The results obtained in the study are presented in the Table 1 and Table 2. Sharma and Knott (1966) transferred the segment carrying Sr25 and Lr19 from the decaploid Agropyron elongatum to common wheat Agatha. These genes, however, could not be utilized in breeding because of their undesirable linkage with yellow flour color which was not commercially acceptable. Knott (1980) induced mutations through EMS and obtained two mutant lines having the normal flour color. The authors used a line Sunstar*6/C80-1 developed by McIntosh (pers commun) with highly reduced yellow pigment as a donor in the backcross program to introgress Sr25/Lr19 into susceptible cultivars. Presently, many of these cultivars are in cultivation either in small pockets or in large areas. Leaf rust resistance gene Lr19 (Agatha) confers total immunity to leaf rust at Wellington as well in other parts of the country. Sawhney et al. (1977) reported that Lr19 conferred seedling resistance to all the leaf rust pathotypes prevalent in India. A wide spectrum of pathotypes of leaf rust prevalent in U.S.A., Canada, Australia, India and other countries are avirulent on Lr19 (Agatha). However, Huerta-Espino and Singh (1994) detected a virulence (CBJ/QQ) on Lr19 in Mexico. Sibikeev et al. (1997) have also identified a pathotype of leaf rust virulent on Lr19 and Lr19d in Saratov and Qrenbhurg districts of Russia.

Since Agatha equals its parent Thatcher in yield, milling and baking quality, the authors do not expect any kind of yield reduction in the backcross lines carrying Lr19 although yield reductions associated with alien genetic transfers have been reported in some cases in hexaploid wheats (The et al. 1988). All the backcross lines were screened under artificial epiphytotic conditions of stem rust and leaf rust infection at Wellington over two seasons. Maximum reactions to both stem and leaf rusts are given in Table 1. Reactions to stripe rust were also recorded and are presented in Table 1, which will benefit the users. The low reaction to stem rust observed in WH 542 carrying Lr19 could be due to the presence of two major alien genes Sr25 and Sr31 The cultivar WH 542 has been postulated to carry Sr31 (Sharma et al. 1997).

McIntosh et al. (1977) reported that Sr25 conferred effective resistance to all the races of stem rust prevalent in Australia. Similarly Roelfs and McVey (1979) reported that Sr25 was effective to all the pathotypes of stem rust in U.S.A. Sr25 is reported to be effective at seedling stage against 19 Indian culture of stem rust pathogen viz., 14, 15, 17, 21, 21A-1, 24, 34, 40, 40-1, 42, 42B, 117, 117A, 117A-1, 122, 184, 194, 222 and 295 (Sawhney and Goel 1981; Patil and Deokar 1996). Tomar and Menon (unpublished) in a detailed study found that Sr25 appeared to be a major slow rusting gene and imparted a high level of resistance to a wide spectrum of stem ust pathotypes prevalent in the Nilgiri hills. The adult plant reaction to stem rust on backcross lines (Table 1) indicated that the gene Sr25 exhibited high to moderate resistance (moderately susceptible pustules appear towards maturity) except where Sr31 was present.

Sunstar*6/C80-1 developed by McIntosh in white seeded background with reduced yellow pigment thus appears to be a elite donor to develop genotypes carrying resistance to stem and leaf rusts for deployment in the southern hills, peninsular and central regions of India where both the rusts occur prominently during the crop season. We evaluated Cook*6/C80-1, another Lr19 derivative with reduced yellow pigment developed by McIntosh and found it totally immune to stem rust probably due to the presence of three slow rusting genes Sr6, Sr25 and Sr36 as Cook carries Sr6 and Sr36. The presence of Sr36 in the line was further confirmed by its high resistance to powdery mildew (Score 0-1). The powdery mildew resistance gene Pm6 is thought to have been derived from Triticum timopheevi along with Sr36 and is located on 2B chromosome (Nyquist 1963). The authors did not use this line in the backcross program as it is late maturing genotype; however, this line will prove useful as an alternative nonrecurrent parent.

The difference in grain yield between backcross lines and their recurrent parents were not significant. However, numerical differences in yield observed among the backcross lines and their recurrent parents were due to rust infection on recurrent parents.

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