number of heterozygous loci interact with the environment, conditions the non-branching trait. That the Milo Burnham environment has an important influence in the expression of non-branching is supported by observations of the same generation material in different years. The sib-pollination of two sister F6 plants is viewed as having given rise to a high percentage of a heterozygous genotype or group of closely related genotypes conditioning the non-branching trait. There is little hope of obtaining a genetic line that consistently produces no, branches at all from the plant material investigated. Sex reversal was also studied through a program of inbreeding and selection in an attempt to genetically fix the character. Five generations of self-pollination of an F7Sib] inbred failed to establish a line that contained l00 percent sex reversal plants. Instead, an almost constant segregation for 50 percent sex reversal plants was observed. The sex reversal material is homozygous for the major genes controlling sex eXpression in cucumbers as proposed by Shifriss (l), but it is necessary to hypothesize incomplete dominance for the accelerator (Acr) gene and some minor polygenic segregation which interacting with the environment may serve to explain the variation pattern observed. On the basis of experience with the material included in these studies, it now seems difficult if not impossible to combine non-branching and sex reversal in a single true Milo Burnham breeding line that could be utilized as a solution to the problems of cucumber vine entanglement and center row fruit encountered with multiple-pick mechanical harvesting. In a cross of MSU 7l3-S x Rhensk Drue it was established that the determinate growth habit of Rhensk Drue is dominant, and that Rhensk Drue is potent in transmitting the ability to develop several fruit at one time. The F] is predominantly female in sex expression and has a number of pistillate blossoms open for pollination at one time. Clusters of pistillate blossoms of which more than one may devel0p simul- taneously into a fruit, while occurring on Rhensk Drue, went unrecorded on the F]. The fruitfulness of the F] lies in its ability to develop fruit at several sequential nodes simultaneously. F2 segregates have been selected for further inbreeding while attempting to maintain the Rhensk Drue fruitfulness and growth habit and improve the fruit size. The force required to pull the stem from the cucumber fruit was studied with Ohio MR-l7 serving as the hard-to-pick variety, Wisconsin SMR-l2 the easy-to-pick variety and Wisconsin SMR-lS as a variety with an intermediate picking force. Picking force and area of stem attachment generally showed the highest degree of linear relationship with fruit length, and fruit length was therefore chosen as the index of fruit size. Ohio Milo Burnham MR-l7 and Wisconsin SMR-IS required a higher picking force than Wisconsin SMR-l2. The position of the fruit in the picking force instrument and date of picking influenced picking force. The order of increasing area of stem attachment was determined as Wisconsin SMR-lZ, Wisconsin SMR-lS, Ohio MR-l7. This relationship was generally true for the harvest season. Fruit harvested late in the season had larger areas of stem attachment than those harvested early in the season. The varietal and date of harvest relationships established for picking force closely followed those for area of stem attachment, and it is preposed that the force required to separate the cucumber stem and fruit is initially dependent upon the stem attachment area. 1Shifriss, O. l96l. Sex control in cucumbers. Jour. Hered. 52:5-l2. A GENETIC STUDY OF CHARACTERS OF THE CUCUMBER, CUCUMIS SATIVUS L., IMPORTANT TO MECHANICAL HARVESTING By Milo Burnham A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture I965 ACKNOWLEDGMENTS Sincerest thanks are extended to the members of my advisory committee, Drs. C.E. Peterson, D. Markarian, M. W. Adams and A. F. Yanders. Drs; E. H. Everson and N. R. Thompson are thanked for replacing Dr. M. W. Adams during his absence in the terminal phase of my program. The H. J. Heinz Company, for their assistance in obtaining the picking force instrument, and the Urschel Engineering Company, for their construction of the instrument, are also thanked. Of the many pe0ple with whom I have been associated here at Michigan State University, I wish to single out Dr. and Mrs. D. Markarian who offered counsel and moral support. Sonja Linda Carlson, my fiancee, not only assisted with the initial field research but served as a continuing inspiration for the completion of this thesis. To these people, I am sincerely grateful. TABLE OF CONTENTS INTRODUCTION ............................................. REVIEW OF LITERATURE ..................................... Labor Situation ..................................... Mechanical Cucumber Harvesters ....................... Growth Habit ........................................ Sex Expression ...................................... Concentration of Fruit Set ........................... Ease of Separation of Fruit from the Stem ........... GENERAL MATERIALS AND METHODS ............................. Cultural Practices ................................... Field ............................................. Greenhouse ........................................ Statistical Methods .................................. EXPERIMENTAL .............................................. LATERAL BRANCHING STUDY .............................. Materials and Methods ............................ Results and Discussion ........................... SEX REVERSAL STUDY ................................... Materials and Methods ............................ Results and Discussion ........................... CONCENTRATED FRUIT SET ............................... Materials and Methods ............................ Results and Discussion ........................... EASE OF SEPARATION OF THE FRUIT FROM THE STEM ........ Materials and Methods ............................ Results and Discussion ........................... SUMMARY ................................................... REFERENCES CITED .......................................... TABLE I0. LIST OF TABLES Mean number of lateral branches per plant, percent non-branching plants and days in the field prior to data recording for the S], 52 and 5% generations of the F6Sib] reduced branc Mean number of lateral branches per plant, percent non-branching plants and days in the field prior to data recording for the S], 82, S ang 53 generations of the F6Sib] reduced branching In re , Mean number of lateral branches per plant, percent non-branching plants and days in the field prior to data recording for the F6Sib], S], 52, S , S 'and S generations of the F6Sib] reduced brancgi Pbannumber of lateral branches per plant, percent non-branching plants and days in the field prior to data recording for the S] and 52 generations of the F7SibA sex reversal inbred, I962, I963, and I96 Mean node of sex reversal and percent plants expressing the character, I962 ..................... Mean node of sex reversal and percent plants expressing the character, I963 ..................... Mean node of sex reversal and percent plants expressing the character, l96h ..................... Mean percent over I962, I963 and l96A of plants of F7SiblS] progenies exhibiting sex reversal and mean node of reversal .......................... Mean percent of plants over four F7SibIS] progenies—exhibiting sex reversal and mean node of reversal ................................... IMean percent of plants of F Sib S progenies exhibiting sex reversal and mean node of reversal, I963 ..................................... ing inbred, I962 ............................. I963 ....................................... ng inbred, l96h .............. Page 30 3] 32 33 A3 AA #5 97 A7 A8 LIST OF TABLES - Continued TABLE II. I2. l3. lh. l5. l6. l7. l8. I9. 20. 2l. Mean percent of plants of F7Sib184 progenies exhibiting sex reversal and mean node of reversal, l96A ..................................... Total degrees of minimum daily temperature below temperatures indicated for the period June l6 to June 30 ................................. Mean number of fruit per plant ..................... Mean number of lateral branches per plant .......... Degree of linear relationship between fruit weight, length and diameter for the varieties Wisconsin SMR-IS, Ohio MR-l7 and Wisconsin SMR-IZ, I96h ....................................... Degree of linear relationship of picking force with fruit weight, length and diameter for the varieties Wisconsin SMR-IS, Ohio MR-l7 and Wisconsin SMR-l2, I964 ............................. Comparisons of dates of picking, varieties and stem positions for homogeneity of re ression of picking force on fruit length, l9 h ............. Degree of linear relationship of area of stem attachment with fruit weight, length and diameter for the varieties Wisconsin SMR-IS, Ohio MR-l7 and Wisconsin SMR-IZ, I964 .............. Comparisons of mean areas of stem attachment for the varieties Wisconsin SMR-IS, Ohio MR-l7 and Wisconsin SMR-l2 for fruit of equal ranges of length on three dates ........................... Influence of date of harvest on mean areas of stem attachment for fruit of equal length ranges of the varieties Wisconsin SMR-IS, Ohio MR-l7 and Wisconsin SMR-l2, I964 .............. Relationship of picking force to area of stem attachment ......................................... Page '48 SI 57 57 68 69 72 75 77 78 80 LIST OF FIGURES FIGURE PAGE I. Picking force instrument built by the Urschel Engineering Company; designed after the Heinz Picking Force Machine for Cucumbers .......... 62 2. Regression of area of stem attachment on fruit length for Wisconsin SMR-IS, July 2h, l96h ............................................... 82 3. Regression of area of stem attachment on fruit length for Ohio MR-l7, July 24, l96h ......... 84 A. Regression of area of stem attachment on fruit length for Wisconsin SMR-IZ, July 2h, I964 ...................................... 86 INTRODUCTION Mechanical harvesting of cucumbers has been of increasing importance in recent years because of the rising costs of production, mostly harvest labor, and the increasing difficulty in obtaining seasonal labor. In past years Michigan has employed large numbers of Mexican farm laborers with the majority being used to pick processing cucumbers. This supply of labor was eliminated on December 3i, I96h with the termin- ation of Public Law 78 under which Mexican Nationals were allowed to enter the United States. Because of this, attention has been more keenly focused on the deveIOpment of mechanical harvesting equipment and adapted varieties. Two approaches to mechanical harvesting of cucumbers are currently being investigated, that of multiple-pick and once-over or destructive harvesting. While emphasis is presently on once-over harvesting, multiple-pick harvesting is still of considerable interest, and work is continuing on further refinement of the harvester. There are a number of problems that must be solved before either method of mechanical harvesting can be successful. Several of these problems are approachable by the plant breeder, and four of them are considered in the present study, they are: 3. 