Annual surveys of pathogen populations have monitored the changing pathotype situation of Puccinia triticina that causes leaf (brown) rust of wheat, to release and deploy rust-resistant cultivars of wheat in India. In surveys during 2009 to 2010, samples of leaf rust infecting wheat were collected from the Solan district of Himachal Pradesh. The samples were established on susceptible wheat cv. Agra Local and pathotypes were identified on three differentials following binomial nomenclature (3). Based on the infection types on sets of differentials, this sample was found different to all the known pathotypes of P. triticina from India. This report records a new pathotype of race group 104 of P. triticina from India. Unique feature of this pathotype is its avirulence to Lr3 (Democrat) and virulence to Lr10, Lr13, Lr23, Lr26. These genes are the most common resistance genes in Indian wheat material (1). It appears to be a result of reverse mutation on Lr3 in pathotype 21R63 (104-3). In 2012, this pathotype was detected in 5% of samples from northern India. The new pathotype produces susceptible infection type on Lr10 to which 104 groups gives mesothetic response (4). When compared to other pathotypes of the 104 group, it was different to pathotype 29R23 (104B) in avirulence to Lr26, to which pathotype 93R57 (104-4) is virulent. All the other pathotypes of the 104 group are virulent to Lr3, to which new pathotypes are avirulent. The new pathotype produces resistant response on Lr2a, Lr3, Lr9, Lr15, Lr19, Lr24, Lr25, Lr28, Lr32, Lr39, Lr45, Lr47, and susceptible response on Lr1, Lr2b, Lr2c, Lr10, Lr11, Lr12, Lr13, Lr14a, Lr14b, Lr14ab, Lr16, Lr17a, Lr17b, Lr18, Lr20, Lr21, Lr22a, Lr22b, Lr23, Lr26, Lr27+31, Lr29, Lr30, Lr33, Lr34, Lr35, Lr36, Lr37, Lr38, Lr40, Lr44, Lr46, Lr48, Lr49, Lr51, and Lr57. It is designated as NHKSP on international differentials. A live culture is being maintained as well as cryo-preserved in the National Repository of Pathotypes at the Regional Station of Directorate of Wheat Research, Shimla. Initial evaluation of 700 Indian and exotic wheat lines revealed that more than 500 lines possesses resistance to this pathotype. The identity of the pathotype was also confirmed by sequencing the internal transcribed spacer region of the rDNA with the primers ITS1/ITS4 (GenBank Accession No. JX020949) (2). Analysis of rDNA sequence identified this pathotype as a variant of P. triticina. The strain was most similar to ANK9538 of P. triticina (Accession No. DQ 147418, 98%) and 77-5 strain of P. triticina (Accession No. JQ360856, 93%). Identification of pathotypes from wheat growing areas in the initial stages is a prime effort that helps in developing ecologically safe, economic, and effective ways to manage wheat rusts.
References: (1) S. C. Bhardwaj et al. Indian Phytopathol. 63:174, 2010. (2) M. A. Innis et al. PCR Protocols: A Guide to Methods and Applications. Academic Press. San Diego, CA, 1990. (3) S. Nagarajan et al. Curr. Sci. 52:413, 1983. (4) S. K. Nayar et al. Indian Phytopathol. 51:290, 1998.