Abscisic Acid Controls Size of Pepper and Watermelon Transplants

Rapid shoot elongation of vegetable transplants can lead to physical damage during transplanting and delay in field establishment. Abscisic acid (ABA) is involved in shoot growth inhibition in plants subjected to water deficit. We examined the effects of ABA foliar application on transplant growth and yield of jalapeno pepper (Capsicum annuum L., ‘Colima’) and triploid watermelon (Citrullus lanatus, ‘Summer Sweet 5244’). In pepper, ABA was applied once (3.8 mM) at 22, 15, and 8 days before transplanting (DBT) or twice (1.9 mM) at 22 and 15 DBT. At the time of transplanting, plant height showed a similar reduction of 10 to 14% for all ABA treatments compared with the untreated-control. In contrast, reductions in shoot dry weight varied from 17 to 35%, with the strongest inhibition induced by the single early application at 22 DBT. This reduction was associated with a decrease in both leaf number and expansion of individual leaf. After transplanting, the plant height difference diminished by the time of harvest, and no difference was found in marketable yield. In watermelon, ABA was applied in the similar timings but with half the rate used for pepper. In contrast to pepper, plant height and leaf number measured at the time of transplanting were unaffected by ABA. However, there was a trend for ABA to inhibit leaf expansion, thereby reducing shoot dry weight. The extent of the reduction was similar for all ABA treatments (16 to 23%), indicating a similar sensitivity to ABA in different transplant ages. Although vine development in the field was somewhat delayed by ABA, it did not cause any yield difference. The absence of yield difference may be due to the use of optimum transplant size for the control. The results suggest that ABA foliar application is effective in size control of vegetable transplants and its growth inhibiting effects are only transient. The effectiveness of this method may depend on species and possibly transplant age.