Disease Expression and Ecophysiological Yield Components in Sunflower Isohybrids with and without Verticillium dahliae Resistance

Abstract

ABSTRACTVerticillium wilt (Verticillium dahliae Kleb.) is an important disease affecting sunflower (Helianthus annuus L.) in most production areas in Argentina, Canada, and the United States. Estimation of yield losses produced by the disease is difficult because of the absence of highly efficient chemical control and resistant hybrids of comparable yield potential. In this work nine pairs of isohybrids with and without resistance to V. dahliae were sown at five different locations and evaluated under natural infection to determine disease induced yield reductions across environments with varying V. dahliae incidence. The effects of the disease on physiological components of growth were studied in a separate trial with three pairs of isohybrids. Disease incidence and severity for resistant isohybrids (R) were zero or nearly zero independently of their genetic background in all locations, indicating the isohybrids were highly resistant or immune. In the most severe environments, grain and oil yield of susceptible isohybrids (S) were nearly 30% less than those of the resistance couterparts. The incorporated resistance resulted in an increased percent radiation interception and radiation use efficiency (RUE). However, the effect of the disease on crop growth rate was evident after flowering. Up to that phenological stage, leaf expansion, radiation interception and photosynyhetic rate did not differ between R and S isohybrids.