Studies for Variability in Alternaria Triticina on Wheat in Bihar
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Date
1999
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Birsa Agricultural University, Ranchi
Abstract
Wheat (T. aestivum L.) is the most widely cultivated crop of the world. Among the wheat growing countries India ranks fourth in terms of productions (63.02 MT) and area (24 M ha) under cultivation with 26 q/ha average yield. In Bihar, it is cultivated in 1.84 M ha with total production of 2.86 MT and average productivity is 15.56 q/ha. It is an important source of food for human consumption, feed for livestock and wheat starch for industrial importance. Wheat crop suffers from many fungal, bacterial and viral diseases which reduce the yield. The leaf blight disease of wheat caused by Alternaria triticina Prasada and Prabhu, is one of the most destructive diseases causing considerable losses in production of wheat in most of the wheat producing areas of India including Bihar and thus neutralizes the costly inputs of the cultivation for higher productivity. In view of its significance, investigations on leaf blight disease of wheat were conducted to find out the variability of the pathogen along with some basic investigations of the disease especially to develop suitable management strategies.
The three isolations of the pathogen were made and designated as A-1 (Ranchi isolate), A-2 (Pusa isolate) and A-3 (Sabour isolate) on the basis of morphological and pathogenic behaviour. The conidia of isolate A-1 were slightly bigger in size (mean 28.9 x 9.8 μm), than the isolate A-2 (mean 26.3 x 6μm) and A-3 (mean 25.8 x 9.5μm). The morphological characters of three isolates on different culture media have been described in detail. While proving the Koch's postulates, a considerable variability in pathogenicity among the isolates were observed. The isolate A-1 was highly virulent as it required less time for infection and produced more number of lesions of bigger size. The isolates also varied in their nutritional requirement in orderto grow and sporulate on different liquid and solid culture media. Potato dextrose agar medium supported maximum growth of all the isolates with significantly superior (mean 68.7mm) performance of isolate A-1. pH 6.0 was found to be optimum for the growth and sporulation of all the isolates and isolate A-1 had significantly superior growth at various pH levels. evaluated followed by isolate A-2 and A-3 which were at par.. Spore germination of all the isolates did not differ significantly with each other at various levels of humidity tried and cent percent RH induced highest spore germination for all the isolates. Isolate A-1 had maximum growth under all the three condition i.e., continuous light, alternate light and continuous darkness over the isolate A-2 and A-3. Photo inhibitory effect on sporulation was evident in all the three isolates of A.triticine. None of the plant other than wheat found susceptible during host range study and their were no variability observed among the isolates of the pathogen regarding their host range. Fath And
The intensity of Alternaria leaf blight increased with increase in the level of nitrogen applications. Phosphorus or Potassium had no significant impact on the disease intensity separately, but reduction in disease development was observed when they were supplemented with the higher dose of nitrogen (250kg/ha). Out of fifty eight wheat cultivars screened only twelve cultivars viz., BAU 33, BAU 2398, BAU 2378, BAU 2395, BAU 2375, HP 1209, KS 26, MACS 9, M 8223, N 59, NI 5439 and PAN 3043 were found resistant to blight disease. Indofil M-45 (0.2%) was found to be best in vitro against the pathogen and reduced the disease intensity and increased the yield in field condition followed by Dithane Z-78 (0.2%).