The dry-air thermotherapy for fruit and berry crop recovery from harmful viruses has become a widely used technology. The method allows virus-free plants to be obtained within one year. The present work examines the heat resistance of pear plants during the recovery from major harmful viruses using dry-air thermotherapy. The method was employed on the pear plants of Belorusskaya Pozdnyaya, Bryanskaya Belitsa, Velesa, Letnyaya Zabava, Zolotoy Vityaz, Aurora, Gera, Chizhovskaya varieties, R-11-9, R-10-3, R-2-4 hybrids and Zagoryevskii rootstock in 2020-2021 at a temperature of 38 °C for 90 days. The recovery was carried out against harmful latent viruses of apple-tree stem pitting (ASGV), apple brown spot (ASPV), chlorosis (ACLSV), apple mosaic virus (ApMV). For thermotherapy, a temperature chamber designed at the FSBO ARHCBAN, having a temperature gradient for root and elevated systems, drip watering, illumination by LED fixtures, was used. The transpiration rate, leaf water content, water loss, water deficiency and recovery of water content were determined. The plant growth parameters of different pear varieties depended on the duration of thermotherapy and varietal features. The Velesa, Zolotoy Vityaz varieties and Zagoryevskii rootstock generated the longest shoots. As compared with winter greenhouse conditions, the transpiration rate decreased 2.1 times, the total water content in leaves increased 1.5 times, the water loss upon heat shock decreased 1.6 times, and the recovery of water content increased 1.8 times. The Bryanskaya Krasavitsa varieties and R-11-9 and R-10-3 hybrids exhibited the highest heat resistance during cultivation in a heat chamber; the Letnyaya Zabava and Zolotoy Vityaz varieties exhibited medium heat resistance; the Belorusskaya Pozdnyaya variety, R-2-4 hybrid and Zagoryevskii rootstock were characterised by low heat resistance. A high positive correlation (r = 0,92) between total water content in leaves and the recovery of water content following heat shock was established. The yield of ASGV, ASPV, ACLSV, ApMV virus-free pear plants in the year following dry-air heat treatment amounted to 83 %.
