VIEW ARTICLE

Resistance

Effect of Energy-Requiring Defense Reactions on Yield and Grain Quality in a Powdery Mildew-Resistant Barley Cultivar. V. Smedegaard -Petersen, Department of Plant Pathology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Copenhagen V., Denmark; O. Stølen, Department of Crop Husbandry and Plant Breeding, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Copenhagen V., Denmark. Phytopathology 71:396-399. Accepted for publication 10 September 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-396.

Respiration and yield were measured in plants of barley cultivar Sultan following inoculations with two races of Erysiphe graminis f. sp. hordei (the powdery mildew pathogen), one avirulent and the other virulent of Sultan. Respiration measurements demonstrated that plants responding resistant to inoculation with the avirulent race had an 80% increase in the rate of respiration starting within 16–24 hr after inoculation and returning to the normal level at the time when respiration started to increase in plants inoculated with the virulent race. Although plants remained entirely free of symptoms after inoculation with an avirulent race, the grain yield was significantly reduced by 7%, and the kernel weight by 4%. The content of grain protein was reduced from 9.75 to 9.38%, equivalent to an 11% reduction in the yield of grain protein. In susceptible, infected plants the grain yield was reduced by 26%, and the kernel weight by 11%. The protein content of grain was reduced from 9.75 to 9.25%, which is equivalent to a reduction in the yield of grain protein by 30%. The results indicate that in inoculated, highly mildew-resistant barley plants there was an increased requirement of host energy, probably due to enhanced biochemical activities involving active defense reactions. The greatly increased respiratory rate deprived the resistant host of energy available for growth, and led to a reduction in grain yield and grain quality, although no visible symptoms appeared.