WI \ “HHWHUHUWtWI“\|MW|\H|H\|\|\{W HO); I-D-O (00105 “£838 Date This is to certify that the thesis entitled MODIFYING REPRODUCTIVE DEVELOPMENT OE SUGARBEET (Beta vngaris L.) WITH GROWTH REGULATORS presented by Hus on D j a j asulmn't a, has been accepted towards fulfillment of the requirements for Ph.D. degree in CrOD Science .’/ .‘ ~—(’ L_/ ’2 ‘-\(..I K/ Cd ’//I /, " Majoi professor 0-7 639 LIBRARY Michigan 36393 IJnhnxéfiy MODIFYING REPRODUCTIVE DEVELOPMENT OF SUGARBEET (EETA VULGARIS L.) WITH GROWTH REGULATORS BY Husen Djajasukanta A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1978 ‘77 (345%; - ABSTRACT MODIFYING REPRODUCTIVE DEVELOPMENT OF SUGARBEET (BETA VULGARIS L.) WITH GROWTH REGULATORS BY Husen Djajasukanta Potential use of growth regulators in hastening or delaying flowering of sugarbeet (ggta vulgaris L.) was studied in the field and in the greenhouse in 1975, 1976, and 1977 at East Lansing, Michigan. Five slowly bolting and two rapidly bolting lines were grown to compare the effects of eight different chemicals at different concentra- tions and frequencies of application applied as foliar sprays. For field experiments, overwintered roots from sugarbeet seed fields inOregon were used. Rooted stem cuttings and seed plants, exposed to different periods of photothermal induction prior to growth regulator treatments, were used in the greenhouse experiments. Five growth regulators appeared to be ineffective on the slowly bolting lines. The applications of gibberellin GA4A7 (2x50 ppm) shortened and ethephon (2,000 or 4,000 ppm) delayed the time of flowering of the rapidly bolting lines SP 6822-0 and UI 1861 x 2161, respectively. Heights of flower stalk (stem) were not affected. ACKNOWLEDGMENTS To the following, I wish to express my sincere appreci- ation and gratitude for their assistance: Dr. Freeman W. Snyder who served as co—chairperson of the Guidance Committee, for his valuable advice and encour- agement throughout my research studies, and helpful criti— cisms in the preparation of this manuscript. Dr. George J. Hogaboam who served as co—chairperson of the Guidance Committee, for providing use of the facilities of USDA Agricultural Research Service, and his critical review of this manuscript Dr. Donald Penner, for his kind service in the Guidance Committee, helpful counsel and assistance in conducting the experiments, and critical review of this manuscript. Drs. Lawrence 0. Copeland and James W. Hanover, for their kind service in the Guidance Committee, and critical reviews of this manuscript. West Coast Beet Seed Company, Abbott Laboratories, and Lilly Research Laboratories, for providing sugarbeet stecklings, gibberellins, and A—Rest, respectively, and various sources on campus for providing other growth regulators. The government of the Republic of Indonesia, for ii the study-leave granted and opportunity given to study in the United States. Finally, a special thanks to my wife Farida, for her patient understanding, and to my children Nugraha, Djatnika, and Indrijani, for their sacrifice in being separated from their parents during these graduate studies. TABLE OF CONTENTS Page List of Tables . . . . . . . . . . . . . . . . . . . v INTRODUCTION . . . . . . . . . . . . . . . . . . . . 1 LITERATURE REVIEW . . . . . . . . . . . . . . . . . 2 MATERIALS AND METHODS . . . . . . . . . . . . . . . 9 Field Experiments with Growth Promoters . . . . 9 Field Experiments with Growth Retardants . . . ll Greenhouse Experiments with Gibberellin . . . . 12 RESULTS AND DISCUSSION . . . . . . . . . . . . . . . 16 Field Experiments . . . . . . . . . . . . . . . 16 Time of Flowering . . . . . . . . . . . . l6 Heights of Flower Stalks . . . . . . . . . 20 Greenhouse Experiments . . . . . . . . . . . . 22 Time of Flowering . . . . . . . . . . . . 22 Heights of Flower Stalks . . . . . . . . . 25 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . 29 LITERATURE CITED . . . . . . . . . . . . . . . . . . 31 iv LIST OF TABLES Table . Page 1 Field Experiments with Growth Promoters at East Lansing, Michigan. . . . . . . . . . . . 10 2 Time of Flowering of Two Slowly Bolting Sugar- beet Lines Sprayed with Gibberellin at East Lansing in 1975 and 1976 Field Experiments. . l7 3 Time of Flowering of Two Slowly Bolting Sugar- beet Lines Sprayed (asaSplit Application) with Different Kinds of Growth Promoter at East Lansing in 1977 Field Experiments . . . . . . 18 4 Time of Flowering of Two Rapidly Bolting Sugar- beet Lines Sprayed with Gibberellin at East Lansing in 1975 Field Experiments . . . . . 