Boron Deficiency in Tea
The first sign of boron deficiency is the restriction in growth of the terminal bud, which becomes dormant. The leaves become dark green, thick and leathery, and they are frequently misshapen and crinkled. The growing point ultimately dies and, as a result of the loss of apical dominance, many axillary buds try to grow but these also die back if boron is in short supply. Clusters of small shoots fill the upper axils after a succession of abortive attempts at shooting. Translucent oil spots on the lower surface of mature leaves have also been reported but such spots do not persist. As the deficiency progresses excess cork develops—first on the upper side of the petiole, but later extending to the main and lateral veins outlining them with a corky streak on both upper and lower surfaces. The veins crack as the cork develops. Corky streaks may develop on the stem rather like elongated lenticels.