Physiological Characteristics Comparison Of Cotton Varieties With Different Sensitivity To Defoliant

【Objective】Cotton is one of the most important economic crops in the world and plays an important role in the economic development of China and the world.Due to its unique natural ecological conditions and resources,Xinjiang has become the largest commercial cotton producing area in China.It is not only the strategic demand of national economic development,but also an important industrial support for long-term stability of Xinjiang.In recent years,with the increasingly serious problems such as lack of rural labour and the rise in labor cost in China,mechanical picking has become the development trend of cotton production.Defoliation is important for mechanical picking.Chemical defoliation with defoliants can promote most of the leaves of cotton plants to fall off,reduce the trash content of mechanically harvested unginned cotton,and decrease the pollution of cotton fibers caused by cotton leaves.The defoliation effect directly affects the quality of cotton harvest.The defoliation effect is not only related to the defoliants type,weather conditions and spraying methods,but also related to cotton varieties.After spraying the same concentration and dosage of defoliant,the defoliation speed and effect of different varieties are different.In order to clarify the response of different varieties to defoliants,4 varieties with different sensitivity to defoliant were used as materials.After spraying defoliant,cotton defoliation rate and several physiological indexes were analyzed and compared,providing a basis for screening and cultivating defoliant-sensitive machine-picked cotton varieties.【Method】Four varieties of Shida 5203,Xinluzao 61,153 and 44-07 with different sensitivity to defoliant were sprayed with 10 m L/mu of thiabene·diuron(the main component was 36% thidiazuron and18% diuron)at the seedling and boll opening stage,respectively.On the 3rd,6th and 9th days after defoliation treatment,the defoliation rate of cotton leaves was measured,the formation of petiole abscission layer was observed,and the sensitivity of different cotton varieties to defoliants was analyzed.Shida 5203 and 153 were selected and sprayed with thiabene·diuron at seedling stage(10m L/mu)and boll opening stage(10m L/mu and 15 m L/mu).On the 3rd,6th and 9th days after defoliation treatment,the total chlorophyll content,chlorophyll a content,protective enzymes(SOD and POD)activity,MDA,ABA and IAA content in cotton leaves were measured to compare and the differences of above physiological indexes between two varieties.【Results and Conclusions】1.The defoliation investigation results showed that Shida 5203,Xinluzao 61,153 and 44-07 had different degrees of defoliation after defoliation treatment.Among them,Shida 5203 and Xinluzao showed obvious defoliation,but 153 and 44-07 did not.On the 3rd,6th and 9th days after defoliation treatment,the defoliation rates of Shida 5203 and Xinluzao 61 were higher than those of 153 and 44-07.Shida 5203 had the highest defoliation rate,and 153 had the lowest.It was found that Shida 5203 and Xinluzao 61 formed abscission layer early at both seeding and boll opening stages,and 153 formed abscission layer the latest among four varieties at boll opening stage.The results showed that defoliation treatment could promote cotton leaf defoliation.Compared with 153 and 44-07,Shida 5203 and Xinluzao 61 were more sensitive to defoliant.Among the four varieties,Shida 5203 was the most sensitive variety to defoliant and 153 was the most insensitive.2.After defoliation treatment with 10 m L/mu of thiabene·diuron at seedling stage,the Pn,Gs,Tr and the content of chlorophyll a,total chlorophyll and IAA decreased significantly,and MDA,ABA content and SOD,POD enzymes activity significantly increased in leaves of Shida 5203 and 153 compared to the control,indicating that the defoliation treatment damaged cotton leaves,destroyed the photosynthetic system,and disrupted the hormones balance.Compared with the insensitive variety 153,the Pn,Gs,Tr and the content of chlorophyll a,total chlorophyll and IAA in the sensitive variety 5203 decreased more significantly,while the content of MDA,ABA and the SOD,POD enzymes activity increased more significantly,indicating that the leaves of sensitive variety were damaged greatly,produced less protective enzymes SOD and POD to resist external aggression,and less IAA and more ABA to promote leaf defoliation.The content of chlorophyll a,total chlorophyll,MDA,IAA and ABA were significantly different between two varieties,which can be used as physiological indexes for screening sensitive varieties at seedling stage.3.After defoliation treatment with 10 m L/mu and 15 m L/mu of thiabene·diuron at boll opening stage,the content of chlorophyll a,total chlorophyll,carotenoids and IAA in leaves were significantly lower than those of control,and MDA,ABA content and SOD,POD enzymes activity were significantly higher than those of control,except for individual time point.The changes of these physiological indexes were consistent with the results at the seedling stage.Under defoliation treatments with 10 m L/mu and 15 m L/mu of thiabene·diuron,the changes of SOD and POD enzyme activities had no significant difference between the two varieties,but the changes of MDA and ABA content showed significant difference between two varieties.Under defoliation treatment with 10 m L/mu of thiabene·diuron,there was no significant difference in the changes of chlorophyll a,total chlorophyll,carotenoid and IAA content between two varieties.Under defoliation treatment with 10 m L/mu of thiabene·diuron,the changes of the above four indexes were significantly different between two varieties,indicating that the concentration of defoliant should be increased at boll opening stage to better distinguish sensitive and insensitive varieties.Therefore,the seedling stage can be used as a key stage for screening sensitive varieties.4.At seedling and boll opening stages,the changes of MDA and ABA content were significantly different between two varieties under defoliation treatments with both 10 m L/mu and 15 m L/mu of thiabene·diuron,therefore,MDA and ABA content can be used as key indexes for screening sensitive varieties.