| Monosomic analysis of adult plant resistance to black
rust in the wheat variety Yaqui-53 M. P. SINGH Division of Botany, Indian Agricultural Research Institute New Delhi-12, India In the present studies, urediospore suspension was used for creating the artificial epidemics. The races included were 15, 21, 21A, 24, 34, 40, 42 and 117 of black rust. The mode of inheritance of field resistance to black rust in the cross of Chinese Spring monosomics with Yaqui-53 resistant parent) indicated the presence of two dominant duplicate factor pairs on chromosome 3A and 6B (Table 1). These findings got confirmation in the normal cross (Chinese Spring x Yaqui-53), where resistance was dominant and a segregation ratio of 15 resistant : 1 susceptible was clearly established. The presence of resistant plants in monosomics 3A and 6B and their reaction indicated, that almost the same type of resistance is shown in these two 'critical' lines. These results suggest that the resistant variety, Yaqui-53, carries two pairs of dominant genes for resistance viz., R1R1 and R2R2, and the susceptible parent Chinese Spring, corresponding alleles r1r1 and r2r2. The presence of comparatively more semi-resistant and susceptible plants in line 7A, may be due to the presence of some minor gene for susceptibility, which may be incapable of expressing itself fully in the presence of dominant genes for resistance or may exert some other modifying action. NYQUIST (1957) showed that the resistance of variety C. 1. 12633 is controlled by duplicate dominant linked genes, (21 cross-over units apart) for stem rust resistance located on chromosome 2B. CAMPBELL and MCGINNIS (1958), using the monosomic series of Redman Spring Wheat in crosses with Prelude, reported that chromosomes 2B, 3B and 4B of Redman carry factors for adult plant resistance to race 56. KRITZINGER (1962) by monosomic analysis of Triticum vulgare varieties, Montana, Kenya Supremo, Kenya Farmer and Timstein indicated that genes for resistence are located on chromosomes 3A, 5A, 2B and 4D respectively. Thus, different workers noted the reaction to stem rust in the adult stage to be conditioned by one or more factors, but by far maximum support has been given for the operation of two factor pairs. SEARS (1962) and subsequent studies by LOEGERING and SEARS (1963) demonstrated the presence of a pollen killing gene on chromosome 6B. The pollen fertility of Yaqui-53 and monosomic 6B cross along with normal Chinese Spring gave no indication of sterility, which demonstrates that there may be another allele at Ki locus on chromosome 6B of Yaqui-53. Resistance of Yaqui-53 is contributed by the wheat varieties Hope, Thatcher and Kenya. The resistance of Hope was observed by several workers to be governed by two pairs of factors CLARK and AUSEMUS 1928, NEATBY and GOULDEN 1930, HAYES et al. (1934). SEARS et al. (1957) reported that genes for adult plant resistance to stem rust are carried on chromosome 3B and 1D in the variety Hope. For resistance of Thatcher, they reported two genes on chromosome 3B and 2B. In the present study, genes for adult plant resistance to stem rust were identified on chromosome 3A and 6B, which are different from these reports (Table 1). This may be due to the resistance in this case being contributed by the third parent, Kenya wheat, or this could be due to different types of interaction involved in the host pathogen relationship, the precise nature of which needs further study. POKHRIYAL (1960, unpublished) observed that Yaqui-53 carries to pairs of dominant duplicate factors for resistance to stem rust. These observations are further confirmed by our results, where by monosomic analysis it has been established that genes for resistance are present in chromosome 3A and 6B of Yaqui-53. |