4. Lateral branching Center row fruit Concentrated fruit set Ease of separation of fruit from the stem This study was initiated before emphasis on mechanical harvesting of cucumbers shifted from the principle of multiple- pick to once-over harvesting. Therefore, while problems I thru h are important to multiple-pick harvesting, only 3 and h are important to once-over harvesting. REVIEW OF LITERATURE Labor Situation Newspapers and farm magazines for over a year have carried articles and editorials concerning the farm labor situation in the United States. This is due to the December 3], I963 termination, after a one year extension, of the Migrant Labor Agreement of I95l between the governments of the United States and Mexico. This agreement, entered into under the provisions of Public Law 78, provided for the recruitmentémulimportation of Mexican farm laborers by the Secretary of Labor of the United States- One major effect of the Migrant Labor Agreement was to reduce the number of Mexicans entering the United States illegally. In I953, the number of arrested illegal entries reached 803,6I8 while in I959 this number was reduced to 3l,l06 (22). The figures for contracted laborers during the same period were 20l,380 in I953, about h40,000 in I959 and has been decreasing each year since to l96h when only about 250,000 were imported (9, 22). Thus, the United States' agricultural labor force faces the possibility of being one- half million hands shorter during the I965 harvest season than it was during the l96h season. Probably the largest single reason for the termination of P.L. 78 is found in Section 503 of the law itself; stating that foreign labor may beimported only if sufficient domestic help is not available (I). The United States Department of Labor feels that sufficient domestic help is now available in the form of unemployed and under employed peOple, and that a domestic farm labor force can be developed with the abolishment of foreign labor. They propose this can be accomplished through improved wages, better housing, improved transpor- tation and better working conditions (A2). At present, all indications are that it will be difficult to raise a domestic labor force to replace the braceros. In southern Florida, hand bills, television, radio and newspaper advertisements failed to raise a critically needed labor force in early l96A (3). In California, attempts to recruit satisfactory help for tomato picking have generally failed, and in a recent report by the University of California on California Agricultural Labor Requirements and Adjustments the investigators say state growers can place little reliance on vacationing teenagers, out-of-state farm workers or unemployed non-farm workers (A, ll). Approximately IA,000 Mexican laborers were employed in Michigan in I963. The majority of these were engaged in picking cucumbers for the Pickle Industry, an industry in which Michigan has ranked first in the nation in acreage and production for many years. The value of the I963 production of processing cucumbers in Michigan has been estimated at 7,329,000 dollars (23). This was the second highest in eight years, although acreage has shown a fairly consistent decline. There has always been a problem in securing adequate pickle harvest labor in Michigan, due to low wages resulting from an unstable production. Until I958, pickers were paid on a crop share basis, which most often resulted in the pickers receiving 50 percent of the cash value of the crop. In I958, the WYRF (Worker Yield Return Formula) was intro- duced as a means for raising the wages of pickers in low yielding fields, and is reported to have resulted in a l0,000 acre reduction the first year after introduction (39). Under this system, pickers received as high as 70 percent of the crOp cash value. In I962, a one dollar per hour minimum wage went into effect in Michigan resulting in some pickers receiving as much as 75 percent of the value of the Crop. Mechanical Cucumber Harvesters The most likely solution to the labor situation and the large volume of material required by vegetable processing operations is mechanical harvesting. DeveIOpment of mechanical harvesting for some vegetable cr0ps has not kept pace with other advances which have resulted in high yields, and many vegetables are therefore still hand harvested. Causes for this slow advancement of mechanical harvesting listed by Holmes (IA) are: l. Vegetables must be handled much more carefully than other crOp products to prevent damage to the product. 2. Vegetable crops generally do not mature uniformly nor at one time. 3. The potential number of mechanical harvesting machines needed has not been large enough to interest many manufacturers. A. Designs of successful vegetable harvesters have not been developed. There have been several attempts to develop mechanical harvesting aids and mechanical harvesters In Michigan and other pickling cucumber producing states. The harvesting aids developed vary from a two-man, single-row, self- propelled machine to one resembling an airplane covering several rows with six men per wing and a fruit sacking operation in the fuselage. The men either sit or lie in a prone position pulling the cucumbers from the vines as the machine passes over the rows. While these aids were designed to reduce the physical effort involved in picking, Holmes (IA) has reported them unpOpuIar with the pickers because of the body position required. Boyette (7) reported little differencein the total number of pounds per acre harvested by the two-man machine and by hand, but machine harvesting took 23 fewer hours and cost $I7.25 less per acre than hand harvesting. Hall and MacGillivray (l0) reported that the harvesting aid carrying l2 men enabled picking 27A pounds per hour where only 80 pounds were picked by the conventional hand method. The first investigations of mechanical cucumber harvesters at Michigan State University began in I957 when four multiple harvest machines were evaluated by Stout and Ries (37) for their efficiency and means of picking. They were either one-way machines (requiring vine training to one side of the row) or two-way machines (not requiring I looked the vine training). The Chisholm-Ryder machine most promising of all those evaluated, and gave a picking efficiency (value of fruit machine harvested/total value of the harvest including hand gleaning) in I958 of 25.A to lLloyd Gilbert, Ravenna, Michigan, inventor of the Chisholm-Ryder machine (Patent No. 2,829,A8A). A3.6 percent. A late I958 picking with a slightly modified machine gave an efficiency value of 79 percent. An important problem encountered with all the machines tested, in addition to varying amounts of vine damage and foliage removal, was the inability to harvest fruit borne within six inches of the base of the plant and commonly refered to as center row fruit. In I959, Michigan State University evaluated a machine of its own construction which combined a number of the principles of the machines tested in I957. Bingley (5) reported that this machine reduced the average cucumber yield by 76 percent and attributed this to vine damage caused by the fruit removal mechanism. Since the machine was of the one-way type, requiring vine training, there was additional vine damage caused by the pneumatic vine trainer deveIOped at Michigan State University in I958 by Leonard (20). The Chisholm-Ryder machine, with its reasonably effective harvest in late I958 caused a great deal of Optimism which increased with the success of the harvester in I959. Twenty-five additional harvesters were built by the Company for use in the I960 season, but these machines met with very little success. Some of the problems encountered as reported by the Chisholm-Ryder Company in a progress report (2) were: I. 7. Pulling of vines and stress on the root system. This was observed under conditions of wet soils, loose soils and luxuriant vine growth. Inefficient picking of small fruit and center row fruit. Because of the structure of the harvester it was impossible to get closer than within six inches of the base of the plants without pulling them from the soil. Small fruit were missed because of insufficient weight to hang down and luxuriant vine growth in which they became entangled. Dirt, stones and other debris which clogged the machine. Soft, stoney land caused difficult Operation of the machine. Difficulty in obtaining clean harvested fruit, free of stones and plant material. Some varieties were very difficult to pick; the fruit did not separate easily from the stem and resulted in additional vine damage and pulling. A skilled Operator was required. Some of these same difficulties were reported by Stout t l. (38) for the Michigan State Multiple Harvester, with the addition Of a limited acreage capacity because Of the necessity Of harvesting the same plants repeatedly. IO Since mechanical vine damage becomes severe after the fourth or fifth picking, attempts were made through cultural, chemical and plant breeding methods to obtain a concentrated fruit production per plant (28, 29, 32, 37, 38). In this way it was hoped that a profitable yield could be obtained with a reduced number of pickings. However, because Of the problems with a multiple type harvester, emphasis was shifted tO investigations Of a once-over or destructive type harvester. All successful mechanical harvesters of crops have been Of the destructive or once-over harvest type. The problems encountered with this method of cucumber harvesting are similar in some respects to those of multiple harvesters, namely; conditions under which the machine will operate and damage and cleanliness Of the harvested product. Another problem common to both methods is that of concentrated fruit set, except that it must be more concentrated for a destructive method Of harvest if a profitable net return is to be realized. Studies by Stout t I. (38) indicated that once-over harvesting of cucumbers is feasible if a large acreage of highly ll productive plants can be harvested by a reasonably low cost machine. This necessitates additional experiments on plant spacing and cultural practices, and also depends on the plant breeder's ability to develop a variety with a concentrated fruit set. Growth Habit While high temperature, levels of nutrition and adequate moisture are conducive to strong vegetative growth of the cucumber plant, it has been observed by a number of researchers that the presence Of a developing fruit exerts an inhibitory effect on further vegetative develOpment. This has led some investigators to believe that developing embryos produce a growth regulating substance which limits further vegetative growth (8, 2I, A0, Al). This substance has not yet been isolated and its presence therefore remains speculative. Genetic studies on vine growth, determinate versus indeterminate growth habit, were reported by Hutchins (l6) and Odland and GrOff (26). Hutchins reported the control of vine type to be monogenic with determinate growth habit l2 dominant to indeterminate. Odland and Groff also showed the character to be monogenic, however, indeterminate vine type was dominant to determinate, and they assumed two determinant vine types.. Another monogenic character studied by Hutchins was plant height. He proposed that tall was partially dominant to shOrt since the F] of tall and short parents was intermediate in height. The determinate parent in Hutchins' study produced very few, short lateral branches. From a study of this trait Hutchins reported that there was no apparent relationship between the number of lateral branches and their length, but that the genetic control of number Of laterals was quantitative. Sex Expression Developing fruit not only have an inhibitory effect on vegetative growth, but also on the production of pistillate flowers and fruit production in general (A0, Al). This is the cause for concern over center row fruit (those borne within six inches of the base of the plant) which are not removed by the multiple-pick harvester. This problem then involves the position of pistillate flowers along the primary stem and lateral branches. l3 'Numerous descriptions Of the sequence of staminate and pistillate flowers on the primary stem of the cucumber plant have been published in past years. In I927, Heimlich (l2) reported that staminate inflorescences may occur in the first or second leaf axil and continue for a number of sequential nodes. Judson (I9) reported that the first pistillate flower occurs several leaf axils above the cotyledons. Shifriss (3A) Offered a thorough description of flower sex type arrangements on the primary stem and classified them as follows: A. MonoeCist - a sequence of staminate nodes - at the base of the plant followed by a sequence of mixed nodes which is in turn followed by a strictly pistillate sequence. 8. Gynoecist - pistillate blossoms at all nodes on the primary stem and lateral branChes. C. Andromonoecist - staminate sequence at the lower nodes followed by a mixed sequence Of staminate and perfect flowers which is followed by a perfect flowered sequence. 0. Hermaphrodite - perfect flowers at all nodes. A series of intergrades between monoecist and gynoecist were classified as subgynoecist and consisted Of the following nodal sequence types: IA A. Staminate phase at the base followed by a pistillate phase. 