Assessment of the vital condition of trees
The evaluation of the vital state of the studied populations of
R. pseudoacacia was conducted according to the method of Nikolaevsky, which allows determining the condition of aboveground shoots, leaf blades and the plant photosynthetic apparatus (Fig 1). The analysis of the vital state showed that individuals from the RPP population scored 39.5 points, corresponding to a good vital state. Individuals from the RPK population had a satisfactory vital state. The high scores of vital state in the RPP population were due to a greater number of living branches in the tree crowns, better foliage in the crowns, a larger number of living leaves and a larger leaf area (Fig 1A, 1B).
A decrease in the vital state of plants in the RPK population was noted due to a significant decrease in foliage coverage by 4-6 points (p<0.05, n = 30) and the number of living leaves in the tree crown by 5.5-6 points (Fig 1C). The parameter of the amount of living leaf area also showed a significant decrease for plants from the RPK population by 1.2-1.5 points, compared to this parameter for plants from the RPP population (p<0.05, n = 30) (Fig 1C). This indicates the presence of a morpho-physiological adaptation strategy elements for plants growing in arid conditions. The total viability score of RPP population individuals of R. pseudoacacia was 39.5, which is 3.5 points higher than in the RPK population (p<0.05, n = 30) (Fig 1D).
ISSR-screening
To identify the intraspecific genetic diversity of
R. pseudoacacia, 18 ISSR primers were tested in both populations. As a result of the testing, 6 ISSR primers were selected for their high efficiency in amplifying a larger number of genomic DNA fragments (Table 2).
During the analysis, ISSR primer UBC808 showed differences in locus polymorphism between the two
R. pseudoacacia populations. The other 5 primers, UBC818, UBC823, UBC826, UBC857, UBC860, had similar polymorphic loci ranging from 20% to 45.5%. DNA marking of the first and second population using selected ISSR primers allowed for the identification of 33 amplified genomic DNA fragments, 14 of which were polymorphic. The number of amplified fragments varied from 3 to 11 depending on the primer. The size of the fragments ranged from 125 to 1250 bp. The highest number of identified fragments was observed with primer UBC826. The remaining 12 primers did not amplify with the samples of isolated genomic DNA and were therefore excluded from further research. For a more detailed evaluation of the effectiveness of the used ISSR primers, the frequency of occurrence of each locus was evaluated in two populations of
R. pseudoacacia, obtained through electrophoresis of amplicons (Table 3). Each analyzed locus of ISSR marker formed a specific spectrum of amplification products in each individual of
R. pseudoacacia in the populations (Fig 2).
Based on the obtained amplicon spectra shown in Fig 1, binary matrices were compiled for further mathematical processing in POPGENE to evaluate the genetic diversity in two populations of
R. pseudoacacia growing in different territories. The results of the evaluation of genetic variability parameters are presented in Table 4.
In population RPK, the average absolute number of alleles and effective number of alleles per locus were higher by 4% compared to population RPP, indicating greater individuality in genetic structure. We also observed a 12% decrease in the N
e parameter compared to N
a in both populations. The results of genetic distance evaluation according to Nei showed that the two populations have high genetic similarity. The Shannon index showed low values for both populations, indicating low inter-population diversity, while the proportion of polymorphic loci was higher in the RPK population at 72%.
Thus, 6 of the 18 primers tested are suitable for the analysis of
R. pseudoacacia DNA polymorphism, since they can be used to identify a large number of loci and evaluate their polymorphism
(Guo et al., 2006). Only 30% of the primers showed effective performance. This may indicate high intraspecific polymorphism in the genetic structure of
R. pseudoacacia. Comparative analysis of multi-locus spectra of amplified products of the studied markers in populations revealed high genetic similarity among individuals. However, plants growing in more arid conditions showed a higher degree of polymorphism, potentially enhancing their survival
(Shaban et al., 2022). At the same time, there is evidence that less adapted genotypes are eliminated under the pressure of stress factors
(Mollashahi et al., 2023). The growing conditions for the first populations of
R. pseudoacacia, growing at a higher geographical point on the Ergeninskaya Upland, were more arid and therefore the vital state was worse than that of the second population.
The features of the relief of the Ergeninskaya Upland have influenced the formation of specific habitat conditions (
Melikhova, 2022), which in turn have contributed to the formation of populations of various tree and shrub species with different degrees of genetic polymorphism. The research confirms the theory that plants with higher genetic polymorphism are more resilient and capable of surviving in arid conditions. Therefore, it is promising to use more genetically polymorphic individuals in populations for selection of tree and shrub species, especially
R. pseudoacacia, to solve the problems of agroforestry and protective afforestation in areas with arid climates.