A transgressive segregation factor (RKN2) in Gossypium barbadense for nematode resistance clusters with gene rkn1 in G. hirsutum

Abstract

Host plant resistance is an important strategy for managing root-knot nematode (Meloidogyne incognita) in cotton (Gossypium L.). Here we report evidence for enhanced resistance in interspecific crosses resulting from transgressive segregation of clustered gene loci. Recently, a major gene, rkn1, on chromosome 11 for resistance to M. incognita in cv. Acala NemX was identified using an intraspecific G. hirsutum cross with susceptible cv. Acala SJ-2. Using interspecific crosses of Acala NemXxsusceptible G. barbadense cv. Pima S-7, F1, F2, F2:3, backcross, and testcross Acala NemXxF1 (Pima S-7xSJ-2), parental entries and populations were inoculated in greenhouse tests with M. incognita. Genetic analyses based on nematode-induced root galling and nematode egg production on roots, and molecular marker analysis of the segregating interspecific populations revealed that gene rkn1 interacted with a gene (designated as RKN2) in susceptible Pima S-7 to produce a highly resistant phenotype. RKN2 did not confer resistance in Pima S-7, but when combined with rkn1 (genotype Aa or aa), high levels of resistance were produced in the F1 and segregating F2, F3, and BC1F1 populations. One SSR marker MUCS088 was identified tightly linked to RKN2 within 4.4 cM in a NemXxF1 (Pima S-7xSJ-2) testcross population. Using mapped SSR markers and interspecific segregating populations, MUCS088 linked to the transgressive gene from the susceptible parent and was located in the vicinity of rkn1 on chromosome 11. Diverse genome analyses among A and D genome diploid and tetraploid cottons revealed that marker MUCS088 (165 and 167 bp) is derived from G. arboreum, A2 diploid genome. These results demonstrated that a highly susceptible parent contributed to nematode resistance via transgressive segregation. Derived highly resistant lines can be used as improved resistance sources in cotton breeding, and MUCS088 can be used to monitor RKN2 introgression in diverse populations. The close genomic location of the transgressive resistance determinants provides an important model system for studying transgressive segregation and epistasis in plants.

Epistasis and complementary gene action adequately account for the genetic bases of transgressive segregation of kilo-grain weight in rice

“…As a result of the difficulty in assessing the contributions of epistasis, epistasis was just assumed to be another major reason for transgression (Rieseberg et al 1999). Wang et al (2008) reported that epistasis was responsible for transgressive segregation in resistance to the root-knot nematode in cotton. In their study, a major gene, rkn1, on chromosome 11 for resistance to Meloidogyne incognita in cv.…”

QTL Analysis for Transgressive Resistance to Root-Knot Nematode in Interspecific Cotton (Gossypium spp.) Progeny Derived from Susceptible Parents

“…Breeding for optimal resistance must be based on selection of progeny with combinations of genes homozygous for resistance. However, a highly susceptible parent can contribute to nematode resistance via transgressive segregation [5]. These crosses can derive highly resistant lines, even when both parents have a susceptible phenotype.…”

“…These crosses can derive highly resistant lines, even when both parents have a susceptible phenotype. Such transgressive segregants can be used as improved resistance sources in crop breeding [5]–[6].…”

“…Wang et al (2008) [5] reported that a segregant factor ( RKN2 ) from one susceptible parent, G. barbadense L. Pima S-7 interacted with a major recessive gene rkn1 from G. hirsutum Acala NemX [8] to produce a highly resistant phenotype in the interspecific cross Pima S-7 x Acala NemX. We also observed that a susceptible genotype Acala SJ-2 contributed to the level of resistance in some F 2:7 (NemX x SJ-2) RI homozygous resistant lines [9].…”

New Tools and Traits for Cotton Improvement

“…A good example of such a trait in cotton is resistance to the root knot nematode (Meloidogyne incognito) where resistance is quantified by destructive sampling of root galling or egg counts of progeny that must be grown under RKN infested conditions (Zhang . DNA markers have been discovered that are linked to resistance to RKN (Niu et al 2007;Wang et al 2008). In addition to cost savings, MAS is a powerful tool to disrupt negative associations that may cause yield drag from certain resistant genetic sources.…”