Wang C, Matthews W C, Roberts P A
Department of Nematology, University of California, Riverside, CA 92521-0415.
J Nematol. 2006 Jun;38(2):250-7.
The root-knot nematode Meloidogyne incognita is a damaging pest of cotton (Gossypium hirsutum) worldwide. A major gene (rkn1) conferring resistance to M. incognita was previously identified on linkage group A03 in G. hirsutum cv. Acala NemX. To determine the patterns of segregation and phenotypic expression of rkn1, F(1), F(2), F(2:3), BC(1)F(1) and F(2:7) recombinant inbred lines (RIL) from intraspecific crosses between Acala NemX and a closely related susceptible cultivar Acala SJ-2 were inoculated in greenhouse tests with M. incognita race 3. The resistance phenotype was determined by the extent of nematode-induced root galling and nematode egg production on roots. Suppression of root galling and egg production was highly correlated among individuals in all tests. Root galling and egg production on heterozygous plants did not differ from the susceptible parent phenotype 125 d or more after inoculation, but were slightly suppressed with shorter screening (60 d), indicating that rkn1 behaved as a recessive gene or an incompletely recessive gene, depending on the screening condition. In the RIL, rkn1 segregated in an expected 1 resistant: 1 susceptible ratio for a major resistance gene. However, within the resistant class, 21 out of 34 RIL were more resistant than the resistant parent Acala NemX, indicating transgressive segregation. These results suggest that rkn1-based resistance in G. hirsutum can be enhanced in progenies of crosses with susceptible genotypes. Allelism tests and molecular genetic analysis are needed to determine the relationship of rkn1 to other M. incognita resistance sources in cotton.
根结线虫南方根结线虫是全球棉花（陆地棉）的一种有害害虫。先前在陆地棉品种阿卡拉NemX的A03连锁群上鉴定出一个赋予对南方根结线虫抗性的主基因（rkn1）。为了确定rkn1的分离模式和表型表达，将阿卡拉NemX与一个密切相关的感病品种阿卡拉SJ - 2进行种内杂交得到的F(1)、F(2)、F(2:3)、BC(1)F(1)和F(2:7)重组自交系（RIL）在温室试验中接种南方根结线虫3号小种。通过线虫诱导的根瘤形成程度和根上的线虫卵产量来确定抗性表型。在所有试验中，个体间根瘤形成和卵产量的抑制高度相关。接种125天或更长时间后，杂合植株上的根瘤形成和卵产量与感病亲本表型没有差异，但在较短的筛选时间（60天）时略有抑制，这表明rkn1根据筛选条件表现为隐性基因或不完全隐性基因。在RIL中，rkn1以主要抗性基因预期的1抗性:1感病比例分离。然而，在抗性类别中，34个RIL中有21个比抗性亲本阿卡拉NemX更抗病，表明存在超亲分离。这些结果表明，陆地棉中基于rkn1的抗性可以在与感病基因型杂交的后代中得到增强。需要进行等位性测试和分子遗传分析来确定rkn1与棉花中其他南方根结线虫抗性来源的关系。
