Growth Regulator Effects on Flowering in Maize

Growth Regulator Effects on Flowering in Maize Eric Bumann July 14, 2008

My Background Research Associate at Pioneer Hi-Bred in Johnston, IA Production research 5 years in greenhouse research B.S. in Horticulture from ISU in 2002 Raised on a farm in Western Iowa

Purpose To evaluate the effects of different plant growth regulators on the life cycle of maize To determine if any inbred or timing effects vary amongst treatments To evaluate the practicality of possible growth regulator treatments in a greenhouse or field environment

Introduction Gibberellins (GA) Potential role as a regulator for flowering found in past genetic studies Dwarf mutants defective in GA biosynthesis flowered later than wild type (King & Evans, 2003) When GA applied the mutants flowered similar to the wild type (Evans & Poethig, 1995) Cytokinins Benzyladenine (BA) Used in fruit production to increase yield and fruit size Independent Pioneer research suggested promise for use as a early flower inducer in maize

Introduction Ethylene Linked to many plant processes (Davies, 1995) Release of dormancy Shoot and root growth differentiation Leaf and fruit abscission and senescence Flower induction Induction of femaleness in dioecious flowers Fruit ripening Liquid ethylene (ethephon) is widely used in many agricultural crops for a number of different purposes

Introduction Shoot apical meristem (SAM) Portion of the plant where the shoot is formed through cell division and differentiation (Medford, 1992) Three phases Vegetative Transition Reproductive Transition from vegetative to reproductive occurs around V5 stage in maize (Tranel et al., 2006)

Materials and Methods 4 inbred genotypes used 4 treatments (Ethephon, GA, BA, and control) 2 rates (1 low and 1 high for each PGR) 3 application timings (V3, V5, and V7) 5 Reps (1 plant per rep)

Materials and Methods Inbred A Used as a male in seed production 107 day RM Inbred B Used as a female in seed production 112 day RM Inbred C Used as a female in seed production 114 day RM Inbred D Used as both a male and female 114 day RM

Materials and Methods Chemicals Treatment 1: Ethephon: Florel Brand 3.9% Ethephon Treatment 2: GA: ProGibb 4% Gibberellic Acid GA3 Treatment 3: BA: MaxCel 1.9% 6-Benzyladenine Rates Florel Rate 1: 250 ppm / 6.35 ml per liter Rate 2: 1000 ppm / 25.4 ml per liter ProGibb Rate 1: 25 ppm / 0.74 ml per liter Rate 2: 100 ppm / 3 ml per liter MaxCel Rate 1: 50 ppm / 2.53 ml per liter Rate 2: 200 ppm / 10.13 ml per liter

Materials and Methods Plants were seeded into 32 cell germination flats 2 weeks after sow date (late V2 stage) plants were selected for uniformity and transplanted into 2 gallon pots At transplant all pots received ½ tsp Osmocote 15-9-12 fertilizer Plants also received 1 tsp of Marathon systemic insecticide and an additional 1 tsp of Osmocote 2 weeks after transplant

Experiment Design Inbreds were blocked in an east to west pattern Four rows within each inbred block represented each rep Two rows of each rep represented 1 rate The application timing was split into 3 blocks running east to west Chemical treatments were randomized within each rate/timing block Split-split-split-plot design

Experiment Design Inbred D Inbred C Inbred B Inbred A N = 1 individual pot receiving 1 treatment within 1 genotype/1 rep/1 application timing/1 rate

Left: Plants in germinating flats Right: Plants shortly after transplant

Materials and Methods When plants were at the appropriate growth stage (V3, V5, & V7) treatments were applied at both rates using a hand held spray bottle

Inbred A Rate 2 Timing 1 Inbred A Rate 2 Timing 3 Inbred C Rate 1 Timing 1 Inbred C Rate 1 Timing 3 Pictures taken approximately 1 month after transplant

Inbred A Rate 2 Timing 1 Inbred A Rate 2 Timing 3 Inbred C Rate 1 Timing 1 Inbred C Rate 1 Timing 3 Pictures taken just prior to harvest

Inbred A Rate 2 Timing 2 Inbred B Rate 2 Timing 2 Inbred C Rate 2 Timing 2 Inbred D Rate 2 Timing 2

Data Collected GDU to first silk GDU to first shed GDU to 95% shed Tassel size (scale of 1-9) Pollen score (scale of 1-9) Final plant height Final plant leaf number Other relevant comments/observations

