RESPONSE OF FOUR SOYBEAN GENOTYPES TO SIMULATED LEAF HERBIVORY IN THE GUINEA SAVANNAH AGROECOLOGY OF GHANA

Studies were conducted at the University for Development Studies, Tamale, Ghana during the 2013 and 2014 cropping seasons to determine the effects of simulated leaf herbivory on growth and grain yield of soybean. Four genotypes of soybean namely, Tax 1834-5E, Tax 1445-3E, Jenguma and Salintuya-1 were subjected to the following four levels of defoliation: 0%, 50%, 75% and 100% at 5 weeks after planting. Some undefoliated plants from each genotype were used as control. The treatment combinations were replicated three times in randomized complete block design. Results revealed that growth of defoliated soybean plants was always reduced. Both complete (100%) and 75% defoliation were detrimental to the growth and grain production of soybean. In general, all defoliated plants had higher values of chlorophyll content than the undefoliated control. It was observed that the response of soybean to above-ground herbivory was related to the time or stage of growth of the plants at the time that herbivory occurs. Plants from the 50% leaf removal especially those from genotype Tax 1834-5E responded well to defoliation by showing compensatory regrowth of shoot and produced higher grain yield than the undefoliated control. The perception by most farmers that any level of defoliation in plants results in significant yield loss is disputed. The present results show that for genotype Tax 1834-5E, up to 50% removal of leaves is not damaging to growth and grain production, provided the stress occurred within the first 5 weeks after planting.