Vandemark G J, Fourie D, Miklas P N
U.S. Department of Agriculture, Grain Legume Genetics and Physiology Unit, Pullman, WA 99164, USA.
Theor Appl Genet. 2008 Aug;117(4):513-22. doi: 10.1007/s00122-008-0795-2. Epub 2008 May 30.
Resistance to common bacterial blight in common bean is a complex trait that is quantitatively inherited. Combining QTL is the current strategy for improving resistance, but interactions among different QTL are unknown. We examined the interaction between two independent QTL present in dry bean breeding line XAN 159. The QTL were studied in a near isogenic population consisting of 120 BC6:F2 plants. Each BC6:F2 plant was evaluated for disease reaction at several time points after pathogen inoculation and the dominant SCAR markers linked with QTL on linkage groups B6 (BC420 approximately QTL) and B8 (SU91 approximately QTL) were interpreted as codominant markers using real time PCR assays. This enabled assignment of BC6:F2 plants to all nine possible genotypes. Reaction to CBB in BC6:F2 plants was characterized by an epistatic interaction between BC420 and SU91 such that: 1) the expression of BC420 was epistatically suppressed by a homozygous recessive su91//su91 genotype; 2) SU91//SU91 and SU91//su91 genotypes conditioned an intermediate disease reaction when homozygous recessive for bc420//bc420; and 3) the highest level of disease resistance was conferred by genotypes with at least a single resistance allele at both QTL (BC420//-; SU91//-). Segregation for resistance among BC6:F3 plants derived from BC6:F2 plants that were heterozygous for both QTL did not deviate significantly from expected ratios of 9 resistant: 3 moderately resistant: 4 susceptible. This is consistent with a recessive epistatic model of inheritance between two loci. These results indicate breeders will realize greatest gains in resistance to CBB by selecting breeding materials that are fixed for both QTL. This is a first report of a qualitative digenic model of inheritance discerning an interaction between two QTL conditioning disease resistance in plants.
普通菜豆对普通细菌性疫病的抗性是一个复杂的数量遗传性状。聚合数量性状基因座（QTL）是目前提高抗性的策略，但不同QTL之间的互作尚不清楚。我们研究了干豆育种系XAN 159中两个独立QTL之间的互作。在由120个BC6:F2植株组成的近等基因群体中对这些QTL进行了研究。在病原菌接种后的几个时间点对每个BC6:F2植株的病害反应进行了评估，并且使用实时PCR分析将与连锁群B6（BC420大约为QTL）和B8（SU91大约为QTL）上的QTL连锁的显性SCAR标记解释为共显性标记。这使得能够将BC6:F2植株归为所有九种可能的基因型。BC6:F2植株对普通细菌性疫病的反应以BC420和SU91之间的上位性互作为特征，具体如下：1）纯合隐性su91//su91基因型对BC420的表达有上位性抑制作用；2）当bc420//bc420为纯合隐性时，SU91//SU91和SU91//su91基因型表现出中等病害反应；3）两个QTL上至少有一个抗性等位基因的基因型（BC420//-；SU91//-）赋予最高水平的抗病性。来自两个QTL均为杂合的BC6:F2植株的BC6:F3植株中抗性的分离与9抗:3中抗:4感的预期比例没有显著偏差。这与两个位点之间的隐性上位遗传模型一致。这些结果表明，育种者通过选择两个QTL均纯合的育种材料，将在普通细菌性疫病抗性方面获得最大的增益。这是关于鉴别植物中两个调控抗病性的QTL之间互作的双基因定性遗传模型的首次报道。
