The root lesion nematode, Pratylenchus neglectus, is an economically damaging pathogen of wheat and other crops. The development of P. neglectus-resistant wheat cultivars would be greatly accelerated through the use of molecular markers, as resistance phenotyping is extremely time-consuming. A greenhouse bioassay was developed to identify resistance phenotypes of doubled-haploid populations. Bulked-segregant analysis was used to identify AFLP markers linked to P. neglectus resistance in the wheat cultivar Excalibur. One resistance-linked AFLP marker was mapped close to chromosome 7A RFLP markers in a densely-mapped Cranbrook/Halberd population. One of the chromosome 7A RFLP probes, cdo347, was genotyped in the Tammin/Excalibur population segregating for response to root lesion nematode and showed 8% recombination with the P. neglectus resistance gene Rlnn1. The marker Xcdo347-7A was validated on Excalibur-and Krichauff-derived DH populations segregating for Rlnn1 and showed 14% and 10% recombination, respectively, with Rlnn1 in these populations.

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BackgroundMedicago truncatula Gaertn. (barrel medic) is cultivated as a pasture legume for its high protein content and ability to improve soils through nitrogen fixation. Toxic concentrations of the micronutrient Boron (B) in agricultural soils hamper the production of cereal and leguminous crops. In cereals, the genetic analysis of B tolerance has led to the development of molecular selection tools to introgress and maintain the B tolerance trait in breeding lines. There is a comparable need for selection tools in legumes that grow on these toxic soils, often in rotation with cereals.ResultsGenetic variation for B tolerance in Medicago truncatula was utilised to generate two F2 populations from crosses between tolerant and intolerant parents. Phenotyping under B stress revealed a close correlation between B tolerance and biomass production and a segregation ratio explained by a single dominant locus. M. truncatula homologues of the Arabidopsis major intrinsic protein (MIP) gene AtNIP5;1 and the efflux-type transporter gene AtBOR1, both known for B transport, were identified and nearby molecular markers screened across F2 lines to verify linkage with the B-tolerant phenotype. Most (95%) of the phenotypic variation could be explained by the SSR markers h2_6e22a and h2_21b19a, which flank a cluster of five predicted MIP genes on chromosome 4. Three CAPS markers (MtBtol-1,-2,-3) were developed to dissect the region further. Expression analysis of the five predicted MIPs indicated that only MtNIP3 was expressed when leaf tissue and roots were assessed. MtNIP3 showed low and equal expression in the roots of tolerant and intolerant lines but a 4-fold higher expression level in the leaves of B-tolerant cultivars. The expression profile correlates closely with the B concentration measured in the leaves and roots of tolerant and intolerant plants. Whereas no significant difference in B concentration exists between roots of tolerant and intolerant plants, the B concentration in the leaves of tolerant plants is less than half that of intolerant plants, which further supports MtNIP3 as the best candidate for the tolerance trait-defining gene in Medicago truncatula.ConclusionThe close linkage of the MtNIP3 locus to B toxicity tolerance provides a source of molecular selection tools to pasture breeding programs. The economical importance of the locus warrants further investigation of the individual members of the MIP gene cluster in other pasture and in grain legumes.

Barley net- and spot-form of net blotch disease are caused by two formae of the hemibiotrophic fungus Pyrenophora teres (P. t. f. teres and P. t. f. maculata). In the present study, suppression subtractive hybridization (SSH) was used in combination with quantitative real-time reverse transcriptase PCR to identify and profile the expression of defence response (DR) genes in the early stages of both barley-P. teres incompatible and compatible interactions. From a pool of 307 unique gene transcripts identified by SSH, 45 candidate DR genes were selected for temporal expression profiling in infected leaf epidermis. Differential expression profiles were observed for 28 of the selected candidates, which were grouped into clusters depending on their expression profiles within the first 48 h after inoculation. The expression profiles characteristic of each gene cluster were very similar in both barley-P. t. f. teres and barley-P. t. f. maculata interactions, indicating that resistance to both pathogens could be mediated by induction of the same group of DR genes. Chromosomal map locations for 21 DR genes were identified using four doubled-haploid mapping populations. The mapped DR genes were distributed across all seven barley chromosomes, with at least one gene mapping to within 15 cM of another on chromosomes 1H, 2H, 5H and 7H. Additionally, some DR genes appeared to co-localize with loci harbouring known resistance genes or quantitative trait loci for net blotch resistance on chromosomes 6H and 7H, as well as loci associated with resistance to other barley diseases. The DR genes are discussed with respect to their map locations and potential functional role in contributing to net blotch disease resistance.

Seedlings of the barley line ‘B87/14’ were resistant to 22 out of 23 Australian isolates of Rhynchosporium secalis, the causal agent of leaf scald.‘B87/14’‐based populations were developed to determine the location of the resistance locus. Scald resistance segregated as a single dominant trait in BC1F2 and BC1F3 populations. Bulked segregant analysis identified amplified fragment length polymorphisms (AFLPs) with close linkage to the resistance locus. Fully mapped populations not segregating for scald resistance located these AFLP markers on chromosome 3H, possibly within the complex Rrs1 scald locus. Microsatellite and restriction fragment length polymorphism markers adjacent to the AFLP markers were identified and validated for their linkage to scald resistance in a second segregating population, with the closest marker 2.2 cM from the resistance locus. These markers can be used for selection of the Rrs.B87 scald‐resistance locus, and other genes at the chromosome 3H Rrs1 locus.