A Novel Root-Knot Nematode Resistance QTL on Chromosome Vu01 in Cowpea

Abstract

The root-knot nematode (RKN) species Meloidogyne incognita and M. javanica cause substantial root system damage and suppress yield of susceptible cowpea cultivars. The narrow-based genetic resistance conferred by the Rk gene, present in some commercial cultivars, is not effective against Rk -virulent populations found in several cowpea production areas. The dynamics of virulence within RKN populations require a broadening of the genetic base of resistance in elite cowpea cultivars. As part of this goal, F and F populations from the cross CB46-Null (susceptible) x FN-2-9-04 (resistant) were phenotyped for M. javanica induced root-galling (RG) and egg-mass production (EM) in controlled growth chamber and greenhouse infection assays. In addition, F families of the same cross were phenotyped for RG on field sites infested with Rk -avirulent M. incognita and M. javanica . The response of F to RG and EM indicated that resistance to RKN in FN-2-9-04 is partially dominant, as supported by the degree of dominance in the F and F populations. Two QTL associated with both RG and EM resistance were detected on chromosomes Vu01 and Vu04. The QTL on Vu01 was most effective against aggressive M. javanica , whereas both QTL were effective against avirulent M. incognita . Allelism tests with CB46 x FN-2-9-04 progeny indicated that these parents share the same RKN resistance locus on Vu04, but the strong, broad-based resistance in FN-2-9-04 is conferred by the additive effect of the novel resistance QTL on Vu01. This novel resistance in FN-2-9-04 is an important resource for broadening RKN resistance in elite cowpea cultivars.

Genomics of Plant Disease Resistance in Legumes

“…Root-knot nematodes (RKN) are the most important pests of cowpea, resulting in huge losses due to their interference with the root architecture, which results in poor development of the plants (Santos et al, 2018). Previously, two resistance genes, Resistance to Root knot ( Rk ) and Rk 2 , were identified to confer resistance against RKN in cowpea (Das et al, 2010; Ndeve et al, 2019). A recent QTL mapping study using RIL population 524B x IT84S-2049 in cowpea resulted in the identification of a major QTL, QRk-vu9.1 , associated with resistance to Meloidogyne javanica reproduction (Santos et al, 2018).…”

Production Systems and Prospects of Cowpea (Vigna unguiculata (L.) Walp.) in the United States

“…Several commercial cultivars of cowpea with resistance to these RKN species have been developed. However, some populations of the nematodes are RK-virulent, meaning that the narrow-based genetic resistance conferred by the RK genes are not effective against those populations [19]. A novel RKN resistance QTL has been identified by researchers at the University of California-Riverside.…”

“…Major breeding programs are housed in South Carolina (USDA), Louisiana (Louisiana State University), California (University of California Riverside), Texas (Texas A&M University) and Arkansas (University of Arkansas) [12]. While the primary objectives of existing breeding programs are to improve grain yield and quality, efforts have also been made to develop varieties with resistance to insects and diseases, which are major constraints to cowpea production [11,19].…”

“…Using these resources, major quantitative trait loci (QTL), and candidate genes for various traits have been reported. These include domestication-related traits [59][60][61], key agronomics traits [9,58,62], seed coat traits [63,64], and biotic stress traits [19,65]. These studies present major advances in cowpea research, including exploring the genetic diversity of domesticated cowpea [9].…”

Dissecting the genetic architecture of quantitative traits in common bean (>i<Phaseolus vulgaris>/i< L.): response to root-knot nematode infection and seed morphology

“…It can also denote the existence of QTL x environment interaction, as the populations were evaluated independently, or even indicate the presence of a different QTL, as distinct alleles might be responsible for the detected effect in the GWAS panel and in the BC2F4 population. In some leguminous crops, such as peanut (Arachis stenosperma), soybean (Glycine max), and especially cowpea (Vigna unguiculata), major QTLs with PVEs higher than those found herein have been associated with resistance to root-galling and egg mass (Caromel and Gebhardt 2011;Huynh et al 2016;Leal-bertioli et al 2016;Passianotto et al 2017;Santos et al 2018;Ndeve et al 2019). Nevertheless, in terms of aspects such as the complexity of these traits in Phaseolus spp.…”