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SELEC'ING POTATO TUBERS IN TH; BREEDII‘EG PROGRAI‘vi \ ‘J ; presented by Clyde Leaon Burton ‘ ~ has been accepted towards fulfillment ‘ of the requirements for _M_..S..__degree in arm Cro ,s . 5 A4: srl 4 '. ‘3': ”gm Major professor 1' Date May 28, 1952 ". I ‘ - ‘ . , ‘> , /~ "Jr ( ‘5 ‘ — T—fihr _“ 1’ , ' '. «l “ vf ' -. - r1 x)“ \. ‘7 .' ’ 1 -, a t 1' ,.- T " /.‘. | t , A \ e a. If. ‘ ‘ .. THE VALUE OF SIZE OF VINE, SET, SIZE AND SHAPE OF TUBERS AS INDEXES FOR SELECTING POTATO TUBERS IN TEE BREEDING PROGRAM by Clyde Leaon_§ynton A THESIS Submitted to the Graduate School of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Farm Crops 1952 ‘1‘. if; 7 CI //4/:)’/Ls- ACKNOW LEDGIWT The writer wishes to express his sincere appreciation to Professor E. J. Wheeler for his valuable suggestions and unfailing interest. Grateful acknowledgment is also due to Professor H. M. Brown for his helpful criticisms and judgment in analyzing the thesis. £ {‘3‘ c; x. .. ..,V' 1. II. III. V. VI. CONTENTS INTRODUCTION 0 REVIEW OF CITED LITERATURE EXPERIMENTAL PROCEDURE RESULTS AND DISCUSSION SUMMARY BIBLIOGRAPHY THE VALUE OF SIZE OF VINE, SET, SIZE AND SHAPE OF TUBERS AS INDEXES FOR SELECTING POTATO TUBERS IN THE BREEDING PROGRAM I. INTRODUCTION Some potato breeders believe that there is a correlation between seedling characters in the greenhouse and their subse- quent performance in the field trials. They feel that these characters are not influenced too markedly by environmental factors, thus allowing a visual classification in discarding a large percentage of the undesirable seedlings grown in the greenhouse. If this were possible it would save time, labor and cost of planting the tubers in the field trials, as well as reducing the arduous task of hand digging them at harvest time. Of the thousands of new potato selections that are grown in the field trials each year, less than ten percent show promise of being of any‘economic value. A heterozygous plant such as the potato can be vegetatively propagated without changing the desirable genotype. With this in mind, it is hypothesized that there is a positive relationship between size, set,.and shape of tubers of seedling lines in the greenhouse and the subsequent behavior of those lines in the field. It has also been assumed that the healthy, vigrous medium to large vine types in the greenhouse will produce similar vines in the field. It is generally known that potatoes with healthy, medium. to large vines are far better producers of tubers than those with small vines. -2- Potatoes grown from true seed, and planted in the greenhouse so as to expedite breeding work, require considerable space and time. This is one of the necessary pregrams that must be followed in potato breeding work and little can be done to reduce the time and space at this point. The next procedure after the greenhouse phase involves the planting of the potatoes in the field for se- lection of desirable types. This operation requires a great deal more space and labor than that of the greenhouse. If 10,000 plants are grown in the greenhouse, this means that more than one acre of tubers will have to be grown in the field,,and it can easily be seen that a method of reducing the number of tubers planted in the field would be useful. In view of the mounting shortage of farm labor and the increased work placed upon the potato breeders and investigators, this experi- ment was designed to seek methods to eliminate part of the laborous task of field harvesting and still recover most of the desirable seedlings when harvested in the greenhouse. ~5- II. REVIEW OF CITED LITERATURE A search of potato literature revealed few observations regarding the problem studied. Meet of the literature has to do with certain physiOIOgical factors or results affecting the growth of the potato plant in one way or another. Livermore (2), studying the correlation of seedling per- formance in the greenhouse and their subsequent yield in the field with 2,000 seedlings of several varietal crosses, found that the association between greenhouse growth and yield in the field was not very strong. "The coefficient of correlation in all cases was too low to permit any confidence in using seedling size in the greenhouse as a means of selecting the better producers." Bushell (1) found that the number of plants per hill within the ordinary range of one to five, is itself not an important factor in yield of potatoes. As a general rule, an increase in number of stalks per hill increases the number of tubers per hill. Werner (5) reports that a new sprout is almost entirely de- pendent upon the seed piece until the first leaves are sufficiently' developed to manufacture more food than they can use. This means that potato plants generally draw upon the old seed piece until the plants are eight to 12 inches tall. -4- III. EXPERIMENTAL PROCEDURE The greenhouse planting was made at the Michigan Agricultural Experiment Station in East Lansing. In the mid-summer of 1950, seeds from eight scab resistant crosses were planted in flats in the greenhouse. When the seedlings were from one-half to one inch in height, approximately 1,000 seedlings representing eight crosses were transplanted to three and one-half inch clay pots that were placed on the greenhouse benches. Here