RAPD markers associated with resistance to blackleg disease in Brassica species

Blackleg, caused by Leptosphaeria maculans, is a serious disease of Brassica species. Genetic analysis of resistance to L. maculans was carried out with 15 accessions from the USDA Brassica germplasm collections, representing diploids (A, C), and tetraploid (AC) genomes, respectively; and 9 cultivars from the National Winter Canola Variety Trials (NWCVT) all carrying AC genomes. All genotypes were screened for blackleg disease at the cotyledonary stage. The results indicated that 46% of the 24 genotypes were resistant, while 54% were susceptible. On the other hand, adult plant screening revealed that all the public genotypes were resistant. In an effort to identify molecularmarkers associated with resistance to blackleg disease, all genotypes were screened with 13 RAPD and 8 SSR markers producing 169 amplified products. Six RAPD markers (OPB01, OPE03, OPE16, OPF10, OPE12, and OPI01) were polymorphic, while the SSR markers were monomorphic. Chi-square analysis indicated that 5 amplified fragments (OPE03-4000, OPE16-1100, OPE16-1300, OPE16-1900, and OPI01- 280) from RAPD primers were significantly associated with blackleg resistance. Thus this study demonstrated that RAPD primers could be effectively used to identify DNA markers that are associatedwith blackleg disease resistance, and that resistance to L. maculans might also exist in the A and C genomes

A conceptual model for the development of Phytophthora disease in Quercus robur

Here, a conceptual model is presented for the development of Phytophthora disease in pedunculate oak. The model is presented using the causal loop diagram tool and gives an overview of how various abiotic and biotic factors, such as soil moisture, nutrient availability and mycorrhizal colonization, may affect the reproduction and the infective capacity of soil-borne Phytophthora species, the susceptibility of the host and subsequent disease development. It is suggested that the link between the root damage caused by Phytophthora species and overall tree vitality is in the assimilation and allocation of carbon within the plants. The potential impact of environmental factors on these processes is discussed. The model is presented with reference to scenarios related to variation in soil moisture and nutrient availability. The need for species-specific validation of the model and the implications of the model are discussed