GENETIC VARIATION IN DROUGHT RESPONSE OF CASTANEA SATIVA MILL. SEEDLINGS

Seedlings from eight families in each of six populations of Castanea sativa were exposed to well watered or periodic drought conditions at 25 and 32°C. The six populations originated from sites in Greece, Italy and Spain contrasting with respect to water availability during the growth period. The seedlings were grown for 14 weeks in growth chambers. Juvenile growth traits and carbon isotope discrimination (Δ) were analysed. The latter provides a reliable approximation of water-use efficiency in C₃ plants. The Spanish Coruna population showed the best growth with an average height of 66 cm in the well-watered treatment at 32°C. Both the population and the family effects were strongly significant for the growth traits with heritabilities in the range 0.45-0.59. The heritability for Δ was slightly lower 0.31±0.07. Across Europe C. sativa populations displayed limited, however significant Δ variability, and thereby genetic variation in adaptedness to drought. There was a negative relationship between growth traits and the xerothermic index at the origin of the populations in all four treatments while there was a positive relationship between Δ and the xerothermic index. There was a positive relationship between Δ phenotypic plasticity and the xerothermic index. The genetic correlations between Δ and growth traits were all negative and especially strong in the 32°C drought treatment. The population differences in the studied juvenile traits call for inclusion of populations originating from environments with a broad span of xerothermic indices in the gene conservation of sweet chestnut.