19 5 Time of Flowering of Rapidly Bolting UI 1861 x 2161 Sugarbeet Line Sprayed (as a Split Application) with Different Kinds of Growth Retardants at East Lansing in 1977 Field Experiment. . . . . . . . . . . . . . . . . . 21 6 Flower Stalk Heights of Two Slowly Bolting Sugarbeet Lines after Spraying with Gibberelin at East Lansing in 1975 and 1976 Field Experiments . . . . . . . . . . . . . . . . . 23 7 Flower Stalk Heights of Two Rapidly Bolting Sugarbeet Lines after Spraying with Gibberel- lin at East Lansing in 1975 Field Experiments. 24 8 Time of Flowering of Stem—Cutting Plants of Slowly Bolting Sugarbeet Line F 66-562-HO Exposed to Different Periods of Photothermal Induction and Sprayed with Gibberellin in the Greenhouse in 1976/1977 . . . . . . . . . 24 9 Time of Flowering of Seed Plants of Rapidly Bolting Sugarbeet Line UI 1861 x 2161 Exposed to Different Periods of Photothermal Induction and Sprayed with Gibberellin in the Greenhouse in 1976/1977 . . . . . . . . . . . . . . . . 25 Table 10 11 Page Flower Stalk Heights of Stem-Cutting Plants of Slowly Bolting Sugarbeet Line F 66-562-HO Exposed to Different Periods of Photothermal Induction, after Spraying with Gibberellin in the Greenhouse in 1976/1977 . . . . . . . . . 27 Flower Stalk Heights of Seed Plants of Rapidly Bolting Sugarbeet Line UI 1861 x 2161 Exposed to Different Periods of Photothermal Induction, after Spraying with Gibberellin in the Green— house in 1976/1977 . . . . . . . . . . . . . 28 vi INTRODUCTION Male and female component plants of sugarbeet (EEEE vulgaris L.) for producing hybrids may fail to flower at the same time under natural conditions. Slowly bolting lines should be hastened to flower or rapidly bolting lines should be delayed from flowering to synchronize time of flowering of both slowly and rapidly bolting lines to allow hybridi- zation. A number of growth regulators have been used success— fully to modify growth and development of numerous plants. Flowering by sugarbeet may be accelerated by gibberellin treatments. Other growth regulators have potential effects in modifying sugarbeet plants. The objectives of this study were to test the hypo- theses that (1) the application of gibberellin and other growth promoting substances of correct concentrations at a given stage of development could shorten the time to flower for slowly bolting sugarbeet plants, and (2) the application of growth retardants of correct concentrations at a given stage of development could lengthen the time to flower for rapidly bolting sugarbeet plants. LITERATURE REVIEW Research results showing modified growth and develop— ment of various plant species by the application of growth regulators have been reported. Many reviews have surveyed the literature on modification of plant growth by growth regulators (Cathey, 1975; Sachs and Hackett, 1969 and 1972; Wittwer, 1968 and 1971; Thomas, 1976; Wareing, 1976). There is evidence of increasing use of gibberellic acid (gibberellin GA3) for a variety of purposes. For example, gibberellic acid has been used to accelerate flower formation in lettuce. Promotion of flower initiation by gibberellic acid is well-known for many long day-requiring rosette plants. Gibberellin GA4A7 mixture is used in hybrid cucumber seed production and for enhancement of fruit set— ting in apples and pears. Among the growth retardants reported effective in a large number of plant species are (2-chloroethy1)trimethyl ammonium chloride (CCC, chlormequat) and succinic acid 2,2—dimethy1 hydrazide (SADH). Two other growth retardants, a-cyclopropyl—a-(p—methoxyphenyl)-5—pyrimidine methanol (ancymidol) and (2-chloroethyl) phosphonic acid (ethephon), have also been used on various plants. CCC, SADH, and ancymidol are used for reducing stem length in a range of ornamental pot plants, nursery crOps and fruit trees. Leaf and flower initiation may be inhibited. CCC is widely used on wheat in western Europe. SADH is extensively used for reducing vegetative growth and promoting flower initiation in tree fruits. The uses of ethephon include the induction and ripening of pineapples. Flower stalks of many vegeta- bles can be reduced by ethephon. Selected research results of experiments with gib— berellin on some plants are cited in this review. According to Bukovac and Wittwer (1967) several biennials grown at temperatures slightly above the critical temperature for flower formation were induced to flower with gibberellin. The normal cold requirement for flowering may be partially or, in few instances, completely replaced by the application of one or several foliar sprays of 100 to 1,000 ppm of gibberellin. Globerson (1972) stated that the combination of root soaking and foliar spraying carrot plants with 100 ppm gib— berellin GA3 (gibberellic acid, GA) caused a higher percent- age of plants to flower than did spraying alone. According to Dickson and Peterson (1960), an aqueous solution of gibberellin at 100 and 1,000 ppm applied five to six times to carrots in greenhouse and in the field, commencing at the six to eight leaf stage, induced earlier and higher percentages of flowering plants. GA sprayed at the rate of 3 to 10 ppm on young lettuce plants increased yield. Treated plants matured about two weeks earlier and the plants had extremely uniform maturity (Harrington, 1960). Flowering of cauliflower (Brassica oleracea var. botrytis) cv. 