Abstract

                                in almost all the rice growing countries of the world. It is by far the most important disease in the Madras State, causing severe losses to cultivators in the years when the seasonal conditions are favourable for the infection and spread of the disease. The only effective method of combating this discase so far known is by growing resistant varieties. The problem of disease resistance in plants has aroused much interest among workers in the field of plant pathology and numerous investigations have been carried out on the morphological characters of the plant in relation to its resistance to diseases. Cobb (1892) was the first to find that the resistance to rust of wheat varieties was correlated with morphological characters. Hursh (1924) found out that the resistance of wheat to Puccinia graminis was correlated with the relative proportion of sclerenchyma to collenchyma, Willaman and others (1925) reported that the varieties of plum that are resistant to disease have a higher crude fibre content, tougher skin and firmer flesh than the susceptible ones. Melhender and Craigie (1927) found that a correlation exists between the resistance of barberry leaves to stem rust and the thickness of the leaf as well as the resistance to puncture of the outer walls of the epidermal cells. Lutman (1919) found that the thickness of the skin determined the resistance of potato tubers to scab.

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