Studies on transmission, host range and management of ash gourd mosaic disease.
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Date
2011
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Department of Plant Pathology, College of Horticulture, Vellanikkara
Abstract
The present investigation, “Studies on transmission, host range and management of ash gourd mosaic disease” was undertaken in the Department of Plant Pathology, College of Horticulture, Vellanikkara during 2009-2011 with an aim to study the symptomatology of the mosaic disease, mode of transmission, host range of the virus, the resistance of available genotypes to mosaic under net house conditions and to evolve a suitable management practice under field conditions.
The sampling survey for the collection of mosaic samples conducted in different locations of Thrissur district revealed the incidence of five types of mosaic symptoms viz., marginal yellowing, yellow-green patch, severe puckering, filiform type and light and dark green patch type on ash gourd leaves. The marginal yellowing was found to be the prominent type of symptom compared to the other four types of mosaic. Under natural condition, yellowing of leaf margin was the major symptom of marginal yellowing type mosaic. But under artificial condition, yellowing of veins and veinlets of the leaf starting from the margin was the prominent symptom. In sap transmission studies, citrate phosphate buffer (0.1 M, pH 7) gave maximum disease incidence (73 per cent) with 23-28 days of incubation. In vector transmission studies, Aphis gossypii gave 59.5 per cent disease incidence and Bemisia tabaci, was unable to transmit the virus.
Biological indexing was done on Petunia hybrida and Vigna unguiculata to identify different viruses infecting ash gourd. Dark necrotic spot was produced in P. hybrida on inoculation with yellow-green patch type and severe puckering type mosaic whereas systemic infection was produced on inoculation with filiform type. Chlorotic spots were produced in V. unguiculata on inoculation with yellow-green patch type and puckering type mosaic whereas systemic infection was produced on inoculation with filiform type. Symptoms were not produced on inoculation with marginal yellowing type in P. hybrida and V. unguiculata. Based on the symptoms produced on V. unguiculata, it was ascertained that the virus causing yellow-green patch type mosaic belong to Cucumber mosaic virus group and the virus causing filiform type of mosaic belong to potyvirus group. The electron microscopic study of the marginal yellowing type and puckering type revealed that they also belong to potyvirus group.
Host range studies of the ash gourd mosaic revealed systemic infection in snake gourd, bottle gourd, ivy gourd, tomato, chilli and cluster bean. Screening of 15 ash gourd genotypes against mosaic disease, revealed that one genotype, Jeevas was resistant to the mosaic with no disease incidence and one genotype BH-205 was moderately resistant (10 per cent incidence). The genotypes BH-206, BH-210, Indu, BHF-2, BHF-3, BHF-4, BHF-6, BHF-7, BHF-8 and BHF-9 were moderately susceptible (20-50 per cent incidence) and BH-216, BH-219 and BHF-5 were susceptible (70 per cent incidence) to mosaic.
Field experiment conducted to evaluate the effect of botanicals, biocontrol agent and chemicals on ash gourd mosaic revealed that all treatments reduced disease incidence, severity and coefficient of infection and increased yield and among them quinalphos (0.05%) was the best.
From the above study, it was concluded that marginal yellowing, yellow-green patch, puckering and filiformy were the major types of ash gourd mosaic and among them, mosaic with marginal yellowing symptom was the prominent one. The ash gourd mosaic was transmissible through sap and aphid. The virus causing marginal yellowing type mosaic belonged to potyvirus group. Snake gourd, bottle gourd, coccinia, tomato, chilli and cluster bean were found to be collateral hosts of the virus. Jeevas, a local genotype was identified as a resistant variety to ash gourd mosaic. The results of field experiment revealed that quinalphos (0.05 per cent) showed maximum effect in reducing mosaic infection.
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