Intensified Alternaria spot disease under potassium deficiency conditions results in acceleration of cotton (Gossypium hirsutum L.) leaf senescence

Abstract

Premature senescence in cotton has been occurring at increasing frequencies and causes serious reduction in yield and quality. In this study, the relationship between potassium (K) deficiency and Alternaria alternata infection, causing leaf senescence in cotton, was investigated. All experiments were performed under controlled laboratory conditions, in which cotton seedlings were treated with various concentration of K for 10 days, followed by inoculating the third and fourth true leaves with A. alternata. Subsequently, both physiological indices reflecting leaf senescence and disease index were measured. The results showed that cotton leaves treated with K deficiency were more susceptible to A. alternata in two aspects. First, the appearance of disease lesions were emerged 1-4 days earlier in cotton leaves treated with various K deficiencies compared to control. Secondly, the disease lesions developed continuously and expanded in treated leaves showing more disease lesions, the size of which increased with decreasing concentrations of K in a dose-dependent manner. In addition, the symptoms of cotton leaf senescence were pronounced in these infected leaves. Acceleration of leaf senescence also reflected in various physiological indices such as increase in electrolyte leakage and MDA content, significant decrease in chlorophyll content and reduction of Fv/Fm ratio. These results provide evidence that the combination of K deficiency and A. alternata infection accelerates cotton leaf senescence. Understanding the key factors causing and promoting cotton leaf senescence should greatly help the management of cotton crops by preventing premature leaf senescence.