EFFECT OF PLANTING DATE AND CULTIVAR ON SENESCENCE IN SWEET CORN

Tissue senescence represents physical and physiological changes in sweet corn (Zea mays var. rugosa Bonaf . ) . Senescence rates in supersweet corn are not well known, nor are the factors which contribute to senescence, Standard (su), supersweet (sh2), and sugary enhancer (se, a homozygous and heterozygous genotype) cultivars were sown on 31 March, 14 and 28 April, and 12 May 1992, and 2, 16 and 30 April, and 14 May 1993. Senescence rates of stalk and shank internodes and cobs were determined at fresh market harvest. Senescence rate increased up through the stalk internodes. In 1992, 'Merit' (su) generally had the highest stalk internode senescence ratings, but 'D'Artagnan' (se, heterozygous) had the highest shank internode senescence ratings. In 1993, 'Florida Staysweet' (sh2) and 'Zenith' (sh2) had the lowest stalk senescence ratings, and 'Incredible' (se, homozygous) the highest shank senescence ratings. Cobs were almost completely senescent in both years. Plants sown at the first (1992) or first and second (1993) planting dates had the lowest stalk and shank internode senescence ratings. Understanding senescence could increase the knowledge of metabolism and development in sweet corn.