8. Same as A with the staminate phase reduced to three or four nodes. C. A sequence of alternating groups of staminate and pistillate nodes, the first sequence being staminate and the last pistillate. Shifriss' genetic basis for sex control in cucumbers is based on at least three groups of hereditary factors; I) qualitative genes that determine potential flower types, 2) polygenes governing the rate of accumulation or depletion of an unknown substance and 3) an accelerator gene (Acr) affecting the rate of the physiological process controlled by the polygenes. In plants classified as monoecist, Shifriss measured sex tendency by designating the position in number of nodes to appearance of the first pistillate flower on the main stem as T], and the point at which the completely pistillate phase begins as T2. On this basis, the higher the value of T], the stronger the male tendency. Incor- poration Of the Acr gene associated with gynoecism into a strong male genetic background through a backcrossing program resulted in a rapid decline of gynoecious plants and a rise to 50 percent of subgynoecists classified as type A. An inbred developed from this type of cross was found to possess high phenotypic plasticity. Shifriss concluded that, “The pattern Of sex differen- tiation during plant development appears to depend upon an interaction between the genes for different kinds Of flowers, the rate genes, the dosage of Acr and the environ- ment.” Mitchell (2A) hypothesized that sex expression in cucumbers is based on the control of endogenous auxin levels. Identification Of these with Shifriss' unknown substance, however, has yet to be accomplished. A The subjects of influence of applied growth regulators, nutrition and environment on pistillate flower production have been well reviewed (I3, 2A, 3l, 32). However, several pertinent facts will be brought out here. Nitch gt 31. (25) reported that long days and high temperatures increased the number Of nodes before the first pistillate flower and suggested that night temperatures might also play an important role. Mitchell (2A) showed that a I0 degree drop l6 in greenhouse night temperature from 70 degrees F. to 60 degrees F. had the effect of reducing the average number Of nodes before the first pistillate flower from 2l to l2. Nitch g£_§l. (25) also noted that both staminate and pistillate flowers may occur at the same node and that pistillate flowers may appear at the lower nodes long after the death Of the staminate flowers that appeared there. Ito and Saito (l8) reported that long days (l5 hours) and high night temperatures (30 degrees C.) applied just before sexual differentiation of the flower primordia delayed production Of pistillate flowers. In another study, Ito and Saito (l7) narrowed this period of environmental influence to ID to - 30 days after germination. During this period, long days and high night temperatures are reported to favor staminate flower formation while short days and low night temperatures favor pistillate flower formation. During this critical l0-30 day period, environmental factors are theorized to effect sex expression by changing the physiological condition Of the plant. Once changed,later treatment failed to alter the effect of conditions experienced at the susceptible period. Nitch t l. (25) proposed a scheme in which I7 climatic factors modify the length but not the order of each flower type phase. Stout and Ries (37) in an attempt to delay flowering or remove early fruit set applied a number of compounds to cucumber plants at several stages Of growth in the field and in the greenhouse. All compounds except gibberellic acid had no effect or injured the plants. Gibberellic acid was effective in delaying pistillate flower formation on the primary stem and increasing the distance to first fruit on the lateral branches, however, responses differed enough to make field application impractical. Concentration of Fruit Set Tiedjens (A0) noted a difference between varieties in their capacity to mature a number of fruit at the same time. Some varieties were capable of maturing five or six fruit at once while others could mature only one or two. This he felt was due to time of flowering; simultaneously fertilized flowers seemed tO develOp equally well while of those fertilized over a period of days only one or two would develOp, those remaining having their develOpment arrested. I8 Putnam (32) found from growth measurements of normally develOping and arrested fruit that both showed similar growth for the first two days after pollination, but after the third day the arrested fruit showed no further increase in size. He credits this fruit develOpment arrest as a major limiting factor in Obtaining concentrated fruit set. Peterson (27) in I960 reported on the develOpment of MSU 7l3-5, a gynoecious inbred cucumber line, and the method of staminate flower induction with gibberellin A3 for maintenance of the inbred (30). In l96l, the Michigan Agricultural Experiment Station released the FI hybrid variety Spartan Dawn of which MSU 7l3-5 is the seed parent (29). It would seem that a plant exhibiting gynoecious sex expression, where there is greater Opportunity for a number of pistillate flowers to be ferilized simultaneously would be capable of develOping more fruit at once than a monoecious variety having a pistillate flower only every fifth to tenth node. Cultural methods directed at Obtaining larger early yields through increased plant pOpulations were also tried. Ries (33) reporting on four years of Spacing studies found 19 that close spacing increased both total and early yields Of pickling cucumbers. Putnam (32) working with the varieties Spartan Dawn and Wisconsin SMR-l8 reported that for once-over harvesting the number Of fruit per plant was consistently greater when the plants were spaced one foot apart in the row compared to those spaced six inches apart though there was no effect of Spacing on flowering habit. Plant populations of A3,560 plants per acre, but none higher, resulted in higher dollar yields than populations of 2l,780 plants per acre. NO difference was found in the number of marketable fruit produced at the first and second picking of either variety although Spartan Dawn consistently produced more fruit than Wisconsin SMR7l8. These studies emphasized the importance of limited vine growth more adaptable to closer planting distances. High plant populations may serve to increase the yield for once-over harvesting, but because Of the additional vegetation would be unadaptable to the multiple-pick harvester. Stout gt il- (38) reported that neither Spartan Dawn or Wisconsin SMR-IB had the low vegetative growth to fruit ratio that was needed in a variety for once-over mechanical harvesting. 20 An investigation of the effects of application of several growth regulating compounds on flowering was made by Putnam (32). The results were inconsistent under varying environmental conditions and it was concluded that applica- tions of the materials tested were not an adequate means Of increasing once-over yields of pickling cucumbers. Ease Of Separation of Fruit from the Stem Up to the time of development of mechanical harvesters for cucumbers it was only a casual observation Of the plant breeder, grower or picker that the fruit of one variety was easier to pull from the vine than that of another. The develOpment Of multiple-pick mechanical harvesters brought attention to the character of ease of stem separation. Fruit that were difficult to remove from the vine caused an unwanted additional thrashing and beating of the vines during the picking process. This not only resulted in reduced plant vigor but also lower production due to the loss of bearing surface, leaves and the arrested develOpment of small fruit caused by a ripening fruit still attached to the vine. 2l The develOpment of a once-over mechanical harvester has lessened the importance of ease of stem separation since the later productivity of the vines is not considered. However, a problem common to both methods Of mechanical harvesting is that of stem retention on the harvested fruit or sections of the fruit breaking away with the stem. Leonard (20) in I958 measured the ease Of separation Of the stem from the fruit (designated picking force) in the field using a spring scale. He reported that picking force did not depend upon time Of day or location Of the fruit on the vine, but may vary with harvest date and variety and is related to fruit weight as an indication of fruit size. Bingley (5) measured picking force in the same manner as Leonard and confirmed what Leonard had suspected; that the picking force fruit size relationship differs between varieties. Wisconsin SMR-l2 required the lowest force for fruit stem separatiOn of the varieties tested. A general weight size relationship of the fruit was established by both Leonard and Bingley. Hutchings 2E.él- (l5) measured the force required for the separation Of the cucumber fruit from its stem with an 22 instrument designed and constructed by the H. J. Heinz Company. On the basis Of preliminary studies, the spring scale used by Leonard and Bingley was not considered to give accurate values. The instrument used by Hutchings _£‘_l. worked on the principle of an air driven cylinder activated and deactivated by the making and breaking of an electrical circuit. During the summer Of l96l a total Of A29 fruit from the two varieties Wisconsin SMR-l8 and Wisconsin SMR-IZ and two breeding lines H IA7 and H IA8 had their stems picked by the instrument over six picking dates. Picking force was summarized only on a variety basis. There has been no work reported on the causal mechanism behind differential picking force between fruit sizes within a variety or between varieties Of pickling cucumbers. Judson (I9) reported that there are either nine or ten vascular bundles in the stem of the pistillatecucumber flower where it branches from the stem, and that if there are nine, one branches in the stem so that there are ten entering the fruit. GENERAL MATERIALS AND METHODS Cultural Practices 5.2.1.51 All plant material and fruit employed in the studies were grown on the Michigan State University Horticulture Farm. Seed were sown in soil and covered with Vermiculite in 2 inch Jiffy Pots in the Plant Science Greenhouses in late May. The seedlings were transplanted to the field during the first two weeks of June of each year. Twelve Jiffy Pots containing two seedlings each were placed in 20 foot rows with the rows four feet apart. For the concentrated fruit set study, plants were thinned to one plant per pot. A spray schedule to control insects and angular leaf spot (Pseudomonas lachrymans) was followed and irrigation water was applied as needed. Greenhouse Cucumber plants for crosses and generation advancement were grown in the Plant Science Greenhouses the winter and spring Of l96l-l962 and I962-I963. Seedlings germinated in 23 2A Jiffy Pots were set in 8 inch clay pots in a steam sterilized mixture of l part sand : l part loam : l part muck. Karathane(Rohm 8 Haas) was used for the control of powdery mildew (Erysiphe chicoracearum). Statistical Methods The CDC 3600 computer of Michigan State University's Computer Laboratory was used for data summarization and calculation of linear correlation coefficients. Analyses of covariance were performed by procedures described by Snedecor (35). Sample means were compared according to procedures described by Steel and Torrie (36). EXPERIMENTAL Lateral Branching Study Materials and Methods An inbred pickling cucumber line of the pedigree (SF x l8-73)25-l* was observed in the Michigan State University breeding plots to have: a reduced number of lateral branches in comparison to the varieties Wisconsin SMR-IS and Wisconsin SMR-l8. One F6Sib] plant with no lateral branches from a population that reportedly segregated l8 out of l9 non-branching plants was self-pollinated in the field. (This Féslblsl and remnant F6Sib] seed were turned over to the author on his arrival at Michigan State University in September l96l with the goal that through additional inbreeding and crossing studies the character of reduced or non-branching would be fixed and its genetic control further elucidated. *SF signifies Shogoin Female, l8-7 and 25-l were released by the Wisconsin Agricultural Experiment Station under the names Wisconsin SMR-l8 and Wisconsin SMR-IS respectively. 