The Significance of the Necrotic Phloem Reaction in the Potato to The Leaf-Roll Virus

Abstract

A modified technique which has facilitated the detection of phloem necrosis in leaf-roll-infected potato plants is described. Placed on a quantitative basis, the necrotic reaction has proved valuable in the estimation of leaf-roll severity in varieties and hybrids. Quantitatively, phloem necrosis has been shown to be tl varietal character which can be influenced by nutritional and environmental conditions. Among varieties and hybrids, a range of necrotic reactions in the phloem from mild to very severe was found, and these reactions were correlated with external symptoms. Severe reactors show a progressive decrease in the amount of phloem necrosis from the stem base to the tip. It is probable that a severe physiological reaction to leaf roll has a well-defined genetic basis, so that the development of hybrids hypersensitive to this virus is possible. This provides a new approach to the problem of leaf-roll resistance in the potato.