F₁ hybrids resistant to leaf rust were backcrossed to respective recurrent parents followed by two backcrosses. The resistant lines at BC₃F₂ stage for stem, leaf and stripe rusts were selfed and the new lines were constituted at BC₃F₅ stage. The constituted lines were further screened against all the three rusts (1995-97) for three seasons under natural epiphytotic conditions at Wellington. The predominant races of leaf rust pathotypes include 11, 77A, 77-1, 77-2, 77-5, 104B and 16, stem rust pathotypes are 11, 40, 40A, 40-1, 117, 117A and 117-1 and stripe rust pathotype I. The seedling tests were also carried out under glasshouse conditions against individual races of stem, leaf and stripe rusts predominantly prevalent in Nilgiri hills, India.


Results

All the constituted lines were free to stem, leaf and stripe rusts except showing low susceptibility (TS) for stripe rusts in one of the derivatives (CLRP 6 X HW 2005) under natural epiphytotic conditions (Table 1). The seedlings of the individual constituted lines when tested under glasshouse condition showed resistant reactions to all the predominant races of leaf rust indicating the transfer of dominant genes Lr9, Lr24 and Lr28 into the constituted lines.

In the crosses involving HW 2005 (carrying A. elongatum derived gene Sr24+Lr24) as donor parent the derivatives were resistant to stem and stripe rusts in addition to leaf rust resistance, though the donor parent was susceptible to stem and stripe rusts.

The lines obtained using PH 127 (carrying Ae. umbellulata derived gene Lr9) as donor parent also gave complete resistance to leaf rust, under both natural epiphytotic condition and glasshouse study (Table 1). Among recurrent parents HD 2329 and HD 2285 were susceptible to all the three rusts but the crosses obtained were resistant to all the three rusts. The re current parents CPAN 4166, CPAN 4167 and CPAN 4168 when crossed to HW 2037 (carrying Ae. speltoides derived gene Lr28) the resultant progenies were resistant to stem, leaf and stripe rusts, indicating the transfer of Lr28 gene.

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