Analysis of Elongation and Thickening of Internodes in Sweet Sorghum (Sorghum bicolor Moench)

An early-maturing cultivar Sucrosorgo 301 (S301) and a late-maturing cultivar Sucrosorgo 405 (S405) were grown in low population (LP: 100cm between rows, 50cm within rows) and high population (HP: 50cm between rows, 20cm within rows). At the early stage, plant length was longer in HP than in LP, though at harvest time it was longer in LP. The lowest ‘elongated internode (≧ 1cm)’ of S301 was the 6th internode (IN6) and that of S405 was IN7. In both cultivars, an elongated internode at the lower part of stem was longer in HP than in LP, while that at upper part was shorter in HP than in LP. The internode diameter was consistently larger in LP than in HP. To analyze the internode growth pattern, the position of a fully expanded leaf on the stem was used for counting plant age (AL): for instance, the plant age for just expanded 10th leaf (L10) was defined as ALIO. A conceptional growth curve of internode elongation was drawn based on IN9~IN12 elongation pattern. IN (n) (n: natural number) rapidly elongated at AL (n + 2) and reached its maximum size at AL (n + 3)~AL (n + 4). Plant density affected the rate of internode elongation. The internode thickening pattern was expressed by two different growth curves. Thickening of IN (n) was not affected by the plant density until AL (n). INn reached a maximum diameter at AL (n + 5) in LP and at AL (n + 2) in HP. So the diameter of IN (n) in LP was larger.