Anomalous behaviour of a wheat leaf rust resistance gene Lr32

The rust resistance gene Lr31 confers resistance to all leaf rust pathotypes reported from India. Anomalous segregation pattern was observed while studying inheritance of Lr32. The F1's of Lr32 were susceptible when TcLr32 was crossed with 5 aestivum cultivars, viz 'Agra Local', PBW 343, H1 077, HUW 234, and UP 2338 but the F2 segregation ratio varied from one cross to other. Genetic background of the cross influenced the nature of resistance of Lr32. The expression of Lr32 shifted from recessive to dominance in certain genetic background. A single recessive gene was responsible for this shift in gene action and therefore, it induced dominance in Lr32 only in homozygous condition. The degree of expression of low infection type reaction of Lr32 was dependent on microenvironment which sometimes gave wrong impression of enhanced resistance when present in combination with Lr32 or Lr26 in seeding as well as adult plant test. Differential gene action of Lr323 may pose problem in detecting the F2 genotype in genetic studies. However, this problem can be tackled through progeny testing.