Epiphytology and losses of downy mildew (Peronospora parasitica) of radish (Raphanus sativus) seed crop

Abstract

An experiment was conducted during 1998-99 on the downy mildew to study epidemiology and loss caused by Peronospora parasitica (Pers Fr. on 'Pus a Chetaki' radish (Raphanlls sativus L.) in short-span. Dense crop geometry had positive correlation with diseasc intensity and was deterrent to potential yield. Maximum disease severity (48.6%) found in 30 cm x 30 cm spacing resulted in 30.3% defoliation of leaves and 17.5% bending of twigs. Thc seed yield losses were 17.3,21.7, 24.8,27.1, 34.3 and 39.6% in 60 cm x 60 cm, 60 cm x 45 cm. 45 cm x 45 cm, 60 cm x 30 cm, 45 cm x 30 cm and 30 cm x 30 cm spacings, respectively, compared with their healthy treatments. A steep increase in disease severity was noticed during February when cumulative weekly dew fall was> 1 mm, leaf-wetness duration> 10 hr, favourable temperature duration (8-24°C) > 20 hr and mean maximum relative humidity> 85%. Diseased specks increased greatly when nieto wet and humid conditions were cycled with diurnal favourable temperature (20-24°C) conditions. For downy-mildew epiphytology in radish, leaf-wetness duration and favourable temperature duration were predominant and deciding dependent variablc, while dew fall and mean maximum relative humidity were lauching pads for multicyclic injection.