Influence of synthetic and natural fungicides, environmental and physiological factors on the uredospore germination of the pathogen causing rust disease in cowpea

Abstract

Cowpea (Vigna unguiculata (L.) Walp.) Is one of the most important pulse crops in Karnataka. Rust disease caused by Uromyces phaseoli var. vignae (Barclay) Arthur is a major threat for its cultivation causing severe yield loss. Among the six fungicides and ten botanicals, maximum per cent inhibition of germination of uredospores was observed at 50ppm in propiconazole 25%EC (78.87%), followed by hexaconazole 5% EC (77.37%). Whereas, least per cent inhibition of uredospores germination was recorded in treatment with tebuconazole 25% EC at 10ppm (67.17%) followed by difenconazole 25% EC (75.70%). Among different botanicals neem extract at 7.5%showed highest inhibition of 68.06%, however, ginger extract at 2.5% recorded least uredospore germination of 26.10%. Inorder to know optimum temperature and relative humidity for Uredininospore germination, an experiment was conducted under at temperature between 5-35 oC and relative humidity regimes ranging between 0-100%. The maximum per cent of uredopsores germination (80.50%)was recorded at 20°C. however germination did not occur at 0°C and 35°C. When the relative humidity was 100 per cent the per cent germination of uredospores was 83.67 per cent which was maximum. No germination occured at zero per cent relative humidity. Different nitrogen and Carbon sources were tested at three different concentrations to study the influence of physiological factors on uredinospore germination. Highest germination was recorded in sucrose at 1.5% (36.10%), whereas in case of 0.5% mannitol least germination (15.60%) was obtained. Among the nitrogen sources KNO3 at 1.5% concentration showed maximum germination of 68.07%, least germination was recorded in NaNO3 at 0.5% with 18.07% germination.