Study On Boll Formation Characteristics And Their Relationship With Photosynthetic Physiology Of Different Drought Tolerance Cotton Under Limited Drip Irrigation

【Objective】Xinjiang is an important cotton producing area in China,and the shortage of water resources is the main factor limiting the high yield of cotton in Xinjiang.Cultivating and cultivating drought resistant cotton varieties with high yield and quality is an important way to ensure the sustainable and stable development of cotton production.Different varieties of cotton have different water requirements.How to use water regulation to maximize the quality of cotton bolls has become one of the hot issues in cotton cultivation research in China.In this thesis,cotton bolls were used as carriers in the process of variety improvement to explore the changing rules of cotton boll development characteristics,plant photosynthetic physiological characteristics,agronomic traits,etc.related to yield formation in different drought resistant cotton varieties,as well as the response to irrigation volume.The research results are of great significance for high-quality cotton boll formation and guiding the optimal allocation of limited agricultural water resources.【Methods】Six varieties of land cotton（Gossypium hirsutum L.）with different drought tolerance were selected in Xinjiang in the past 30 years and in different years,1990s（90s of last century,hereinafter referred to as 90s）,2000s（00s）and 2010（10s）.The split-zone design is adopted,the main area is drip water treatment,and two treatment levels of limited drip irrigation 3300 m³·hm^-2（W1）and conventional drip irrigation 4800 m³·hm^-2（W2）are set,and the sub-zone is the variety,which is No.1,No.6,No.17,No.22,No.53 and No.74 of Xinlu Zao,numbered（C1-C6）.The effects of drip irrigation on biomass accumulation and distribution,bell-forming characteristics and photosynthetic physiological evolution characteristics of different cotton varieties were systematically studied.The main results are as follows:【Results】1.The response of yield composition and water use efficiency to drip irrigation of different cotton varieties was studied.At 10-50 days after flowering,the bud bell biomass of C6 was 20.1%higher than that of C2 under W1.Among the same cultivars,the leaf and bud bell biomass of C6 decreased by 1.1-60.3%and 5.7-31.5%respectively compared with W2 under W1.The lint yield of C6 was 7.98%lower than that of W2 under W1.With the change of varieties,the output of seed cotton and lint cotton of cotton varieties in different generations showed an increasing trend.Among them,the output of seed cotton and lint cotton of 10s increased by 32.2%,17.2%,42.7%and 16.4%respectively compared with 90 and 00s.The improvement of cotton water use efficiency（WUE）mainly comes from the increase in yield.Under the condition of limited drip irrigation,the water use efficiency increased with the change of varieties.2.The response of bell-forming characteristics and yield to drip irrigation of different cotton varieties was studied.With the advancement of the growth period,the number of bells of each cotton variety showed a trend of first increasing and then decreasing,and the effects of different water treatments on the number of bells of each cotton variety were all W2>W1.Under W1 treatment,the number of bells in cotton decreased40-50 days after flowering,the drop-off rate increased,the drop-off rate of C1 increased significantly by31.9%compared with C5,and the distribution rate of C5 shell between the two varieties was lower than that of C6.The correlation analysis of bell-forming characteristics and yield showed that 50 days after flowering,the yield was positively correlated with the number of bells,and negatively correlated with the shedding rate.The correlation analysis of bell-forming characteristics and water use efficiency showed that there was a significant positive correlation between bell shedding rate and water use efficiency 20 and 30 days after flowering,and a significant positive correlation between bell width and bell number and water use efficiency20 and 50 days after flowering.3.The responses of gas exchange parameters,photosynthetic leaf area and chlorophyll content to drip irrigation of different drought-tolerant cotton varieties were studied.Under W1 treatment,the net photosynthetic rate of the main stems and leaves of each cotton variety was lower than that of W2 treatment10-50 days after flowering,and the average Pn of C6 was 22.0%,25.3%,14.4%and 20.0%higher than that of C5 and C4 at 40 and 50 days after flowering.Under W1 treatment,there was no significant difference in Y（II）of different generations after flowering 50 days.Under W2 treatment,Y（II）of different generations showed C6>C4>C5>C2>C1>C3 50 days after flowering.During the process of variety replacement,the chlorophyll content of the main stem of cotton showed a clear trend of increase.The Pn of the main stem leaves showed a trend of increasing first and then decreasing 10-50 days after flowering,with the average Pn of the C6 cultivars being the highest.The primary light energy conversion efficiency（Fv/Fm）of 10S cultivars is relatively high 20-40 days after flowering.The correlation analysis between photosynthetic physiology and bell-forming characteristics showed that the bell-forming number was positively correlated with the net photosynthetic rate（Pn）and photosystem Y（II）.Therefore,under the condition of limited drip irrigation,the high net photosynthetic rate,chlorophyll content and photosynthetic leaf area in the growth period during variety replacement can ensure that the photosynthetic capacity is maintained at a high level,which is conducive to the synthesis and transport of leaf photosynthetic products,and lays a physiological foundation for the increase of yield.【Conclusion】There was no significant difference in the yield of cotton lint between the two drip irrigation treatments,and the water use efficiency of each cotton variety increased under the limited drip irrigation treatment.The yield of seed cotton and lint cotton of various cotton varieties showed an increasing trend with the replacement of varieties,among which,the yield of seed cotton and lint cotton of 10s and two cotton varieties increased by 32.2%,17.2%,42.7%and 16.4%compared with 90 and 00s.The correlation analysis between yield and bell-forming characteristics showed that there was a significant positive correlation between yield and bell number,and the correlation analysis between bell-forming characteristics and photosynthetic physiological indexes showed that the bell-forming number was positively correlated with net photosynthetic rate（Pn）and photosystem Y（II）.It shows that the increase of yield depends on the increase of the number of bells,and the development of cotton bolls through the influence of photosynthetic sources,from the perspective of the components of cotton boll,the decrease of dry weight of cotton bolls is mainly due to the decrease of the dry weight of the bell shell,with the replacement of varieties,the dry weight of the bell shell of the 10s variety is lower than that of other years,and the dry weight of fiber and cottonseed shows an increasing trend,while the 10s variety maintains a higher Pn,so that more photosynthetic products are transported to the boll,thereby increasing the cotton yield.