Fundo de Defesa da Citricultura-Fundecitrus, Departamento de Pesquisa e Desenvolvimento, 14.807-040, Araraquara, São Paulo, Brazil.
Phytopathology. 2019 Jan;109(1):44-51. doi: 10.1094/PHYTO-04-18-0114-R. Epub 2018 Nov 13.
During the development of a citrus fruit, many cycles of infection by Xanthomonas citri subsp. citri may occur leading to the development of a range of characteristics of citrus canker lesions scattered across the fruit surface. This study aimed to determine whether the size of the lesions, their distance from the peduncle, and the number and time of appearance of the lesions on fruit of sweet orange were associated with premature fruit drop. A multiple linear regression analysis revealed a negative relationship between the fruit detachment force and the lesion diameter, the proximity of the nearest lesion to the peduncle and the number of lesions. A survival analysis demonstrated that these characteristics significantly influenced the probability and the time that a cankered fruit remained attached to the tree. More than 90% of dropped fruit had large lesions (>5 mm) but not all fruit with large lesions dropped before harvest. Approximately 50% of the harvested fruit had lesions >5 mm. On the harvested fruit remaining on the tree, although large, the lesions had a smaller diameter, were located farther from the peduncle, and were less numerous than those observed on dropped fruit. Small canker lesions neither reduced the detachment force nor the survival of fruit in the tree. The earlier a fruit expressed canker symptoms, the higher the probability the fruit developed large lesions near the peduncle and/or developed lesions in greater numbers. This study provides a better understanding on the relationship between the time of appearance of lesions of citrus canker on fruit and premature fruit drop. This information defines the critical period for fruit protection and may be used to improve disease management.
在柑橘果实发育过程中，可能会多次感染柑橘溃疡病菌亚种柑橘（Xanthomonas citri subsp. citri），导致果实表面出现一系列溃疡病斑特征。本研究旨在确定甜橙果实上病斑的大小、距果柄的距离、病斑数量和出现时间是否与果实早落有关。多元线性回归分析表明，果实脱落力与病斑直径、最近病斑距果柄的距离和病斑数量呈负相关。生存分析表明，这些特征显著影响溃疡果挂在树上的概率和时间。超过 90%的落果有大的病斑（>5mm），但并非所有大病斑的果实都在收获前掉落。大约 50%的收获果实有>5mm 的病斑。在树上剩余的收获果实上，尽管病斑较大，但直径较小，距果柄较远，数量也较少。小的溃疡病斑既不会降低果实的脱落力，也不会影响其在树上的存活率。果实出现溃疡症状越早，靠近果柄形成大病斑和/或形成更多病斑的可能性就越高。本研究更好地了解了柑橘溃疡病在果实上出现的时间与果实早落之间的关系。这些信息确定了果实保护的关键时期，可用于改善病害管理。
