Screening of bitter gourd germplasm and advanced breeding lines against powdery mildew

Abstract

Powdery mildew caused by Podosphaera xanthii is a devastating fungal disease in bitter gourd growing areas of India inflicting more than 70% losses. Resistance sources were identified among 31 genotypes of Momordica charantia, M. charantia var. muricata and M. balsamina based on screening under natural field and artificial epiphytotic condition at seedling stage. The genotypes varied with respect to percent disease index (PDI), area under disease progressive curve (AUDPC) and the apparent rate of disease spread in unit time period (r). The mean PDI under natural and artificial screening ranged from 0.0 to 100.0 and 0.0 to 94.4, respectively. The genotypes, IIHR-80-1-2 and IIHR-80-1-3 (M. balsamina) were free from disease, whereas, IIHR-144-1 (M. charantia var. muricata) showing mild symptoms with PDI of 1.8 and 4.3 under natural and artificial screening, respectively at later stage were also resistant. Genotypes IIHR-40-1 and IIHR-49-34-5 were moderately susceptible (PDI ˂ 40) PDI was highly correlated with AUDPC under both natural and artificial screening (r = 0.99, 0.95; P ˂ 0.01). Also PDI under natural field screening was highly correlated with the artificial screening under controlled conditions. The highest apparent infection rate (r) was recorded in the genotype, Arka Harit (1.29), whereas, it was the least in IIHR-80-1-2 and IIHR-80-1-3 (0.00). Statistical analysis of disease severity over time using non linear growth model revealed that 97% of variability in disease progression over time was captured by nonlinear logistic model. The rate of disease severity was maximum at t = 2–3 weeks in susceptible and t = 4.24 in moderately susceptible genotype IIHR-40-1, inferring that management strategies may be undertaken within the period identified to avoid loss. The newly identified resistant sources may be used for developing powdery mildew resistant bitter gourd varieties/hybrids.