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Genetically based location from triploid populations and gene ontology of a 3.3-mb genome region linked to Alternaria brown spot resistance in citrus reveal clusters of resistance genes.

ABSTRACT: Genetic analysis of phenotypical traits and marker-trait association in polyploid species is generally considered as a challenge. In the present work, different approaches were combined taking advantage of the particular genetic structures of 2n gametes resulting from second division restitution (SDR) to map a genome region linked to Alternaria brown spot (ABS) resistance in triploid citrus progeny. ABS in citrus is a serious disease caused by the tangerine pathotype of the fungus Alternaria alternata. This pathogen produces ACT-toxin, which induces necrotic lesions on fruit and young leaves, defoliation and fruit drop in susceptible genotypes. It is a strong concern for triploid breeding programs aiming to produce seedless mandarin cultivars. The monolocus dominant inheritance of susceptibility, proposed on the basis of diploid population studies, was corroborated in triploid progeny. Bulk segregant analysis coupled with genome scan using a large set of genetically mapped SNP markers and targeted genetic mapping by half tetrad analysis, using SSR and SNP markers, allowed locating a 3.3 Mb genomic region linked to ABS resistance near the centromere of chromosome III. Clusters of resistance genes were identified by gene ontology analysis of this genomic region. Some of these genes are good candidates to control the dominant susceptibility to the ACT-toxin. SSR and SNP markers were developed for efficient early marker-assisted selection of ABS resistant hybrids.

SUBMITTER: Cuenca J

PROVIDER: S-EPMC3792864 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Genetically based location from triploid populations and gene ontology of a 3.3-mb genome region linked to Alternaria brown spot resistance in citrus reveal clusters of resistance genes.

Cuenca José J Aleza Pablo P Vicent Antonio A Brunel Dominique D Ollitrault Patrick P Navarro Luis L

PloS one 20131008 10

Genetic analysis of phenotypical traits and marker-trait association in polyploid species is generally considered as a challenge. In the present work, different approaches were combined taking advantage of the particular genetic structures of 2n gametes resulting from second division restitution (SDR) to map a genome region linked to Alternaria brown spot (ABS) resistance in triploid citrus progeny. ABS in citrus is a serious disease caused by the tangerine pathotype of the fungus Alternaria alt ...[more]

PMID: 24116149

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Project description:Brown spot of citrus caused by Alternaria citri is one of the emerging threats to the successful production of citrus crops. The present study, conducted with a substantial sample size of 50 leaf samples for statistical reliability, aimed to determine the change in mineral content in citrus leaves after brown spot disease attack. Leaf samples from a diverse range of susceptible citrus varieties (Valentia late, Washington navel, and Kinnow) and resistant varieties (Citron, Eruka lemon, and Mayer lemon) were analyzed. Significant variations (p ≤ 0.05) in mineral contents were observed across reaction groups (inoculated and un-inoculated), types (resistant and susceptible), and varieties of citrus in response to infection of Alternaria citri. The analysis of variance showed significant changes in mineral levels of citrus leaves, including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), sodium (Na), iron (Fe), and copper (Cu). The results indicate that the concentration of N and P differed by 6.63% and 1.44%, respectively, in resistant plants, while susceptible plants showed a difference of 6.07% and 1.19%. Moreover, resistant plants showed a higher concentrations of K, Ca, Mg, Zn, Na, Fe, and Cu at 8.40, 2.1, 1.83, 2.21, 1.58, 2.89, and 0.36 ppm respectively, compared to susceptible plants which showed concentrations of 5.99, 1.93, 1.47, 1.09, 1.24, 1.81, and 0.31 ppm respectively. Amounts of mineral contents were reduced in both resistant as well as susceptible plants of citrus after inoculation. Amount of N (8.56), P (1.87) % while K (10.74), Ca (2.71), Mg (2.62), Zn (2.20), Na (2.08), Fe (3.57) and Cu (0.20) ppm were recorded in un-inoculated group of citrus plants that reduced to 3.15 and 0.76% and 3.66, 1.40, 0.63,0.42, 0.74, 1.13 and 0.13 ppm in inoculated group respectively. It was accomplished that susceptible varieties contained lower ionic contents than resistant varieties. The higher concentrations of ionic contents in resistant citrus varieties build up the biochemical and physiological processes of the citrus plant, which help to restrict spread of pathogens. Further research could explore the interplay between mineral nutrition and disease resistance in citrus, potentially leading to the development of new disease-resistant varieties.

Project description:Alternaria brown spot is one of the most important diseases of tangerines and their hybrids worldwide. Recently, outbreaks in Mediterranean areas related to susceptible cultivars, refocused attention on the disease. Twenty representatives were selected from a collection of 180 isolates of Alternaria spp. from citrus leaves and fruit. They were characterized along with reference strains of Alternaria spp. Micro- and macroscopic characteristics separated most Alternaria isolates into six morphotypes referable to A. alternata (5) and A. arborescens (1). Phylogenetic analyses, based on endopolygalacturonase (endopg) and internal transcribed spacer (ITS), confirmed this finding. Moreover, a five-gene phylogeny including two anonymous genomics regions (OPA 1-3 and OPA 2-1), and the beta-tubulin gene (ß-tub), produced a further clustering of A. alternata into three clades. This analysis suggested the existence of intra-species molecular variability. Investigated isolates showed different levels of virulence on leaves and fruit. In particular, the pathogenicity on fruit seemed to be correlated with the tissue of isolation and the clade. The toxigenic behavior of Alternaria isolates was also investigated, with tenuazonic acid (TeA) being the most abundant mycotoxin (0.2-20 mg/L). Isolates also synthesized the mycotoxins alternariol (AOH), its derivate alternariol monomethyl ether (AME), and altenuene (ALT), although to a lesser extent. AME production significantly varied among the six morphotypes. The expression of pksJ/pksH, biosynthetic genes of AOH/AME, was not correlated with actual toxin production, but it was significantly different between the two genotypes and among the four clades. Finally, ten isolates proved to express the biosynthetic genes of ACTT1 phytotoxin, and thus to be included in the Alternaria pathotype tangerine. A significant correlation between pathogenicity on leaves and ACTT1 gene expression was recorded. The latter was significantly dependent on geographical origin. The widespread occurrence of Alternaria spp. on citrus fruit and their ability to produce mycotoxins might represent a serious concern for producers and consumers.

Dataset Information

Genetically based location from triploid populations and gene ontology of a 3.3-mb genome region linked to Alternaria brown spot resistance in citrus reveal clusters of resistance genes.

Publications

Genetically based location from triploid populations and gene ontology of a 3.3-mb genome region linked to Alternaria brown spot resistance in citrus reveal clusters of resistance genes.

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