'Hilary Seale' was accelerated maximally by a combination of cold treatment and gibberellin GA3 (50 ppm) (Leshem and Steiner, 1968). Salter and Ward (1972) con- cluded that gibberellin GA had little effect on crop 4A7 maturity characteristics of cauliflower plants. Flowering was induced in Einia elegans under non- inductive 24-hour photoperiods by the application of gib- berellic acid (100 mg/l), although flowering was later than under inductive 8-hour photoperiods (Sawhney and Sawhney, 1976). May and Bula (1971) reported that 85 to 90% of red clover plants (Trifolium pratense L.) of the single-cut cv. 'Tammisto' maintained under an inductive photoperiod but noninductive thermoperiod treated with two foliar sprays of gibberellin GA3 initiated floral stems within 4 weeks after treatment. Garrod (1974), Gaskill (1957),and Snyder and Wittwer (1959) have reported effects of gibberellins on sugarbeet plants. Garrod studied the effects of GA on young (vegeta- tive) sugarbeet plants. According to Gaskill, with at least one bolting—resistant sugarbeet cultivar, gibberellic acid can serve as a substitute for a substantial part of the photothermal induction treatment normally required for satisfactory reproductive development. Snyder and Wittwer concluded that flowering in sugarbeet may be accelerated and even induced with gibberellin if treatments (repeated spray application of solutions of 1,000 ppm to growing tips) are accompanied by exposure of the plants to a long (18-hour) photoperiod. Results of experiments with different kinds of growth retardants cited in this review further involved with a variety of mostly horticultural crop plants. According to Shanks (1969), ethrel, a mixture of (2—chloroethyl) phos— phonic acid and related compounds, has shown activity in dwarfing of several flower crops. Shanks (1972) also reported that SADH was ineffective but CCC (chlormequat) and ancymidol retarded growth of several cultivars of Chinese hibiscus (Hibiscus rosa-sinensis L.), inducing shorter nodes and more and earlier flowering during summer months. The length of terminal shoots was also reduced by ethephon. Ethephon reduced flowering and stimulated the growth of lower axillary shoots of unpruned plants. Foliar spray of 50 ppm ancymidol was effective in reducing internode elongation of five tropical, foliage horticultural plant species as reported by Henley and Poole (1974). SADH (10,000 ppm) reduced internode elongation in two other Species studied. According to Dorrell (1973), SADH and CCC (1,000 and 10,000 ppm) reduced total plant height of cultivars of sun- flower (Helianthus annuus L.). Flowering was also delayed. Less stem elongation of various plants was reported by Cathey and Stuart (1961) when the potting soil was treated with CCC and other growth retardants. According to Hackett and Sachs (1967), the growth retardant cycocel ((2-chloroethyDtrimethy1 ammonium chloride) promoted flowering of rooted cuttings of Bougainvillea grown under short days. GA3 greatly delayed flowering. In comparing the effectiveness of some growth re- tardants, Cathey and Heggestad (1973) concluded that foliar sprays of ancymidol were at least 80 to 500 times more active than chlormequat in retarding stem elongation of cultivars of poinsettia (Euphorbia pulcherrima Willd.). According to Marshall, Joiner, and Witte (1974) ancymidol reduced heights of midcentury hybrid lily ’Enchant— ment' but not the size of the inflorescences. A single spray application of ancymidol (0.125 mg/ lO—cm pot) or two 0.5% sprays of SADH at 2-week intervals reduced height of five cultivars of garden type Chrysanthe— mums grown as single plants in pots (Wilfret, 1974). According to Hebb, Witte,and Sheehan (1974) ancymidol (2, 4, and 8 ppm) applied as soil drench reduced height of two cultivars of standard Chrysanthemums. SADH (1,250, 2,500, and 5,000 ppm) reduced heights of plants grown under 2-week photoperiod treatment. Ancymidol delayed flowering. 