boron, a mineral element required in minute quantities for healthy vine growth, and thus called a micronutrient. Boron deficiencies in vines are commonly found where soil acidity and rainfall are high. Boron is required for the movement of sugars and the synthesis of auxins in the plant. A major effect of boron deficiency is poor fruit set caused by the effect on pollen tube growth affecting germination, which can result in substantial reductions in yield. Bunches on boron-deficient vines often have many small berries. A quality gain from having more and smaller berries (see berry size) is possible but this effect, while tantalizing, has not been proven.