Carbon partitioning in the boll plays an important role in fiber quality in colored cotton

Assays were conducted to examine the photosynthesis of stem leaves and subtending leaves of cotton bolls, the fiber-quality parameters length, strength and micronaire, and dry matter accumulation in fibers, seeds and burs during fiber development in the colored cotton cultivars ZX-1 and G-7 and the white cotton cultivar LMY28. The results showed that fiber-quality parameters were all lower in ZX-1 and G-7 than in LMY28. The final dry weight of fiber was significantly lower in ZX-1 and G-7 than in LMY28, whereas the final dry weights of the seed and bur were both significantly higher. The seed harvest index was significantly lower in ZX-1 and G-7 than in LMY28 after 35 days post anthesis, when the seed harvest index decreased in colored cotton and increased in white cotton. These results indicated that the differential carbon partitioning in the boll was a key factor that resulted in poor fiber-quality parameters length and strength in colored cotton. Further, the time required for rapid dry matter accumulation (T) and the maximum speed of fiber thickening (V_m) were both significantly lower in ZX-1 and G-7 than in LMY28 for fiber strength, and the maximum speed of dry matter accumulation (V_m) differed significantly for the dry matter accumulation in the fiber, seed and bur between colored cotton and white cotton. These results show that V_m is a key factor for dry matter accumulation in the fiber, seed and bur, as well as for fiber strength.