'Sovereign' Fl cultivar of marigold (Tagetes erecta L.) plants grown in a complete nutrient solution and treated with a weekly foliar spray of SADH were significantly shorter than the controls. Grown under short days, the flowering was delayed up to 8 days by SADH (McConnell and Struckmeyer, 1970). Applied to short-day, Great Northern Nebraska No. 1 sel. 27 dry bean (Phaseolus vulgaris L.) line, 500 ppm CCC promoted early flowering when plants were grown under long photoperiod (Coyne, 1969). Foliar sprays of ethephon retarded the height of onion (Allium cepa L.) and when applied to non-bolting plants partially prevented seed stalk emergence and reduced seed yield of early developing inflorescences. Two field applications of 480 ppm ethephon, starting when 75% of the plants had visible seed stalks, reduced seed stalk heights (Levy, Ventura, and Kedar, 1972). Bolting of cos lettuce (Lactuca sativa L. var. romana) was delayed by treatments with CCC and SADH (Nothman, 1973). Promising results of the use of gibberellin and other growth regulators in modifying plants were used as a basis of experiments reported herein to study the potential use of growth regulators to synchronize time of flowering of male and female component plants for producing hybrid sugarbeet. In addition to growth regulators mentioned in the selected references cited, 2,4—D and urea also have been studied. According to Howell and Wittwer (1954) foliar applications of 2,4-D to sweet potato resulted in flowering. Although urea is generally used as fertilizer, in tions it has potential use as a growth regulator. MATERIALS AND METHODS Field Experiments with Growth Promoters Four experiments in 1975 and two experiments each in 1976 and 1977 were conducted to test whether growth promoters would hasten sugarbeet plants to flower. Naturally cold- induced roots from sugarbeet seed fields in Oregon were planted in May at East Lansing, Michigan. The roots were stored in the cold room at 5°C for two months and then transferred to the field. Pests and diseases were con- trolled as needed. The sugarbeet lines used, their_bolting character- istic and the growth promoters applied in all field experiments with growth promoters are listed in Table 1. Field experiment numbers 5 and 6 repeated field experiment numbers 1 and 2, respectively. A randomized block design was used in all experiments. Treatments were replicated four times in 1975 and 1976, and three times in 1977 experiments. The experimental unit was a single-row plot, consisting of 4 plants in 1975 and 10 plants in 1976 and 1977. The rows were 90 cm apart with 30 cm spacing between plants within each row. The growth promoter treatments were different con- centrations, either as single or equally-Split applications. In the 1977 experiments all growth promoters were applied 10 .pcofipmwnu Mowao mcflpsaocH m :ogmmnum M MGHD m ou¢.m m savao m mam meflnaon mazoam Gm gm seas m m condense m GQHD m als.m m navao m mam mefluson sagosm am am span a He memo mefiuaon sezofim «mIGGmImG m Gems o as Davao menusog saaoam palms m mass m Hm aand mefluson Savage“ oummmm mm mean a Hm saaao mqfluaon savages seam x Hows Hp mama m Ho 4 aw meanesn Razoam «mumsmnaw a mean N am passe meflbaon SHBOHO sfilms m mums H OHDmHHobomumnu oEmz musmfiumwua HOHOEOHm How» .02 mo Hwnfidz sasouw mafia pmwnummsm .umxm .cmmH£0HE .mcflmcmq ummm pm mumuofioum £D3OHO swag mucmEHHonm camflm .H Danae 11 in equally-split applications. Urea, 2,4-D, and ethphon were applied in low concentrations. Each plant received a foliar spray of growth promoter in water with Tween 20 at 0.1% by volume added as surfactant. Approximately 3 m1 of solution per plant were applied for the 1975 experiments and 10 ml for the 1976 and 1977 experi- ments. Plants sprayed with water were used as checks. The plants were sprayed 2 to 3 weeks after planting. In split applications, the plants were resprayed one week later. Growth responses measured and analyzed were (1) time of flowering, calculated as days from planting to first flower appearance, and (2) heights of flower stalks (stems) in cm at weekly intervals for a couple of weeks starting from one week after treatment. Averaged data per plant were analyzed following statistical procedure of analyses of vari- ance and the associated tests of significance and compari— sons. Data were obtained from bolting plants per plot which survived during the experiments, 2 to 4 plants in 1975 and 3 to 9 plants in 1976 and 1977 experiments. In the 1977 experiments only time of flowering was recorded. Field Experiments with Growth Retardants Two experiments were conducted in 1977 to test whether growth retardants would delay the flowering of sugarbeet plants. The location, source