Some effects of leaf-roll virus on the development and growth of the potato plant

Abstract

A detailed field trial and other experiments were made to explore the effects of leaf roll on the growth of different varieties of potato. The shoots of a tolerant variety, Up to Date, were little changed in size by infection at emergence, but during the early vegetative stage of development the growth rate of the haulm was reduced. The shoots of an intolerant variety, Bismark, were probably smaller in size at emergence, and for a period during the vegetative stage of development the tops of the plants grew at the same reduced rate as those of Up to Date and three other varieties. These other three varieties, which were intermediate in tolerance, were intermediate in growth reaction between Up to Date and Bismark. The tolerant variety, Up to Date, during the first stages of tuberation, reacted to infection without serious changes in length of stolons or time of initiation of tubers. The intolerant variety, Bismark, reacted with a shortening of stolons and a hastening of tuber initiation. The reduction in size of various parts of the plant was greater for intolerant than for tolerant varieties. The numbers of leaves developing on the main axes of both tolerant and intolerant varieties were reduced by infection. The reduction in the proportion of leaf area contributed by axillary shoots to the total leaf area of infected plants, was similar in the tolerant and intolerant variety, in spite of the difference in the size of the plants. In the intolerant variety, Bismark, there was a change in type of axillary growth above ground as well as a change in vigour. The course of development of the foliar parts of the plant during maturity and senescence demonstrated the serious alteration in growth characteristics of the infected plants of the intolerant variety Bismark. There was relatively little alteration in the tolerant variety, Up to Date. Incomplete data suggest that losses in yield due to infection are not due to a reduction in efficiency per unit of leaf area in the production of tubers by infected plants. The reduction can be accounted for on the basis of reduced growth rate, loss in size of haulm. The repercussions of these findings on the problem of breeding for resistance against leaf roll are mentioned.