Contribution of leaf position and planting material to sweet potato (Ipomoea batatas (L.) Lam) growth and yield

Results revealed that under field conditions, variety and defoliation at different leaf positions generally showed no interaction with each other. The creeping type variety, VSPS showed faster canopy growth resulting in earlier time (5 days) of canopy closure compared to a bushy type (VSP1). Moreover, it gave relatively higher LAI [leaf area index] for the first 75 days of growth and superior vine length. Higher root dry matter content was observed for VSPS than VSP1. Leaf defoliation of 50% and 25% of total leaves from the base resulted in a reduced intercepted PAR [photosynthetically active radiation] amounting to 48% and 30%, respectively. Defoliation done before the start of root initiation (25 DAP) regardless of extent, delayed the time of canopy closure. Although defoliation reduced LAI and CGR [crop growth rate] in sweet potato, the onset of root initiation was not delayed. Other parameters such as the number of storage roots initiated, mean weight per storage root, root yield and total dry matter yield were similarly not affected by defoliation at those stages. Dry matter production increased progressively with time where most of the dry matter produced at the early stage of growth came from vegetative plant parts (stems, leaves and roots) while storage roots contributed most of the dry matter produced at later stage. Apical cuttings showed superior performance over basal cuttings in terms of percent survival, early canopy development and onset of tuberous root initiation. Basal cuttings regardless of the variety resulted in greater number of non-marketable roots. The variation on number of storage roots between plants was significantly reduced when VSP1 (bushy type) was used compared to the VSP5 (creeping type). Similarly, harvesting at 105 or 120 DAP resulted in a marked reduction in plant to plant variability on number of storage roots, number of marketable roots and number of lateral branches. Furthermore, mean weight per storage root and weight of marketable roots were found to have significant positive correlation with root yield.