What are plant growth regulators (PGRs)? Agrichemicals with plant hormones, or hormone like compounds, as active ingredients

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1 Plant growth regulators to control grape berry abscission Matthew Fidelibus Viticulture & Enology UC Davis & KARE What are plant growth regulators (PGRs)? Agrichemicals with plant hormones, or hormone like compounds, as active ingredients Current uses for plant growth regulators in CA viticulture Break dormancy/promote budbreak in interior valleys and coastal areas lacking adequate chilling; hydrogen cyanamide (DORMEX) Reduce cluster compaction by rachis stretching and/or stimulating flower abscission; gibberellic acid (various brands) 1

2 Current applications for plant growth regulators in CA viticulture Increase fruit set (forchlorfenuron [CPPU]) Increase fruit size; GA and/or CPPU Stimulate anthocyanin accumulation to improve color of red and black varieties; ethephon and/or abscisic acid (various ethephon products, ProTone) Non treated 150 ppm ABA 300 ppm ABA 2

3 Some viticultural uses of PGRs in other countries Inhibiting sucker growth (napthalene acetic acid) Reducing shoot growth (prohexadione calcium) Induce seedlessness of certain varieties (gibberellins and tetracycline; asia) Postharvest defoliation in tropical regions (ethephon) Broad Trends in PGRs for Grapes Many contemporary table grape varieties dependent on PGRs, but breeding programs have developed varieties with minimal PGR needs Desire to minimize agrochemical residues Use the safest, most natural chemistries Identify unique responses that add value Example of conventional breeding toward naturally large berry size: Autumn King table grape, natural (no PGR) berry size 3

4 Abscisic acid, a natural active ingredient, newly available for improving table grape color Screening studies to identify novel & potentially useful responses Compounds that induce an abscission layer, abscission agents, could reduce fruit detachment force and improve the quality of machine harvested grapes, and improve the quality of ready to eat table grapes Tearing reduces the quality of machine harvested raisin grapes 4

5 Picking causes the stem-end of grapes to tear Tearing may limit the quality and shelf life of fresh cut, or readyto eat table grapes What would consumers pay for better quality? 5

6 Objectives Identify potential abscission agents Develop potential use pattern Understand physiology 6

7 Fruit detachment force (FDF) Fruit detachment force (kg) Days after treatment (DAT) MeJA (mm) z a a a a AB a B b B a B a A AB a B b AB a AB a A A b C c C b BC ab AB A b B c B b B b B 7

8 Dry scar Wet scar Stem end condition MeJA (mm) Pedicel on berry (%) Dry scar (%) b b b a a 8

9 Fruit abscission (%) Fruit detachment force (kg) Days after treatment (DAT) MeJA (mm) c 0.5 c 0.5 c c 0.4 c 0.4 c 2 0 C 0.2 BC 0.3 c ABC 0.3 c ABC 0.6 c AB 10 0 B 1.2 B 16.1 b A 20.0 b A 24.4 b A 20 0 C 4.4 C 26.5 a B 35.8 a AB 42.3 a A Reducing FDF & promoting dry stem scars is desirable; preharvest berry abscission is undesirable Can we improve efficacy by combining active ingredients? Methyl jasmonate & ethephon, an ethylenereleasing agent, induce abscission at high concentrations Combining different a.i.s may enable reduced rates of either, and shed light on abscission physiology 1 aminocyclopropane 1 carboxylic acid (ACC), the natural biochemical precursor of ethylene, might be better alternative to ethephon 9

10 Effects of MeJA and ACC on grape berry ethylene production Effects of MeJA and ACC on grape berry FDF Fruit detachment force (N) Days after treatment 2 3 ACC (mg L-1) MeJA (mm) Significance ACC < < <0.01 MeJA <0.01 <0.01 <0.01 <0.01 <0.01 ACC*MeJa < Effects of MeJA and ACC on grape berry abscission Abscised berries (%) MeJA ACC Days after treatment (mm) ( mg L-1) a 0.0 a 0.0 a 0.3 a 0.0 a a 0.0 a 0.16 a 0.1 a 0.2 a a 0.0 a 1.8 b 16.3 a 3.6 b a 6.9 b 21.6 a 21.3 a 36.0 a Significance ACC <0.01 MEJA <0.01 <0.01 ACC*MeJA <

11 Summary MeJA and ACC interact to promote abscission related processes, possibly, in part, due to effects on ethylene biosynthesis However, ethylene biosynthesis per se is not enough to promote abscission, and some varieties produce ethylene in response to treatment, but don t abscise. 11

12 Acknowledgements Jacqueline Burns, UF Peter Petracek, Valent BioSciences Lorena Uzquiza Thiago Costa 12