Effect of inoculation methods and plant age on seedling blight of castor caused by Alternaria ricini and its management with fungicides.

摘要

Seedling blight of caster (Ricinus communis) caused by Alternaria ricini is an important disease affecting both seed and foliage yield. Castor leaves, the primary food for Eri silkworm (Philosamia riccini), are damaged heavily at seedling stage by A. ricini reducing the foliage yield considerably in North eastern region of India. This study was undertaken to determine the most susceptible stage of the crop and effective fungicidal management of this disease. Castor plants of varying ages (11, 18 and 25 day-old) were inoculated with A. ricini (1x104 spores ml-1) using two methods (spray and smear). In all inoculation methods, plants inoculated at 11 and 18 DAE (days after emergence) revealed significantly higher severity, over those inoculated at 25 DAE as well as the uninoculated control. In in vitro test, among the systemic fungicides the triazoles like penconazole, propiconazole and hexaconazole were best (100%) and significantly superior in inhibiting the growth of the fungus at all concentrations (0.025, 0.05 and 0.1%), while among the non-systemic fungicides mancozeb at all three concentrations (0.1, 0.2 and 0.3%) and zineb at 0.3% were very effective (100%). Field studies on the efficacy of fungicidal sprays on seedling blight severity revealed that disease intensity was lowest in mancozeb applied plots (19.00 PDI) followed by propiconazole (42.22 PDI) over the untreated control. Fungicide treated plots also had increased foliage yield (10.6 mt ha-1).