Abstract
BackgroundThe southern root-knot nematode (Meloidogyne incognita; RKN) is one of the most important economic pests of Upland cotton (Gossypium hirsutum L.). Host plant resistance, the ability of a plant to suppress nematode reproduction, is the most economical, practical, and environmentally sound method to provide protection against this subterranean pest. The resistant line Auburn 623RNR and a number of elite breeding lines derived from it remain the most important source of root-knot nematode (RKN) resistance. Prior genetic analysis has identified two epistatically interacting RKN resistance QTLs, qMi-C11 and qMi-C14, affecting gall formation and RKN reproduction, respectively.ResultsWe developed a genetic population segregating only for the qMi-C14 locus and evaluated the genetic effects of this QTL on RKN resistance in the absence of the qMi-C11 locus. The qMi-C14 locus had a LOD score of 12 and accounted for 24.5 % of total phenotypic variation for egg production. In addition to not being significantly associated with gall formation, this locus had a lower main effect on RKN reproduction than found in our previous study, which lends further support to evidence of epistasis with qMi-C11 in imparting RKN resistance in the Auburn 623RNR source. The locus qMi-C14 was fine-mapped with the addition of 16 newly developed markers. By using the reference genome sequence of G. raimondii, we identified 20 candidate genes encoding disease resistance protein homologs in the newly defined 2.3 Mb region flanked by two SSR markers. Resequencing of an RKN resistant and susceptible G. hirsutum germplasm revealed non-synonymous mutations in only four of the coding regions of candidate genes, and these four genes are consequently of high interest.ConclusionsOur mapping results validated the effects of the qMi-C14 resistance locus, delimiting the QTL to a smaller region, and identified tightly linked SSR markers to improve the efficiency of marker-assisted selection. The candidate genes identified warrant functional studies that will help in identifying and characterizing the actual qMi-C14 defense gene(s) against root-knot nematodes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2954-1) contains supplementary material, which is available to authorized users.
Highlights
The southern root-knot nematode (Meloidogyne incognita; RKN) is one of the most important economic pests of Upland cotton (Gossypium hirsutum L.)
The Southern root-knot nematode (Meloidogyne incognita, RKN) is the most important parasitic nematode of Upland cotton inflicting economic losses through direct damage to the plant root system and indirectly through increasing severity of other root diseases such as Fusarium Wilt caused by Fusarium oxysporum f. sp. vasinfectum
Our objectives were to: (1) develop and map new simple sequence repeats (SSR) markers to construct a dense linkage map near the qMi-C14 locus, (2) estimate the genetic effect of qMi-C14 on RKN resistance and (3) predict putative candidate genes responsible for the qMi-C14 resistance by identifying genes that encode for leucine rich repeat (LRR)-containing proteins within the Quantitative trait locus (QTL) interval
Summary
The southern root-knot nematode (Meloidogyne incognita; RKN) is one of the most important economic pests of Upland cotton (Gossypium hirsutum L.). The ability of a plant to suppress nematode reproduction, is the most economical, practical, and environmentally sound method to provide protection against this subterranean pest. Plant-parasitic nematodes are important pests in agriculture and are found across a broad range of climatic conditions. The Southern root-knot nematode (Meloidogyne incognita, RKN) is the most important parasitic nematode of Upland cotton inflicting economic losses through direct damage to the plant root system and indirectly through increasing severity of other root diseases such as Fusarium Wilt caused by Fusarium oxysporum f. The broad host-range of RKN leaves cotton growers with few profitable options to adopt crop rotation as a means of nematode management [2]. Nematicides applied at planting fail to provide season long protection; the future availability of most widely used cotton nematicide, aldicarb, is uncertain
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