Screening of field resistance to downy mildew (Pseudoperonospora cubensis) disease in an indigenous and exotic collection of cucumber

Abstract

An experiment was conducted to identify sources of resistance to downy mildew in cucumber. A total of 148 genotypes, along with susceptible checks, were evaluated under natural epiphytotic field conditions using percent disease index (PDI) and area under the disease progress curve (AUDPC) as criteria. Disease severity was recorded on a 0 to 9 scale at fortnightly intervals on 10 randomly selected plants per genotype, for a total of four assessments until crop termination. Genotypes were classified into four reaction groups based on average PDI: highly resistant (0–20%), moderately resistant (21–40%), moderately susceptible (41–60%) and highly susceptible (>60%). Substantial variability in disease response was observed. Only two genotypes, PI-197086 and PI-197088, were highly resistant, with the lowest PDI (≤ 20%) and AUDPC values (788.54–885.24), indicating slow disease development. Four genotypes (Gol Kheera-1, Gol Kheera-2, IC-345573 and IC-613461) were moderately resistant (AUDPC 1048.93–1269.25), while five (IC-332344, IIHR-82, IC-398675, Pusa Uday and PI-330628) were moderately susceptible. The remaining majority, including several commercial cultivars and advanced lines, were highly susceptible (PDI >60%). The predominance of susceptible entries highlights the vulnerability of current cucumber germplasm and the narrow genetic pool for disease resistance. PI-197086 and PI-197088 represent promising primary donors, with moderately resistant genotypes providing additional diversity for durable resistance breeding.