Data GDUs calculated using the following formula GDUs = (tempmax + tempmin)/2 50 Statistical analysis showed no significant differences (P 0.05) between the different timings and rates of the chemicals Exception: Ethephon rate 2 was significant in delaying flowering when compared to rate 1 though both rates were significant when compared to all other treatments Data was then evaluated on the chemical level only Only ethephon was significant (P 0.05) with delaying silk and shed in all inbreds Exception: GA was significant with hastening GDU to silk in Inbred A only

Inbred A response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Shed * A Chemical Ethephon GA 37.59 10.44 88.04268 3.6 0.00053 20.75 GDU_Shed * A Chemical Ethephon BA 23.29 10.44 88.04268 2.23 0.02827 20.75 GDU_Shed * A Chemical Ethephon Control 31.8 10.44 88.04268 3.04 0.00307 20.75 GDU_Shed A Chemical GA BA -14.3 9.74 87.99579-1.47 0.14574 19.36 GDU_Shed A Chemical GA Control -5.79 9.74 87.99579-0.59 0.55372 19.36 GDU_Shed A Chemical BA Control 8.51 9.74 87.99579 0.87 0.3849 19.36 response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Silk * A Chemical Ethephon GA 89.45 22.78 82.20239 3.93 0.00018 45.32 GDU_Silk * A Chemical Ethephon BA 57.12 22.78 82.20239 2.51 0.01414 45.32 GDU_Silk A Chemical Ethephon Control 39.87 22.33 82.05118 1.79 0.07781 44.42 GDU_Silk A Chemical GA BA -32.33 21.13 81.9038-1.53 0.12973 42.04 GDU_Silk * A Chemical GA Control -49.58 20.76 82.00703-2.39 0.01923 41.3 GDU_Silk A Chemical BA Control -17.25 20.76 82.00703-0.83 0.40854 41.3

Inbred B response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Shed * B Chemical Ethephon GA 45.16 8.09 71.85405 5.58 0 16.13 GDU_Shed * B Chemical Ethephon BA 39.27 8 71.20406 4.91 0.00001 15.95 GDU_Shed * B Chemical Ethephon Control 41.13 8 71.20406 5.14 0 15.95 GDU_Shed B Chemical GA BA -5.89 8.09 71.85405-0.73 0.46866 16.13 GDU_Shed B Chemical GA Control -4.02 8.09 71.85405-0.5 0.62021 16.13 GDU_Shed B Chemical BA Control 1.87 8 71.20406 0.23 0.81609 15.95 response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Silk * B Chemical Ethephon GA 55.95 15.25 86.15818 3.67 0.00042 30.32 GDU_Silk * B Chemical Ethephon BA 70.84 15.08 86.0965 4.7 0.00001 29.98 GDU_Silk * B Chemical Ethephon Control 61.47 15.08 86.0965 4.08 0.0001 29.98 GDU_Silk B Chemical GA BA 14.89 15.08 86.0965 0.99 0.32631 29.98 GDU_Silk B Chemical GA Control 5.52 15.08 86.0965 0.37 0.7152 29.98 GDU_Silk B Chemical BA Control -9.37 14.91 85.98651-0.63 0.53157 29.64

Inbred C response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Shed * C Chemical Ethephon GA 65.07 9.56 86.92939 6.81 0 19 GDU_Shed * C Chemical Ethephon BA 53.77 9.56 86.92939 5.62 0 19 GDU_Shed * C Chemical Ethephon Control 48.19 9.67 86.9725 4.99 0 19.22 GDU_Shed C Chemical GA BA -11.3 9.56 86.92939-1.18 0.24038 19 GDU_Shed C Chemical GA Control -16.88 9.67 86.9725-1.75 0.0844 19.22 GDU_Shed C Chemical BA Control -5.58 9.67 86.9725-0.58 0.56559 19.22 response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Silk * C Chemical Ethephon GA 102.2 16.09 86.87218 6.35 0 31.98 GDU_Silk * C Chemical Ethephon BA 84.7 16.09 86.87218 5.26 0 31.98 GDU_Silk * C Chemical Ethephon Control 71.69 16.28 86.91672 4.4 0.00003 32.36 GDU_Silk C Chemical GA BA -17.5 16.09 86.87218-1.09 0.27988 31.98 GDU_Silk C Chemical GA Control -30.51 16.28 86.91672-1.87 0.06422 32.36 GDU_Silk C Chemical BA Control -13.01 16.28 86.91672-0.8 0.42629 32.36