of planting materials, and experimental design were the same as for the other experiments. Sugarbeet roots of two rapidly bolting lines 12 UI 1861 x 2161 and SP 6926-0 were planted in May, but most plants of SP 6926—0 line failed to survive so only one ex- periment could be conducted. The effects of four different growth retardants were compared in a randomized block design with three replications. The growth retardants were CCC, SADH, ancymidol and ethephon, each at three different concentrations in equally-split applications. Other methods and procedures employed for this experi- ment were the same as for the 1977 experiments with growth promoters. Time of flowering was measured and analyzed. There were 3 to 9 surviving and bolting plants in each plot. Greenhouse Experiments with Gibberellin Four greenhouse experiments in 1976/1977 were conducted to test whether gibberellin GA4A7 would hasten flowering of sugarbeet. In an effort to have more precise control and measurement of experimental plant variables, genetically identical clones, obtained from stem cuttings, were used in two experiments, and from split roots in a third experiment. The fourthexperiment involved plants grown from seed. (The experiments were conducted in the Michigan State University Plant Science greenhouses. Stem cuttings were obtained from bolting plants. Cuttings were made from several plants to obtain a greater numbertofclonal groups. To obtain split roots, seeds were planted and grown until the plants were large enough to 13 split into two halves longitudinally through the growing tips. One half of the split root was used for gibberellin treatment and the other half was used as a control. Prior to the application of gibberellin, the plants or clones were exposed to different degrees of photothermal induction in the cold room, 8 and/or 10 weeks for rapidly bolting, and 10 and/or 12 weeks for slowly bolting lines. The temperature of the cold room for induction was kept at about 5°C. The plants were illuminated continuously by incandescent lamps. The plants were grOWn on vermiculite in 15-cm pots supplied daily with nutrient solution containing Ca, K, NH4, Mg, Fe, N03, C1, H PO 2 4' Pests and diseases were controlled as needed. 504 ions and trace elements. Gibberellin was applied as a lO-ml foliar spray per plant 2 to 3 weeks after photothermal induction, during the post-induction period in the greenhouse. When double spray- ing was done, the second spray was applied 1 week after the first. The post—induction temperature was increased gradually each week for the first 3 weeks from a maximum of 13 to 16 to 20°C. Supplemental light from fluorescent lamps was used to obtain a 14 to 16-hour daylength. In greenhouse experiment I, stem cuttings of slowly bolting F 66-562—HO sugarbeet line were used. The plants were exposed to photothermal induction for 12 weeks. Two gibberellin treatments, and a check, were compared in a completely randomized design with five single-plant 14 replications. Solutions of GA4A7 as ProGibb 2% LC in water were Tween 20 added as surfactant were applied. Check plots were sprayed with water. Green house experiment II was similar to the greenhouse experiment I. However, for this experiment length of photo- thermal induction was 10 weeks. Four gibberellin GA4A7, I as ProGibb, treatments, and a check, were compared in a com- pletely randomized design with five replications. Grown for approximately 2 months the experimental plants remained vegetative. The plants were then reinduced photothermally for 10 weeks. The five treatments were applied again as before. In greenhouse experiment III, split roots of both slowly bolting F 66—562-HO and rapidly bolting UI 1861 x 2161 lines were used. The half roots were photothermally induced for 10 weeks. A group of half roots was sprayed with four different GA4A7 treatments. Another group of half roots served as checks. Five replicated paired comparisons were made for each line and treatment. Similar to greenhouse experiment II, since the experimental plants remained vege- tative for approximately 2 months after gibberellin treat- ments, photothermal reinduction and gibberellin retreatment were done as before. Seed plants of the two sugarbeet lines used in green- house experiment III were also used in green house experiment IV. Photothermal inductions were 8 and/or 10 weeks for the rapidly bolting and 10 and/or 12 weeks for the slowly 15 bolting lines. Three GA4A7 treatments, and a check, were compared in a completely randomized design with_five replica- tions. Most plants (90%) of the slowly bolting F 66—562-H0 did not bolt, hence only the experiment with