25 26 Six F6SibISl generation plants identified as 2l00-l to 2l00-6, grown in the greenhouse the winter of l96l- I962, showed very little branching. Self-pollinations were Obtained on five of these; 2l00-l, 2, 3, A and 6. Two F6Sib182 plants, 02-l and 02-2, from 2l00-2 were grown and self-pollinated in the greenhouse the spring of I962 and produced six and two lateral branches respectively. Populations Of the seven progeny Obtained from greenhouse self-pollinations and of the F6SibISI parent were grown in the I962 field Observation plots. Plants bearing zero or one lateral branch were self-pollinated in the field, however, because of the lateness Of pollination and a severe infection Of angular leaf spot (Pseudomonas lachrymans) no seed were Obtained. The progeny from 02-2 bore the lowest mean number Of lateral branches per plant and was selected for further inbreeding in the I962-I963 winter greenhouse. Twenty- four F6SibIS3 generation plants designated 8l3-l to 8l3-2A were grown and self-pollinations obtained on all except 8l3-7. Records of lateral branching were not taken on these plants. 27 Five plants, designated 8ll-l to 8ll-5, of the remnant F6Sib] seed stock which resulted in l8 out Of I9 non-branching plants in l96l were self-pollinated in the I962-I963 winter greenhouse. Populations from self-pollinations Of the 8II, 8I3 and four of the 2l00 series were grown in the I963 field plots. Self-pollinations of two non-branching plants, one from 8l3-l and the other from 8l3-8 were Obtained. NO further inbreeding was performed, however, progenies observed during the I962 and I963 seasons plus the two 55 8l3 self-pollinations and the remnant F6Sib] seed were planted for Observation in the l96A field plots. The closely related inbred genetic material, utilized in the sex reversal study, in which selection for reduced branching was not practiced was Observed for lateral branching the summers of I962, I963 and l96A. In an attempt to further elucidate the genetic control of lateral branching, the variety Wisconsin SMR-IS and the F7Sib] sex reversal inbred were chosen as normal branching parents. F], F2 and backcross generation seed between these two normal branching parents and the F6$iblsl reduced branching inbred were obtained in the l96l-l962 winter 28 greenhouse. The backcross parents were not those which served to produce the F15, but were from self-pollinations of the original plants. Observations on branching habit were made in the field plots during the summers of I962, I963 and l96A over a period of four weeks beginning approximately six weeks after setting the plants in the field. Records of the number of lateral branches produced on the primary stem were taken on individual plants on a destructive harvest basis. Only those laterals Of a length greater than six inches and possessing an actively growing shoot tip were recorded. Short lateral extension from the primary stem possessing two or three nodes and terminating in a cluster of blossoms were present on some plants of the reduced branching inbred but were not recorded. Attempts were made to keep all large develOping Open-pollinated fruit off the plants prior to record taking in order that the plants would remain vegetative. Results and Discussion The mean number of lateral branches per plant, percent non-branching plants per progeny and age Of the plants in 29 days from date of setting in the field for the reduced branching inbred and the sex reversal inbred for I962, I963 and l96A are listed in Tables I thru A. Only four non-branching plants were recovered in I962, and all were in the S3 progeny of 02-2. In I963, an increase in the percent of non-branching plants was Observed for progenies identical to those planted in I962. Two 51 lines, 8ll-3 and 8ll-5, first Observed in I963, were outstanding in that both contained l00 percent non-branching plants for pOpulations of 25 and 29 plants respectively. The 23 SA progenies originating from 02-2, of which two are listed in Tables 2 and 3, expressed a wide variation in mean number of branches per plant in I963, ranging from 0.A7 'to l.90. The percent non-branching plants in the 23 progenies ranged from 0 to 60 percent. In l96A, non-branching plants were Observed in all progenies of the reduced branching inbred that were grown, although in most cases the percent non-branching plants differed from those observed in I962 and I963. The role of the environment in expression Of lateral branching is Table 1. Mean number of lateral branches per plant, percent non- 30 branching plants and days in the field prior to data recording for the $1, 82 and 33 generations of the F53161 reduced branching inbred, 1962. Population Mean fiNon- Generation No. Branches SE1; n12 CV13 Branching Days 31 2100 1.56 .175 9 33.59 0 41 32 2100-1 2.46 .190 24 37.93 0 41 52 2100-2 2.24 .217 29 52.23 0 41 32 2100-3 2.06 .111 34 31.50 0 41 32 2100.4 2.27 .179 30 43.22 0 41 32 2100.6 2.62 .234 21 40.84 0 41 33 02-1 1.50 .10A 24 34.07 0 66 33 02-2 1.12 .133 25 59.28 16 66 Ll Standard error of the mean. [2 Number of observations. [3 Coefficient of variation. 3l Table 2. Mean number of lateral branches per plant, percent non- branching plants and days in the field prior to data ;e§::dingdfordtge Slhi:2,1:gr:3d ig6generations of the 6 1 re uce ranc g , POpulation Mean 5 Non- Generation No. Branches SE n CV Branching Days 51 811-1 1.60 .25A 15 61.56 13.30 57 31 811-2 .A3 .1A8 21 157.67 66.60 57 51 811-3 0.00 - 25 - 100 58 51 811-A .A0 .163 15 158.00 66.60 58 31 811-5 0.00 - 29 - 100 58 $2 2100-A .60 .152 20 113.33 50.00 A6 32 2100-6 .86 .186 21 99.30 38.00 50 S3 02-1 .58 .1A0 19 10A.83 A7.30 A8 S3 02-2 .79 .16A 15 90.38 36.80 A8 SA 813-1 .A7 .165 15 136.17 60.00 70 SA 813-8 .6A .225 1A 131.Al 57.10 59 32 Table 3. Mean number of lateral branches per plant, percent non- branching plants and days in the field prior to data recording for the F Sibl, $1, 82, S , Sn, and 35 generations of the F6Sib1 reduced branching inb d, l96A. 5 Non- Branching Ihys Population Mean Generation No. Branches SE n CV ngibl 811 .65 .232 20 166.15 65.00 56 51 811-1 1.89 .360 18 80.95 27.70 58 51 811-2 1.00 .272 9 81.60 55.50 58 51 811-3 1.10 .378 10 109.09 30.00 58 31 811-4 .76 .275 21 165.79 66.60 58 31 811-5 .83 .205 24 120.48 50.00 58 S1 2100 1.57 .272 21 .79.62 23.80 59 32 2100-1 1.80 .427 15 92.22 33.30 52 32 2100-2 1.64 .284 17 71.34 11.80 52 52 2100-3 1.04 .266 24 125.00 41.60 56 82 2100-4 .75 .210 24 137.33 54.10 56 52 2100.6 1.70 .281 17 68.24 17.60 56 33 02-1 1.32 .258 22 91.67 31.80 56 33 02-2 2.19 .261 16 47.49 6.20 56 5“ 813-1 2.30 .317 20 61.74 10.00 58 sh 813.8 2.53 .500 17 81.42 17.60 58 55 36215 1.85 .406 13 78.92 23.00 58 35 36375 1.35 .242 17 73.85 17.60 58 [a From.self-pollination of a non-branching plant of 813-1. [b From.self-pollination of a non-branching plant of 813-8. 33 Table A. Mean number of lateral branches per plant, percent non- branching plants and days in the field prior to data recording for theS and 82 generations of the F7Sib1 sex reversal inbred, 19 2,1963 and 196A. Population Mean i Non- Generation NO . Branches SE n CV Branching Days 1962 81 2103-1 6.13 .654 15 41. 27 0 51 51 2103-2 4.45 .388 22 40. 90 0 52 31 2103-3 4.75 .494 12 36.00 0 52 31 2103-5 3.95 338 19 37 22 0 52 52 32-2 2.62 .241 13 33.24 0 72 1963 31 2103-1 2.05 .212 20 46.15 0 49 31 2103-2 2.56 .197 23 36.95 0 49 51 2103-3 2. 38 .201 21 38.70 0 48 51 2103-5 2.83 .196 24 33.99 4.17 50 32 31-2 2. 25 .228 20 45.38 5.00 49 32 32-1 2.64 .289 14 40.91 0 48 32 32-2 2.91 .270 22 43.64 4.55 48 1964 31 2103-2 2.81 .242 26 43.77 0 38 31 2103-5 1.74 .180 23 49.60 4.35 38 32 31-2 2.96 .165 24 27.26 0 38 32 32-1 2.26 .303 23 64.25 13.04 38 32 32-2 2.50 .113 12 49.60 0 38 3A revealed on Observing samples from the same populations under three different environments (2l00-A, 2l00-6, 02-l and 02-2, Tables I, 2 and 3). The influence Of the environment on lateral branching was also evident in the sex reversal inbred which responded similarly to the reduced branching inbred in the same years (Table A). The genotype environment interaction resulted in the production of a greater number of lateral branches in I962 than in I963 or l96A. Comparing the relative values of coefficients of variation, the reduced branching inbred appears more variable than the sex reversal inbred. However, when dealing with a low mean number of lateral branches in a population containing many non-branching plants, a small amount of variation can result in a large coefficient Of variation. In contrast, a high mean number Of lateral branches with correspondingly more variation can result in a moderately low coefficient of variation. Thus, the reduced branching material is not as variable in the production of lateral branches in comparison to the sex reversal material in I963 and l96A as the coefficients of variation indicate. 35 It is evident that plant material having a genetically determined though environmentally influenced low number of lateral branches is available. However, attempts thru inbreeding and selection to obtain a genetic line or lines that consistently produced a constant number of lateral braches or none at all were unsuccessful. Considering the level of inbreeding, F6Sib], as an indication to approaching homozygosity it is possible that the variation observed within and over years resulted from a lack Of genetic buffering. The reduced branching inbred could then possibly be considered genetically homozygous or near homozygous with high phenotypic plasticity. An alternative explanation is that Sib-pollination Of two F6 sister plants resulted in a genotype or group Of genotypes which conditioned the non-branching character. The advanced generation of inbreeding would therefore only give an illusion of approaching homozygosity, and much of the variation observed in progeny from the self-pollinations would instead be due to genetic segregation. Under a system of inbreeding, as practiced, the percent of heterozygous individuals in a pOpulation should 36 decrease with each additional generation of self-pollination. If non-branching is conditioned by heterozygosity, the percent of individuals expressing the character will be reduced with each additional generation of self-pollination. This was in fact found tO be the case. In I963, 51, 52, S3 and SA generation mean percents of non-branching plants were 69.30, AA.00, A2.05 and 30.69 respectively. In l96A, the mean percents of non-branching plants for the FéSib], s], $2, 33, sh and 55 were 65.00, 42.27, 3|.68, 19.00, 13.80 and 20.30 respectively. Thus, with each additional . generation of self-pollination there was an almost consistent decline in the mean percent of non-branching plants. It would therefore seem that the original sib- pollination of two sister plants resulted in a genotype or group Of closely related genotypes that conditioned non-branching under certain environmental conditions. With this information, the Sib-pollination can be viewed as a cross Of two inbred but not genetically identical plants. The resulting F] though not genetically homogeneous apparently contained a high percentage Of genotypes which under certain environments condition non- branching. The genetic non-homogeneity of the F] is 37 supported by the lack of uniform performance of it and the F2 populations within a given year, and the environmental influence is evident in the variation of percent of non- branching plants in the pOpulations over years. Sampling error may also enter into the variation Observed in the populations grown in more than one year, but in most instances the variation Observed in the same genetic lines over years is too great to be due to sampling error alone. It is perhaps now more correct to view the S], 82, S3, SA and 85 as F2, F3, FA: F5 and F6 generations respectively. Though there is a decrease in percent non-branching plants with each additional generation of self-pollination, it is extremely difficult to speculate on the number of controlling genetic factors. A system of polygenic inheritance is supported by the continuous variation Observed in percent plants expressing the non-branching character and the fact that all but one population grown in I963 and all in l96A contained non-branching plants. Adding to the difficulty of interpretation are environmental' influence and sampling error. Whether the polygenic 38 system proposed by Hutchins (l6) for control of lateral branching and the one apparently involved in non-branching are one and the same remains to be determined. There also exists the possibility of a genetic threshold, which is based on a number of heterozygous loci and interaction with the environment, controlling non-branching. The crosses of the reduced branching inbred to normal branching lines add very little if anything to clarification*. of inheritance of lateral branching. Since the reduced branching parents were in fact from segregating F2 progenies, interpretation of FI and F2 segregation