Boron and Cytokinin Combinations Modulate Shoot Tip Necrosis and Improve Subculture Efficiency in Grapevine Micropropagation

This study was conducted to determine the effects of different combinations of BAP (6-Benzylaminopurine) and boric acid (H₃BO₃) on the morphological development during the initial and first subculture stages of the Ekşi Kara grape cultivar under in vitro conditions. The evaluated parameters included shoot formation rate, number of shoots per explant, shoot length, fresh shoot weight, leaf area, number of nodes, and shoot tip necrosis. The findings indicated that BAP applications had notable effects particularly on shoot formation, shoot length, and fresh shoot weight. The highest fresh shoot weight (2.934 g) was obtained from the combination of 1.0 mg/L BAP and 1.18 mg/L boric acid, which also led to the formation of multiple shoots (6 shoots per explant). PCA analysis revealed a strong association between this treatment and the parameters representing shoot development. While boric acid alone had limited influence, its effectiveness increased when combined with appropriate BAP doses. The results suggest that specific combinations of plant growth regulators and micronutrients may enhance morphological development during the in vitro propagation process.