UI 1861 x 2161 was continued to finish. Growth responses measured and analyzed were the same as in field experiments. Time of flowering was calculated as number of days after photothermal induction to first flower appearance. The single—plant plot data were analyzed similar to the other experiments. RESULTS AND DISCUSSION Field Experiments Time of Flowering. Results of field experiments in 1975 and 1976 (experiment numbers 1, 2, 5, and 6; see Table 1) suggested that treating with foliar sprays of different concentrations and frequencies of application of gibberellin GA4A7 did not significantly shorten the time of flowering of two slowly bolting sugarbeet lines, F 69-546—H4 and F 73-17 (Table 2). Similarly, the experiments in 1977 (experiment numbers 7 and 8; see Table 1) also indicated that foliar spraying different kinds of growth promoter (gibberellins GA3 and GA4A7, 2,4—D, urea, and ethephon) at different con- centrations as equally-split applications to slowly bolting sugarbeet lines EL 36 and E1 31 grown in the field did not significantly shorten the time of flowering (Table 3). On the other hand, results of the field experiments in 1975 (experiment numbers 3 and 4; see Table 1) showed that rapidly bolting sugarbeet line SP 6822-0 treated with double foliar spraying of gibberellin GA4A each at 50 ppm, 7' flowered in a significnatly shorter time. However, gib- berellin GA4A7 did not shorten significantly the time of flowering of rapidly bolting line UI 1861 x 2161 grown in the field (Table 4). l6 17 Table 2. Time of Flowering of Two Slowly Bolting Sugarbeet Lines Sprayed with Gibberellin at East Lansing in 1975 and 1976 Field Experiments. GA4A7 1975 1976 Treagggnts F 69—546-H4 F 73-17 F 69-546-H4 F 73—17 ——————— Days to First Flower Appearance--—------ Check 43.2 a 40.6 b 39.4 c 34.4 d 50 46.3 a 40.7 b 39.6 c 33.8 d 2x50 47.1 a 37.0 b 40.0 c 34.6 d 100 48.0 a 41.4 b 39.7 c 34.7 d 2x100 45.3 a 43.6 b 39.1 c 35.3 d 200 43.8 a 40.3 b 39.3 c 34.4 d Data in each column followed by the same letter are not significantly different at 0.05 probability level. Table 3. Lines Sprayed Time of Flowering of Two Slowly Bolting Sugarbeet (as a Split Application) with Dif— ferent Kinds of Growth Promoter at East Lansing in 1977 Field Experiments. Treatments ppm EL 36 EL 31 Days to First Flower Appearance Check 45.4 a 46.3 b GA3 100 45.1 a 46.0 b GA3 300 45.8 a 44.3 b GA3 500 45.6 a 45.5 b GA4A7 50 44.4 a 42.8 b GA4A7 100 44.8 a 47.9 b GA4A7 200 46.3 a 44.5 b 2,4—D 10 48.5 a 44.7 b 2,4-D 100 46.4 a 45.8 b 2,4-D 1000 47.1 a 42.8 b Urea 100 45.8 a 44.7 b Urea 2000 45.6 a 49.7 b Urea 4000 44.6 a 47.7 b Ethephon 5 47.2 a 47.4 b Ethephon 100 44.4 a 45.9 b Ethephon 1000 45.9 a 50.2 b Data in each column followed by the same letter are not significantly different at 0.05 probability level. 19 Table 4. Time of Flowering of Two Rapidly Bolting Sugar- beet Lines Sprayed with Gibberellin at East Lansing in 1975 Field Experiments. GA A Treatments SP 6822—0 UI 1861 x 2161 4 7 ppm Days to First Flower Appearance Check 34.2 a 38.0 C 50 34.0 a 37.5 c 2x50 30.7 b 37.5 c Data in each column followed by the same letter are not significantly different at 0.05 probability level. The genetic program for flowering of plants is not expressed until the right time. Some plants have devices that sense when the correct season for flowering has arrived. Plants have built-in mechanisms which respond to environ— mental stimuli such as daylength (photoperiodism) or cold treatment (vernalization). Some also respond to chemical stimuli and initiate flowering. Gibberellic acid has strong effects on bolting and flowering in many plants. It has been found to replace both vernalization and photoperiodic induction in many long—day plants. Gibberellic acid causes flowering in many rosette plants. One possible explanation is that gibberellic acid is essential in the stimulation of growth leading to bolting, which is a prerequisite to flowering. However, in these studies, gibberellins GA3 (gibberel- lic acid) and GA4A7 were not effective in stimulating 20 flowering of the slowly bolting sugarbeet, a rosette plant, lines. The difference in response to gibberellin between different sugarbeet lines was presumably due to different genotype. The rapidly bolting line SP 6822-0 was responsive to gibberellin GA It may have an insufficient amount of 4A7. endogenous gibberellic acid, so that it was responsive to the applied gibberellin. Other chemicals (2,4-D, urea, and ethephon at low con- centrations) were ineffective as growth promoting substances on sugarbeet. Foliar spraying of growth retardant ethephon at 2,000 and 4,000 ppm as equally-split