Does indole alkaloid gramine confer resistance in barley to aphid Rhopalosiphum padi?

Accessions of cultivated barley (Hordeum vulgare ssp. vulgare) and its wild progenitor Hordeum vulgare ssp. spontaneum (H. ssp. spent.) were screened for gramine content at the seedling stage. H. ssp. spent, generally had hig her gramine concentration compared with cultivated spring barley. Thus gram ine concentrations might be raised in modern barley through crossings with selected H. ssp. spent. accessions and repeated back-crossings (BC) of sele cted offspring to cultivated barley. In the present study, the barley culti var Lina was used as the recurrent parent. Lina was exceptional among the t wo-rowed barleys in that it contained moderate levels of gramine, whereas m ost of the others were very low in gramine. Chromosome-doubled haploid line s (DHs) from the first generation (F-1) had a skewed distribution towards h igher gramine concentrations and so had the first back-cross generation (BC 1F1-DHs). A hairy plant surface, another character proposed to confer resis tance to aphids, was also found among some of the plants in the breeding ma terial. BC1F1-DHs with a high proportion of the Lina genome, as determined in an analysis of PCR-based molecular markers, in addition to high gramine concentrations and hairy plant bases in two cases were tested for resistanc e to the barley pest Rhopalosiphum padi. However, based on aphid performanc e and preference tests, there were no indications that either high gramine concentrations or hairiness conferred resistance to R. padi when compared w ith Lina and a variety very low in gramine (Golf). The pattern was the same when the F-1 generation was evaluated in aphid performance tests along wit h Lina, Golf, and the six H. ssp. spont. parents. Aphid weight was consiste ntly low on only one of the six H. ssp. spent, parents. Since previous repo rts of a positive relationship between gramine concentrations and resistanc e to R. padi were based on studies in Chile and Japan, a Chilean R, padi po pulation was compared with three Swedish populations, but the responses of all four populations were similar.