Detecting the Sr2-linked gene for seedling chlorosis in South African wheat cultivars
1999
Pretorius, Z.A.
Sr2 is widely regarded as an important gene for resistance to wheat stem rust caused by Puccinia graminis f. sp. tritici. Selection for Sr2 is usually based on either the occurrence of pseudo-black chaff mediated by the Sr2-linked Pbc gene, or the restriction of rust pustules to stem areas immediately above the nodes. More recently, a gene (sc) for seedling chlorosis has been shown to be linked to Sr2. To investigate expression of the sc gene in South African wheats, seedlings of 54 cultivars were grown at 25 .C in a greenhouse cubicle without supplementary lighting and inoculated with pathotype 34-1,2,3,4,5,6 (culture 74-L-1) of P. graminis f. sp. tritici when plants reached the one-and- a-half to two-leaf stage. Suneca, Hartog and Cranbrook were included as Sr2 controls. Based on seedling chlorosis detected on the first three seedling leaves, and pseudo-black chaff and stem rust severity in the field, Sr2 appears to be present in SST25, SST38, SST86, SST107, SST822, Elize, Gamtoos, Inia, Palmiet and PanLE12. No seedling chlorosis was detected in Adam Tas and Marico, both which expressed pseudo-black chaff and low stem rust scores in the field. Only slight flecking was observed on seedlings of SSTI6, a cultivar which was heterogeneous for stem rust reaction in the field and displayed no black chaff. Confirmation of the presence of Sr2 in South African wheat cultivars is considered valuable in terms of anticipated durability of resistance to stem rust of wheat
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