Nematology Dep., University of California-Riverside, 3401 Watkins Drive, Riverside, CA 92521, USA.
BMC Genomics. 2011 Jan 5;12:8. doi: 10.1186/1471-2164-12-8.
Macrophomina phaseolina 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 [Vigna unguiculata (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 M. phaseolina 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).
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 (Glycine max) and Medicago truncatula, candidate resistance genes were found within mapped QTL intervals. QTL Mac-2 explained the largest percent R2 and 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 Mac-6 and Mac-7 QTLs with maturity-related senescence QTLs Mat-2 and Mat-1, respectively. Homologs of the ELF4 and FLK flowering genes were found in corresponding syntenic soybean regions. Only three Macrophomina 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 Macrophomina infection.
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.
炭疽菌是一种新兴的、破坏性强的真菌病原体，在高温和干旱胁迫下会导致作物产量严重损失。越来越多的疾病发病率报告强调了该病原体在全球的广泛流行及其对作物产量抑制的贡献。在豇豆[Vigna unguiculata（L）Walp。]中，已鉴定出有限的低水平宿主抗性来源，但遗传基础尚不清楚。在这项研究中，我们报告了对炭疽菌的强宿主抗性来源的鉴定，以及在由基因衍生的单核苷酸多态性（SNP）和扩增片段长度多态性（AFLP）组成的豇豆遗传图谱上的假定抗性基因座的遗传图谱。
使用三年田间试验中的植物死亡率数据和两个温室试验中的疾病严重程度评分，鉴定了 9 个数量性状基因座（QTL），占表型方差（R2）的 6.1%至 40.0%。根据注释基因 SNP 以及与大豆（Glycine max）和紫花苜蓿（Medicago truncatula）的同线性，在映射的 QTL 区间内找到了候选抗性基因。解释最大百分比 R2 的 QTL Mac-2 在三个田间和一个温室试验中被鉴定出来，该 QTL 峰与来自果胶酯酶抑制剂编码基因的 SNP 标记共定位。抗性表达的成熟效应由 Mac-6 和 Mac-7 QTL 与成熟相关衰老 QTL Mat-2 和 Mat-1 共定位指示。在相应的大豆同源区域中发现了 ELF4 和 FLK 开花基因的同源物。仅三个炭疽菌抗性 QTL 与先前在同一群体中映射的延迟干旱诱导早衰 QTL 共定位，这表明介导豇豆对干旱胁迫和炭疽菌感染反应的遗传机制大不相同。
本研究鉴定出有效的宿主抗性来源。QTL 图谱和同线性分析确定了含有抗性因子的基因组位点，并揭示了具有进一步功能基因组学分析潜力的候选基因。
