Physiological Response of Okra to Flea Beetle Herbivory as Measured by Leaf Loss, Chlorophyll Disruption, and Dry Matter Yield

Abstract

Okra, Abelmoschus esculentus (L.) Moench, is attacked by the adult chrysomelid flea beetles, Podagrica spp. Information on physiological disruptions that occur due to flea beetle infestation affecting okra yield loss is incomplete. Screenhouse and field experiments were established to examine the effects of insect populations on leaf abscission, chlorophyll concentration, and biomass partitioning. Okra plants were grown in wire mesh screen cages and artificially infested with flea beetles, P. uniforma Jac., at population densities of 0, 5, 10, 20, 30, and 40 pairs per plant at 3 weeks after sowing (1 pair = 1 male and 1 female). In both experiments, okra plants had increased leaf abscission up to 100% at the 40-pair level in response to P. uniforma–induced injury. There were no significant differences in chlorophyll concentrations of plants at 0-, 5-, and 10-pair levels of infestation, suggesting the use of a compensatory mechanism by plants; at the 20-pair level a significant reduction occurred. Number of leaves per plant, shoots, roots, and dry fruit and total dry matter yield were reduced with infestation above the 20-pair level. More biomass was partitioned into roots at the 5- and 10-pair levels, but insect damage at populations beyond these levels completely suppressed the plant's ability to partition biomass. Dry fruit yields were reduced more than 50% when beetle populations increased beyond 20 pairs in both experiments. There was a correlation between insect density and number of leaves per plant and shoot, root, dry fruit, and total dry matter yield. The reduction in okra leaf production and chlorophyll content and increase in leaf abscission as a result of flea beetle infestation apparently resulted in a reduction in dry matter yield. The 20-pair level appeared to be the damage threshold of the insects. Physiological disruptions induced by the flea beetle at this level overcame the plants' ability to compensate for damage and caused significant reductions in leaf production, chlorophyll content, and dry matter yield and an increase in leaf abscission.