Inbred D response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Shed * D Chemical Ethephon GA 47.89 7.38 71.7371 6.49 0 14.71 GDU_Shed * D Chemical Ethephon BA 41.82 7.38 71.7371 5.67 0 14.71 GDU_Shed * D Chemical Ethephon Control 44.46 7.38 71.7371 6.03 0 14.71 GDU_Shed D Chemical GA BA -6.07 7.29 71.2371-0.83 0.40801 14.54 GDU_Shed D Chemical GA Control -3.43 7.29 71.2371-0.47 0.63905 14.54 GDU_Shed D Chemical BA Control 2.63 7.29 71.2371 0.36 0.71896 14.54 response sig Inbred Effect Chemical Chemical Estimate StdErr DF tvalue Probt LSD GDU_Silk * D Chemical Ethephon GA 64.36 15.78 86.83503 4.08 0.0001 31.37 GDU_Silk * D Chemical Ethephon BA 65.36 15.78 86.83503 4.14 0.00008 31.37 GDU_Silk * D Chemical Ethephon Control 65.3 15.78 86.83503 4.14 0.00008 31.37 GDU_Silk D Chemical GA BA 1 15.61 86.74057 0.06 0.94906 31.03 GDU_Silk D Chemical GA Control 0.93 15.61 86.74057 0.06 0.95245 31.03 GDU_Silk D Chemical BA Control -0.07 15.61 86.74057-0 0.9966 31.03

Data Inbred A (across all rates and timings) 1500 1450 1400 GDU 1350 1300 1250 1200 GDU Shed GDU Silk GDU 95% Shed 1150 1100 Ethephon GA BA Control Treatment

Data Inbred B (across all rates and timings) 1500 1450 1400 GDU 1350 1300 1250 GDU Shed GDU Silk GDU 95% Shed 1200 1150 1100 Ethephon GA BA Control Treatment

Data Inbred C (across all rates and timings) 1500 1450 1400 GDU 1350 1300 1250 1200 GDU Shed GDU Silk GDU 95% Shed 1150 1100 Ethephon GA BA Control Treatment

Data Inbred D (across all rates and timings) 1500 1450 1400 GDU 1350 1300 1250 1200 GDU Shed GDU Silk GDU 95% Shed 1150 1100 Ethephon GA BA Control Treatment

Other Data Plant heights were greatly decreased with ethephon but were not effected by other treatments Ethephon produced smaller tassels with somewhat reduced pollen quality than the other treatments Leaf numbers were not changed between all treatments Ethephon produced an increase in poor quality silks and ears and all other treatments were similar to control

Conclusion Ethephon was the only PGR with any significant changes in flowering timing across all inbreds GA did produce a significant decrease in time to silking by 50 GDU in inbred A only Plant quality was greatly reduced in the ethephon treatments

Conclusion and Next Steps There may be some effect on GDU to silk emergence when applying GA for some inbreds Ethephon may help to delay flowering if rates can be adjusted to prevent plant quality issues As of now the Pioneer greenhouses are not planning any future research on these PGRs

Acknowledgments Dr. Allen Knapp Pioneer Hi-Bred Entire greenhouse staff MS in Agronomy program and staff

References Medford, J.I. (1992). Vegetative Apical Meristems. Plant Cell, Vol. 4, 1029-1039. Knapp, A. & Gladon, R. (2005). Eric Bumann s Creative Component Project Agreement. Attachment 1, Proposal to Modulate the Life Cycle of Maize Phase 1: Increase Earliness by the Induction of Floral Development. Unpublished. Tranel, D., Knapp, A., Perdomo, A. (2006). Tassel Development Events Leading to Pollen Production: A Timeline. CSSA Poster King, R. & Evans, L. (2003). Gibberellins and Flowering of Grasses and Cereals: Prizing Open the Lid of the Florigen Black Box. Annual Review Plant Biology, Vol. 54, 307-328 Evans, M. & Poethig, R.S. (1995). Gibberellins Promote Vegetative Phase Change and Reproductive Maturity in Maize. Plant Physiology, Vol. 108, 475-487 Gardner, F., Pearce, R.B., Mitchell, R. (1985). Physiology of Crop Plants. Iowa State University Press. Ames, IA Davies, P.J. (1995) The Plant Hormones: Their Nature, Occurrence and Functions. Plant Hormones: Physiology, Biochemistry and Molecular Biology. Edited by Davies, Kluwer Academic Publishers, Norwell, MA