Some comments on two recent papers in euphytica concerning stem rust resistance in wheat

✍ Scribed by D. R. Knott

• Publisher: Springer
• Year: 1981
• Tongue: English
• Weight: 200 KB
• Volume: 30
• Category: Article
• ISSN: 0014-2336
• DOI: 10.1007/bf00038784

✦ Synopsis

Two recent papers in Euphytica concerning resistance to stem rust (Puccinia graminis tritici ERIKS, and HENN.) in wheat (Triticum aestivum L.) have left a number of questions unanswered. SAWNEY et al. (1978) reported that the wheat cultivar Chhoti Lerma carried two, independent, recessive genes for resistance to race 122 of stem rust. When it was crossed with a susceptible cultivar, the F, generation segregated in a ratio of 7 resistant (R): 9 susceptible (S). When Chhoti Lerma was crossed with the 21 Chinese Spring monosomics, 19 crosses segregated 7R:9S but the crosses with monosomics 1D and 7D segregated 1 R :3S. The authors concluded that the two genes are on chromosome 1 D and 7D. However, in the two critical crosses the ratios should not be lR:3S. If the recessive genes are ineffective when hemizygous, then only some of the nullisomic plants will be susceptible and most of the plants will be resistant. While superficially the results appear to make sense, they can only be accepted if some explanation can be given for the aberrant 1 R :3S ratios.

In another paper, SAWHNEY et al. (1979) studied the inheritance of resistance to stem rust in two wheat lines, E5883 and E6032,* to four races of stem rust. The resistance of E5883 to races 15C, 21 and 40 was reported to be due to a single dominant gene in each case, while its resistance to race 122 was reported to be due to a single recessive gene (no data were given). E5583 was crossed with lines carrying single genes for stem rust resistance and the F, seedlings were tested with races to which both E5583 and the single gene lines were resistant. The cross with Kenya 58-Mq" (Sr6) did not segregate (195R:OS), showing that E5583 carries Sr6. The cross with Red Egyptian-Mq6 (Sr8) did not segregate when tested with race 122, although there were only 44 plants (the segregation does not fit the expected 13R : 3S, P c: 0.005). However, with race 21 the cross segregated 173R:6S, which does lit the expected 15R:lS ratio. Thus, the results conflict. Tests of the single gene lines indicated that Sr6 conditions resistance to races 15C and 40, and probably to race 21 (type 2,3"). Thus the single dominant gene for resistance to races 15C, 40 and 21 in E5583 must be Sr6. The authors conclude that E5583 also carries Sr8, which is shown to condition resistance to races 21 and 122. If it