Avocado (Persea americana), an important fruit crop, is under threat from an invasive disease, laurel wilt. The pathogen, Raffaelea lauricola, spreads rapidly in the xylem of infected trees and causes a lethal vascular wilt. A previous study showed that variation in susceptibility to the disease exists among different races of avocado, with the West Indian race being most susceptible. To help elucidate potential explanations for differences in susceptibility, xylem characteristics were examined for fourteen avocado cultivars from the Guatemalan, Mexican, and West Indian botanical races. Samples of each cultivar were assessed for vessel size, vessel density, vessel aggregation, and xylem-specific potential hydraulic conductivity. The West Indian race had significantly greater mean vessel diameters, mean maximum vessel diameters, and xylem-specific potential hydraulic conductivities than the Guatemalan and Mexican races (p 0.05). There were no significant differences among the races for vessel aggregation or vessel density. Cultivars of the Mexican and Guatemalan races generally had smaller mean vessel diameters, mean maximum vessel diameters, and mean xylem-specific potential hydraulic conductivities than the West Indian race; however, there was considerable variation among cultivars of the Mexican race. Statistically significant differences in vessel grouping indices and vessel solitary fractions were evident among some cultivars but to lesser extents than were found for vessel size. This study indicates that larger vessel diameters and greater potential hydraulic conductivities exist in the West Indian, compared with the Guatemalan and Mexican races. We suggest that these attributes may be contributing factors in the greater susceptibility to laurel wilt that is evident in the West Indian race.

中文翻译：

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Persea americana植物小种木质部特征的变化及其对病原体Raffaelea lauricola易感性的潜在影响

鳄梨（Persea americana）是一种重要的水果作物，正受到侵袭性病害——月桂枯萎病的威胁。病原体 Raffaelea lauricola 在受感染树木的木质部迅速传播，并导致致命的血管枯萎病。之前的一项研究表明，鳄梨的不同种族之间存在对该疾病的易感性差异，其中西印度种族最易感。为了帮助阐明易感性差异的潜在解释，对来自危地马拉、墨西哥和西印度植物品种的 14 个鳄梨品种的木质部特征进行了检查。评估每个品种的样品的容器大小、容器密度、容器聚集和木质部特定的潜在水力传导率。西印度人的平均血管直径、平均最大血管直径、和木质部特定的潜在水力传导率高于危地马拉和墨西哥人种 (p 0.05)。在血管聚集或血管密度方面，种族之间没有显着差异。与西印度人种相比，墨西哥和危地马拉人种的栽培品种通常具有较小的平均容器直径、平均最大容器直径和平均木质部特定潜在水力传导率；然而，墨西哥人种的品种之间存在相当大的差异。在一些栽培品种中，血管分组指数和血管孤立分数的统计学显着差异是明显的，但程度低于血管大小。这项研究表明，与危地马拉和墨西哥种族相比，西印度群岛存在更大的血管直径和更大的潜在水力传导率。