Abstract
In natural environments, plants develop adaptive mechanisms at the cellular and molecular levels to cope with many external factors, e.g., insects and soil pathogens. We studied physiological stress induced by different levels of foliage removal (defoliation 30% and 60%) and by infection of root rot pathogen Phytophthora plurivora on the common Polish tree species, Betula pendula, grown in an open greenhouse. This study showed that P. plurivora damaged the root system which negatively impacted all morphological parameters. However the loss of 30% of the leaves had a positive effect on defense responses. Chlorophyll-a fluorescence parameters indicated a decrease in photosynthetic efficiency in defoliated plants, but plants inoculated with the pathogen had a higher performance index showing increased vigor of the infected plant than birches. The study demonstrated the intense immunity response of birch to P. plurivora through the expression of Hsp90 and Hsp83 genes. The trees weakened by P. plurivora became more susceptible to infection by Erysiphe ornata var. ornata.
Highlights
We examined several photosynthetic parameters: the total performance index of photosystem II (PI total), the time at which the maximum fluorescence value was reached (Tfm), the initial fluorescence representing the emission by excited chlorophyll molecules in the antenna structure of the photosystem II (Fo), the maximum fluorescence value (Fm), variable fluorescence (Fv), the maximum photochemical quantum yield of PSII (Fv/Fm), the area across the fluorescence curve between Fo and Fm (Area), absorbed photons (ABS)/RC—absorption flux per RC, TR0/RC—trapped energy flux per RC, ET0/RC—electron transport flux per RC, DI0/RC—total energy dissipated per reaction center [28]
The pathogen alone (p < 0.01) or in combination with both levels of defoliation (p = 0.04 and p < 0.01) negatively affected the diameters of the root collar, significantly decreasing its width compared to the control (Figure 1, Tables S2 and S3)
Parameters: PI total—the total performance index of photosystem II, Tfm—the time at which the maximum fluorescence value was reached, Fo—the initial fluorescence representing the emission by excited chlorophyll molecules in the antenna structure of the photosystem II, Fm—the maximum fluorescence value, Fv—variable fluorescence, Fv/Fm—maximum photochemical quantum yield of PSII, Area—the area across the fluorescence curve between Fo and Fm, ABS/RC—absorption flux of antenna Chls per RC (RC—reaction center), TR0/RC—trapped energy flux per RC, ET0/RC—electron transport flux per RC, DI0/RC—total energy dissipated per reaction center
Summary
Silver birch (Betula pendula Roth.) is a common deciduous tree species in the temperate and boreal climates of the Northern Hemisphere [1]. Silver birch trees growing in forests by exposing them to different biotic and abiotic stresses that negatively affect tree growth and development [2]. Infections caused by pathogenic fungi are significant biotic factors leading to the phenomenon of birch dieback [3]. Phytophthora species are important plant pathogens that infect many forest, ornamental, and crop plants [4].
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