Abstract
Bark cankers accompanied by symptoms of decline and dieback are the result of a destructive disease caused by Phytophthora infections in woody plants. Pathogenicity, gas exchange, chlorophyll a fluorescence, and volatile responses to P. cactorum and P. plurivora inoculations were studied in field-grown 10-year-old hybrid poplar plants. The most stressful effects of P. cactorum on photosynthetic behaviour were found at days 30 and 38 post-inoculation (p.-i.), whereas major disturbances induced by P. plurivora were identified at day 30 p.-i. and also belatedly at day 52 p.-i. The spectrum of volatile organic compounds emitted at day 98 p.-i. was richer than that at day 9 p.-i, and the emissions of both sesquiterpenes α-cubebene and germacrene D were induced solely by the Phytophthora inoculations. Significant positive relationships were found between both the axial and the tangential development of bark cankers and the emissions of α-cubebene and β-caryophyllene, respectively. These results show that both α-cubebene and germacrene D are signal molecules for the suppression of Phytophthora hyphae spread from necrotic sites of the bark to healthy living tissues. Four years following inoculations, for the majority of the inoculated plants, the callus tissue had already closed over the bark cankers.
Highlights
Introduction iationsPhytophthora species are pathogenic fungi-like organisms, belonging to the kingdomChromista/Stramenopiles and the “SAR” (Stramenopiles, Alveolata, and Rhizaria) supergroup [1]
principal component analysis (PCA) based on multivariate associations among the identified volatile organic compounds (VOCs) showed that the two Phytophthora species were oppositely separated from the control plants (Figure 4)
D, we found that the greater axial length of the canker triggered a greater emission of this sesquiterpene (r = 0.54, p = 0.046). These results reveal very interesting findings that, while all the above VOCs responded sensitively to the axial development of bark cankers, only α-cubebene and β-caryophyllene were emitted in increased amounts following the tangential spread of the cankers
Summary
Experiments were conducted on 10-year-old clonally micropropagated plants of the hybrid poplar clone T-14, Populus tremula L. 70 × (Populus × canescens (Ait.) Sm. 23), growing in the experimental field plot at Zvolen, Slovakia (48◦ 350 N, 19◦ 080 E, 297 m a.s.l.). Artificial inoculations of P. cactorum and P. plurivora isolates on hybrid poplar plants were performed on 20th June 2017, i.e., at day 0, using the underbark inoculation test at breast height. The plant stem diameter at breast height was 8.25 ± 0.21 (S.E.) cm Both of the isolates used, P. cactorum isolate SFB057 (GenBank accession number JX276094) and P. plurivora isolate SFB182 (GenBank accession number KF234740), were isolated from mature poplar trees without visible crown symptoms that were surrounded by diseased trees. Inoculated plants were regularly inspected and control re-isolations from randomly selected plants within both Phytophthora treatments were performed. Both gas exchange and chlorophyll a fluorescence measurements were conducted at day −1 (19/06) prior to infection to ensure there were no differences among the examined treatments. All measurements were conducted on seven randomly chosen plants per treatment
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