STUDIES ON POWDERY MILDEW OF SUMMER SQUASH (Cucurbita pepo L.)

BHARMERA, POOJA

STUDIES ON POWDERY MILDEW OF SUMMER SQUASH (Cucurbita pepo L.)

Date

2018-09

Authors

BHARMERA, POOJA

Publisher

UHF,NAUNI

Abstract

ABSTRACT Powdery mildew is an important disease of summer squash (Cucurbita pepo L.) in Himachal Pradesh. Present investigations were undertaken with an objective to study the occurrence, symptomatology, correct identity of the pathogen involved, pathogenicity, relationship of environmental factors with disease development, screening of germplasm and to evolve an effective disease management strategy. The disease was found prevalent in moderate to severe form in Solan district of Himachal Pradesh. The characteristic symptoms were observed on leaves, petioles and stems while no symptoms were observed on fruit. On the basis of anamorphic characters like ectophytic mycelium, unbranched conidiophores with cylindrical foot cell, ellipsoidal conidia, 31.53 × 20.34 μm in size, presence of fibrosin bodies in conidium, forked/simple germ tube and absence of appressorial formation and teleomorphic characters like presence of cleistothecia, variable number of myceloid appendages, single ascus with 8 ascospores, the associated pathogen was identified as Sphaerotheca fuliginea (Schlect) Poll. as the causal agent of this disease. Pathogenecity test showed that both i.e. cotyledonary and first true leaves were susceptible to disease with incubation period ranging from 168 to 188 h and latent periods from 206 to 228 h, respectively. Maximum conidial germination and germ tube length was recorded at 25 °C and 100 per cent relative humidity. Moderate air temperature coupled with high relative humidity and cumulative rainfall helped significantly in disease development. Out of 18 cvs./lines/hybrids only one i.e. Korean House F1 showed moderately susceptible reaction whereas eleven cvs./lines/hybrids were observed as susceptible and rest six exhibited highly susceptible reaction. Among all fungicides evaluated, carbendazim proved most effective at all concentrations followed by dinocap (500ppm) and wettable sulphur (1000ppm) and completely checked the conidial germination and germ tube elongation under in vitro conditions. Among different fungicides evaluated under field conditions, four azoxystrobin (0.1%) sprays were significantly most effective followed by carbendazim (0.1%) in reducing the severity of the powdery mildew to 14.33 and 17.67 per cent and increased fruit yield to 5.32 and 5.07 kg/plot, respectively. Among different natural products, botanical, bio control agent and SAR chemicals evaluated against the disease under field conditions di potassium hydrogen phosphate (0.9%) was statistically superior and reduced the powdery mildew severity to 21.33 per cent and increased fruit yield to 4.20 kg/plot.