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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Improvement of Citrus for Enhanced Resistance to Biotic and Abiotic Stresses

Location: Subtropical Insects and Horticulture Research

Title: Incidence and severity of Asiatic citrus canker on citrus and citrus–related germplasm in a Florida field planting

Authors
item Stover, Ed
item Richardson, Matthew
item Driggers, Randall
item Hall, David
item Duan, Ping
item Lee, Richard

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2013
Publication Date: January 2, 2014
Citation: Stover, E.W., Richardson, M.L., Driggers, R., Hall, D.G., Duan, Y.P., Lee, R.F. 2014. Incidence and severity of Asiatic citrus canker on citrus and citrus–related germplasm in a Florida field planting. HortScience. 49:4-9.

Interpretive Summary: In this study we evaluated citrus canker susceptibility in plants grown from seed of 94 types of citrus and other genera related to citrus. Plants were exposed to high levels of citrus canker in the field and disease was assessed in Sept. 2010, July 2011, Oct. 2011, May 2012, and Sept. 2012. Plants grown from seedlings of 14 parent types did not show canker disease at any date: these were all in genera other than citrus, with only Microcitrus and Eremocitrus being cross-compatible with citrus. The kumquat hybrid C. halimii, two accessions of C. reticulata, C. nobilis, and C. sunki were the only citrus species in the group that had a low severity (% total leaf area showing symptoms) on each date of assessment. Fourteen of the 16 progeny of C. reticulata and related parent genotypes were in the group with the lowest incidence and severity of citrus canker on two or more assessment dates. Progeny of Poncirus and its hybrids, as well as those of C. maxima, C. limon and related species were the most severely diseased at all assessment dates. There were few instances in which plants from different accessions of the same species had markedly different responses to ACC: progeny of C reticulata ‘Fremont’ displayed more severe canker compared to several other C reticulata groups, and C. aurantium ‘Zhuluan’ displayed much lower incidence and severity of canker compared to several other accessions designated C. aurantium. Information on canker susceptibility in diverse citrus and citrus relatives may prove useful for breeding programs aimed at reducing canker susceptibility and will provide useful guidance for researchers interested in mechanisms of canker resistance and susceptibility.

Technical Abstract: Xanthomonas citri ssp. citri (Hasse), is the causal agent of Asiatic citrus canker (ACC), a commercially important disease in Florida citrus, as well as in many other regions. In this study we evaluated occurrence of foliar lesions from ACC on progenies of 94 seed-source genotypes (hereafter called “parent genotypes”) of citrus and citrus relatives in the field in East-central Florida to identify the relative susceptibility to ACC. Eight seedlings were planted per parent genotype, in a randomized complete block planting, but the number of plants assessed in some genotype groups was reduced by mortality at some or all sampling dates. Plants experienced ambient exposure to high Xcc inoculum pressure and plants were assessed in Sept. 2010, July 2011, Oct. 2011, May 2012, and Sept. 2012. The incidence and severity of ACC lesions was assessed using non-parametric analyses to compare progeny from the 94 parent genotypes. Progeny of 14 parent genotypes were not observed to be diseased with ACC at any date: these were all in genera other than citrus, with only Microcitrus and Eremocitrus being cross-compatible with citrus. The kumquat hybrid C. halimii, two accessions of C. reticulata, C. nobilis, and C. sunki were the only citrus species in the group that had a low severity (% total leaf area showing symptoms) on each date of assessment. The aforementioned accessions had an incidence and severity of ACC lesions < 4% in 2011 and 2012, but 26-38% in 2010 when no chemical control for ACC was applied in the adjoining blocks at our field site. Fourteen of the 16 progeny of C. reticulata and related parent genotypes were in the group with the lowest incidence and severity of ACC on two or more assessment dates. However, for analysis of only the most symptomatic leaves on each plant, ten C. reticulata parent genotype progenies were in the most resistant category on the Sept. 2012 assessment, despite having a low incidence and severity of ACC symptoms overall. Progeny of Poncirus and its hybrids, as well as those of C. maxima, C. limon and related species were the most severely diseased at all assessment dates. There were few instances in which progeny of different accessions of the same species had markedly different responses to ACC: progeny of C reticulata ‘Fremont’ displayed more severe ACC compared to several other C reticulata groups, and C. aurantium ‘Zhuluan’ displayed much lower incidence and severity of ACC compared to several other accessions designated C. aurantium. Information on ACC susceptibility in diverse citrus and citrus relatives may prove useful for breeding programs aimed at reducing ACC susceptibility and will provide useful guidance for researchers interested in mechanisms of ACC resistance and susceptibility.

Last Modified: 10/1/2014
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