Resistance and systemic dispersal of Xanthomonas fragariae in strawberry germplasm (Fragaria L.)

Abstract

The angular leaf spot disease caused by Xanthomonas fragariae is an important plant disease with major impact for the strawberry nursery industry. Currently there is no plant protection product available for controlling the disease effectively. Planting of resistant cultivars seems to be promising, but all commercially used cultivars are susceptible and no donor with a high level of resistance has yet been found. Therefore, a total of 145 genotypes from the Fruit Genebank Dresden (Germany) were evaluated for resistance to X. fragariae by artificial inoculation. Six genotypes were classified as partly resistant, out of which only two (US4808 and US4809) are octoploid. Fragaria vesca f. alba, Fragaria nilgerrensis ‘Yunnan’, F. vesca ‘Illa Martin’ and F. moschata ‘Bauwens’ were also classified as partially resistant, but they are only of limited use for breeding because of their variable ploidy level. Fully resistant genotypes could not be detected. The systemic dispersal of the bacteria in strawberry plants was investigated after inoculation of leaves with X. fragariae strain XF3.9.C and the GFP‐tagged strain XF3.9.C(pKAN). The systemic spread was evaluated after 3, 7, 14 and 28 days post‐inoculation (dpi) by nested PCR and fluorescence microscopy. After 3 dpi, X. fragariae could be found in all tissues tested including the inoculated leaf, its petiole, the rhizome, the heart bud up to the youngest fully expanded leaf and its petiole. The systemic spread was also detectable in partially resistant genotypes.

Genome-based population structure analysis of the strawberry plant pathogen Xanthomonas fragariae reveals two distinct groups that evolved independently before its species description

“…Long distance spread is mainly due to international transport of plant material through human trade [ 33 ]. Spread often happens via asymptomatic strawberry plants, when symptoms are not detectable by visual inspection at the moment of the plant material exportation [ 34 ]. In the early infection stage, symptoms include water-soaked foliar lesions, appearing as light green spots, which are transparent when viewed with transmitted light [ 27, 35 ].…”

A diagnostic tool for improved detection of Xanthomonas fragariae using a rapid and highly specific LAMP assay designed with comparative genomics

“…Spread of X. fragariae often occurs through export of symptomless infected strawberry plants for planting, in which the disease has not been detected by visual inspection (Moltmann & Zimmermann, 2005;Bestfleisch et al, 2015). Detection from symptomless plants is difficult because it is not clear which tissue to sample and the X. fragariae concentration may be low (EPPO, 2006).…”

Reproductive compatibility studies between wild and cultivated strawberries (Fragaria × ananassa) to obtain “bridge species” for breeding programmes

“…On the other hand, Rieseberg and Carney () and Goulet, Roda, and Hopkins () suggest that hybridization might have numerous evolutionary consequences, such as increasing genetic diversity. In that sense, Bisognin () and Bestfleisch et al () consider that an increased diversity in cultivated germplasm may reduce the vulnerability of crops against pathogen attack ( Colletotrichum sp., Xanthomonas fragariae ) and allow the incorporation of new cultivar specific traits, since many characters of agronomic importance are available in the wild germplasm related to cultivated strawberries. For the aforementioned reason, hybrids obtained at the present work could be used as bridge between wild related species and cultivated varieties of strawberry, and probably could allow the introduction of important agronomic traits in local varieties, such as resistance to pathogens as Colletotrichum sp, a genus that causes severe economic losses (Pardo et al, ; Salazar et al, ), Xanthomonas fragariae (Bestfleisch et al, ), Botrytis cinerea (Tomas‐Grau et al, ).…”