Specific nature of the integrative (complex) effect of environmental factors on hazelnut cultivars in the Russian humid subtropics

Corylus pontica K. Koch is a valuable nut crop. The expediency of the crop’s large-scale cultivation calls for measuring the parameters of agroclimatic indicators, ranging in variability, intensity, and duration of their impact. Environmental factors were assessed using phenological techniques based on recording the flowering and fruiting dates, recognized as the function demonstrating the complex effect of these factors on the hazelnut yield throughout the crop’s perennial cycle. Climate change urges the selection of adaptable cultivars for such areas where limiting factors are turning into stressors. Dependence of hazel cultivars on climate indicators (air temperature and humidity, and total precipitation) was observed in the phases of harvest formation. The crop’s genotypic diversity contributed to the specific nature of the complex effect produced by environmental factors. Peculiar responses of hazel plants to weather conditions in both flowering and fruiting phases were instigated by the biology of their development. Flowering started in January and depended on air temperature and humidity. Fruiting was affected by air temperatures and precipitation amounts (in July/August). Dependencies between yield and weather were well expressed, with module values of 0.86–1.0 (p < 0.05). The effect size of limiting factors is better measured with the coefficient of determination (%), a direct indicator of the correlations between harvest and weather factors. Flowering (I–III) under unpredictable conditions is regarded as a “critical” stage in the ontogenesis of hazel trees. No less critical is the fruiting phase, occurring simultaneously with the setting and differentiation of generative organs for the next year’s yield. Registration of limiting factors and their variations over the perennial plant cycle made it possible to recommend cvs. ‘Cherkesskiy-2’, ‘Anastasiya’, ‘Kristina’ and ‘Viktoriya’ as adaptable to the subtropics of Krasnodar Territory