Seedling resistance to Rhizoctonia and Pythium spp. in wheat chromosome group 4 addition lines from Thinopyrum spp.

Abstract

Chromosome 4 from Thinopyrum spp. confers the ability to regrow after a sexual cycle and senescence in hexaploid wheat (Triticum aestivum), and is associated with resistance to the necrotrophic eyespot pathogen, Oculimacula yallundae. We sought to determine whether robust root growth or other traits controlled by chromosome 4 enhanced resistance to necrotrophic root pathogens. To this end, we tested seedlings of the hexaploid wheat ‘Chinese Spring’ (CS) having chromosome 4E from Th. elongatum (CS4E) or 4J from Th. bessarabicum (CS4J) for their response to Rhizoctonia solani AG8, R. oryzae or Pythium ultimum. Seedling damage was evaluated on the basis of disease severity (for Rhizoctonia spp. only), root weight, total root length, and first leaf true length (Pythium spp. only), after 14 days of growth in infested soil. All but the first of these variables were evaluated as the ratios of the means of inoculated to non-inoculated seedlings, to correct for inherent differences in root development among the lines. The CS4E and CS4J chromosome addition lines generally displayed resistance to both R. solani AG8 and R. oryzae, having reduced disease severity ratings, no significant decreases in root weight, and moderate decreases in root length compared with CS. The chromosome addition line CS4E and the amphidiploid CS-Thinopyrum elongatum exhibited the best resistance to P. ultimum. Thinopyrum elongatum, the donor of chromosome 4E, also displayed resistance to R. solani AG8, R. oryzae and P. ultimum, despite having short, fine roots. Our findings indicate that these chromosome addition lines encode genetic sources of seedling resistance to the three soil-borne pathogens. Although Thinopyrum chromosomes and wheat chromosomes do not recombine during meiosis, chromosome engineering techniques can be employed to transfer these novel sources of resistance to wheat.