applications to rapidly bolt— ing line UI 1861 x 2161 grown in the field in 1977 signifi- cantly delayed the time of flowering. SADH, ancymidol and CCC did not delay the time of flowering significantly (Table 5). Growth retardants appear to function as anti—gibberel- lins. The endogenous regulation of flower initiation, which is governed by gibberellin, could be affected by applied growth retardant. It was evident that rapidly bolting line UI 1861 x 2161 was responsive to ethephon. Perhaps, the insufficient content of endogenous gibberellic acid to sti- mulate flowering was augmented by the applied ethephon. Heights of Flower Stalks. Results of both 1975 and 1976 field experiments indicated that gibberellin GA4A7 did not significantly increase the heights of flower stalk (stem) of slowly bolting sugarbeet lines F 69—546-H4 and 21 Table 5. Time of Flowering of Rapidly Bolting UI 1861 x 2161 Sugarbeet Line Sprayed (as a Split Applica— tion) with Different Kinds of Growth Retardants at East Lansing in 1977 Field Experiment. Treatment Days to First Flower Appearance PPm Check 34.9 a SADH 500 35.5 a SADH 1000 35.3 a SADH 2000 36.3 a Ancymidol 2 37.4 a Ancymidol 4 37.7 a Ancymidol 8 36.8 a CCC 100 35.7 a CCC 2000 35.4 a CCC 4000 37.0 a Ethephon 100 34.7 a Ethephon 2000 44.2 b Ethephon 4000 41.2 b Data followed by the same letter are not significantly different at 0.05 probability level. 22 F 73—17 at all times of measurements (Table 6). Similar results were also found from 1975 field experiment with two rapidly bolting lines SP 6822-0 and UI 1861 x 2161 sprayed with gibberellin GA4A (Table 7). 7 Stimulation of growth leading to bolting is a pre- requisite to flowering. The growth regulators used in these studies did not significantly increase or decrease the heights of flower stalks. The growth regulators in these studies were ineffective in both modifying the height of flower stalk and time of flowering of all sugarbeet lines studied, except in two cases, where GA4A7 shortened time of flowering of sugarbeet line SP 6822-0, and ethephon delayed time of flowering of sugarbeet line UI 1861 x 2161. Greenhouse Experiments Time of Flowering. Stem—cutting plants of slowly bolting line F 66—562-HO, exposed to either 12 or 10 weeks of photothermal induction, and sprayed with different concentra— tions, either as single or split application, of gibberellin GA4A7 (experiments I and II) flowered at about the same time as unsprayed control plants (Table 8). Most of the plants did not bolt in the experiments using split roots of sugar- beet lines F 66—562-HO and UI 1861 x 2161 (experiment III). Gibberellin GA4A7 did not shorten significantly the time of flowering of rapidly bolting line UI 1861 x 2161 grown in the greenhouse (experiment IV) with prior photo- thermal induction of either 10 or 8 weeks (Table 9). 23 Table 6. Flower Stalk Heights of Two Slowly Bolting Sugar— beet Lines After Spraying with Gibberellin at East Lansing in 1975 and 1976 Field Experiments. GA4A7 1975 1976 Tregggents F 69-546—H4 F 73—17 F 69-546-H4 F 73-17 Week 1: Check ——— ——— 11.5 a 15.5 b 50 ——- -—- 14.3 a 15.0 b 2x50 —-— ——- 14.1 a 17.3 b 100 —-— --- 14.0 a 17.9 b 2x100 --— --— 14.1 a 13.4 b 200 —-- --- 14.7 a 14.1 b Week 2: Check 40.1 c 48.1 d 35.5 e 40.7 f 50 31.6 c 50.6 d 40.9 e 39.2 f 2x50 35.1 c 52.5 d 42.9 e 44.0 f 100 29.7 c 47.0 d 41.8 e 44.0 f 2x100 33.8 c 39.8 d 41.9 e 40.7 f 200 40.0 c 50.0 a 40.4 e 39.8 f Week 3: Check 68.7 g 66.7 h 42.0 i 57.0 j 50 50.1 g 65.5 h 51.4 i 55.5 j 2x50 55.5 g 75.9 h 54.5 i 59.0 j 100 43.2 g 69.5 h 51.6 i 57.3 j 2x100 57.1 g 62.0 h 56.2 i 54.1 j 200 63.1 g 70.4 h 53.6 i 53.6 j Week 4: Check 102.1 k -—— --— ——- 50 97.4 k —-— -—— ——— 2x50 95.3 k —-- --— -—— 100 91.8 k —-- --- —-- 2x100 91.4 k ——— -—- ——- 200 87.6 k —-- ——— --- Groups of data in each column followed by the same letter are not significantly different at 0.05 probability level. 24 Table 7. Flower Stalk Heights of Two rapidly Bolting Sugar— beet Lines After Spraying with Gibberellin at East Lansing in 1975 Field Experiments. GA A Treatments SP 6822-0 UI 1681 x 2161 4 7 PPm Week 2: Check 63.3 a 72.5 b 50 62.3 a 83.6 b 2x50 68.5 a 76.3 b Week 3: Check ’——- 85.0 c 50 ——- . 98.1 c 2x50 --— 91.2 c Groups of data in each column followed by the same letter are not significantly different at 0.05 probability level. Table 8. Time of Flowering of Stem-Cutting Plants of Slowly Bolting Sugarbeet line F 66-562-HO Exposed to Dif- ferent Periods of Photothermal Induction and Sprayed with Gibberellin in the Greenhouse in 1976/1977. GA4A7 Period of Photothermal Induction Treatment 12 weeks 10 weeks PPm Days to First Flower Appearance Check 50.6 a 67.2 b 50 54.8 a 70.6 b 2x50 54.8 a 65.4 b 100 -—- 68.4 b 2x100 ——- 63.2 b Data in each column followed by the same letter are not significantly different at 0.05 probability level. 