Changes in C/N Ratio of Subtending Leaf of Cotton Boll and Its Relationship with Cotton Boll Dry Matter Accumulation and Distribution

Fourteen cotton (Gossypium hirsutum L.) cultivars differing in yield were used to study the C/N ratio in the subtending leaf of cotton boll and its effect on boll dry matter accumulation and distribution. The 14 cultivars were clustered into 3 groups according to different changing patterns of C/N ratio in the subtending leaf of cotton boll. There were significant differences in dynamic changes of the C/N ratio and dry weight per boll among the 3 groups. Group III show much higher C/N ratio than Groups I and II from 10 to 17 d of boll age, and it maintained the C/N ratio of approximately 2.5 after 24 d of boll age. Group III also showed the widest changing range and the highest average values during the whole boll development. The boll dry matter accumulation of Group III took the longest time period and the lowest accumulating rate, which resulted in the highest final dry weight per boll and boll weight. The distributions of dry matter in cotton boll (percentages of boll-shell, seed, and lint) were not significantly different among the 3 groups. The C/N ratio in the subtending leaf of boll had no correlation to lint percentage and lint yield. The results indicated that the dynamics of the C/N ratio in the subtending leaf of cotton boll are significantly different among genotypes. A favorable pattern for dry matter accumulation in cotton boll is the sharp decrease in C/N ratio from 10 to 17 d of boll age, which is maintained at a relatively higher level after 24 d of boll age.