Resistance of Selected Alfalfa Strains to Ozone¹

Abstract

Fourteen strains of alfalfa, Medicago sativa L., were evaluated for sensitivity to ozone. Plants were exposed to 20 parts per hundred million (pphm) v/v for 4 hr at 26C, 92% relative humidity, and an illumination of 2,000 ft‐c. The variety ‘Team,’ developed partially in greenhouses and routinely selected for resistance to foliar injury, was more tolerant of ozone than varieties not so selected. We believe that this is the first report demonstrating the effectiveness of greenhouse selection, during periods of high levels of air pollutants, as part of a program to expedite the development of plant varieties resistant to phytotoxicants.