Varietal Resistance of Peas to Pea Aphid Biotypes Under Field and Greenhouse Conditions

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Abstract
Infestation of 13 varuetues and selections of peas (Pisum sativum L.) by winged migrants of the pea aphid (Acyrthosiphon pisum (Harris)) (= Macrosiphum pisi (Harris)) was carefully measured to detect possible mechanisms of variety preference. At early seedling stage (1 to 6 inches tall) color of the foliage was correlated with the alighting response of winged aphids. Migrants and colonies were in greatest numbers on a variety with yellowish-green foliage in lesser numbers on varieties with green foliage and least abundant on a variety with deep-green foliage. At early growth stage, increased varietal plant height had a barrier effect that favored a higher initial infestation by migrants. At full growth stage, increased varietal plant height had an exposure effect that reduced ensuing aphid population because of taller stems, longer internodes and lesser dense foliage. Antibiosis did not play a significant role in peas grown in rows but would likely express itself in a solid stand crop as it did under field cage tests. Temperature and aphid biotypes modified the expression of antibiosis and the rating of pea varieties for resistance. The knowledge acquired is useful in understanding the nature of antibiosis in peas. Some specific techniques to be used in testing peas for resistance to the pea aphid were determined.