Seedling reaction of Thatcher (Triticum aestivum L.) near isogenic lines with adult plant leaf rust resistance genes Lr34 and Lr37

Shikha Agarwal, A.K.Sharma and R.G.Saini

Department of Genetics and Biotechnology, Punjab Agricultural University, Ludhiana- 141 004 (Punjab), India

Leaf rust caused by Puccinia triticina is an important disease of wheat causing yield losses world over. Use of adult plant resistance genes in development of leaf rust resistant cultivars is gaining in importance because such genes often provide long lasting resistance. The adult plant resistance gene Lr34 is frequently identified from wheats having proven record of durable resistance to leaf rust (McIntosh 1992). Another adult plant resistance gene Lr37 is also effective against many races from India (Saini et al. 1998). Thus, the gene Lr37 also has potential for use in the Indian subcontinent. The nursery test to detect adult plant resistance genes at seedling stage can be helpful to the breeders because this saves time and resources. The present report describes seedling reaction of the adult plant resistance genes Lr34 and Lr37 against three Indian leaf rust races at two temperatures which may be useful in selection of these genes at seedling stage.

Two Thatcher near isogenic lines RL6058 (6*Thatcher/PI58548) and RL6061 (6*Thatcher/ PI208316) both carrying Lr34, and RL6081 (VPM1/ 6*Thatcher) carrying the other adult plant resistance gene Lr37, were tested for seedling infection types along with am? susceptible cultivar Agra Local against leaf rust races 11, 63 and 106 at 14.5°C and 20°C. Five rows each containing 15-20 seeds of wheat accessions to be tested were planted in 8.5" x 4.5" sized bread boxes. Agra Local was sown as a control in every 6th row. First leaf of seven-day-old seedlings was inoculated separately with races 11, 63 and 106. These were incubated for 16 hours at 100% relative humidity at 20 plus or minus 1°C and then transferred to glass houses maintained at 14.5°C and 20°C. The observations on infection types on seedlings kept at 14.5°C and 20°C were recorded 21 and 14 days after inoculation respectively, according to Stakman et al. (1962). The result of observations are given in Table 1. RL6058 carrying Lr34 showed low reaction against races 11, 63 and 106 at 14.5°C but at 20°C this line was resistant only to race 106. The line RL6061 also showed resistance at 14.5°C against the races 11, 63 and 106 but at 20°C this line showed resistance against races 63 and 106 only. These results indicate that the gene Lr34 in RL6058 and RL6061 expresses at 14.5°C against races 11, 63 and 106. The low reaction of RL6058 against race 106 and of RL6061 against races 63 and 106 at 20°C was assumed to be caused by additional gene (s). The line RL6081 having Lr37 showed low reaction against races 11 and 106 and it was susceptible to race 63 both at 14.5°C and 20°C. This indicates that Lr37 can also be detected at seedling stage similar to Lr34. Because the reaction pattern of RL6081 is different than that of the lines RL6058 and RL6061 both carrying the gene Lr34, the accessions carrying the genes Lr34 and Lr37 can be distinguished using seedling reaction against races 11 and 63 at 14.5°C and 20°C.

Variation in expression of the gene Lr34 in different genetic backgrounds, growth stages and environments is reported to exists. Shiwani et al. (1990) reported two adult plant genes for leaf rust resistance from the line RL6058 which is considered as reference line for the gene Lr34. The present results also suggest that the differential expression of the gene Lr34 in RL6058 and RL6061 may be due to additional gene (s) carried by these accessions.