patterns were not attempted. : The problem of the possible existence of two polygenic systems, one for non-branching and the other for number of lateral branches, will be extremely difficult to resolve. If non-branching in the material studied is in fact conditioned by a particular minimum number of heterozygous loci, there is little or no hope of Obtaining a true breeding non-branching line from it. 39 Sex Reversal Study Materials and Methods An Inbred, F7 pickling cucumber line of the pedigree (SF x l8-72)25-l)563* was observed in the Michigan State University pickle breeding plots to produce no pistillate blossoms below the tenth node on the primary stem and pistillate blossoms at the tenth node and all above. Two sister plants were sib-pollinated and the resulting seed labelled as 2l03 was turned over to the author in the fall of l96l for study Of this type of sex expression tendency which will be referred to as sex reversal. Six Sib] plants labelled 2l03-l to 2l03-6 were grown in the greenhouse the winter of l96l-l962 and self- pollinations Obtained on four Of them; 2l03-I, 2, 3 and 5. None of the six plants exhibited the reversal character in the greenhouse, but exhibited two patterns of sex tendency. All six plants had an initial staminate phase with 2l03-l, 2 and 3 exhibiting an alternation of one staminate node one pistillate node after the initial pistillate node until Observations ceased at about node 30. *563 was named NAPPA 63 by Associated Seed Company A0 2l03-A, 5 and 6 displayed the same alternating phase, as just described, after the initial staminate phase and after the 23rd or 2Ath node displayed a completely pistillate phase until Observations ceased at about node 30. Populations from self-pollinations of four of these plants were grown in the field observation plots during the summers of I962, I963 and l96A. The remnant 2l03 F7Sib] seed was grown in I962. During the spring of I962, one 51 plant, 3I-2, from 2l03-l and two 51 plants, 32-l and 32-2, from 2103-2 were grown and self-pollinated. 3l-2 exhibited an initial male phase, nodes 2-l0, a female phase from nodes lI-AO and then two more male nodes. 32-l developed staminate blossoms at nodes 2-ll, l3, l5 and pistillate blossoms at nodes I2, IA and l6-22. 32-2 develOped staminate blossoms at nodes 2-l6, l8 and pistillate blossoms at nodes l7 and l9-55. The progeny from 32-2 was grown the summer of I962 and all three progenies were grown the summers of I963 and 1964. I For additional inbreeding, 22 52 plants from 3l-2 were grown in the greenhouse the spring of I963. These plants Al designated 8l5-l to 8l5-22 were self-pollinated and seed obtained from 20 of them. A similar group of 23 plants from 32-2 designated 8l2-l to 8l2-23 were self-pollinated and seed Obtained from I9 of them. Of the A5 plants grown, three from 32-2 exhibited a sex reversal. The remaining plants all exhibited an initial staminate phase followed by a phase of varying length of mixed flower types followed by a pistillate phase in all but two cases. The 39 resulting progenies were grown in the I963 field observation plots. Seventeen self-pollinations of sex reversal plants from six S3 progenies were Obtained during the summer Of I963 and were grown with their parental lines during the summer of l96A. The eleven SA progenies of 8l2 parentage and the six of 8I5 parentage were designated as 9l2 and 9l5 respectively. The flower sex type developed at each node of the primary stem was recorded on each plant in a pOpulation on a destructive harvest basis. Those plants showing a sex reversal were pulled from the ground and nodal flower sex types recorded. Data on lateral branching were also recorded for use in the lateral branching study. 42 Results and Discussion Considering the original F7Sib] generation as an F] of two inbred parents, the subsequent $1, $2, S3 and SA populations from self-pollinations have been designated as F2, F3, F4 and F5. The mean node of sex reversal and the percent of sex reversal plants in the various generations for I962, I963 and l96A are shown in Tables 5, 6 and 7 respectively. The non-sex reversal plants in each Of the populations grown displayed a wide range of variation in sequence Of arrangements of staminate and pistillate flowers on the primary stem, but no plants exhibited the gynoecious form of sex expressions. A number Of plants had a sex expression similar to that listed by Shifriss (3A) as subgynoecious type C. Little attention was devoted to the arrangement of staminate and pistillate flowers on lateral branches. However, lateral branches exhibiting a staminate phase, a mixed phase and a pistillate phase were observed as well as lateral branches exhibiting only a pistillate phase. Staminate flowers at the first and second nodes of laterals produced after those exhibiting only a pistillate phase were also Observed. A3 Table 5. Mean node of sex reversal and percent of plants expressing the character, 1962. Population neon Percent Generation No. Node n S.E. c.v. Plants c.v. F1 2103 10.10 10 .744 23.30 47.61 F2 2103-1 12.75 8 .414 9.18 57.14 F2 2103-2 13.89 9 .696 15.03 47.36 F2 2103-3 13.50 6 .224 4.06 50.00 F2 2103-5 12.80 10 .249 6.16 52.63 Pooled F2 Individuals 13.21 33 .237 10.32 51.56 Pooled F2 Families 13.24 4 .277 4.18 51.78 8.50 r3 32-2 10.62 8 .684 18.21 61.53 Table 6. the character, 1963. AA Mean node of sex reversal and percent of plants expressing Population Mean Percent Generation No. Node n S.E. C.V. Plants C.V. F2 2103-1 9.A3 7 1.620 A5.39 35.00 F2 2103-2 11.00 1A .858 29.19 60.86 F2 2103-3 11.A3 7 .812 18.00 33.33 F2 2103-5 8.78 9 .997 34.07 37.50 Pooled F2 Individuals 10.2A 37 .538 31.93 A2.0A Pooled F2 Families 10.16 A .62A 15.31 Al.67 30.97 F3 32-2 9.22 9 .596 19.40 40.90 F3 31-2 7.75 8 .9A0 3A.3l A0.00 Pooled Fh Individuals 812 12.6A 227 .197 23.A5 50.AA Pooled EA Families 812 12.89 19 .360 12.19 50.52 27.51 Pooled F4 Individuals 815 11.59 226 .20A 26.A7 53.18 Pooled F“ Families 815 11.39 20 .A20 13.53 53.A6 32.65 A5 Table 7. figncgzgzciirseiltgzversal and percent of plants expressing Population Mean Percent Generation No. Node n S.E. c.v. Plants c.v. F2 2103-1 11.88 16 .256 8.64 57.14 F2 2103-2 13.33 12 .820 21.30 46.15 F2 2103-3 13.50 6 .846 15.36 60.00 92 2103-5 13.00 9 .333 7.69 39.13 Pooled F2 Individuals 12.74 43 .292 15.04 49.42 Pooled 72 Families 12.93 4 .364 . 5.63 50.60 19.18 F3 32-2 1A.38 8 .755 14.85 66.66 P3 31-2 12.33 10 .582 17.51 62.50 Pooled 34 Families 812 14.97 4 .412 5.51 42.64 14.73 Pooled F4 Families 815 13.25 2 .592 6.31 33.23 15.36 Pooled F5 Individuals 912 14.55 130 .165 12.95 49.06 Pooled r5 Families 912 14.64 11 .340 7.68 49.36 23.09 Pooled F5 Individuals 915 13.46 50 .331 17.39 40.98 Pooled 15 Families 915 13.58 6 .686 16.50 40.54 21.24 A6 A few plants approaching sex reversal type had a node with both a pistillate and staminate flowers above the completely staminate phase thus reducing the phase Of mixed flower types to one node. Plants possessing such an arrangement were not classified as sex reversal. The three year means of percent sex reversal plants in the populations and node of reversal for those plants exhibiting the character of the four F2 populations did not differ significantly (Table 8). .On a yearly basis, the mean percent of sex reversal plants in the four F2 populations did not differ significantly though it was lower in I963. The mean node of sex reversal was significantly lower in I963 than in I962 and I96A (Table 9). A comparison of the I963 pooled FA families designated as 8l2 and 8l5 showed no significant difference in mean percent of sex reversal plants, but a significant difference in the mean node Of reversal (Table IO). Self-pollination of sex reversal plants in four F“ families of the 8l2 group and two FA families Of the 8l5 group resulted in progeny which when combined by parentage did not differ in mean percent sex reversal plants or mean node of sex reversal (Table II). A7 Table 8. Mean percent over 1962, 1963 and l96A of plants of F7Sib1$ progenies exhibiting sex reversal and mean node of reverse Mean percent sex reversal Mean node of sex reversal 2103-1 49.76 i 7.38 a 11.35 1 .99 a 2103-2 51.46 i 4.71 a 12.74 i .88 a 2103.3 47.78 i 7.78 a 12.81 i .69 a 2103-5 43.09 I 4.78 a 11.53 it 1.37 a Means not followed by a common letter are significantly different, odds 19 to 1. Table 9. Mean percent of plants over four F7Siblsl progenies ex- hibiting sex reversal and mean node of reversal. Mean percent Mean node of sex reversal sex reversal 1962 51.78 I. 2.09 a 13.24 1 .28 a 1963 41.67 i 6.45 a 10.16 i .63 b l96A 50.60 111.85 a 12.93 3; .36 a Means not followed by a common letter are significantly different, odds 19 to l. A8 Table 10. Mean percent of plants of F7Sib1$ progenies exhibiting sex reversal and mean node of reversal, 1963. Mean percent Mean node of sex reversal sex reversal 812 [l 50.52 t 3.19 a 12.89 i_.36 a 815 72 53.46 i 3.90 a 11.39 i .42 b [1 Mean of 19 progenies. [2 Mean of 20 progenies. Means not followed by a common letter are significantly different, odds 19 to 1. Table 11. Mean percent of plants of F7Sib1$n progenies exhibing sex reversal and mean node of reversal, l96A. Mean percent Mean node of sex reversal sex reversal 912 [I A9.36 _+_; 3.AA a 1A.6A 1; .33 a 915 [2 40.54 1; 2.72 a 13.58 .t .69 a [1 Mean of 11 progenies from.A lines. [2 Mean of 6 progenies from 2 lines. Means not followed by a common letter are significantly different, Odds 19 to lo A9 The F2 generation of a cross in which the parents are of different homozygous genetic constitutions is the generation of greatest genetic variation as a result Of maximum gene segregation. The ensuing F3, FA, F5, ...... families developed from F2 individuals, except where selected individuals are of genetic constitution similar to that Of the F], show decreasing amounts Of genetic variation within families while that between families may approach genetic variation of the F2. 0n reviewing the I962 data (Table 5), the mean node Of reversal of the four F2 populations, the pooled F2 individuals and the pooled F2 families are all higher than that of the FI' The coefficients of variation on the other hand are all lower, indicating less variation in node of reversal within the F25 than within the F]. Regarding the percent Of plants exhibiting sex reversal, all center around 50 percent. ' The data for I963 (Table 6) show more variation in mean node of sex reversal and percent of sex reversal plants in the populations. The mean node of reversal for the I963 pooled F2 families is significantly lower at the .05 50 level (Table 9) than for I962 and l96A. Temperature data for the period June l6 to June 30 for the three years (Table l2) show that during this IS day period the plants in the field were exposed to colder night temperatures during I963. In view of the findings of Ito and Saito (I7) and Mitchell (2A) it is expected that the first pistillate blossoms would be formed at a lower node for the season in which colder night temperatures were experienced during the critical period. In l96A (Table 7), the mean node Of reversal of the F2 families, pooled F2 individuals and pooled F2 families approximates the I962 values. Again, the percent of individuals expressing a sex reversal is centered around 50 percent. The mean node Of sex reversal and percent sex reversal plants in the pooled F5 and F5 individuals and families do not show more variation in comparison to the other generations than would be expected on an environmental basis (Table 6 and 7). 