Barley Yellow Dwarf Symptom Severity in Oat Affected by Plant Growth Stage at Infection and Plot Type

Lack of a standard method for evaluation of barley yellow dwarf (BYD) symptoms may result in inconsistency for genetic evaluation. The BYD symptoms were determined in oat, Avena sativa L., subsequent to virus infection at three plant growth stages and with two types of field plots. Five treatments: noninoculated; and inoculated at the two- to three-leaf (transplanted), three-leaf, four- to five-leaf, and stem elongation stages (direct seeded) were whole plots. Five oat cultivars were subplots. Two types of plots, hill and space planted, were whole units across the five cultivars. Seven traits were measured: BYD symptoms, plant height, heading date, grain yield and yield components. The plot types were not significantly different and there was a high correlation between the types of plot for these characters. Cultivar rank was similar at all growth stages, indicating that sensitive cultivars may be severely damaged by BYDV infection at any stage of development. Small differences among cultivars for tolerance to BYDV were detected, subsequent to infection at the stem elongation stage under conditions of moderate temperatures and well distributed rainfall during the growing season. The plants that were transplanted after inoculation at the two- to three-leaf stage were more severely affected by BYDV than plants that were seeded in the field and inoculated at the three-leaf stage. Differences among cultivars were most distinct for BYD symptom, kernel weight, grain yield, number of kernels per panicle and plant height. Inoculation at the three-leaf stage resulted in maximum differences among cultivars and hill plots involved minimal effort for BYDV evaluation. The research was supported in part by CNPq (Natl. Res. Counc. of the Ministry of Science and Technology) of Brazil Graduate Training Grant no. 200858-85.8, and by The Quaker Oats Co. Purdue Univ. Agric. Exp. Stn. Journal no. 11809.