Age-dependent effectiveness of exogenous abscisic acid in height control of bell pepper and jalapeño transplants

• Foliar ABA spray suppressed transplant height of jalapeño by up to 20%.
• The effectiveness of height control was age-dependent.
• Foliar ABA spray caused overall growth delay in bell pepper transplants.
• Growth modulation by ABA was transient with no negative impact on yield.
• ABA can be used as a height control or growth holding agent for pepper transplants.

Height control of vegetable transplants is important for improving their adaptability to shipping and transplanting operations. Abscisic acid (ABA) inhibits stem elongation but can also induce undesirable growth modification. To optimize its application timing for effective height control, we examined age-dependent sensitivity of various growth variables to ABA in two pepper cultivars (Capsicum annuum L.). Bell pepper ‘Excursion II’ seedlings were sprayed once with 3.8 mM ABA at 25, 18, or 11 days before transplanting (DBT), or twice with 1.9 mM ABA at 25 and 18 DBT. Jalapeño ‘Colima’ seedlings were sprayed once with 3.8 mM ABA at 22, 15, or 8 DBT, or twice with 1.9 mM ABA at 22 and 15 DBT. For all treatments, the application rate was 0.71 mg ABA per plant with the spray volume of 0.61 L m−2 (0.71 ml/plant). Only ‘Excursion II’ maintained significantly shorter plant height in all ABA treatments until the transplanting stage, ranging from 80% to 88% of the control. By contrast, leaf chlorosis and overall growth delay were induced by ABA in ‘Colima’. Age-dependent sensitivity to ABA was evident in leaf area of both cultivars, and in stem diameter and shoot and root biomass of jalapeño ‘Colima’, all of which showed maximal reductions when 3.8 mM ABA was applied at the cotyledon stage (first application). These results suggest that ABA is effective in height control for bell pepper ‘Excursion II’, and that it should be applied at least one week after the emergence of first true leaf to minimize the negative side effects. Importantly, subsequent field evaluations demonstrated that the growth modulation by ABA was only transient with no negative impact on marketable yield.