Analysis of morphophysiological indicators in the leaf apparatus of apple-tree species in the Central Black Earth Region of Russia

Background. Wild species of Malus Mill. and their hybrids are important as genetic sources of disease and pest resistance in the breeding of apple cultivars and clonal rootstocks. Therefore, introduced genotypes should be accompanied by a long-term comprehensive study to assess the effectiveness of acclimatization and the potential for further utilization in breeding programs.

Materials and methods. The study involved 24 apple-tree accessions – wild species and their hybrids. Main morphological and physiological parameters of leaves were analyzed. To assess the degree of variability of the studied indicators, variation coefficients and ratios of the maximum to minimum arithmetic means were calculated.

Results. Significant differences were found in the morphological and physiological parameters of the leaf apparatus. Among the morphological indicators, the leaf index showed the least variability (C_v = 13.2%), while the leaf blade area showed the greatest span (C_v = 32.0%). Highly positive correlations were observed between the corresponding values of the area and linear dimensions of leaf blades (R = 0.72…0.93). During the growing season, the effective quantum yield of photosystem II showed less variability (C_v = 16.5…37.6%) than stomatal conductance (C_v = 37.5…50.1%). No correlations of high and medium levels were found between the photosynthesis and transpiration intensity rates during any of the measurement periods during the growing season. Three apple-tree genotypes demonstrated maximum stability of photosynthesis and transpiration parameters (C_v < 15%): M. niedzwetskyana Dieck (k-29424), M. sylvestris (L.) Mill. (k-6144), and hybrid 14-1 (M. sieboldii × pollen mixture from apple-tree rootstocks).

Conclusion. The leaf apparatus of the studied apple-tree accessions exhibited significant differences in its morphological and physiological indicators. They can be used as marker traits to assess the degree of the species’ heterogeneity.

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