Genes conferring low seedling reaction to Mexican pathotypes of Puccinia recondita f. sp. tritici, and adult-plant responses of recent wheat cultivars from the former USSR

Abstract

Fifty-five spring bread wheat (Triticum aestivum L .) cultivars, mostly released between 1975 and 1991 in eight leaf rust-prone spring wheat growing regions of the former USSR, were tested in the seedling growth stage for reaction to 15 Mexican pathotypes of Puccinia recondita f. sp . tritici . In total, seven known and at least two unknown genes were identified, either singly or in combinations : Lr3 (7 cultivars), Lr10 (14), Lr13 (5), Lr14a (1), Lr16 (1), Lr23 (3); the unknown genes were identified in 14 cultivars . The first unknown gene could be either Lr9, Lr19, or Lr25; however, the second unknown gene in 9 cultivars was different from any named gene . Twelve of the 15 pathotypes are virulent for this gene, hence its use in breeding for resistance will be limited . The cultivars were also evaluated at two field locations in Mexico with two pathotypes in separate experiments. The area under the disease progress curve and the final disease rating of the cultivars indicated genetic diversity for genes conferring adult plant resistance . Based on the symptoms of the leaf tip necrosis in adult plants, resistance gene Lr34 could be present in at least 20 cultivars . More than half of the cultivars carry high to moderate levels of adult plant resistance and were distributed in each region .

GENETIC PREDICTION OF LEAF RUST RESISTANCE THROUGH CROSSING BETWEEN TWO Lr,s AND FIVE EGYPTIAN WHEAT VARIETIES.

“…Genes Lr12, Lr22a, Lr22b and Lr35 are known to be effective only in adult plant, McIntosh et al (1995). Similar results were suggested by Singh et al (1995) and Kolmer (2002). The susceptibility of leaf seedlings of the nearisogenic lines (NIL) possessing Lr37 probably resulted from the warmer conditions (15-25 "C ).…”

Genetic protection of wheat from rusts and development of resistant varieties in Russia and Ukraine

“…The reactions of 55 spring wheat varieties released in the USSR from 1975 to 1991 were studied in Mexico (Singh et al 1995). Almost half of the cultivars had high or moderate degrees of adult plant resistance.…”

First report of leaf rust pathotypes virulent to highly effective Lr‐genes transferred from Agropyron species to bread wheat

“…For example, the combinations Lr 13 + 26; Lr 23 + 26; Lr 13, 27+31 + ? are very highly effective in Mexico, Central and South American regions (Singh andRajaram 1991, Singh 1993). The seedlings of Mexican bread wheat cultivars, which carry Lr-gene combinations, displayed different infection types when inoculated with the pp 19K, pp 19, pp Ag'l and pp Ag'2 pathotypes, as indicated in Table 2b.…”

“…Ideally, we would hke to add the genes Lr 13 and Lr 17 from 'Inia 66' (Singh and Rajaram 1991) to the Lr 19d of 'Indis'. These Lr genes, namely Lr 19, 19d, Ag'l, Ag'2 and 38, which derive from the genus Agropyron are highly effective and have not been overcome until now.…”

“…Agropyron intermedium (Host) Beauv has also been investigated for rust resistance, but only one gene {Lr 38) has been assigned in the Catalogue of gene symbols for wheat (Mclntosh et al 1993). In the literature available to us we failed to find reports about pathotypes virulent to the genes Lr 19,19d,Ag'l,Ag'2 and 38. Researchers from difFerent parts of the world have all rated these genes as highly effective to all pathotypes of leaf rust (Singh and Rajaram 1991, Singh 1993, Singh et al 1995, Marais 1992, Sibikeev et al 1995, Dyck and Friebe 1993.…”