the seedlings were allowed to grow until the last of November at which time they were harvested. The potato seedlings were grown in number 2 plastering sand, were watered regularly and were supplied with a standard nutrient solur tion to secure the best growth under fall greenhouse conditions. The temperature varied from.65 to 75 degrees F. No artificial lights were used during the experiment. No unusual conditions were observed in the greenhouse. ‘ A population of only 1,000 plants was used because of the exacting and time-consuming measurements that had to be made. After approximately 15 weeks of growing, when ten percent of the leaves showed yellowing, the plants were harvested. The greenhouse data included a classification of the vines into three groups; small medium and large, according to the height and fullness of the vine. A more accurate measurement of the vine size was also made using a relative scale of one to ten. The very smallest vines were called one, and the very largest vines, ten. The smallest vines were approximately four inches in height and the largest vines approxi- mately 16 inches in height (Figure I and II). The class range was -5- 1 5/8 inches. By placing the vines into ten classes, it was believed that this would give a better indication of growth of each plant than by merely classifying the vine as small, medium, or large. The vines were also noted as being thin, medium, or heavily leaved. Vines observed as small were measured and re- corded as l,,2,,5 thin,,5 medium, and 4 thin. Those vines ob- served as medium were in classes 5 heavy, 4 medium, 4 heavy to 6 thin, 6 medium, and 7 thin. The vines observed as large were in classes 6 heavy, 7 medium, 7 heavy to 10 heavy.. This was true of all three measurements; greenhouse, July 17 and August 20. At'the same time data were recorded as to the number of tubers set, and the length and width to the nearest tenth of a centi- meter of all tubers. The tubers from each plant were placed in a one pound kraft bag on which was indicated the plant number. Those of a cross were put tOgether in a sufficient number of 25 pound bags on which was indicated the cross number. They were then placed in storage until planting time in the spring. The field studies of the problem were conducted at the Michigan Agricultural Experiment Station at Lake City, Michigan. Planting date was May 50, 1950. The largest tuber from each vine harvested in the greenhouse was planted as a one hill unit in the field. The hills were spaced 18 inches apart and there were 40 hills per row. The distance be- tween rows was 56 inches. The soil was relatively uniform.and was -6- considered to be desirable for high potato production. Standard cultural pactices, such as fertilization, spraying, irrigation, cultivation, etc. were carried out through the growing season. There were no unusual weather conditions during the summer. Although there was a severe epiphytotic of late blight in the area,,the experiment station kept ahead of the disease by con— tinuous spraying and, as a result, none of the plants in this experiment were seriously infected. on July 17, when the potato plants were in full flower (Figure III) a measurement of the growth of vines was taken by using a relative scale from one to ten. The very smallest vines, or the number one class, were approximately five inches high, and the largest, the number ten class, were approximately 19 inches high. The class range was 1 5/8 inches. It was also noted as to whether the vines were thin, medium, or heavily leaved. The plants were observed as being small, medium, or large in height. At the same time another observation;was made on the large plants as to whether they had healthy, vigorous vines or non-healthy, spindly' vines. On August 20th, when 15 percent of the vines were beginning to turn yellow (Figure IV), the same procedure used on July 17th, as to note taking,.was again followed.. The relative scale had to be re- vised to compensate for the prOgress made in vine growth.. The average height of the number one class potato vines was seven inches, -7- and the approximate height of the number ten vines was 26 inches. The class range was 2 1/4 inches. During the first week in September the experiment was harvested. Each hill was dug separately by hand (Figure V). The data recorded included the number of tubers per hill over one-half inch in diameter. This was to determine the relationship between number of potatoes set in the greenhouse and the number produced in the field. The number of stalks per hill was noted. So as to obtain a statistical analysis of tuber shape and size, the length and width, to the nearest tenth of a centimeter, of the largest tuber from each hill was taken. A note as to the tuber selection rating of each hill, whether "poor", "fair", "good , or “excellent" was recorded. 