Field Resistance of Cotton to Myrothechini leaf spot (Myrothecium roridum Tode ex Fr.) and Alternaria leaf spot (Alternaria macrospora Zimm.) diseases

摘要

The unimportant fungal foliar diseases namely Myrothecium leaf spot and Altemaria leaf spot in late seventies and early eighties have become economically important and destructive after the introduction of synthetic pyretbroids for the control of bollworms. The diseases assume a serious form in seasons of prolonged rainfall and humidity and is hardly noticeable during relatively dry periods. Diploid cottons suffered serious injuries. Four hundred and three germplasm lines were screwed under inoculated unprotected conditions during 1994-96 crop seasons. Against Myrothecium leaf spot disease, 33 entries belonging to G. hirsutum and intra hirsutum hybrids were recorded in the immune grade of the reactions. Majority of the entries were in moderately susceptible grade. Most varieties of the American cottons were found susceptible while the oriental species did not suffer severe damage even under favourable conditions. Only 30 entries belonging to both G. hirsutum and G. arboreum and their hybrids were noticed in immune grade against Alt em aria leaf spot disease. Against both these diseases only 3 entries were noticed in immune grade while only 2 entries were in resistant grade of reactions.