25 Table 9. Time of Flowering of Seed Plants of Rapidly Bolting Sugarbeet Line UI 1861 x 2161 Exposed to different Periods of Photothermal Induction and Sprayed with Gibberellin in the Greenhouse in 1976/1977. GA4A7 Period of Photothermal Induction Treatment ppm 10 weeks 8 weeks Days to First Flower Appearance Check 26.8 a 34.0 b 50 26.8 a 35.8 b 2x50 26.4 a 33.8 b 100 26.8 a 41.0 b Data in each column followed by the same letter are not significantly different at 0.05 probability level. Results of the greenhouse experiments supported the results of field experiments. The application of gibberel— lin in greenhouse experiments might have been more effective when the length of photothermal induction had been much shorter than the critical thresholds for flower induction, so that gibberellin could have replaced partial requirement of photothermal induction. Heights of Flower Stalks. Results of greenhouse exper- iments indicated that gibberellin GA did not significantly 4A7 increase the heights of flower stalk of slowly bolting sugar- beet 1ines F 66-562-HO at all times of measurements (Table 10). As presented in Table 11 rapidly bolting line UI 1861 x 2161, exposed to either 10 or 8 weeks and sprayed or not sprayed with gibberellin GA had about the same 4 7' heights of flower stalk. 26 Since gibberellin GA4A7 was found ineffective in modifying time of flowering it could be expected that it was also ineffective in modifying height of flower stalk. 27 Table 10. Flower Stalk Heights of Stem-Cutting Plants of Slowly Bolting Sugarbeet Line F 66-562—HO Exposed to Different Periods of Photothermal Induction, after Spraying with Gibberellin in the Greenhouse in 1976/1977. GA4A7 Period of Photothermal Induction Treatment ppm 12 weeks 10 weeks Week 1: Check 21.6 a —-- 50 21.0 a -—- 2x50 29.4 a —-- Week 2: Check 43.8 b -—- 50 43.2 b ——— 2x50 55.8 b --- Week 3: Check 61.2 c --- 50 61.6 c --— 2x50 73.2 c --- Week 4: Check 72.2 d 32.4 e 50 73.2 d 17.2 e 2x50 80.4 d 30.0 e 100 --- 23.0 e 2x100 —-— 36.0 e Week 5: Check 82.4 f 66.3 g 50 84.2 f 53.3 9 2x50 86.8 f 77.0 g 100 ——- 61.8 9 2x100 ——- 83.8 9 Week 6: Check --- 89.8 h 50 --- 75.5 h 2x50 ——— 108.0 h 100 -—- 85.0 h 2x100 -—- 111.8 h Groups of data in each column followed the same letter are not significantly different at 0.05 probability level. 28 Table 11. Flower Stalk Heights of Seed Plants of Rapidly Bolting Sugarbeet Line UI 1861 x 2161 Exposed to Different Periods of Photothermal Induction, after Spraying with Gibberellin in the Greenhouse in 1976/1977. GA4A7 Period of Photothermal Induction Treggfient 10 weeks 8 weeks Week 1: Check 35.2 a —-- 50 38.6 a ——— 2x50 39.8 a --— 100 34.6 a --— Week 2: Check 85.2 b 28.0 c 50 89.4 b 32.0 c 2x50 93.6 b 39.6 c 100 86.2 b 15.2 c Week 3: Check 108.0 d 73.8 e 50 110.8 d 74.6 e 2x50 113.6 d 73.0 e 100 106.6 d 40.8 e Week 4: Check --- 106.0 f 50 -—— 109.2 f 2x50 —-- 90.0 f 100 --- 77.2 f Groups of data in each column followed by the same letter are not significantly different at 0.05 probability level. SUMMARY AND CONCLUSIONS The problem of eliminating differences in time of flowering of male and female component plants in making hybrids of sugarbeet under natural conditions needs to be solved in one way or another. Successful use of various growth regulators in other plants or crops led to an effort to try them on sugarbeet plants. In this investigation an attempt was made to study the effects of eight different chemicals with both promoting and retarding effects on plants. Although the problem is under natural conditions, field and also greenhouse experi- ments were conducted to have greater control of environ- mental variables. Five slowly bolting and two rapidly bolting lines were included in the study. Seed plants and clones were grown. The growth regulators were applied as a foliar spray, either as single or split applications, at different concentrations. The responses measured and recorded were times of flowering and heights of flower stalk (stem). The two rapidly bolting lines appeared to be respon— sive to the application of two kinds of growth regulators. Gibberellin GA4A7 could shorten and ethephon could delay the time to flower of SP 6822—0 and 01 1861 x 2161 lines, respecitvely. The heights of flower stalk were not affected. 29 30 The difference in responses to different growth regu- lators between different sugarbeet lines was probably due to different genotype. 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