Disruption of Phloem Transport by the two South African Biotypes of the Russian Wheat Aphid [Diuraphisnoxia Kurdjumov (Homoptera: Aphididae)] Feeding on Barley (Hordeumvulgare L.)

Abstract

We investigated the comparative effects of the feeding of two South African biotypes of the Russian wheat aphid (RWA, DiuraphisnoxiaKurdjumov), RWASA1 and RWASA2, on the phloem transport functionality of three selected exotic RWA-resistant barley (Hordeumvulgare L.) lines. RWASA2 is known to breed faster and as a more aggressive feeder, causing more severe damage than RWASA1 on host plants. We examined the phloem transport capacity of the barley lines, using the phloem-mobile fluorophore, 5,6-carboxyfluorescein diacetate (5,6-CFDA).Feeding by the newly-emerged more aggressive RWASA2 biotype caused a more marked decrease in phloem transport capacity, compared to RWASA1, during both short- and long-term feeding exposure. The extensive phloem damage was mirrored in a significant reduction in transport capacity in non-resistant PUMA, but not to the same extent in the USDA lines, indicative of reduced resistance when these lines were subjected to the South African RWA biotypes. The resistant lines should therefore be explored in breeding programmes for development of RWA-resistant barley lines in South Africa.