Kiwifruit reserves: balancing vine growth and fruit productivity

Storage of large amounts of carbohydrate in the fruit, roots and wood during summer and autumn is vital to produce both high-quality kiwifruit and also to support vine development in the following season. Our study showed that new shoot growth of 'Hayward' vines occurs during the first 100 days after budbreak (DAB) in spring. During this period, vine reserves became depleted, with total carbohydrate concentrations in both roots and wood decreasing by 3-fold and root death occurring in late spring. Although shoots became autotrophic by 30-40 DAB, the concentrations of reserves continued to decline until the end of shoot growth, indicating that insufficient carbohydrate was available from photosynthesis to support the growth and metabolism of the rest of the vine before the end of shoot growth. Once the canopy was established and fruit set had occurred, photosynthate supply was shared between storage in roots and wood, current season's cane and root growth, as well as in fruit development over the remainder of the season. If the supply of carbohydrate was altered or the balance changed during this period, fruit quality, as well as flower production and shoot growth in the following season, was affected. Hence, it is essential to balance vine growth, fruit development and reserve storage to achieve consistent yields of high-quality kiwifruit.