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- Intraspecific variation of anatomical and chemical defensive traits in Maritime pine (Pinus pinaster) as factors in susceptibility to the pinewood nematode (Bursaphelenchus xylophilus)Publication . Zas, Rafael; Moreira, Xoaquín; Ramos, Miguel; Lima, Marta R. M.; Silva, Marta Nunes da; Solla, Alejandro; Vasconcelos, Marta; Sampedro, LuisKey message Migration ability of the PWN through wood branch tissues of adult Maritime pine trees significantly differed among Iberian provenances and this variation was related to differences in anatomical and chemical defensive traits. Abstract The pinewood nematode or pine wilt nematode (PWN; Bursaphelenchus xylophilus) is one of the most dangerous threats to European coniferous forests, especially for the susceptible Maritime pine (Pinus pinaster), a valuable forest resource in South Western Europe. The PWN is vectored by beetles of the genus Monochamus (Coleoptera, Cerambycidae) and once inoculated in healthy branches, it quickly migrates downward to the main trunk through the resin canal system. Therefore, the anatomy of the resin canal system may modulate its migration and proliferation rates. Using material from nine Maritime pine Iberian provenances established in a common garden trial, we investigated whether these provenances differed in their (1) resin canal anatomy, (2) concentration of chemical defences (non-volatile resin and total polyphenolics) in stems and (3) ability of the PWN to migrate through the pine woody tissues in ‘in vitro’ bioassays. Whether variation in anatomical and chemical defensive traits relates to differences in PWN migration across populations was also investigated. Significant intraspecific variation in anatomical and chemical defensive traits and in nematode migration rates through pine tissues was observed. Moreover, the variation in nematode migration rate among pine provenances was related to differences in both anatomical and chemical features. Overall, this study highlights the role of plant genetics in the development of defensive traits against this harmful coniferous pest. The observed intraspecific variation should be taken into account when considering breeding as a strategy to provide areas of high risk of PWN with resistant genetic material.
- Traumatic resin ducts induced by methyl jasmonate in Pinus sppPublication . López‑Villamor, Adrián; Zas, Rafael; Pérez, Andrea; Cáceres, Yonatan; Silva, Marta Nunes da; Vasconcelos, Marta; Vázquez‑González, Carla; Sampedro, Luis; Solla, AlejandroKey message Exogenous MJ does not alter the resin duct structure of pines in the cortex, but increases the number, density and mean size of resin ducts in the secondary xylem, particularly in Pinus sylvestris and P. radiata. Abstract Methyl jasmonate (MJ) is an organic compound capable of modulating defence responses in plants. Exogenous application of MJ has been shown to modify the structure of the resin canal system in conifers by inducing the formation of dense concentric bands of traumatic resin ducts in the xylem. Because inducibility of resin ducts has been little explored across pine species, 3-year-old Pinus pinaster, P. pinea, P. sylvestris and P. radiata trees were sprayed with 0, 25 and 50 mM solutions of MJ, and plant growth, external symptoms and histology were assessed 60 days after treatment. Exogenous application of MJ diminished primary or secondary growth in all species (61 and 25%, respectively) and caused needle damage in P. sylvestris. Exogenous MJ did not alter the resin duct structure of Pinus spp. in the cortex. In the secondary xylem, however, the effect of MJ differed considerably between species: ducts, duct density and area covered by ducts increased in P. sylvestris and P. radiata, but not in P. pinaster and P. pinea. In MJ 50 mM-treated trees, resin duct abundance peaked at the first half of the ring in P. sylvestris and at one-third distance from the previous ring in P. radiata. In MJ treated P. radiata trees, large traumatic axial resin ducts, 120–160 μm in diameter, were aligned in the secondary xylem. The study helps to elucidate macroevolutionary aspects of inducibility of resin-based defences in the genus Pinus, where varying responses to MJ could reveal different defence strategies among species.