THE SYNTHETIC PRODUCTION OF OAT VARIETIES RESISTANT TO RACE 6 AND CERTAIN OTHER PHYSIOLOGIC RACES OF OAT STEM RUST

Abstract

At the present time, oat varieties that are classed as resistant to Puccinia graminis Avenae Erikss. & Henn. are only resistant to a certain number of the ten physiologic races. With the object of combining in a single variety resistance to as many races as possible, a cross was made between the varieties Hajira Strain and Joanette Strain. Hajira Strain is susceptible to Races 4, 6, 8, and 10, and Joanette Strain to Races 2, 6, 7, 8, and 9. The latter variety gives an indeterminate reaction to Races 5 and 10. Both parents are susceptible to Races 6 and 8.From this cross 93 pure lines were obtained. Under greenhouse conditions, 71 were resistant at the seedling stage to Race 6 at 60° F. At 65°–70° F., approximately one-third of these were resistant to Race 6, one-third semi-resistant, and one-third susceptible. At more advanced stages of growth, namely, fifth-leaf, boot, and heading, representative lines from each of these classes were resistant to Race 6 at 60° F. At 65°–70° F. all showed regional resistance: at the fifth-leaf stage, the tip end of the uppermost leaf only was susceptible; at the boot stage, numerous pustules were present on the uppermost node and internode but the remaining parts were free from infection; at the heading stage, only one or two fairly large pustules occurred on the uppermost node or internode.Six lines that were consistently resistant to Race 6 at 60° F. and 65°–70° F. were tested at the seedling stage at 60°, 65°–70° F., and 75°–80° F., to Races 1, 2, 3, 4, 5, 6, 7, 8, and 10. At the low and intermediate temperatures, these lines were resistant to the nine races. At the high temperature, they were susceptible to Race 6, gave an indeterminate reaction to Races 1, 4, and 5, and were resistant to all the other races.Under field conditions, six lines classed as resistant at 65°–70° F., five classed as semi-resistant, and four as susceptible, were tested to Race 6. All these lines behaved similarly: infections of a semi-resistant type appeared on the uppermost internodes, while other parts of the plants were free from infection.The standard varieties used as checks, namely, Hajira Strain, Joanette Strain, White Russian, and Victory, were susceptible to Race 6 in all the greenhouse experiments, and, with the exception of White Russian, in the field test. In the latter test, White Russian was semi-resistant.