Tolerance to Barley Yellow Dwarf Virus in Oats

JEDLINSKI, H., W. F. ROCHOW, and C. M. BROWN. 1977. Tolerance to barley yellow dwarf virus in oats. Phytopathology 67: 1408-1411. Disease severity was highly correlated with reduction in plants of each of the three tolerant lines than from plants of yield of three pairs of sister oat lines representing F7 each of the three lines that lacked tolerance. These data show generation progenies that transgressively segregated for that meaningful direct tests of BYDV concentration can be marked tolerance and intolerance to barley yellow dwarf used to study the mechanism of tolerance, which appears to virus (BYDV) infection. Less BYDV was extracted from involve a suppression of BYDV replication. Additional key words: aphids, cereal viruses. The use of tolerant oat (Avena sativa L.) cultivars is heritability for BYDV reaction was high in the F2, F3, F4, currently the only practical means of controlling the and F5 generations. Genetic results, which will be barley yellow dwarf virus (BYDV) disease. Although published elsewhere, showed that the progenies, each much progress has been made in breeding tolerant oats (5, derived from a different F2 plant, transgressively 6, 7, 8, 18), little is known about the mechanism of this segregated for higher and lower levels of tolerance to resistance to the aphid-transmitted virus. For some virus BYDV than did the respective parents. The three pairs of diseases an explanation for tolerance is based on oat lines used in these studies were quite similar; their suppression of virus replication (3,4, 13, 17,23,25). Most reaction to BYDV was the major identifiable such studies have involved viruses that are relatively easy differentiating character. Consequently, each of the three to assay because they are mechanically transmissible and pairs will be referred to as sister lines. reach high titers in infected plants. The disease severity and percentage yield reductions We used pairs of sister oat lines in preliminary tests of were determined at Urbana under field conditions, by the thesis that a mechanism for resistance to BYDV is using methods similar to those reported previously (19). suppression of virus replication in the tolerant oat lines. One isolate of BYDV, Champaign-6, was used as This paper describes direct evaluations of disease severity inoculum in both years. The oat seeds were planted in the for the paired oat lines, and shows that estimates of virus field at the end of April, with two replications in 1972, and titers in such lines can be used to study the mechanism of three replications in 1974. The plantings were made in tolerance, despite limitations of working with phloemhills spaced 0.457 m (1.5 ft) apart, 12 plants per hill. To limited, vector-dependent luteoviruses, such as BYDV. minimize contamination, we isolated plots containing plants to be inoculated from those serving as controls by a 4.57-m (15-ft) border of a mixture of different oat MATERIALS AND METHODS cultivars. The plants were inoculated at an early tillering Six oat lines were used in all experiments. The lines stage by exposing them to approximately 20 viruliferous Rhopalosiphumpadi (L.) per plant for a period of 3 days. were derived from crosses made at Urbana, Illinois, from The inoculation feeding was stopped by spraying all parents selected for tolerance to two vector-nonspecific plants, including the border plants, with r, O-dimethyl Sisolates of BYDV described previously (18, 19). All pntsicu gborderpla wh 0, 0-dithyl 5parental oat selections were relatively tolerant and (N-methylcarbamoylmethyl) phosphorodithioate diffnt t erenceions dee seltverty t ramngthe a (dimethoate) in a water emulsion at the rate of 1.24 kg consequently differences. in disease severity among the active material per hectare (1.1 pounds active material per lines were small, especially in the greenhouse. Generally, acre). Two disease severity evaluations were made: one at first symptom development; and the other, shortly before Copyright © 1977 The American Phytopathological Society, 3340 the plants matured. Pilot Knob Road, St. Paul, MN 55121. All rights reserved. The virus concentrations of BYDV extracted from each