Abstract
The commercial yield of cucurbit crops infected with Cucumber mosaic virus (CMV) severely decreases. Chemical treatments against CMV are not effective; therefore, genetic resistance is considered the primary line of defense. Here, we studied resistance to CMV in cucumber inbred line ‘02245’ using a recombinant inbred line (RIL) population generated from a cross between ‘65G’ and ‘02245’ as susceptible and resistant parents, respectively. Genetic analysis revealed that CMV resistance in cucumber is quantitatively inherited. Analysis of the RIL population revealed that a quantitative trait locus (QTL) was found on chromosome 6; named cmv6.1, this QTL was delimited by SSR9-56 and SSR11-177 and explained 31.7% of the phenotypic variation in 2016 and 28.2% in 2017. The marker SSR11-1, which is close to the locus, was tested on 78 different cucumber accessions and found to have an accuracy of 94% in resistant and moderately resistant lines but only 67% in susceptible lines. The mapped QTL was delimited within a region of 1,624.0 kb, and nine genes related to disease resistance were identified. Cloning and alignment of the genomic sequences of these nine genes between ‘65G’ and ‘02245’ revealed that Csa6M133680 had four single-base substitutions within the coding sequences (CDSs) and two single-base substitutions in its 3’-untranslated region, and the other eight genes showed 100% nucleotide sequence identity in their exons. Expression pattern analyses of Csa6M133680 in ‘65G’ and ‘02245’ revealed that the expression levels of Csa6M133680 significantly differed between ‘65G’ and ‘02245’ at 80 h after inoculation with CMV and that the expression in ‘02245’ was 4.4 times greater than that in ‘65G’. The above results provide insights into the fine mapping and marker-assisted selection in cucumber breeding for CMV resistance.
Highlights
Cucumber mosaic virus (CMV) is a plant pathogenic virus of the genus Cucumovirus in the family Bromoviridae [1]
The F1 hybrids had a Disease indices (DI) of 35.80 in 2016 and a DI of 34.72 in 2017 and exhibited symptoms that were more similar to the susceptible parent (‘65G’) than to the resistant parent (‘02245’) (Table 1 and Fig 2A)
This study used the recombinant inbred line (RIL) population derived from a cross between cucumber inbred lines ‘65G’ and ‘02245’ to determine the genetic basis for resistance to CMV
Summary
Cucumber mosaic virus (CMV) is a plant pathogenic virus of the genus Cucumovirus in the family Bromoviridae [1]. It has a worldwide distribution and a very broad range of hosts, and it was first reported in 1934 in cucumbers that showed mosaic symptoms [2]. Throughout their whole growth cycle, cucumber crops can be damaged by CMV; damaged plants exhibit symptoms that include strong leaf mosaic patterns and leaf distortion, stunted growth, reduced.
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