5] Table 12. Total degrees of minimum daily temperatures below tem- peratures indicated for the period June 16 to June 30. [l 70°F. 60°F. 50°F. A0°F. 1962 195 60 3 0 1963 259 123 A1 5 1964 152 45 10 0 71 Obtained from daily temperature data recorded at the Michigan State University Horticulture Farm. 52 It appears that the original F] resulting from Sib-pollination of two sister F7 sex reversal plants in l96l was a cross between two individuals homozygous for the major genes controlling sex expression but still segregating for some Of the polygenes involved. The amounts Of variation within and between the F2, F3, FA and F5 individuals and families, with consideration Of environmental influence, do not indicate extensive segregation and do not differ greatly from that of the F]. Shifriss (3A) hypothesized and found support for two pairs of qualitative genes and a group of polygenes which in interaction with the environment result in the expression of the various recognized sex types. The sex reversal material of the present study comes under Shifriss' classification of subgynoecious type A, and accordingly is homozygous for the dominant accelerator gene (Acr) and the dominant pistillate flower gene (G). Shifriss found such a combination in conjunction with a polygenic background for strong male tendency to be a 53 subgynoecist with high phenotypic plasticity. Homozygosity of the Acr gene is supported by the fact that with repeated selfing no monoecists with a strong male genetic background appeared in the pOpulations. The polygenic background for the strong male tendency of the sex reversal inbred was Obtained from the three initial crossings to the variety Wisconsin SMR-l8, the outcross to Wisconsin SMR-IS and the cross to NAPPA 63. If the level Of inbreeding of the sex reversal plants is taken as support for genetic homozygosity, an explanation of the approximately 50 percent non-sex reversal plants and the variation of types of sex tendency within this group is necessary. A possible explanation can be found in postulation Of partial dominance or variance in expressivity of the Acr gene. Partial dominance is chosen over penetrance since a lack of expression of the Acr gene would result in a strong male monoecious type of sex expression, and this was not observed. A causal mechanism for this partial dominance is difficult to supply since the Acr gene has proven quite stable under widely varying environmental 5A conditions. It seems possible that in the presence of such a system the segregation of a number of polygenes may come to light in the approximately 50 percent non-reversal plants. With full dominance of Acr expressed it is again possible that the manifestation of segregation of polygenes is repressed to the point Of only affecting the node number at which sex reversal takes place. This mechanism in combination with environmental variation is thus capable ’Of creating the variation pattern observed. Concentrated Fruit Set Materials and Methods The dwarf determinate, monoecious EurOpean cucumber variety Rhensk Drue was observed in the greenhouse and the I962 field plots to produce clusters Of pistillate flowers. It was also noted that the plants were capable of develOping several fruit at one time and quite Often more than one fruit per node. Plants Of Rhensk Drue are of the bush type, branching, early flowering and susceptible to major cucumber diseases. The fruit are small, nearly 55 round, fine spined, thin walled with early maturing seeds and of unacceptable type for commercial use. The cluster flowering and multiple fruit develOpment are of primary interest since in comparison the predominantly female hybrids and monoecious varieties commercially grown in the United States produce only one pistillate flower per node and will rarely develOp more than two or three fruit on the plant at one time. Since the success Of once-over mechanical harvesting depends on the development of a plant type of intermediate vine length possessing a concentration of early develOping fruit with a low vine/fruit ratio, the cross between the gynoecious inbred MSU 7l3-5 and Rhensk Drue was made to evaluate the potency of the Rhensk Drue characters. The parents, FI and the commercial variety Wisconsin SMR-IS were grown in the field in a completely randomized design the summer of I963. Fruit were harvested on six dates, approximately one week apart with the first harvest on July 20 and the sixth on August 22. Harvested fruit were counted with no records of grade being taken. Immediately 56 after the sixth harvest the plants were pulled from the ground and the length of the primary stem and except for Rhensk Drue the number of lateral branches recorded. Results and Discussion' The F] progeny of MSU 7l3-5 x Rhensk Drue produce one or two nodes of staminate flowers and are classed as predominantly female in sex expression. The F] comes into production early in the season which is important for the low vegetation/fruit ratio desired for once-over mechanical harvesting. The mean number Of fruit per plant for Rhensk Drue, MSU 7l3-5, the F] of MSU 7l3-5 x Rhensk Drue and Wisconsin SMR-IS for the individual and total over six harvests are presented in Table I3. The Fl plants are fruitful early in the season and retain their fruitfulness throughout the season. The number of fruit harvested from the plants of Wisconsin SMR-IS, because of the wide plant spacing and close picking, give the impression of a fruitfulness that does not exist in commercial plantings. 57 Table 13. Mean number of fruit per plant. flgrvests line 1 2 3 A 5 6 Total Rhensk Drue .37 2.15 A.A0 3.55 A.lO 3.62 18.17 MSU 713-5 .32 1.1A 1.91 2.86 A.0A 8.09 18.36 MSU 713-5 x Rhensk Drue 1.58 6.00 8.A6 8.38 9.08 13.67 A7.l7 Wisconsin SHRpl5 .35 2.65 A.09 A.39 5.35 A.70 21.52 Table 1A. Mean number of lateral branches per plant. line Lateral Branches Wisconsin SHE-15 A.27 a MSU 713-5 2.2A b MSU 713-5 x Rhensk Drue A.21 a Means not followed by a common letter are significantly different, odds 99 to 1. 58 An examination Of the fruitfulness of the F] plants showed it to be conditioned by their ability to develOp a number of fruits at sequential nodes and not necessarily by an increase in fruit bearing surface, lateral branches (Table IA). Tiedjens (A0) reported that concentrated fruit set may be aided by having several pistillate flowers fertilized at the same time. Gynoecious sex expression afforded the ideal conditions for this to occur, yet the commercial predominantly female hybrids do not carry as high a concentrated fruit set as it was hoped they wOuld. The MSU 7l3-5 x Rhensk Drue F] has a predominantly female type of sex expression, but in addition must possess some other factor which enables it to develOp fruit at sequential nodes simultaneously. The F] Vines are of determinate type growth indicating the presence of the dominant gene for determinate growth habit discussed by Odland and Groff (26) rather than the recessive gene of Hutchins (l6). The Fl vine length lies between that Of the two parents, but if it falls on the mid-parent is not known. Vine measurements after the last harvest showed the determinate short parent to have a mean vine length of 26 inches, the indeterminate long parent 60 inches and the F] 56 inches. Growth Of the F] had 59 terminated while that Of MSU 7l3-5 would have continued had the plants not been harvested. F2 plants of the MSU 7I3-5 x Rhensk Drue cross showing improved fruit size were selected for further inbreeding and selection. This material and advanced generations from it now comprise some of the most important plant material of the Michigan State University Cucumber Breeding Project. The present objective is to maintain the plant type and fruiting habit of the Rhensk Drue parent while improving the fruit quality. It is then hoped that a Fl hybrid between the improved Rhensk Drue and a gynoecious inbred will be as fruitful as the original cross and bear marketable fruit. 60 Ease of Separation of the Fruit from the Stem Materials and Methods The ease of separation of the cucumber fruit from its stem was measured with an instrument designed after that used by Hutchings g£_al. (IS). The Urschel Engineering Company of Bowling Green, Ohio was contracted by the H. J. Heinz Company to construct a duplicate of the Heinz Picking Force Machine for Michigan State University. The instrument with some modifications of the original model to provide a more workable and compact unit is illustrated in Figure l. The instrument consists of a pair of spring loaded gripper pliers mounted on the shaft of a double action air activated cylinder. Compressed air enters a pressure regulator and air filter before passing through a spring loaded A-way hand Operated valve which when depressed permits air to enter the tOp Of the cylinder causing a downward movement of the gripper pliers and when released allows air to enter the base of the cylinder returning the pliers to their initial position. The instrument was 6l .mconEJOJU L01 oc_comz oOLOu mc_xo_a ~c_oz on» Lemme pocm_mmc..>cdeOo mc_cooc_mcm _OLOmL: ecu >6 u__:n OCOEJLumc_ OOLOm mc_xo_a ._ oL:m_u 62 Figure l 63 Operated at A0 p.s.i. of compressed air. By means Of an air intake flow regulator situated in the air line between the hand valve and the cylinder, the speed with which air enters the cylinder and forces the gripper pliers down is regulated. In Operation, a cucumber fruit with stem attached is placed in the adjustable trough and the projecting stem gripped in the pliers. Depressing the hand valve activates the cylinder and the gripper pliers move down. Resistance Offered by the stem is registered on a force guage where a free swing indicator mounted on the force guage face glass registers the maximum pressure develOped in the cylinder prior to separation of the stem from the fruit. Once the stem is pulled free from the fruit the pressure in the cylinder drOps rapidly to zero and the force required tO separate the stem from the fruit recorded. Upon releasing the hand valve the gripper pliers are forced back to their initial position. A problem encountered on initiating downward movement of the stem grippers was that the force Of static friction, that force necessary to start movement, was registered on the force guage. This should not have been a problem since 6A the force of static friction is less than the force required to pull most stems from the fruit, but the initial kick of the force guage indicator often caused the free swing indicator on the force guage face to register up to four or five pounds of force. This problem was first overcome by manually rapidly moving the free swing indicator needle to the zero position once downward motion began. It was later found that giving the gripper pliers a short downward pull after their return to the starting position resulted in no registration of the force of static friction. There was no problem with the force of sliding friction, that force necessary to give the gripper pliers continuous downward movement prior to meeting resistance Offered by the stem and fruit attachment. The air line supplying compressed air at the base Of the cylinder which moved the gripper pliers to their starting position was removed and the outlet in the hand valve closed. This was .done since the compressed air entering the cylinder on releasing the hand valve caused such a rapid return of the grippers that on reaching the tOp Of their stroke the whole system received a shock that 65 caused the free swing indicator needle to be displaced and the force datum lost. This problem could most likely have been corrected by inserting an air flow regulator in the air line. This was not done, and the gripper pliers were returned to their starting position manually. NO serious attempt was made to determine the validity of the values recorded from the force gauge since the object of the study was to gain information on relative picking force for fruit sizes and varieties and not true picking force values. One series of tests was made to determine the correlation of values registered on the picking force instrument with those of a spring scale. The values of the picking force machine were consistently higher than those of the spring scale, but the two were correlated with an r value of .90. Three varieties of cucumbers characterized by differences in picking force were employed in the study. The variety Wisconsin SMR-l2 served as an easy to pick variety, ' Ohio MR-l7 a hard to pick variety and Wisconsin SMR-l5 lying somewhere between the two. Fruit Of a range Of sizes Of the three varieties were cut from plants in the 66 field with their stems attached, and the stems removed on the picking force machine. Following this, the weight, length and diameter of each fruit was recorded. The stem of a cucumber fruit is not straight, but curved, due to the weight Of the fruit and its hanging position on the plant. Depending on the position of the fruit cut from the plant, the curve Of the stem may face in any one of many directions. Fruit were placed in the trough of the picking force machine with the stem in one Of three positions; I. SS - stem sideways, stem curve in a plane ' parallel to a table top. 2. SU - stem up, the curve of the stem facing upward toward the ceiling. 