Evaluation of genetic differentiation among healthy and infected Buxus hyrcana with boxwood blight using RAPD and ISSR markers

Abstract

Background: Buxus hyrcana (boxwood) is an endangered species in the Hyrcanian forests in the north of Iran. This tree is threatened by habitat loss but faces additional threats from the introduced disease the boxwood blight (caused by the fungus Calonectria pseudonaviculata syn. Cylindrocladium pseudonaviculatum, Cy. buxicola) and the potential effects of climate change. As wide range of genetic polymorphism is necessary to ensure successful adaptation to rapid climatic changes. Methods: Genetic diversity and differentiation between 15 healthy and 15 infected trees of each of two populations were studied using RAPD and ISSR molecular markers. Results: High-band polymorphism was found in pooled samples of B. hyrcana using both ISSR (58%) and RAPD (73%) markers. The ISSR data and the combined data set classified the trees into two groups. However, data from RAPD clustered the trees into three groups. These results indicate different degrees of genetic variation in the sequences of the tested B. hyrcana genomes targeted by the two marker types used. Genetic variation was found to be relatively high, with most of the diversity occurring within populations. Analyses of healthy versus infected pooled samples based on both marker types indicated that genetic diversity parameters were mostly higher in healthy trees. Conclusions: Boxwood blight has had a major effect on B. hyrcana, killing individual stems quickly especially in dense populations and reducing population size (as observed in all populations). Considerable within-population diversity, and higher genetic variability in healthy trees than infected ones, suggested conservation efforts should focus on survivor trees in each population and consider the establishment of tree reservations. Propagation of plants from seeds is preferred, since it would include the widest range of genetic variation.

Adaptive evolution of chestnut forests to the impact of ink disease in Spain

“…Pathogens encountering susceptible hosts can change the size and genetic structure of tree communities (Agrawal & Stephenson, 1995;Weste et al, 2002), causing a significant drop in gene diversity and triggering multilocus associations in the post-epidemic population (McDonald et al, 1998). Populations with limited phenotypic plasticity and low genetic variation are expected to have difficulty coping with invasive pathogens (Shanjani et al, 2018;Burdon & Laine, 2019). However, little is known about the interplay of evolutionary factors, the impact of invasive pathogens, and the structure of tree populations in shaping the genetic variation and adaptation of susceptible hosts.…”

“…Detection of outlier loci (those with unusually high or low levels of variation and differentiation) is therefore useful to separate genome-wide effects caused by demographic processes from adaptive locus-specific effects (Luikart et al, 2003). Several studies have described adaptive evolution of plant pathogens (e.g., Möller & Stukenbrock, 2017;Sánchez-Vallet et al, 2018), but few have addressed changes in the genetic structure of hosts due to pathogens (Shanjani et al, 2018) or evolution of plant-pathogen interactions (Burdon & Laine, 2019).…”

Consequence of habitat specificity: a rising risk of habitat loss for endemic and sub-endemic woody species under climate change in the Hyrcanian ecoregion

“…Most present-day Buxus hyrcana populations are seriously threatened and devastated by the spread of boxwood blight and box-tree moth (Alipour and Walas 2023;Nacambo et al 2014). Although the genetic diversity in the species currently remains relatively high (Esmaeilnezhad et al 2020;Salehi Shanjani et al 2018), there is a justified concern for the loss of variability, especially if genetic drift becomes a dominant evolutionary force and is accompanied by an observed reduction in population size which are likely to get worse under future climate change. Another possible consequence of the climate-driven range shifts might be increasing sympatry among closely related species, potentially triggering hybridization.…”

The impact of climate change on disease in wild plant populations and communities

“…The strategy that allows natural populations to deal with such consequences has been termed adaptive escape, and depends on the size of the population and the level of genetic variation for quantitative resistance present (Ennos, 2015). Thus, there is considerable benefit in withinpopulation diversity and higher genetic variation in healthy rather than infected trees (Salehi Shanjani et al, 2018; Table 1). The potential for adaptation, for example to increasing temperature, is an important feature that needs further study, especially where there is current niche conservatism across a temperature range as found for the pine wood nematode (Pimentel & Ayres, 2018; Table 1).…”