Studies On The Growth Characteristics And Salt-tolerance Mechanism Of Upland Cotton Under Salinity Stress

The effects of salinity stress on the seed germination, photosynthesis, forming and shedding trendence of squares and bolls, and other agronomic characteristics and fiber quality of upland cotton (G.hirsutum L.) was carried out systematacially in this paper, using two salt-tolerant and one salt-sensitive cultivars as materials. Other characters such as the variation in ingredients and contents of chlorophyll in upland cotton leaves, and the distribution of Na+, K+ and Ca2+ within the plant parts of upland cotton was studied as well, during the stress influenced by salinity, in order to explain the salt-tolerance mechanism of cotton. In addition, the alternaive method to alleviat the harmful effects of salinity stress on cotton was discussed, and the main results are as follows.1. The effects of salinity stress on the growth and development of upland cotton(1)The seed germination: Under condition of 0.5% NaCl, the seed germination of the three upland cotton cultivars was inhibited significantly, germinating biability and germination percentage under stress were significantly lower than that of CK (without stress). There was a significant difference in salt tolerance among the cultivars, according to the germination experiment.(2) The photosynthesis and transpiration: The photosynthesis of the three upland cotton cultivars was inhibited significantly by salinity stress, and the inhibition effects response mainly to the utilization for strength sunlight. The net photosynthesis rate of upland cotton has two peaks as well under salinity stress in one day, but the net photosynthesis rate were not obvious or very low during the peak stage. The effect of salinity stress on the transpiration rate was also greatly, and the transpiration rate was lower significantly and its recoveration was very slowly.(3) Agronomic characteristics and fiber quality: Under condition of salinity stress,the formation of squares number declined significantly, about 40-60% of CKs, and the square shedding rate increased significantly. The net number of spares and bolls per individual plant reached to the peak on July 15 , that was increased before, from July 9th to July 15th, and decreased continually after that day, and reached to a stabilized level of 7~8 squares per plant. Comparing with CK, the total square number per plant decreased significantly. The number of boll, fruiting branch, Sympodials and plant height of individual plant decreased significantly in the condition of salinity stress. Seed cotton yield and lint cotton yield decreased significantly as well. The fiber quality, comparing with its respective CK, the fiber length and yellow chroma of the three cultivars were decreased under salinity stress condition, and the micronaire value was differently among the three cultivars, that of 'ZMS35', which has a higher salt tolerance one to salinity stress, was increased, and it was decreased for 'ZMS07' and 'ZMS41', which were suspective to salinity stress. Fiber strength was great variation among three cultivars, while the fiber uniform had no obvious variation between salinity stress and non- salinity stress.(4) The variation of the chlorophyll content and ingredient: Under the condition of salinity stress, the content of total chlorophyll, chlorophyll-a and chlorophyll-b increased in the first day after treatment with salt, but decreased continually two days after the treatment of salt, and the difference between treatment and non treatment were enlarged gradually. In addition, the value of chlorophyll-b/chlorophyll-a was decreased gradually.2. Ion distribution in cotton plant under salinity stress conditionUnder the condition of salinity stress, K+ content in 'ZMS41' and 'ZMS07', which were susceptive to salinity stress, was decreased significantly in the root but increased 'ZMS35', the salt tolerance cultivar. However, the K+ content in the leaves was decreased in all three cultivars, especially in the leaves of 'ZMS35'. The value of root's K / leave's K was higher than that under the non- salinity stress condition. The Na+ contents were higher in the root and leaves but lower in the flowers greatly under salinity stress than that of CK. Under alinity stress condition, the contents of Ca2+ in leaves, root and flowers were decreased significantly, comparing with that of CK, and that variation indicated that salinity stress could inhibited significantly the absorbility of Ca2+. Under...