Incidence of Asiatic citrus canker on Trifoliate orange and its hybrid accessions in a Florida field planting

Authors: Stover, Eddie; RAMADUGU, CHANDRIKA - University Of California; ROOSE, MIKEAL - University Of California; Krystel, Joseph; Lee, Richard; Keremane, Manjunath

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2021
Publication Date: 5/3/2021
Citation: Stover, E.W., Ramadugu, C., Roose, M., Krystel, J.A., Lee, R.F., Keremane, M.L. 2021. Incidence of Asiatic citrus canker on Trifoliate orange and its hybrid accessions in a Florida field planting. Journal of the American Society for Horticultural Science. 56(5):525–531. https://doi.org/10.21273/HORTSCI15684-20.
DOI: https://doi.org/10.21273/HORTSCI15684-20

Interpretive Summary: Asiatic citrus canker (ACC) is an important disease in many citrus varieties. Distinctive ACC leaf blemishes (lesions) were evaluated on trees grown from seed of 84 diverse and distinct Citrus trifoliata and hybrids between Citrus trifoliata and other Citrus species and hybrids. These seed-source trees are maintained by the University of California at Riverside’s citrus variety collection (CVC) with seed distributed by the USDA citrus gene bank (National Clonal Germplasm Repository for Citrus and Dates, Riverside, California), and each type of source tree is designated by a unique CRC number. Trees produced from seed-source trees were planted Aug, 2013 in a replicated randomized manner at the Fort Pierce USDA grove. Plants were visually assessed Aug, 2017, Sept. 2019, and Sept. 2020 for percentage of leaves with ACC lesions on each tree (ACC incidence) and percentage of leaf area covered by lesions on the worst affected leaf on each tree (ACC severity). The ACC pathogen was verified to be associated with the lesions by lab means. Progeny were compared by seed-source trees (referred to by CRC number) using a ranking-based statistical method. Incidence of ACC (percentage of leaves displaying symptoms), ranged from 8-80% (mean 49%) of leaves affected in 2017, from 4-58% (mean 29%) in 2019, and 8-46% (mean 25%). In 2017, of 49 Citrus trifoliata seed-source tree types, only four separated from the two highest ACC-incidence statistical categories (CRC 3345, 3484, 3888, and 4017) while 29 of the 35 Citrus trifoliata hybrid seed-sources displayed lower ACC-incidence which separated from the two highest statistical categories. In 2019, of the Citrus trifoliata, only six separated from the highest ACC-incidence statistical category (CRC 3330, 3484, 3547, 3549, 3876, and 3888) while all 35 Citrus trifoliata hybrids displayed lower ACC-incidence and separated from the highest statistical category, and 26 hybrids separated from 18 of the Citrus trifoliata. In 2020, only three Citrus trifoliata, separated from the highest ACC-incidence statistical category (CRC 2861, 3549, and 3888) and 20 hybrids separated from 18 of the Citrus trifoliata. By seed-source, ACC incidence was correlated between each pair of the three years. Overall, hybrids of Citrus trifoliata with other citrus types displayed markedly reduced ACC sensitivity compared to Citrus trifoliata, indicating that this trait is readily overcome in breeding.

Technical Abstract: Asiatic citrus canker (ACC) foliar lesions were evaluated on progenies of 84 seed-source genotypes (“parent genotypes”) from NCGRCD, of Citrus trifoliata and hybrids between Citrus trifoliata and other Citrus species and hybrids. Trees were planted Aug, 2013 in a CRD at the Fort Pierce USDA grove. Plants were visually assessed Aug, 2017, Sept. 2019, and Sept. 2020 for distinctive ACC lesion incidence and severity. Progeny were compared by parent genotypes using non-parametric analysis. Incidence of ACC (percentage of leaves displaying symptoms, verified by polymerase chain reaction (PCR) to be associated with Xanthomonas citri pv. citri) across parent genotypes ranged from 8-80% (mean 49%) of leaves affected in 2017, from 4-58% (mean 29%) in 2019, and 8-46% (mean 25%). In 2017, of 49 C. trifoliata parent genotypes, only four separated from the two highest ACC-incidence statistical categories (CRC 3345, 3484, 3888, and 4017) while 29 of the 35 Citrus trifoliata hybrids displayed lower ACC-incidence which separated from the two highest statistical categories. In 2019, of the Citrus trifoliata, only six separated from the highest ACC-incidence statistical category (CRC 3330, 3484, 3547, 3549, 3876, and 3888) while all 35 Citrus trifoliata hybrids displayed lower ACC-incidence and separated from the highest statistical category, and 26 hybrids separated from 18 of the C. trifoliata. In 2020, only three Citrus trifoliata, separated from the highest ACC-incidence statistical category (CRC 2861, 3549, and 3888) and 20 hybrids separated from 18 of the C. trifoliata. By parent genotype, ACC incidence was correlated between each pair of the three years with r2 of 0.39, 0.57 and 0.65. Of 34 hybrids validated, similar numbers had Citrus trifoliata, grapefruit (C. x aurantium var. racemosa), and sweet orange (C. x aurantium var. sinensis) chloroplasts. Chloroplast type affected ACC incidence and severity, but not in a consistent manner. Near-isogenic groups within Citrus trifoliata, as determined by DNA markers, were associated with some statistically different ACC sensitivity. Overall, hybrids of Citrus trifoliata with other citrus types displayed markedly reduced ACC sensitivity compared to Citrus trifoliata, indicating that this trait is readily overcome in breeding.