Resistant and susceptible plant hosts of the Russian wheat aphid, Diuraphis Noxia (Mordvilko), were used to evaluate the relationships between damage rating indices and quantitative measurements of plant damage. The degree of association between percentage of leaf chlorosis, leaf rolling, and plant stunting, indicated that these occur independently. Damage ratings based on percentage of chlorosis accurately identified highly resistant and highly susceptible entries. When compared with quantitative plant measurements, the most reliable plant damage rating was plant stunting expressed as the percentage of height of a noninfested control. No significant relationships between leaf rolling and quantitative plant measurements were found. However, aphid-caused reductions in leaf turgor were closely related to the amount of chlorosis.
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Burd et al. (1993) studied this question.