Genotypic Differences In The Changing Of The Matters Involved In Cotton Fiber Thickening Development And Its Relationship To Fiber Strength

The secondary wall thickening stage is a key period for cotton fiber strengthformation. Physiological properties of cotton fiber thickening development determinefiber strength formation. In this study, we chose cotton cultivars with great differencein yield and fiber strength for the field experiments carried out in Nanjing, JiangsuProvince (cotton belts in lower basin of the Yangtze River) in 2004 and 2005. Thestudy focused on: (1) C/N ratio variability in the leaf subtending cotton boll and itsrelationship to cotton boll dry matter accumulation and distribution; (2) Genotypicdifferences in the changing of the matters (soluble sugar, sucrose,β-1,3-glucan andcellulose) involved in cotton fiber thickening development and its relationship to fiberstrength formation; (3) Genotypic differences in the changing of the matters involvedin cotton fiber thickening development and its relationship to fiber strength formationin cotton seasonal bolls. The main results were as follows:1. C/N ratio variability in the leaf subtending cotton boll and its relationship tocotton boll dry matter accumulation and distributionThe C/N ratio dynamic changes in the leaf subtending cotton boll could besimulated with quadratic: y=at~2+bt+c (y stands for the C/N ratio and t stands for bollage (d)). Correlation analysis indicated that the main eigenvalues of the C/N ratiodynamic change had fearfully significant correlation relationships with dry matterweight per boll (sum of boll shell, seed and fiber dry matter weight per boll) and bollweight, but not with lint percentage and boll shell percentage. The dynamic change ofC/N ratio in the leaf subtending cotton boll could be clustered into 3 type: (1) TheC/N ratio changed very gently and always stayed near 2.0 during whole boll age. Theboll dry matter accumulation went through the shortest speedy rising period with thehighest velocity, which resulted in the lowest final dry matter weight per boll and bollweight. (2) The C/N ratio declined dramatically from 6.0 during the period from 10thto 17th day of boll age and stayed around 2.5 after the 24th day of boll age. During thewhole boll age, it had an extraordinary wide varying range and a high average value. The boll dry matter accumulation went through the longest speedy increasing periodwith the lowest velocity, which resulted in the highest final dry matter weight per bolland boll weight. (3) The C/N ratio was not significantly different from the one in (2)after the 24th day of boll age, but much lower before then, and the final dry matterweight per boll and boll weight were all lower than the ones in (2). No significantdifference was detected in dry matter distribution in each part of cotton boll amongthe three groups, and no notable relationship was observed between the final lintpercentage, as well as the lint yield, and the characters of the C/N ratio in the leafsubtending cotton boll.2. Genotypic differences in the changing of the matters involved in cotton fiberthickening development and its relationship to fiber strength formationSoluble sugar, sucrose,β-1,3-glucan and cellulose in cotton fiber all correlated withfiber thickening development tightly. Compared with the fiber of middle and lowstrength fiber genotype cotton, the fiber of high strength fiber genotype cotton hadhigher soluble sugar and sucrose contents at 10th day of boll age, lower ones beforeboll opening, which resulted in higher soluble sugar and sucrose transformed ratesduring whole boll age, and higher sucrose content increment during the period from24th day to 31th day of boll age. At the same time, it had a remarkable higher peakvalue ofβ-1,3-glucan content at the very beginning of secondary wall thickeningfollowed by a sharp drop to a very low level. The dynamic change characters ofsoluble sugar, sucrose andβ-1,3-glucan content in the fiber of high stength fibergenotype cotton optimized cellulose accumulation process: a longer period taking forcellulose speedy accumulation and a tempered rate in cellulose deposition, and it wasbeneficial to high strength fiber formation. Genotypic differences in dynamic changesof soluble sugar, sucrose andβ-1,3-glucan contents cause the differences in celluloseaccumulation characters and lead to the genotypic variation in cotton fiber strengtheventually.3. Genotypic differences in the changing of the matters involved in cotton fiberthickening development and its relationship to fiber strength formation in cottonseasonal bollsThere were significant genotypic differences in the dynamic changes of solublesugar, sucrose andβ-1,3-glucan contents in pre-summer boll and summer boll fiber, which resulted in the genotypic differences in pre-summer boll and summer boll fiberstrength. For pre-summer boll and summer boll, the fiber of high strength fibergenotype cotton had higher soluble sugar and sucrose transformed rates during wholeboll age, at the same time, it had a remarkable higher peak value inβ-1,3-glucancontent at the very beginning of secondary wall thickening followed by a sharp dropto a very low level. The cellulose accumulation process was tempered and the finalfiber strength was higher. Phenomenons observed in the fiber of low strength fibergenotype cotton were opposite. In early autumn boll and late autumn boll, there wasno significant genotypic difference in the dynamic changes of soluble sugar andsucrose content, cellulose accumulation and the dynamic change of fiber strength,however, the genotypic differences in the dynamic change ofβ-1,3-glucan contentwere still observed, it might be one of the reasons for early autumn boll and lateautumn boll fiber strength genotypic difference formation.In conclusion, the genotypic difference in the dynamic change of the leafsubtending cotton boll C/N ratio is significant, it affects on cotton boll dry matteraccumulation. The C/N ratio declined dramatically from a high level during theperiod from 10th to 17th day of boll age and remained at a higher level after the 24thday of boll age is beneficial to cotton boll dry matter accumulation. The characters ofsoluble sugar, sucrose andβ-1,3-glucan content dynamic changes during cotton fiberthickening development affect on cellulose accumulation character and play animportant role in cotton fiber strength formation. Genotypic differences in thedynamic changes of soluble sugar, sucrose andβ-1,3-glucan contents duringpre-summer boll and summer boll fiber thickening development are significant, theyare the primary reason for genotypic difference in the fiber strength of pre-summerboll and summer boll. But for early autumn boll and late autumn boll fiber, there wasno significant genotypic difference in the dynamic changes of soluble sugar andsucrose content, cellulose accumulation and the dynamic changes of fiber strength,the genotypic differences inβ-1,3-glucan content dynamic change maybe one of thereasons resulting in fiber strength genotypic difference of early autumn boll and lateautumn boll.