An hypothesis concerning the development of the red leaf disorder in cotton (Gossypium hirsutumL.)

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Abstract
The development of the physiological disorder of cotton known as ‘rooidood’, ‘red leaf disorder’ or ‘potassium deficiency syndrome’ has not yet been explained. Several stress conditions have been associated with this disorder, including low N levels in leaves, low K levels in leaves and soils, high water table, soil compaction, salt accumulation in soil, wilting disorders, windy conditions and large boll loads. The plant's mechanism to avoid carbohydrate starvation in case of untimely stomatal closure, which is dropping of squares and young bolls, cannot function if only large developing bolls are present late in the season. The red leaf disorder may be the result of an alternative mechanism to avoid starvation of inabscisible bolls, to the detriment of assimilates and nutrients of unproductive leaves. All of the mentioned stress conditions associated with the disorder can cause stomatal closure. A large boll load or sink should aggravate the photosynthate shortage of the plant under any such stress. The unmasking of anthocyanin in leaves due to chlorophyll breakdown during the premature senescing process, following stomatal closure, seems to be responsible for the characteristic red colour.