Genetic variation in height, diameter and second flushing in four-year old maritime pine progeny tests in Türkiye

A maritime pine (Pinus pinaster Ait.) breeding program was initiated in Türkiye by selecting plus trees from plantations across the country. Quantifying genetic variation in growth traits is essential for this program. Four-year old trees from 140 open-pollinated maritime pine families were assessed for height (HT), root collar diameter (D) and number of shoots in the fourth growing season (S) in three progeny test plantations (Kefken, Gebze and Çatalca) in northwest Türkiye. Growth was greater in Kefken, followed by Gebze and Çatalca. Both individual tree (h_i²) and family mean (h_f²) heritability estimates were greatest for HT (h_i²=0.22 and h_f² =0.77) followed by D (0.16 and 0.59) and S (0.08 and 0.45). While genetic correlation between HT and D was strong (r_A=0.72), S was correlated moderately with HT (0.56) and weakly with D (0.11). Genotype × environment interaction was significant only for D. While modest genetic gains (up to 15.20 % over the average of family means) from selections at age four seem possible for growth, changes in patterns of genetic variation and interrelationships among the traits as the trees age remains to be explored in the future.