Histopathological Studies of Rhizoctonia solani Infection Process in Different Cultivars of Mungbean [Vigna radiata (L.) Wilczek]

Aerial/web blight of mungbean is caused by Rhizoctonia solani Kuhn. The infection process of R. solani was studied on the leaves of susceptible (Pusa Vishal) and resistant (Hum-1) cultivars of mungbean. Leaves and stem of 21 days old cultivars of mungbean were inoculated with the mycelium of freshly growing culture (2 mm) of R. solani isolate (RDLM1) and incubated at 28 °C for different time intervals (3, 6, 18 and 24 h). On the susceptible genotype Pusa Vishal, infection cushions and necrotic lesions were developed after 18 h of inoculation. However, on the resistant genotype Hum-1 no lesions were visible till 24 h of inoculation. The hyphae of R. solani were observed penetrating through two ways (1) direct penetration-by swollen hyphae, lobate appressorium and infection cushion, (2) indirect-stomatal penetration. Differences were also observed in number of infection cushion formed in susceptible (45.37) and resistant (30.87) genotypes after 18 h of inoculation. Typical lesion formation after 18 h of inoculation on susceptible genotype was also validated in KPM-32, KPM-33, KPM-36, KPM-37, KPM-38, KPM-39, KPM-42, KPM-43, IPM-09-3 and IPM-02-3 genotypes of mungbean. Clear cut differences were also observed in transverse section of stem after 18 h of inoculation, where maximum colonization of stem was observed on cortex pith region.