Multiline cultivars — how their resistance influence leaf rust diseases in wheat

Summary To understand how multiline cultivars of wheat develop better protection against leaf rust, seven experimental multilines with 0, 28, 40, 50, 58, 60 and 70% susceptibility were subjected to leaf rust epiphytotics in the field along with their pure line components. A mixture comprising 12 leaf rust races, 10, 11, 12, 17, 20, 63, 77, 106, 107, 108, 162 and 162 A was used.Both the initial inoculum (Xo) and rate of increase (r) of leaf rust were substantially reduced in the multiline cultivars. Xo was reduced by 45–75% and the over-all infection rate (r) by as much as 16% over the average of components.As a result of reduced Xo and r, the intensity of leaf rust in the multilines was also significantly affected at all stages of rust development. It was reduced from 32,10 to 89.54% over the average of components differing from one multiline to another and also from time to time. The susceptible recurrent parent, Kalyansona at the peak period of rust infection exhibited 86.75% severity while in the multilines it ranged from 5.80 to 35%.The rate of increase in the multilines was found to be proportional to the logarithm of the proportion of susceptible plants in the host mixture.Further, it was found that even if as many as 50% susceptible plants are present in a multiline they would not suffer much from leaf rust damage.