Adaptive responses of pear cultivars to low-temperature stress in the spring period.

The pear is one of the most famous pome crops. It occupies about 7 % of the total area of perennial fruit crops in Russia. Orchard plantings are predominantly composed of foreign European cultivars. Spring frosts, which are typical for the southern regions of the country, lead to significant crop losses. This study determined the response characteristics of pear flower buds to low-temperature stress. The Crimean cultivar Dzhankoyskaya Pozdnyaya, two cultivars - Leven and Flamenco - of Krasnodar selection and the interspecific hybrid Kieffer were investigated. Flower buds at different developmental stages were exposed to a climatic chamber for 12 hours at temperatures -1.5…-2 °C. After stress exposure, the activity of certain antioxidant enzymes was determined, along with the content of phenolic compounds, malondialdehyde, and the gene expression level of its enzymes and proteins involved in cold adaptation. It was revealed that the autumn-ripening cultivar Kieffer, under conditions of the Krasnodar region, begins to bloom earlier than other studied cultivars, making it more susceptible to recurrent frosts. This is evidenced by high values of malondialdehyde and the activity level of superoxide dismutase. The Russian cultivars, Leven (winter cultivar) and Flamenco (summer cultivar), showed the highest activity of peroxidase and gene expression of PcDREB2, PcCAP160, PcCOR413, PcPOX1, with a reduced level of malondialdehyde. These cultivars typically emerged from dormancy later compared to Kieffer. The Crimean winter-ripening cultivar was closer to the interspecific hybrid in terms of the studied parameters but showed lower enzyme activity and gene expression levels. The obtained results suggest that under pear cultivation conditions in the southern region of the country, where spring frosts are possible, cultivars with flowering starting in the second-to-third decade of April and high indicators of antioxidant enzyme activity (primarily peroxidase) and gene expression levels of PcDREB2, PcCAP160, and PcCOR413 demonstrate greater resistance.