0f the original 1,000 seedling lines grown in the greenhouse, approximately 915 were harvested. The indicated reduction in numbers of lines was due to various factors. No losses were due to failure to germinate or due to diseases. The degree of association of several of the characters studied was determined by the coefficient of correlation. IV. RESULTS AND DISCUSSION The probability of obtaining a relationship between the performance of potato seedling lines grown in the greenhouse and their subsequent behavior in the field is complicated by the self-evident fact that the two phases of the experiment were grown under different environmental conditions. It is difficult to determine when size and habit of vine” set, size, shape and selection rating of tubers are the result of genetic factors, or when they are the result of non-gentic factors. It is assumed that the differentiation, development, and proper functioning of the vegetative organs of plants would be influenced somewhat in the same way, if all plants were grown. under identical environmental conditions. In other words, if the soil, light, and moisture were such that they would induce vines to grow taller, then proportionately, all vines would be taller. The potato seedlings were grown under unferm conditions both in the gréhhouse and in the field. Size of Vine In general there seems to be a practical relationship be- tween greenhouse vine size and field vine size. The average coefficient of correlation between vine size in the greenhouse and in the field, July 17, was 0.52; and in the field,,August 20, was 0.47,,Table 1. Table 2 is a table obtained from the scatter-diagrams of the eight crosses. It shows the greenhouse vine sizes and the rela- tive rank of the vine sizes when measured July 17, and again on: -9- August 20. The rating of a vine as small in the greenhouse does not mean that the tuber from that small vine will always produce a small vine in the field. This similar condition is also true for vines rated as medium or large in the greenhouse. It should be noticed, however,,that 85 percent of the lines producing large vines in the greenhouse produced large vines in the field on July 17, and that 51.8 percent of the lines producing medium vines in the greenhouse produced similar sizes in the field, and that 75 percent of the lines rated small in the greenhouse were rated as small or medium in the field. While there was not as strong a relationship as might be desired, the relationship was strong enough to be of practical value. Table 5 gives the distribution of the various seedling lines when grouping is made according to date when observational notes were taken on vine-size, (large, medium, or small) and according to the tuber-selection rating made in the field at harvest time. Only lines whose tuber rating was "excellent" were likely to have passed the harvest-time screening test. THE COEFFICIENT OF CORRELATION THE EIGHT CROSSES -10- TABLE 1 OF THE DIFFERENT FACTORS COMPARED WITHIN Factors Number of cross correlated ‘ l 2 5 4 5 6 7 8 Av.* GH‘* Vine height 050 062+ .47 051 056 .52 .40 056 0.52 July 17 vine height GH vine height .52 .42 .58 .49 .55 .45 .59 .49 .47 Aug. 20 vine height GH tuber Bet 057 019 011 056 017 015 010 025 .21 Field tuber set GH tuber set 021 .14 .19 059 040 .29 020 - .27 Field set/stalk G’H tLIber length .15 029 026 015 059 029 040 025 027 Field tuber length on tuber width .20 .27 - .50 .40 .58 .25 .27 ~52 Field tuber width GH tuber ratio .29 .49 .45 .44 .29 - - - .41 Field tuber ratio Population of 99 105 49 69 85 561 55 145 each cross Degrees of freedom 97 101 AL7 67 81 514 51 .141 Level of signif- .195 ~195 0288 0252 0217 .115 0275 0159 icance at 5% Level of eignif— .254 .254 .512 .285 .148 .554 .208 icance at 1% * Z value used ** Greenhouse MCDCOCEZEIM'JJQ -11- TABLE 2 TWO WAY TABLES SHOWING GREENHOUSE VINE SIZE AND THE RELATIVE RANK OF THE VINE SIZES WHEN MEASURED JULY 17 AND AUGUST 20 Small Medium Large .3 .3 .3 5 ti 3 E E3 3 E3 5: tag: a. (3;: 0* (fig :3 . h . $4! 5 3H o :2 33%; :2 Duo 2: tho EH July 17 Small 50 16.0 179 57.2 84 26.8 515 Medium 16 4.2 121 51.8 244 64.0 581 Large 5 1.4 54 15.4 184 85.2 221 Total 69 554 512 915 August 20 Small 112 55.8 170 54.5 51 9.9 515 Medium 45 11.5 259 62.7 99 26.0 581 Total 165 514 258 . 915 -12- It is seen that of the lines whose vine size was classed as small in the greenhouse only three produced “excellent" tubers. By dis- carding all small plant lines in the greenhouse a considerable reduction, 54 percent, in the field layout could be made. These same three lines represent 10 percent of the total number of lines with tuber rating of “excellent". The saving in field work would seem to warrant this lost however. When the observational notes were taken at flowering time, 258 plants were recorded as having large, healthy, vigorous vines. The harvest time data on tuber type showed that, within this group of 258 plants there were included all but one of the "excellent" hills and all but 12 of the "good” hills. When the observational notes on vine size were made one month later (August 20), only 160 plants were indicated as having large, healthy, vigorous vines. These included 15 (or 50 percent) of the "excellent" tuber hills and 45 out of 115 "good" tuber hills. This was a considerable drop in accuracy of prediction when compared with the notes taken at flowering time. On July 17 (Table 2) there were 512 plants measured as large, August 20 there were only 258 large vines. This may indicate that a certain few vines grew more rapidly than the majority of the other vines, thus alterating the predictions in such a way that an accurate picture of the field could not be seen. The vines that produced considerable vegetative growth after flower- ing time generally set "poor" tubers. 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