Effects of different seeding dates on pattern of internode length in sorghum variety 'Kazetachi'.

Sorghum (Sorghum bicolor Moench) stems, which have many internodes, are the main organs harvested for feed and biofuel materials. Sorghum reportedly has three types, characterized by individual internode length based on the internode position from base to top: (1) ever-increasing type, with internode length increasing from the base to the top internode; (2) unimodal type, with internode length in approximately the middle internode position that is longer than in lower or upper positions, except at the neck internode of the panicle; (3) bimodal type, for which the internode lengths alternately increases and decreases twice before reaching the peduncle. Sorghum variety 'Kazetachi', an ultralate-maturity variety in Japan with strong lodging tolerance, showed patterns with many peaks. It is a multimodal pattern in internode length. Furthermore, this variety shows large variation in the number of peaks per plant and the internode position with a peak among plants. This report describes internode length pattern analysis of 'Kazetachi' and the assessment of seeding date effects on the pattern. Seeds were sown on 20 May, and 3 and 18 June in 2009 in the northern part of Japan. Internode lengths were measured at harvest in early November. Peaks in the internode length pattern of each plant were 4-7, including both distinct and vague peaks. Pattern analysis using the internode position with a distinct peak contributed to the distinction among patterns on each seeding date. Although internode positions showing a distinct peak differed among patterns of different seeding dates, the period during which the internode with distinct peaks elongated rapidly appeared to be almost identical among them, suggesting that the internode length in 'Kazetachi' is characterized more by environmental factors than by genetic factors.