3. SD - stem down, the stem curve facing downward. Groups of approximately 60 fruit Of a range of sizes of each variety were harvested in each of these positions. The point Of attachment of the stem to the fruit was also studied on the three varieties. All stem tissue was removed from the end of the fruit leaving a scar designated as the area of stem attachment. After a short period 67 to allow for drying of the wound, the area of stem attachment was recorded by inking the end Of the fruit on a stamp pad and leaving an imprint on paper. The actual areas were determined by means of a planimeter. Weight, length and diameter Of these fruit were also recorded. Results and Discussion Fruit weight, length and diameter all serve as indicies of fruit size and are highly correlated with one another (Table l5). In most instances there is a significant correlation between picking force and each Of the three fruit measurements (Table I6). Of the correlation coefficients Of picking force with fruit weight, length and diameter determined for each variety, date Of picking and position Of the fruit in the picking instrument, the highest degree Of linear relationship was usually found to be between picking force and fruit length. On the basis Of this relationship, fruit length was chosen as the index Of fruit size for comparisons of varieties, dates Of picking and position of the fruit in the instrument. Table 15. Degree of linear relationship between fruit weight, 68 length and diameter for the varieties Wisconsin SHE-15, Ohio DIR-17 and Wisconsin STIR-12, l96A. Correlation Coefficients [2 Variety Date Positionn [1 WI. w/ D L/D n sun-15 8-3 ss . 913 . 956 . 948 59 8-11 53 . 947 . 945 . 975 59 8-11 so . 942 . 968 . 970 54 8-19 SU . 914 . 948 . 962 58 8.11 SD . 871 . 955 . 917 46 8-19 so . 904 . 916 . 944 56 Mil-17 8-3 SS . 853 . 93A . 938 70 8-11 85 . 864 . 914 . 930 59 8-19 55 . 922 . 936 . 920 58 8-11 SU . 896 . 949 . 951 60 8-19 511 . 867 . 935 . 936 59 sun-12 8-3 ss . 889 . 930 . 902 79 8-11 88 . 934 . 950 . 931 57 8-11 SU . 938 . 944 . 955 57 8-19 511 .883 .895 .886 55 8-11 SD . 940 . 951 . 964 57 8-19 SD . 896 . 939 . 924 56 [1 In reference to placement of the fruit in the instrument for picking force determinations. [2 All correlation coefficients significant, Odds 99 to l. 69 Table 16. Degree of linear relationship of picking force with fruit weight, length and diameter for the varieties wisconsin SHE-15, Ohio MR-l? and Wisconsin sun-12, 196A. Stem Correlation Coefficients Variety Date Position Weight Length Diameter n sun-15 8-3 SS .708**71 .612** .592** 59 8-11 33 .265*72 .191 .313* 59 8-11 30 .236 .191 .176 54 8-19 SU .464** .542** .437** 58 8-11 SD .489** .710** .586** 46 8-19 SD .643** .733** .671** 56 MR-17 8-3 ss .330** .353‘* .350** 70 8-11 33 .531** .632** .534** 59 8-19 SS .575** .701** .539** 58 8-11 SU .477** .469** .440** 60 8-19 50 .433** .571** .AS7** 59 SMR-lz 8-3 ss .017 .176 .017 79 8-11 58 .510** .512** .520** 57 8-11 SU .691** .678** .614** 57 8-19 SU .351** .A90** .319* 55 8-11 SD .A59** .522** .A9l** 57 8-19 SD .605** .641** .608** 56 71 *6 Significantly different from 0, adds 99 to 1. 72 * Significantly different from 0, odds 19 to 1. 70 Analysis Of covariance was used to test for homogeneity of regression of picking force on fruit length for the comparisons made. By adjusting the pOpulations of fruit to the same mean length, homogeneity of regression coefficients could be tested as well as the equality of mean picking forces. Stated more Simply, it was possible to determine if the regression lines were parallel and if so, by adjusting the pOpulations to the same mean fruit lengths the regression lines were the same. Prior to making these comparisons it was necessary to have homogeneity of variance of fruit length and picking force for the sample pOpulations, and because of this it was not possible to make all the comparisons that were initially planned. The problem of non-homogeneity Of variance Of fruit length and picking force no doubt arose from the sampling procedures. Comparing the dates of picking for the two varieties Ohio MR-l7 and Wisconsin SMR-l2 (Table I7), a higher picking force was required to separate the stem from the fruit on the latter date. 7l Comparing varieties for the same date and position in the picking force instrument, both Wisconsin SMR-IS and Ohio MR-l7 required a Significantly higher force to pull the stem from the fruit than Wisconsin SMR-l2 (Table I7). Although a comparison of the varieties Ohio MR-l7 and Wisconsin SMR-l5 could not be made, it is suspected that Ohio MR-l7 would have a higher picking fOrce than Wisconsin SMR-IS. The position of the fruit in the picking force instrument was found to have a Significant influence on the force required to pull the stem from the fruit. In all comparisons made, the position of stem down resulted in a significantly higher picking force than stem Sideways, and stem Sideways resulted in a significantly higher picking force than stem up (Table I7). The variety Ohio MR-l7 could not effectively be picked in the stem down position because the stem frequently pulled out Of the gripper pliers. The differences encountered in stem positions are thought to be due to the mechanical advantage afforded by the position in effecting the removal Of the stem from the fruit. 72 Table 1?. Comparisons of dates of picking, varieties and stem positions for homogeneity of regression of picking force on fruit length, l96A. Same variety and stem pgsitionI different date. Stem Variety Position Dates and Mean Picking Forces (Lbs.) MR-l7 SS Aug. 11 3.A2a Aug. 19 3.73a SHE-12 SD Aug. 11 2.86s Aug. 19 3.26b Different varieties, same stem position and date. Data, POSTTTOn Varieties and Hegp Pickigg_Forces (Lbs.l Aug. 11 SD SMR-15 3.26s SHE-12 2.86b Aug. 11 SU FIR-l7 2 . 97a STIR-12 2 . lAb Aug. 11 SS MR-l? 3.A2a SHE-12 2.38b Same varietyI different stem pgsitionsI same date. Variety £532. Stem Positions and Mean Pickin Forces Lbs. SHE-12 Aug. 19 SU 2.6Aa SD 3.26b MR-l7 Aug. 11 SS 3.A2a SU 2.97b SHE-12 Aug. 11 SS 2.39s SU 2.1Ab SMR-lz Aug. 11 ss 2. 39a SD 2. 86b sun-12 Aug. 11 SU 2.1Aa SD 2.86b Means not followed by a common letter are significantly different, odds 19 to l. 73 Leonard (20) suspected a varietal difference in the picking force fruit weight relationship he determined. Bingley (5) confirmed this with the varieties Wisconsin SMR-IS, Wisconsin SMR-l8 and MSU 23l. In the present study, of the three varietal comparisons made, the relationship of picking force to fruit length was found to be the same, i.e., for each comparison the regression coefficients were not Significantly different and the regression lines were therefore parallel. The elevation of the regression lines were, however, different indicating that while the fruit length picking force relationships were not significantly different, there was a varietal difference in picking force. For the ten comparisons listed in Table I7, the regression lines of each pair are parallel and after adjusting the sample populations to the same mean fruit length the regression lines are at significantly different elevations except for Ohio MR-l7 on August II and I9. In determining the degree Of linear relationship between the area of stem attachment and fruit weight, 7A length and diameter, significant simple correlation coefficients were found in all instances (Table I8). The highest degree Of relationship was in most cases with fruit length, and fruit length was therefore again chosen as the index Of fruit size. In attempting to make varietal comparisons the problem Of non-homogeneity Of variance was again encountered. It was necessary to adjust the pOpulations to eliminate the difficulty in order that the desired comparisons could be made. The populations in this case were adjusted by forming pairs of observations of equal fruit length from the two pOpulations to be compared. This process in effect guaranteed samples Of identical fruit lengths and the differences in the mean areas of stem attachment were tested by a't“test. This process was repeated for each varietal comparison and for each date comparison. For the three dates on which areas of stem attachment were recorded the relationship Of Ohio MR-I7 having a larger mean area Of stem attachment than Wisconsin SMR-l5 and Wisconsin SMR-l5 having a larger mean area of stem 75 Table 18. Degree of linear relationship of area of stem attachment with fruit weight, length and diameter for the varieties Wisconsin SHE-15, Ohio NR-l? and Wisconsin SHE-12, l96A. Correlation Coefficientsll Variety Date Weight length Diameter n sun-15 7-20 .576 .606 .594 48 7-24 .679 .783 .764 137 8-20 . 835 . 907 . 868 74 MR-l? 7-20 .790 .739 .856 AB 7-ZA .6A5 .781 .777 131 8-20 .591 .712 .612 50 sun-12 7-20 .591 .637 . 588 46 7-24 .588 .651 .598 136 8-20 .488 .642 .624 59 [1 All correlation coefficients significantly different from 0, 99 to l. 76 attachment than Wisconsin SMR-l2 held true except on August 20 (Table I9) when Wisconsin SMR-IS had a significantly greater area of attachment than Ohio MR-I7. Fruit harvested on August 20 had larger areas Of stem attachment than those harvested earlier (Table 20). The varietal order established for ease Of picking force coincides with that for area of stem attachment. Also, fruit harvested at a later date have a larger area Of stem attachment and exhibit a higher picking force. It is not presently possible to Obtain data on picking force and area Of stem attachment from the same fruit Since there is not a clean separation Of fruit and stem tissue. Any attempts to determine a relationship between the two must therefore involve synthetic populations. These populations were constructed using the area of stem attachment data from July 2A for the three cucumber varieties and the stem sideways picking force data from August 3 for Wisconsin SMR-IS and August II for Ohio MR-l7 and Wisconsin SMR-I2. Picking force and area of stem attachment data were paired on the basis of fruit length, diameter or weight, and the degree 77 Table 19. Comparison of mean areas of stem attachment for the varieties Wisconsin SHE-15, Ohio MR-l? and Wisconsin SHE-12 for fruit of equal ranges of length on three dates. July 20, 1964 m Mean Area of Stem Attachment (cmz) SHE-15 .333:.017a (24)Ll .3341. 020a (23) MEI-17 .3A0:I_-.017a (24) 3423017,, (22) sun-12 V .195¢.011h (23) .2131.01Ab (22) July 24, 1964 m Mean Area of Stem Attachment (c1112) sun-15 5375.009. (72) FIR-17 .351i.010a (72). sun-12 2415,0061. (72) August 20, l96A My Mean Area of Stem Attachment (cmz) sun-15 .A99_-l;.029a (32) .396¢.019a (41) 1111-17 .A20i.021b (32) .AOAi.026a (23) SHE-12 .283;1—_.01Ab (41) .3221.015b (23) [1 Number of observations per mean. Means not followed by a common letter are significantly different, adds 19 to l. 78 Table 20. Influence of date of harvest on mean areas of stem attach- ment for fruit of equal length ranges of the varieties Wisconsin SMRpl5, Ohio MR-l? and Wisconsin SHE-12, l96A. Mean Area of Stem Attachment (cmz) Variety July 20 August 20 sun-15 .333: .016 (2A)a ”A .470 i .024 (24)a 1111-17 .378: .017 (24)a .461 1 .020 (2A)b sun-12 .185: .015 (15)a .304 i .026 (15)b Means not followed by a common letter are significantly different, odds 19 to 1. 79 of linear relationship Of picking force to area of stem attachment determined (Table 2I). These values, depending on the variety, add varying support to the concept Of picking force dependence on area of stem attachment. Among several considerations that must be taken into account is the variation in area Of stem attachment for fruit of the same length (Figures 2, 3 and A). On the basis Of the variation in area of stem attachment for fruit Of the same size and the possibility Of fruits Of widely differing sizes having equal areas Of stem attachment it is under- standable why a consistent significant relationship of picking force to area Of stem attachment failed to be detected in the synthetic populations. There is no reason to expect fruit of equal Size to have equal areas Of stem attachment, and though not investigated in the present study, position of fruit on the vine seems a likely area for future study. Bingley .gglgl. (6) reported that picking force did not depend on the position of the fruit on the vine, but their method of picking force determination was less precise than that used 80 Table 21. Relationship of picking force to area of stem attachment. Correlation Coefficients Variety Weight Diameter length sun-15 71 .146 .272* .519W 101-17 [_2 .439" .508" .402" 3101-12 73 .271 .132 .067 [l Picking force data, 8-3, SS; area of stem attachment data 7-2A. [2 Picking force data, 8-11, SS; area of stem attachment data 7-2A. [3 Picking force data, 8-11, SS; area of stem attachment data 7-2A. 8l .cumco_ _mnoo mo u_:nm OLOE no ago» now co_um_>oo.cnmocmum oco a acumoLaOL noc__ _mo_ouo> one .sem_ .sa >_se .m_-azm c_ncoom_z tom somco_ o_uae co oceanomuum Ecum to mono 1O co_mmoLmom .N OL:m_u 82 mmé 00$ mud om.m mNdm 00.0. mhd OWN mud 00d ma... N On:m_u mum-102.1 1.5sz tax."