Genetic analysis of tolerance to the root lesion nematode Pratylenchus neglectus in the legume Medicago littoralis

Abstract

BackgroundThe nematode Pratylenchus neglectus has a wide host range and is able to feed on the root systems of cereals, oilseeds, grain and pasture legumes. Under the Mediterranean low rainfall environments of Australia, annual Medicago pasture legumes are used in rotation with cereals to fix atmospheric nitrogen and improve soil parameters. Considerable efforts are being made in breeding programs to improve resistance and tolerance to Pratylenchus neglectus in the major crops wheat and barley, which makes it vital to develop appropriate selection tools in medics.ResultsA strong source of tolerance to root damage by the root lesion nematode (RLN) Pratylenchus neglectus had previously been identified in line RH-1 (strand medic, M. littoralis). Using RH-1, we have developed a single seed descent (SSD) population of 138 lines by crossing it to the intolerant cultivar Herald. After inoculation, RLN-associated root damage clearly segregated in the population. Genetic analysis was performed by constructing a genetic map using simple sequence repeat (SSR) and gene-based SNP markers. A highly significant quantitative trait locus (QTL), QPnTolMl.1, was identified explaining 49% of the phenotypic variation in the SSD population. All SSRs and gene-based markers in the QTL region were derived from chromosome 1 of the sequenced genome of the closely related species M. truncatula. Gene-based markers were validated in advanced breeding lines derived from the RH-1 parent and also a second RLN tolerance source, RH-2 (M. truncatula ssp. tricycla). Comparative analysis to sequenced legume genomes showed that the physical QTL interval exists as a synteny block in Lotus japonicus, common bean, soybean and chickpea. Furthermore, using the sequenced genome information of M. truncatula, the QTL interval contains 55 genes out of which five are discussed as potential candidate genes responsible for the mapped tolerance.ConclusionThe closely linked set of SNP-based PCR markers is directly applicable to select for two different sources of RLN tolerance in breeding programs. Moreover, genome sequence information has allowed proposing candidate genes for further functional analysis and nominates QPnTolMl.1 as a target locus for RLN tolerance in economically important grain legumes, e.g. chickpea.

A second set of XEGIP-encoding genes resides on chromosome 8 of potato and tomato.

“…It would be of interest to determine if specific XEGIP proteins could be translocated to other parts of the plant. Regions of the legume genome harboring XEGIPs have been associated with resistance to the root-attacking nematode Pratylenchus neglectus (Oldach et al 2014), thus there may be specific pests and pathogens that are differentially affected by individual XEGIPs. In tobacco, one XEGIP was studied and shown to have an effect on susceptibility to a bacterial pathogen, but no effect on two fungal pathogens (Xie et al 2008).…”

Plant vascular system-feeding Psyllidae (Hemiptera) and Nematoda genomes encode family 12 glycosyl hydrolases

“…These inhibitor proteins, referred to as xyloglucan-specific endoglucanase inhibitor proteins, are generally represented by two or three copies in the dicot genome, and up to 12 copies in potato and tomato (Jones 2012). They are produced in response to both abiotic and biotic stresses and can be found in the apoplast and xylem fluids (Houterman et al 2007), and have been suggested to be associated with resistance to the root lesion nematode Pratylenchus neglectus (Rensch) Filipjev and Schuurmans Stekhoven (Rhabditida: Pratylenchidae) (Oldach et al 2014). Screening of xyloglucan-specific endoglucanase inhibitor proteins for interaction with insect glycosyl hydrolase 12 enzymes may provide a novel method for interfering with psyllid or nematode feeding and/or pathogen transmission.…”

Resistance to root‐lesion nematode Pratylenchus neglectus identified in a new collection of two wild chickpea species (Cicer reticulatum and C. echinospermum) from Turkey

“…Pratylenchus neglectus is a migratory, endoparasitic, vermiform root‐lesion nematode (RLN) that invades, feeds and reproduces in the roots of many cereal and pulse crops, including chickpea. Symptoms of infestation include root necrosis and reduced root branching, which results in the reduction of crop yield (Oldach et al, 2014). P .…”