Abstract:  Xinjiang, as the largest cotton producing?area in China, often suffer from low temperature meteorological disasters such as “late spring cold” in cultivation, which leads to different degrees of rotten seeds, rotten buds and dead seedlings every year, resulting in “difficult emergence and seedling protection”, affecting cotton growth and development and yield and quality formation. With the development of seed coating technology, the above problems of “difficult emergence and seedling protection” in cotton field in normal years have been effectively solved by coating cotton seeds with seed coating formulation. However, it is still difficult to ensure a high rate of seedling conservation in the field in the year with serious low temperature damage, so it is urgent to study new technologies and products to improve the low temperature tolerance of cotton seedling. In addition, carboxin is a succinate dehydrogenase inhibitor fungicide, which has the function of internal absorption and conduction in the plant. Its mechanism is mainly to inhibit the activity of succinate dehydrogenase of pathogenic bacteria, result to interfere with its respiration, hinder energy metabolism, inhibit the growth of pathogenic bacteria, and cause its death, so as to achieve the purpose of disease control. Recent studies have shown that the treatment with carboxin coating plays a major role in control on cotton seedling damping-off?disease, and can promote the growth of cotton, and can also enhance the ability of the field cotton seedlings to tolerante cold stress. But, it is not clear about the effect of carboxin on the germination of cotton seeds, especially the effect of carboxin on the germination characteristics of cotton seeds under low temperature stress. Therefore, in order to reduce the influence of low temperature stress on the germination ability of cotton seeds, the effects of the carboxin from seed coating formulation on the cotton seed germination characteristics under low temperature stress was explored. In this study, ‘Xinluzao 50’ cotton seeds coated with six gradients of carboxin, which were 0 (inert component only), 4.2%, 5.7%, 7.2%, 8.7% and 10.2%, were sown in plastic boxes with sand and were exposed to four temperature treatments at 25℃, 18℃, 15℃ and 12℃.The uncoated cotton seeds exposed to the same temperature treatments served as the control group (CK). Sand?culture?was?adopted?to?study?the effect of carboxin on the germination and dry matter transfer of cotton seeds under low temperature stress to explore the effect of carboxin on improving the cold resistance of cotton. The results showed that the germination index of cotton seed uncoated was the highest under normal temperature (25℃), and the germination rate was 80.5%. The germination index of cotton seed uncoated decreased with the decrease of temperature, which indicated that the germination index of cotton seed was seriously affected by low temperature stress, while the germination index of cotton seed coated with carboxin was the highest under normal temperature (25℃), and the germination rate was 96.0%. With the decrease of temperature, the germination indices of all treatments with coating with carboxin decreased slowly, which indicated that carboxin could obviously alleviate the damage of low temperature stress on seed germination.Under the same temperature, with the increase of the content of carboxin in seed coating agent, the other indices increased first and then decreased, except the respiratory consumption of seeds decreased first and then increased. The germination process of cotton seeds coating with carboxin was 2?4 days earlier than that in the treatment of seed uncoated and seed coating without carboxin; the seed vigor and growth of the treatment without carboxin was lower, and the fresh weight was significantly reduced, resulting in the dry matter accumulation was also significantly reduced; the average adversity resistance coefficient of the treatment uncoated cotton seeds and without carboxin coated cotton seeds was only 0.68 and 0.70, respectively, while that of the treatment with carboxin was 0.73?0.91. Our results showed that carboxin could enhance the seed vigor, advance the germination process, increase the germination rate and promote the growth of seedlings, and enhance the ability of seedlings to resist damage from the low-temperature climate during the germination period of cotton.

Key words:  Carboxin, Germination rate, Germination index, Vigor index, Adversity resistance coefficient, Dry matter conversion efficiency, Cotton, Seed germination, Low temperature stress.