Differential Senescence of Maize Hybrids following Ear Removal

Abstract

Visual senescence symptoms and associated changes in constituent contents of 3 field-grown maize hybrids (Pioneer brand 3382, B73 .times. Mo17 and Farm Service brand 854) were compared in response to ear removal. Whole plants were harvested at 8 intervals during the grain-filling period, and analyzed for dry matter, total N and nitrate N, P, sugars and starch. Upper leaves of earless P3382 and B73 .times. Mo17 showed reddish discoloration by 25 days after anthesis (DAA) and all leaves had lost most of their chloropyll by 40 DAA. In striking contrast, leaves of earless FS854 plants remained green and similar in appearance to eared controls throughout the grain-filling period. For all hybrids, ear removal led to a decrease in dry weight, reduced N, total N and P contents of the total plant and an increase in carbohydrate content of the leaves and stalks, relative to respective controls. Although changes in carbohydrate and N contents, which previously had been associated with senescence, were observed for all earless hybrids, there changes were followed by accelerated senescence and early death only for P3382 and B73 .times. Mo17. By 30 DAA, earless P3382 and B73 .times. Mo17 plants ceased to accumulate dry weight, total N and P, indicating a termination of major metabolic activities. In contrast, earless FS854 plants retained a portion of these metabolic activities until 58 DAA, indicating a role for roots in determining rate of senescence development. Thus, the course of senescence was more accurately reflected by measurements of metabolic activities than by measurements of metabolite contents at any given time. The ear per se does not dictate the rate or completion of the senescence process, and implicated an association between the continued accumulation of N and associated root activities with the delayed senescence pattern of the earless FS854 plants. Studies involving control senescence among species must also consider genotypic influences within species.