Resistance of Sweetclover to the Sweetclover Aphid1

Abstract

An evaluation of resistance to the sweet clover aphid (Therioaphis riehmi (Börner)) was made among commonly grown sweet clover varieties and the more promising breeding lines. This evaluation, made both in the greenhouse and under field conditions, was based on aphid populations and on plant survival under heavy aphid infestations. A highly significant negative correlation was demonstrated to exist between aphid populations and plant survival. Of the plant materials evaluated, the breeding line N13 and the variety Spanish were the most resistant whereas common yellow was the most susceptible. Great variability existed both within and between the strains and varieties tested. Plant age had a pronounced effect on resistance. The older plants demonstrated the greatest resistance among most of the materials tested. The least influence of plant age was shown by the most resistant (N 13) and the most susceptible (common yellow) entries. The outlook for combating the sweet clover aphid through the development and use of aphid-resistant varieties appears promising.