Resistance of potato seedling varieties to the natural spread of leaf roll

Abstract

Potato seedlings were exposed to field spread of leaf roll from adjacent rows in an area where leaf roll spreads consistently year after year. Parents used at first included commercial American and European varieties reputed to be resistant to leaf roll, and a few of the crosses contained some seedlings resistant to the natural spread of leaf roll. When these resistant seedlings were used as parents, the resulting crosses generally were more resistant to field spread than crosses of other kinds. Greater resistance in one of the parents did not always mean greater resistance in the cross. Greater resistance in a cross (on the basis of percentage of seedlings showing any leaf roll) was not necessarily correlated with the percentage of total plants showing leaf roll in the infected seedlings. Field resistance in given seedlings and varieties varied from one season to another on the same farm. Although green peach or spinach aphids (Myzus persicae) probably are an important factor in the field spread of leaf roll, aphid resistance in seedlings is not necessary for field resistance to leaf roll. It is possible to combine field resistance to leaf roll with many characteristics considered commercially desirable in this country.