Relationship between nitrate ion concentrations in petiole juice measured by the handy reflecting photometer and vine growth and fruit quality of 'Kyoho' grapes [Vitis]

To determine the relationship between NIC (nitrate ion concentration in petiole juice) and fruit quality, sampling conditions of the petioles were investigated in 'Kyoho' grapes with a long-pruning system for seeded berry production. The results indicated that the average NIC should be determined using 3 petioles near the first spike from 5-7 shoots 45-60 cm-long obtained between 10:00 am and 1:00 pm. The NIC determined by the above conditions showed a significant negative correlation with sugar concentration in the fruit at harvest. Two other indices, SHT (length of current shoot at distal position of lateral branch) and BUD (percentage of sprouting buds on a mother shoot) were also established. When the relationships between these 3 indices and fruit quality were studied at harvest, high quality fruits with sufficient enlargement, high sugar content and low acid content were often produced by vines showing low NIC, long SHT and high BUD. The indices presented here will be useful for producing high quality fruit in 'Kyoho' grape culture.