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Morphological components of yield in sweet potato (Ipomoea batatas (L.) Lam.) Soenarto

Abstract

Growth and productivity were analyzed in two cultivars of sweet potato (Ipomoea batatas (L.) Lam.): a bushy type (cv BO 44T3) and a spreading type (cv BO 129T9). Two main aims were to determine how tuberous root yield and aboveground morphological measures respond to population density in different growing seasons, and to identify morphological measures of aboveground plant parts that are indicators of high tuberous root yield. In addition, the study was used to compare several techniques of plant growth analysis. Two field experiments were performed using randomized complete block designs. One was repeated in 1995 and 1996 and involved a single final harvest after the cultivars were grown at three levels of plant population density. The second was carried out in 1996; it involved a sequence of harvests performed at different times during crop growth at a single population density. Five different techniques were used to analyze the experimental results: conventional plant growth analysis, inverse yield-density regression analysis, allometric analysis, path analysis and yield component analysis. These procedures offered complementary interpretations in that each provided new perspectives on plant performance. The two cultivars arrived at similar final tuberous root yields through different chronologies of growth. Increasing population density reduced tuberous root yield along with most other measures of growth. Responsiveness to population density, i. e., intraspecific competition, differed among the different plant measures and years, and the two cultivars did not always respond to density to the same degree. Where significant differences were found between years, the responsiveness was always higher in the year that was less favourable to growth (1996). Some effects of population density on tuberous root yield were direct, but indirect effects on yield via responses of aboveground measures were stronger. Throughout growth, the addition and expansion of leaves were positively correlated with tuberous root growth. At the final harvest, variation in number of stems per plant was an important indicator of variation in tuberous root yield.

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