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Abscisic Acid and Abscission of Young Cotton Bolls in Relation to Water Availability and Boll Load¹

A field experiment was conducted to determine whether two factors, water deficit and fruit load, that are known to affect fruit abscission might also affect the concentrations of ABA in young cotton (Gossypium hirsuturm L. ‘Deltapine 70’) bolls. The effects of water deficit were estimated by comparing ABA concentrations and abscission rates of boils in control and stressed plots, and by following changes during irrigation cycles. The effects of fruit load were determined by removing about 4/7 of the flowers in partially defruited plots, and by comparing changes as boll load increased during the season.

Both ABA concentration and abscission rate of bolls increased with water deficit and decreased with relief of stress by irrigation. Boll abscission rates increased as boll load increased, and were lower in the partially defrulted than in the fruited plots. Bolls in the partially dcfruited plots contained less ABA on some, but not all, harvest dates. Watei: deficit apparently had a greater effect than boll load on the ABA content of young bolls.

The results indicate that water deficit increases the ABA content of cotton bolls, and they provide additional circumstantial evidence that ABA is one regulator of young boll abscission in cotton. However, differences in ABA content did not account for increased boll abscission rate with increasing boll load during the season nor for differences in abscission between fruited and partially defruited plants.

Key Words: ABA • Boll-shedding • Competition • Ethylene • Fruit-loss • Gossypium hirsutum L. • Hormones • Irrigation • Stress

² Plant physiologist and research leader, USDA, SEA-AR, Western Cotton Research Laboratory, 4135 E. Broadway, Phoenix, AZ 85040.

Received for publication June 1, 1981.