EPIDEMIOLOGY AND MANAGEMENT OF ALTERNARIA BLIGHT ON SEED CROP OF CARROT (Daucus carota)
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Date
2013
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Punjab Agricultural University, Ludhiana
Abstract
Surveys conducted during 2011 and 2012 revealed that Alternaria blight of carrot was observed at all the locations on all the cultivars. The disease incidence and severity was the highest on Local varieties as compared to PAU recommended varieties. The highest disease severity was observed on local variety grown at village Bohan in district Hoshiarpur, while the lowest disease severity on Selection-21 grown at PAU Ludhiana. Alternaria radicina and Alternaria dauci were found to be associated with the disease. Alternaria radicina has highest frequency than Alternaria dauci on carrot plants. Maximum colony growth and sporulation of Alternaria radicina was observed on carrot leaf agar followed by unmbel extract agar medium. Lowest colony growth and sporulation was observed on Czapek‟s Dox agar medium. Maximum colony growth and sporulation was observed at 25°C temperature followed by 30°C, whereas no colony growth was observed at 35°C. Most suitable range of temperature was found to be 25 to 30°C. Maximum colony growth of Alternaria radicina was observed at pH 6, whereas maximum sporulation was observed at pH 7. The disease severity increase with the increase in the age of plants and a positive correlation between plant age and disease severity was observed. Similarly disease severity increased with the increase in the leaf wetness period. A positive correlation was found between leaf wetness period and disease severity. A minimum 8 hr of leaf wetness was required to cause infection on carrot plants. All three non systemic fungicides proved less effective than systemic fungicides. Among systemic fungicides ED50 values for difenconazole and propiconazole was less than 1μg/ml, while for hexaconazole and azoxystrobin was 1.0 and 5.9 μg/ml respectively. Among non systemic fungicides ED50 value was 17 for chlorothalonil, whereas it was 44 μg/ml for mancozeb. Under field conditions all systemic fungicides proved highly effective in controlling the disease as compared to non systemic fungicides. Azoxystrobin + Difenconazole @ 0.1 per cent proved most effective in checking the disease than other tested fungicides.
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