Control of Reproductive Sink Yield in Mung Beans

Pattern of 14C-assimilate partitioning and effects of growth substance application were studied in relation to a single reproductive axis on plants of Vigna radiata (L.) Wilczek (mung bean). The root system provided a large sink for assimilates especially during flowering and fruit setting. Fruit number and total seed weight were little altered by application of 1-napthaleneacetic acid (NAA), gibberellic acid (GA3) or 6-benzylaminopurine (BAP) during bud swelling, flowering or fruit setting but BAP treatment throughout reproductive development significantly increased both fruit number and total seed weight. It is argued that reproductive sink yield is restricted by a limited supply of assimilates from source leaves. This restriction may operate indirectly in that assimilate supply to the root system determines the supply to the shoot of root-synthesised growth substances that regulate abscission of reproductive structures. However, the possibility of direct assimilate limitation, or shortage of other substances essential for reproductive development, cannot be discounted.