THE EFFECT OF VARIOUS METHODS OF BREAKING RESISTANCE ON STEM RUST REACTION AND CONTENT OF SOLUBLE CARBOHYDRATE AND NITROGEN IN WHEAT LEAVES

Abstract

The resistance of Khapli wheat to a number of races of stem rust, Puccinia graminis (Pers.) f. sp. tritici (Erikss. and Henn.), was broken after treatment with maleic hydrazide, DDT, detaching the leaves, and "searing" (heat treatment at the base of the leaf). In addition, the reaction of several other varieties to a number of races of stem rust was altered from resistant to susceptible by detaching and searing.DDT and searing caused marked increases in carbohydrate and soluble nitrogen levels, while maleic hydrazide caused smaller increases. There were no differences in carbohydrate levels, and only a slight difference in soluble nitrogen, between plants kept at 65° and 75° F., the temperatures at which McMurachy is respectively resistant and susceptible to rust. Insoluble nitrogen decreased after searing and DDT at rates approximately equal to those of the control. Insoluble nitrogen decreased at a faster rate in leaves kept at 75° F. than at 65° F. It remained fairly constant in leaves treated with maleic hydrazide.The data support the concept that substrate availability is of major importance in rust development.