Genic SNP markers and legume synteny reveal candidate genes underlying QTL for Macrophomina phaseolina resistance and maturity in cowpea [Vigna unguiculata (L) Walp.]

<p>Abstract</p> <p>Background</p> <p><it>Macrophomina phaseolina </it>is an emerging and devastating fungal pathogen that causes significant losses in crop production under high temperatures and drought stress. An increasing number of disease incidence reports highlight the wide prevalence of the pathogen around the world and its contribution toward crop yield suppression. In cowpea [<it>Vigna unguiculata </it>(L) Walp.], limited sources of low-level host resistance have been identified, the genetic basis of which is unknown. In this study we report on the identification of strong sources of host resistance to <it>M. phaseolina </it>and the genetic mapping of putative resistance loci on a cowpea genetic map comprised of gene-derived single nucleotide polymorphisms (SNPs) and amplified fragment length polymorphisms (AFLPs).</p> <p>Results</p> <p>Nine quantitative trait loci (QTLs), accounting for between 6.1 and 40.0% of the phenotypic variance (R²), were identified using plant mortality data taken over three years in field experiments and disease severity scores taken from two greenhouse experiments. Based on annotated genic SNPs as well as synteny with soybean (<it>Glycine max</it>) and <it>Medicago truncatula</it>, candidate resistance genes were found within mapped QTL intervals. QTL <it>Mac-2 </it>explained the largest percent R²and was identified in three field and one greenhouse experiments where the QTL peak co-located with a SNP marker derived from a pectin esterase inhibitor encoding gene. Maturity effects on the expression of resistance were indicated by the co-location of <it>Mac-6 </it>and <it>Mac-7 </it>QTLs with maturity-related senescence QTLs <it>Mat-2 </it>and <it>Mat-1</it>, respectively. Homologs of the <it>ELF4 </it>and <it>FLK </it>flowering genes were found in corresponding syntenic soybean regions. Only three <it>Macrophomina </it>resistance QTLs co-located with delayed drought-induced premature senescence QTLs previously mapped in the same population, suggesting that largely different genetic mechanisms mediate cowpea response to drought stress and <it>Macrophomina </it>infection.</p> <p>Conclusion</p> <p>Effective sources of host resistance were identified in this study. QTL mapping and synteny analysis identified genomic loci harboring resistance factors and revealed candidate genes with potential for further functional genomics analysis.</p

Breeding system in Trifolium glanduliferum (Fabaceae)

© The Royal Society of New Zealand 2007Trifolium glanduliferum Boiss. var. nervulosum (Boiss. & Heldr.) Zoh., glandular (or gland) clover is an annual pasture species, with Mediterranean origin, recently introduced into Australia. The species was previously reported as self-pollinating. Studies with four accessions originating from Israel clearly suggest that Trifolium glanduliferum is a highly self-incompatible species, which requires vectors including bees to ensure pollination. Unpollinated bagged and hand tripped florets showed no signs of pollen tube growth and no seed set, while cross-pollinated florets showed pollen tube growth and gave high seed set. A high pollen:ovule ratio suggested that the species is between facultative outcrossing and obligate outcrossing.Ramakrishnan M. Nair, David M. Peck, Trevor D. Rowe, Ian S. Dundas, and Kate Dowlin

Evolution of enhanced reproduction in the hybrid-derived invasive, California wild radish (Raphanus sativus)

Evolution is receiving increased attention as a potentially important factor in invasions. For example, hybridization may have stimulated the evolution of invasiveness in several well-known plant pests. However, the mechanism for success of such hybrid-derived lineages remains unknown in the majority of the cases studied. Here we ask whether increased reproductive success (in terms of maternal fitness) has evolved in an invasive lineage with confirmed hybrid ancestry. We compare the relative fitness of the non-native, hybrid-derived California wild radish (Raphanus sativus) to that of its two progenitor species in field experiments at different sites and in different years. We found that California wild radish has high survivorship and produces more fruits per plant and more seeds per plant than either of its progenitors in several environments. Furthermore, populations of California wild radish display a strong genotype-by-environment interaction, indicating that maintenance of genetic and phenotypic diversity between populations may be responsible for the weed’s ability to invade a wide breadth of California habitats. Our results suggest that hybridization may contribute the evolution of enhanced invasiveness and, also, that by limiting the introduction and subsequent hybridization of congeners, we may be able to prevent the evolution of new invasive lineages