Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/31/2006
Publication Date: 5/31/2007
Citation: Sim, S., Diesberg, K., Casler, M.D., Jung, G. 2007. Mapping and comparative analysis of QTL for crown rust resistance in an Italian x perennial ryegrass population. Phytopathology. 97:767-776. Interpretive Summary: Perennial ryegrass is an important grass for both forage and turf applications. Crown rust is a devastating disease of perennial ryegrass, reducing its forage yield and quality and its turf quality and persistence. This study was the first to identify specific genes that confer host-plant resistance in perennial ryegrass to this disease. Two major genes and several minor genes were identified, most having been transferred from Italian ryegrass to perennial ryegrass. These results will be useful to other forage and turf grass breeders and to their customers who use ryegrass seed for forage or turf.
Technical Abstract: Crown rust (Puccinia coronata f.sp. lolli) is a serious fungal foliar disease of perennial ryegrass (Lolium perenne L.) and Italian ryegrass (L. multiflorum L.) which are important forage and turf species. A number of quantitative trait loci (QTL) for crown rust resistance were previously identified in perennial ryegrass under growth chamber or greenhouse conditions. In this study, we conducted a QTL mapping of crown rust resistance in an Italian x perennial ryegrass population under natural field conditions at two locations over two years. Four QTL for resistance to crown rust were detected and source of the resistance appeared to be from Italian ryegrass variety ‘Floregon’. Two of them on linkage groups (LGs) 2 and 7 in the resistant parent MFA map were consistently detected regardless of year and location. The others, specific to year and location, were located on LGs 3 and 6 in the susceptible parent MFB map. The QTL on LG2 was likely to correspond to those previously reported in three unrelated perennial ryegrass mapping populations but the QTL on LGs 3, 6 and 7 were not. This suggests that our interspecific ryegrass population could provide a new genetic resource for crown rust resistance. However, the QTL on LGs 2, 3 and 7 were closely located in the syntenic genomic regions where resistance genes to crown rust (P. coronata f.sp. avenae) in oat (Avena sativa L.) were previously identified. It indicates that orthologous resistant genes to different formae speciales of crown rust might be present between two grass species, ryegrass and oat. In addition, we mapped four RFLP loci for three key ryegrass lignin genes encoding caffeic acid-O-methyltransferase (OMT), cinnamyl alcohol dehydrogenase (CAD), and cinnamoyl CoA-reductase (CCR) on LG7. These loci were distant with ~16 cM from the QTL on LG7, suggesting no tight linkage between them. Results from the current study facilitate understanding of crown rust resistance and its relationship with lignin biosynthesis, but also will benefit ryegrass breeders for improving crown rust resistance through marker-assisted selection