ONTOGENY AND SULFUR FERTILITY AFFECT LEAF SULFUR IN SHORT-DAY ONIONS

Five short-day onion (Allium cepa L.) cultivars grow?l with high (4.0 meg S/liter) and low (0.1 meg S/liter) S fertility were evaluated for ontogenetic changes in leaf S concentration and the association between leaf S concentration and final bulb pungency as reflected by pyruvate formation. Cultivars differed in leaf S concentration at each of eight sampling dates during growth and development, but the pattern of leaf S accumulation among cultivars was similar. Leaf S concentration increased during early plant development while in a nonbulbing photoperiod, but decreased as bulbing progressed to maturity with high and low S fertility. The decline in leaf S concentration during bulbing was more severe with low than with high S fertility. Leaves that were left to dry on the mature bulb lost most of their S, especially with 0.1 meg S/liter, a result that could have implications in final bulb flavor intensity. Correlations generally were poor between leaf and final bulb S concentration or pungency.