Response of barley cultivars to infestations of the two South African biotypes of the russian wheat aphid

Abstract

A second biotype of the Russian wheat aphid, Diuraphis noxia Kurdjumov code-named RWASA-2, a more virulent and fast breeder than the earlier RWASA-1, was reported from wheat farms in South Africa in 2007. There is an urgent need to characterize the effects of this new biotype on infested plants in order to assist the breeding programme in developing effective resistant cultivars that curb this emerging biotype and its destructive effects on our cultivated cereals. This study investigates and compares the feeding related damages caused by RWASA-1 and RWASA-2 through resulting chlorosis, evidence of leaf rolling as well as changes in aphid population levels on both resistant and non-resistant barley (Hordeum vulgare) cultivars. The results from this experiments revealed that RWASA-2 feeding caused a higher chlorosis levels in the non-resistant PUMA than was the case when exposed to feeding by RWASA-1. Interestingly, chlorosis ratings were significantly higher during RWASA-1 feeding than RWASA-2 feeding only in resistant barley lines. Leaf rolling was more severe on PUMA but lower in resistant cultivars. Population growth analysis revealed that RWASA-2 reproduced faster than RWASA-1, a reduction in growth was observed in resistant lines in comparison to the non-resistant PUMA, with a greater reduction recorded on a resistant - STARS-9301B line. Therefore, we suggest that the US developed resistant barley lines should be explored further as they may represent as yet unidentified resistant germplasm, which could be introduced into locally developed barley lines in South Africa and other regions of the world where this RWA is a problem.

Keywords: Barley, Chlorosis, Leaf roll, Resistance, Russian Wheat Aphid (RWA), Aphid Biotypes, Tolerance