Division of Genetics, I.A.R.I., New Delhi
The identification and location of the genes for seedling resistance to two races of black rust -40 and 24-were undertaken on two wheat varieties, Lerma Rojo and Sonora 64 through monosomic analysis. The resistance in case of both the races in the above two varieties was found to be thermosensitive.
1. Race 40.—In Lerma Rojo the resistance to race 40 was found to be controlled by a pair of dominant factors located on 6A at normal temperatures, while at slightly higher temperatures (65°F to 77°F) it was governed by another two pairs of recessive factors one each on chromosomes 3B and 4A. In Sonora 64 the resistance to this race was controlled by two pairs of dominant duplicate factors at normal tmperatures (54.5 to 68°F), while at the temperature range of 65°F to 77°F, it was controlled by two pairs of complementary factors. The chromosomes involved were the same at both the temperatures namely, 6A and 6B.
2. Race 24.—Resistance to race 24 in Lerma Rojo was found to be controlled by two pairs of independently inherited factors located one each on chromosomes 2D and 4B giving a ratio of 12VR: 3MR: 1S, whereas, at slightly higher temperatures, two pairs of dominant complementary factors located on 4B and 6A and a minor gene on 2D were involved in conditioning resistance. The inheritance of resistance to race 24 in Sonora 64 X Chinese Spring was similar to that in Lerma Rojo X Chinese Spring. The genes for resistance were located on 4B and 6B of Sonora which act independently at normal temperatures (54.5°F to 68° F) and in complementary manner at the temperature range of 65° to 77°F. In addition, at slightly higher temperature (65°F to 77°F) a minor gene carried by 6A of Sonora 64 was also involved.
