Effect of Defoliation Timing and Severity on the Yield and Nutritive Value of Phaseolus vulgaris L.

Abstract

The effects of removal of one (33%) or two (66%) leaflets per matured leaf of P. vulgaris L. within different growth periods on the yield and nutritive value of the plants were investigated.  Leaf removal was done during vegetative (V), flowering (F) and pod development stages (P).  There was no correlation between total number of pods and seeds.  The plants had a significant increase in seed yield when defoliation was done at 33%F (at P=0.05). There was a significant decrease in pod and seed yield when defoliation was done at pod development stage (at P=0.05).  Defoliation had no effect on the weight of seeds produced.  There was a significant increase in carbohydrate content of seeds at 66V but a significant decrease at 33F and when defoliation was done at pod development stage (at P=0.05).  A significant (at P = 0.05) decrease in protein content of seeds occurred as defoliation level increased from 0% to 66% at all growth stages.  The stage of defoliation, the level of defoliation and the rate of leaf re-growth are factors that could have affected the effect of defoliation on the yield of P. vulgaris.  Other causes include the delay in senescence of lower remaining leaves.  Defoliation of P. vulgaris for the use of the green leaves results in the production of lower quality seeds as defoliation reduces the protein content drastically.  Hence, defoliation should be discouraged.  However, where it cannot be avoided due to non-availability of other vegetable plants or animal feeds, it should be done at 33% defoliation ( a leaflet per leaf) appreciably, before fruit set.