Studies On Heterosis Of Lint Yield For The "CMS" System-Derived Hybrid Cotton "Zheza 166" And Its Agronomic Management

The successful development of the cotton hybrid by using a new CMS system in China has highlighted the possibility of a largely increased cotton yield through full utilization of heterosis. The newly released cotton hybrid Zheza 166 proved the advantage in lint yield over its parents as well as the commonly used commercial varieties. However the performance of growth and yield formation for the hybrid varied greatly year and location, indicating that it is imperative to make clear of the physiological characterization of this hybrid in determining the corresponding agronomic. Besides, the comparison of physiological characterization between the hybrid line and its parents as well as the commercial varieties will allow us to make the insight into the mechanisms of heterosis. Accordingly the relevant experiments were conducted in this research, aiming at (1) determining cotton heterosis by comparing the growth and physiological traits between hybrid line and its parents; (2) identifying the growth and physiological responses of hybrid line to different climatic locations and agronomic practices so as to illustrate the stability of heterosis in a wide range of environments; (3) knowing the effect of some agronomic factors on growth and yield formation of hybrid cotton, thus arriving at a desirable management scheme of hybrid cotton production for the particular location. The main results obtained are as follows:1. Two cotton hybrids, produced by CMS system and artificial emasculation, respectively had significant higher plants, which may is principally due to more rapid leaf initiating rate and plant height gain per day during the duration from square formation to early flowering stages as well as more active growth at late stage. Moreover, Zheza 166 is a bit late maturity relative to Simian 3, the conventional cultivar. Therefore the hybrid is likely to become luxury in growth when it is exposed to the environments with high fertility or much fertilizer application, indicating that the practices against the possible luxury growth should be particularly emphasized in the production of the cotton hybrid.2. Although the hybrid cotton, Zheza 166 showed the basically same trend as CCRI 29 and Simian 3 in the dynamics of square appearance and boll setting during the development, but the significant difference existed between them in daily increase of squares and bolls per plant in that Zheda 166 is smaller than Simian 3 at early stage, but the case is just opposite at late stage. At last, Zheza has significant more squares and bolls per plant, indicating that the hybrid is much larger in terms of physiological sink. Moreover, the maximum boll setting time of the hybrid is well fitted to the light and temperature conditions suitable for boll as well as fiber development, which may in part explain the higher lint yield and better fiber quality. The comparison of the hybrid and conventional cultivar in lint yield showed that full realization of yield potential in Zheza 166 is, to great extent dependent on increasing of the bolls before frost season. So it is important to stimulate early growth and square and boll setting by agronomic practices.3. Zheza 166 have higher N and P contents in functional leaves, which is attributed to the better development at late stage. Meanwhile it has higher chlorophyll content and lower intercellular CO2, and more active photochemistry capacity after fully flowering, thus resulting in higher photosynthetic rate, compared with Simian 3 and CCRI 27. It is substantially higher photosynthetic rate that makes Zheza 166 produce more carbohydrates at late growth stage for use in boll and fiber development.4. The optimal plant density in terms of the boll number varied with the locations, and Jinghua, which has higher temperature in growing season than other two locations required lower plant density. Meanwhile, the effect of N application on boll number also differed among locations in that Jinghua required more N fertilizer for more boll production. Zheza 166 had the basically s...