Variation in xylem characteristics of botanical races of Persea americana and their potential influence on susceptibility to the pathogen Raffaelea lauricola

R A Blanchette,B W Held,C D Lund,J L Konkol,R C Ploetz,G L Beier

doi:10.1007/s40858-020-00397-y

R A Blanchette, B W Held + Show 4 more

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https://doi.org/10.1007/s40858-020-00397-y

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Abstract

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), which in turn did not differ for any of these variables (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.

Highlights

Laurel wilt is a lethal disease of plants in the Lauraceae family that is caused by an ambrosia beetle symbiont, Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Raffaelea lauricola T.C
In the study we present here, three, five, and six cultivars of the Guatemalan, Mexican, and West Indian races, respectively, were examined for vessel size, density, aggregation, and xylem-specific potential hydraulic conductivity
No significant differences were found among the races in vessel aggregation and vessel density (VD)

Summary

Introduction

Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Harrington et al 2008). The disease has caused significant damage to native ecosystems in the southeastern United States (Fraedrich et al 2008) and threatens the global production of a valuable food crop, avocado (Persea americana Mill.) (Ploetz et al, 2017). In the USA, there were 56,580 acres of avocado in production during the 2017–2018 season, with an estimated value of approximately 390 million dollars (National Agricultural Statistics Service 2018). The USA imported avocados from Mexico in 2018 worth more than 2 billion dollars (Economic Research Service 2019)

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