Panicle Differentiation and Spikelet Number Related to Size of Panicle inPennisetum americanum

Abstract

The size of the developing panicle of pearl millet (Pennisetum americanum (L.) Leeke) was studied during panicle differentiation (from panicle initiation to the completion of spikelet production) in plants grown in pots or in the field and supplied with varying levels of nitrogen. The duration of panicle differentiation required a constant thermal time (day degrees) under all nitrogen supplies. However, the rate of growth of the developing panicle during this phase was retarded by low nitrogen supply. During panicle differentiation, it appeared that the developing panicle had to reach a critical size before developmental events such as the initiation of spikelet primordia commenced; timing of developmental events was related to the size of the developing panicle. The number of spikelets produced depended on the rate of growth of the differentiating panicle and the duration of the phase of spikelet initiation (from appearance of the first spikelet primordium to completion of spikelet differentiation). Low nitrogen supply reduced the number of spikelets produced, by retarding the rate of growth of the differentiating panicle; this delayed the time to initiation of spikelets and thereby reduced the duration of spikelet initiation. All spikelets (irrespective of nitrogen supply on the mainstem and on tillers) occupied the same area of panicle surface at the completion of differentiation of the panicle and at anthesis.