COMPARATIVE ASSESSMENT OF PHISIOLOGICAL PARAMETERS AND ANATOMICAL AND MORPHOLOGICAL FEATURES OF LEAVES OF THE GENUS <i>PYRUS </i>L. TO IDENTIFY SOURCES OF ADAPTIVITY TO THE IMPACT OF SUMMER STRESS FACTORS IN BREEDING
In condition of humid subtropical zone of Russia during 2002-2020, the degree of drought resistance of pear varieties and hybrids was assessed by anatomical, morphological and physiological parameters to study their adaptation mechanisms. Research's objects - different genotypes of genus Pyrus L. (varieties: Bere Zhiffar, Vega, Williams, Red Williams, Chernomorskaya Yantarnaya, Yuzhanka, Nektarnaya, Slavyanka, Verbena, Luchistaya, Bere Bosk, Rassvet, hybrid 8520, Kilchu). A set of physiological, anatomical and morphological indicators was used to assess the adaptability of the studied pear varieties to stress factor of the summer period (high temperature and low water-holding). It is established that change in the physiological processes affect the anatomical and morphological structure of the leaf. The assessment of drought resistance of the studied varieties and hybrids by the nature of changes in the parameters of the water regime is given. It was determined that water-holding capacity of the leaf blade in all genotypes has a high inverse dependence (r= -0,77) on the number of stomates on lower epidermis of the leaf. According to quantitative ratio of chlorophylls a and b, the varieties Bere Zhiffar, Bere Bosk and Chernomorskaya Yantarnaya were identified, confirming stability of the pigment system to water deficit at the most arid period. Continuous modification of the photosynthetic function of leaves associated with productivity and viability was noted. It was found that the influence of stressful weather conditions leads to the appearance of such xeromorphic traits in the genotype as increased development of the palisade parenchyma layer and a decrease in the number of stomates per unit surface. Varieties Red Williams, Chernomorskaya Yantarnaya, Vega and Rassvet are identified by the complex of the above characteristics as the most adaptive to the abiotic stress factors of the summer period of humid subtropics. Revealed adaptive features of these varieties allow to use them in breeding as sources of resistance to drought.