— 02 mm.— _ _ . — _ xmo.+ mo_.u> _ _ _ q _ _ _ — 0.. 1 C) OI 1 ID 9! 1 C) K) 1 to m 1 C) q- 1 IO q- 1 C) ‘Q I I0 '0. END - 1N3WHOV11V W315 :IO VBUV .Lumco_ _maoo mo u_:Lm OLOE Lo Lao» no» co_um_>OU pumccmum Oto « ucomoLaoL moc__ _mo_uno> osh .aom. .aN >_ae .a_-az o_ao tom rooco_ o_stm co ucossomuum scum 10 mean mo co_mmoLmom 83 .m On:m_u 8A m mu:m_u mmzoz_ 1 IPGZNJ tam... mbé once mm...» 00.6. ohm on.» mN.m 00.» whw OWN mN.N OO.N m: _ A _ _ _ _ _ _ _ _ — _ m— xmo.+ mN_.u > low. 1 mm. 10¢. \ ¥ 1 on. 1 mm. .. ON. 0N. 10v. aWO-lNBWHDVllV W313 :IO VBUV 85 .Lumco_ _maoo mo u_:nm oLOE 20 L301 201 co_um_>oo oumccmum oco u ucomoLQoL moc__ _mo_oao> one .aom. .aa >_so .N_-mzm c_mcoon_z not cease. o_sae co ucoELOmuum Eoum to mean 10 co_mmonmom .: On:m_u 86 J On:m_u 05102.1 15.0sz tam... 0N.¢ 00.0 0h.m 00.0 0N0 00.0 0EN, O0.N 0N.N DQN 0b.. 00.. 1 _ . _ _ — . _ _ _ u d X0001. N__.u> a 9 Q 1 C) N 1 C) N) 0 6 . m. . 61 . zwo-mawuovuv W318 .-10 vauv 1 C) “- L1 I!) St 87 in this study and the number Of fruit harvested may not have been sufficient to detect a difference. Fruit of equal size borne on different areas of the cucumber plant may have different areas Of stem attachment and therefore different picking forces. There have been no studies Of environmental influence on picking force though it is very possible that under conditions Of moisture Stress a higher picking force is required than under conditions Of adequate moisture. Taking these factors into consideration, it is presently felt that the force required to pull the stem from the fruit is initially determined by the area of stem attachment. In breeding cucumbers for multiple-pick mechanical harvesting selection Should be practiced for small areas of stem attachment to facilitate easy fruit removal. Varieties in which there is little or no increase in area of Stem attachment with increasing fruit Size might also prove useful providing the initial stem area is not a large one. Wisconsin SMR-l2 is an example of such a variety as there is less Of an increase in stem attachment area with increasing fruit Size than in Wisconsin SMR-IS and Ohio MR-l7 (Figures 2, 3 and A). 88 The progressive increase in area of stem attachment and picking force that occurs during the harvest season may be due to the advancing age and senescence Of the plants, environmental changes or both of these factors. If plant age and senescence are the primary contributing factors then the increaSe in stem attachment area and picking force are of importance to multiple-pick but not to once-over mechanical harvesting. In breeding and selecting for both methods of mechanicaT harvesting, it is important not to select for the smallest possible stem attachment area. With small attachment areas it is possible that the vine pick-up mechanisms might literally Shake the fruit from the plants befOre the vines encounter the fruit removal mechanisms. 89 SUMMARY Four characters considered important to successful mechanical harvesting of cucumbers were studied. Reduced lateral braching, sex reversal, concentrated fruit set and ease of separation of the stem from the fruit are important to multiple-pick mechanical harvesting. Concentrated fruit set and ease of separation of the stem from the fruit are important to once-over mechanical harvesting. Genetic control of lateral branching was studied through a program Of inbreeding of a reduced branching inbred in an attempt to establish a non-branching genetic line. The F6Sib] generation contained a high percentage of non-branching plants, and with the ensuing five generations of self-pollination the mean percent of non- branching plants decreased. Though a program Of inbreeding failed to fix the non-branching character, it may still be possible to incorporate it in an Fl hybrid variety utilizing the prOper inbred parents. 90 Sex reversal was also studied through a program of inbreeding and selection in an attempt to genetically fix the character. Five generations Of self-pollination of an F7Sib] inbred failed to establish a genetic line that contained IOO percent sex reversal plants. Instead, an almost constant segregation for 50 percent sex reversal plants was Observed. On the basis Of experience with the material included in these studies, it now seems difficult if not impossible to combine non-branching and sex reversal in a single true breeding line that could be utilized as a solution to the problems Of cucumber vine entanglement and center row fruit encountered with multiple-pick mechanical harvesting. In a cross of MSU 7l3-5 x Rhensk Drue it was established that the determinate growth habit of Rhensk Drue is dominant, and that Rhensk Drue is potent in transmitting the ability to develOp several fruit at one time. The F] is predominantly female in sex expression and has a number of pistillate blossoms Open for pollination at one time. Clusters of pistillate blossoms of which more than one may develOp into a fruit simultaneously, while occurring on Rhensk Drue, went unrecorded in the F]. 9I The force required to pull the stem from the cucumber fruit was studied with Ohio MR-l7 serving as the hard to pick variety, Wisconsin SMR-l2 the easy to pick variety and Wisconsin SMR-IS as a variety with an intermediate picking force. Picking force and area of stem attachment generally ShOwed the highest degree Of linear relationship with fruit length, and fruit length was therefore chosen as the index of fruit size. Ohio MR-l7 and Wisconsin SMR-IS required a higher picking force than Wisconsin SMR-l2. The position of the fruit in the picking force instrument and date Of picking influenced picking force. The order of increasing area Of stem attachment was determined as Wisconsin SMR-IZ, Wisconsin SMR-IS, Ohio MR-l7. This relationship was generally true throughout the harvest season. Fruit harvested late in the season had larger areas of stem attachment than those harvested early in the season. Seasonal changes in area Of stem attachment and picking force if primarily conditioned by plant age and senescence are important to multiple-pick but not once-over mechanical harvesting. Caution Should be exercised in breeding and selecting cucumbers for mechanical harvesting not to develOp a variety in which the fruit can be shaken from the vines before encountering the fruit removal mechanism. 92 REFERENCES CITED Anonymous. I957. Information concerning entry Of Mexican agricultural workers into the United States. Bureau Of Employment Security Farm Placement Service. BES NO. F-IA6. United States Department of Labor. Anonymous. I960. CRCO pickle picker I960 Operations. Chisholm-Ryder Co., Inc. Niagra Falls, New York (unpublished). Anonymous. l96A. State News - Florida, Help. Amer. Veg. Grower l2(5):A8. Anonymous. l96A. State News - California, It may be the last. Amer. Veg. Grower l2(5):50. Bingley, G.W. I959. Construction, evaluation and efficiency studies of a mechanical cucumber harvester. M.S. Thesis. Michigan State University, East Lansing, Michigan. , R.K. Leonard, W.F. Buchele, B.A. Stout and S.K. Ries. I962. Mechanical cucumber harvesting. Agr. Engineering A3(l):22-25,3A. Boyette, F.B. I963. Pick cukes in comfort. Res. and Fmg., N.C. 22(2):6. Dearborn, R.B. I936. Nitrogen nutrition and chemical composition in relation to growth and fruiting of the cucumber plant. Cornell Unv. Agr. Expt. Sta. Memoir I92. Duchaine, W.J. I96A. Imported labor fills big need - Mexican braceros important to Michigan crop harvests. State Journal, Lansing-East Lansing, Michigan, August 2A, p.Fl,6. IO. II. I2. l3. IA. IS. l6. I7. l8. 93 Hall, B.J. and J. H. MacGillivray. I956. Mechanical cucumber picking. Calif. Agric. l0(l): Hayes, J. l96A. The bracero program is dead. Amer. Veg. Grower l2(ll): 7. ' Heimlich, L.F. I927. The development and anatomy of the staminate flower Of the cucumber. Amer. Jour. Bot. IA:227-237. HeSIOp- -Harrison, J. I957. The experimental modification of sex expression in flowering plants. Biol. Rev. 32: 38- -90 Holmes, E.S. I960. Mechanical aids and equipment for harvesting vegetables in Florida. Proc. Fla. State Hort. Soc. 72:I97-l99. Hutchings, I.J., C.A. John, J. Prend and C.C. Wyatt. I962. An instrument for the measurement of the force required for the separation Of cucumber fruit from the peduncle and for the measurement of the firmness of tomato fruit. Proc. Amer. Soc. Hort. Sci. 8I:A87-A92. Hutchings, A.E. I9A0. Inheritance in the cucumber. Jour. Agr. Res. 60(2):ll7-I28. Ito, H. and T. Saito. I957. Factors responsible for the sex expression of Japanese cucumber. VI. Effects Of artificially controlling day length and night temperature during the various stages Of seedling development in the nursery bed. J. Hort. Assn. Japan 26: -8 (Hort. Abstr. I958. 28:68 Abstr. NO. AZA) I957. Factors responsible for the sex expression Of Japanese cucumber. VII. Effects of long day and high night temperature treatment applied for a short period at the various stages of seedling develOpment on the sex expression Of the flowers. J. Hort. Assn. Japan 26: IA9- l53 (Hort. Abstr. 28:229 Abstr. No. lAl8). 20. 2]. 22. 23. 24. 25. 26. 27. 28. 29. 9A Judson, J.E. I929. The morphology and vascular anatomy of the pistillate flower of the cucumber. Amer. Jour. Bot. l6:69-86. Leonard, R.K. I958. Mechanical cucumber harvesting. ILS. Thesis. Michigan State University, East Lansing, Michigan. McColIum, J.P. I934. Vegetative and reproductive responses associated with fruit develOpment in the cucumber. Cornell Agr. Expt. Sta. Memoir I63. Meister, R.T. l96A. Rose colored glasses are costly. Amer. Veg. Grower l2(l0):34. Michigan Department of Agriculture. l96A. Michigan Agricultural Statistics. Mitchell, W.D. I962. Physiological and biochemical aspects of flower sex expression in cucurbits with special reference to Cucumis sativus L. Ph.D. Thesis. Michigan State University, Eastfansing, Michigan. Nitch, J.P., E. Durtz, J. Livermann and F. Went. I952. The development of sex expression in cucurbit flowers. Amer. Jour. Bot. 39:32-h3. Odland, M.L. and D.W. Groff. I963. Linkage of vine type and geotrOpic response with sex forms in cucumbers, Cucumis sativus L. Proc. Amer. Soc. Hort. Sci. 82:358-369. Peterson, C.E. I960. A gynoecious inbred line of cucumbers. Mich. Agr. Expt. Sta. Quart. Bul. h3:40-92. I963. Remodeling the cucumber. Libby's ContractCrOps 2(5):8-ll. and D.J. DeZeeuw. I963. The hybrid pfckling cucumber Spartan Dawn. Mich. Agr. Expt. Sta. Quart. Bul. £6:267-273. 30. 32. 33. 34. 35. 36. 37. 38. 39. 95 and L.D. Anhder. I960. Induction of staminate flowers on gynoecious cucumbers with gibberellin A3. Science l3l:l673-l67h. Phatak, S.C. I959. Studies on floral biology, sex expression and sex ratio in cucumber (Cucumis sativus L.) Thesis for the Associateship of the Indian Agr. Res. Inst., New Delhi. Putnam, A.R. I963. Horticultural aspects concerned with the production of pickling cucumbers for once-over harvest. M.S. Thesis. Michigan State University, East Lansing, Michigan. Ries, S.K. I957. The effect of spacing and supplemental fertilizer application on the yield of pickling cucumbers. Mich. Agr. Expt. Sta. Quart. Bul. 40:375-38I. ' Shifriss, 0. l96l. Sex control in cucumbers. Jour. Hered. 52:5-I2. Snedecor, G.W. I956. Statistical Methods. Iowa State College Press. Ed. 5 Steel, R.G.D. and J. H. Torrie. I960. Principles and Procedures of Statistics. McGraw-Hill Book Company, Inc. Stout, B.A. and S.K. Ries. I959. A progress report on the development of a mechanical cucumber harvester. Mich. Agr. Expt. Sta. Quart. Bul. hl:699'7l8. and A.R. Putnam. I963. The feasibility of a once-over mechanical harvester for pickin cucumbers. Mich. Agr. Expt. Sta. Quart. Bul. 45: 07-4l6. Stuckman, N.W. I959. Michigan pickling cucumbers - the grower, the picker and the WYRF. Mich. Agr. Expt. Sta. Quart. Bul. h2:2-23. 96 40. Tiedjens, V.A. I928. Sex ratios in cucumber flowers as affected by different conditions of soil and light. Jour. Agr. Res. 36:72l-7h6. AI. . I928. The relation of environment to shape of fruit in Cucumis sativus L- and its bearing on the genetic potentialities of the plants. Jour. Agr. Res. 36:795-809. #2. Toan, C.S. l96A. National council formed by agricultural employers. Amer. Veg. Grower I2(8): 1 - I9. IIIIIIIII H I.“ I" I1 ms 3800 030