Chilling Stress-the Key Predisposing Factor For Causing Alternaria Altemata Infection And Leading To Cotton (Gossypium Hirsutuni L.) Leaf Senescence

Cotton premature senescence results in reduced lint yield and poor fiber properties, thus constitutingan important constraint to cotton yield and quality. Understanding the causes of cotton early leafsenescence would help us to protect cotton from premature leaf senescence through appropriatemanagement.The key factors for causing and promoting cotton premature leaf senescence are still unclear. In thiswork, leaf premature senescence resistant cultivar XLZ33and susceptible cultivar XLZ13were chosento be experimental materials. The relationship between the pre-chilling stress and Alternaria alternatainfection for causing cotton leaf senescence had been investigated under precisely controlled laboratoryconditions with four to five leaves stage cotton plants.(1) Chilling stress pre-treatments could promote A. alternata infection and cause leaf spot disease inchilling stress pre-treatments conducted with various low temperatures for3days or various durations at16/12℃. However, the differences in process and severity for the leaf spot disease could be obviouslydistinguished between XLZ13and XLZ33. Compared to XLZ13, the appearance of lesions for XLZ33were later, the disease index for XLZ33were significantly lower.(2) The results showed short-term chilling stress could cause a certain degree of physiologicalimpairment to cotton leaves, which could be recovered to normal levels in2–4days when the chillingstresses were removed. When these chilling stress injured leaves were further inoculated with A.alternata, the pronounced appearance and development of leaf spot disease, and eventually thepronounced symptoms of leaf senescence, occurred on these cotton leaves. The onset of cotton leafsenescence at this condition was also reflected in various physiological indexes such as irreversibleincrease in malondialdehyde (MDA) content and electrolyte leakage, irreversible decrease in solubleprotein content and chlorophyll content, and irreversible damage in leaves’ photosynthesis ability. Thepresented results demonstrated that cotton leaves were firstly get injured by chilling stress pre-treatment,then susceptible to A. alternata, and at last entered into accelerated senescence process.(3) Results of the present study indicated that infection of cotton leaves with A. alternata induceddramatic ethylene production, whereas insignificant ethylene production increase only occurred at4-6days after inoculation. There is a positive correlation between the development of Alternaria disease andethylene production. Ethylene has long been known as a major hormone in hastening leaf senescence. Itmay be assumed that the production of ethylene increased under the development of Alternaria diseasein leaves caused the accelerated senescence progress.This research has firstly demonstrated that the chilling stress acted as the key predisposing factor forcausing A. alternata infection and leading to cotton (Gossypium hirsutum L.) leaf senescence. Thisstudy deepened the research of key factors causing premature senescence which mainly from thephysiological aspects before by connecting physical damage and pathogen infection. It could beexpected that the understanding of the key factors causing and promoting cotton leaf senescence would be helpful for taking appropriate management steps to prevent cotton premature leaf senescence.