Corm yield response to different isolates of bacterial leaf blight pathogen (<i>Xanthomonas axonopodis</i> pv. dieffenbachia (McCulloch & Pirone) Vauterin) of cocoyam (<i>Colocasia esculenta</i> (L) Schott)

Abstract

A study was conducted in 2019 to evaluate cocoyam yield response to four xanthomonad isolates (CE2, CE3, CE4 and CE6) causing bacterial leaf blight in Zaria, Nigeria. Five treatments consisting of corms inoculated with the four bacterial isolates and untreated plants were replicated five times and arranged in a completely randomized design (CRD) in the screen house. Symptoms were observed two weeks after germination (WAG) and records on disease severity were taken 3 WAG and thereafter at weekly interval until 18 WAG. Eight months after planting, corms were harvested, weighed and corm diameter measured. Yield loss was calculated, correlation and regression analyses were done. Records on disease severity showed the highest severity, ranging between 12.8 % and 38 % were recorded on plants inoculated with isolate CE2, followed by CE6 (7.0 % - 29.0 %) and CE4 (6.6 % - 28.6 %). The least severity was observed on plants inoculated with CE3 (6.8 % - 24.8 %). Control plants did not show symptoms of the disease. Corm diameter and yield among the isolates were highest in CE3 (8.4 cm and 48460 kg/ha) and the least in CE2 (5.0 cm and 40120 kg/ha). There were negative and highly significant correlations between disease severity and the yield of corms (r = -0.87; P<0.01). Regression analysis showed adjusted coefficient of determination (R2) as 0.760 (76%) with a unit increase in disease severity resulting in a decrease of 257.8 kg/ha in corm yield. In conclusion, bacterial leaf blight significantly reduced the yield of cocoyam, as higher disease severity resulted in lower yield.