Chemical control of blossom blight disease of sarpagandha caused by<i>Colletotrichum capsici</i>

Abstract

Sarpagandha (Rauvolfia serpentina Benth) is grown in different parts of India and its adjoining countries for its root which is the chief source of several important alkaloids like ajmalicine, ajmaline, isoajmaline, rauvolfinine, reserpine and serpentine. Blossom blight caused by Colletotrichum capsici is one of the most serious diseases of sarpagandha in the North Indian plains. Eight fungicides, namely Benomyl, Carbendazim, Chlorothalonil, Mancozeb, Metalaxyl-mancozeb, Propiconazole, Thiram and Thiophanatemethyl were evaluated against the spore germination and mycelial growth of Colletotrichum capsici under in vitro condition. The results indicated that Mancozeb, Metalaxyl-mancozeb, Propiconazole and Thiram inhibited percent spore germination at the dose of 2 - 10 g/ml, while Benomyl, Carbendazim and Thiophanate-Methyl were ineffective even at 250 g/ml concentration. Propiconazole, Carbendazim, Benomyl, Mancozeb and Metalaxyl-mancozeb were highly effective inhibiting 50% mycelial growth at 2.8, 4.6, 6.0, 9.3 and 11.2 μg/ml, respectively, while Thiophanate-methyl, Chlorothalonil and Thiram were relatively less effective showing 50% mycelial growth inhibition at 25.2, 27.2 and 31.3 μg/ml, respectively. The effective fungicides were further employed for the protection of sarpagandha from blossom blight disease in the field during the year 2006 and 2007. The results of the two years (2006 and 2007) of field experiments indicated that disease incidence was significantly reduced in all the treated plots over unsprayed control. The spray of Mancozeb and Carbendazim produced highest protection that is >80% in both the years against blossom blight disease and their treatments also produced healthy and highest seed yield per plant.

Key words: Blossom blight, Colletotrichum capsici, fungicides, Rauvolfia serpentina, sarpagandha.