Extent and mechanism of yield reduction in sweetpotato grown for tops and roots
1999
Nguyen, B.L. | Bautista, O.K. (Ministry of Agriculture and Food Industry (Vietnam). National Inst. of Agricultural Science)
Experiments were conducted to determine the extent and mechanism of root yield reduction due to regular harvesting of tops in 3 cultivars of sweet potato [Ipomoea batatas (L.) Lam]. The yields of `UPL-SP1' and `Miracle', which are viny and `VSP-2', which is bushy, were similarly affected by topping. The more frequent the topping, the yield reduction, especially of the larger roots, was greater. Plants topped every 2 and 4 weeks yielded 11.41 and 14.98 t/ha, respectively, compared with 17.75 in the untopped plants. There was no effect on yield if plants were topped before root bulking, slight if topped up to root bulking, and drastic if topped up to harvest time. Frequent topping resulted in more branches and lesser or smaller leaves, thereby decreasing leaf area index, consequently decreasing dry matter, starch and moisture content, but no change in harvest index. Topping increased ABA and IAA oxidase of storage roots and decreased IAA in both leaves and roots. The increase in ABA resulted in reduced transport of carbohydrate to the roots. Hence, root weight decreased. The decrease in IAA reduced root number and weight. The vegetative phase was lengthened and the storage root development phase was delayed. Cytokinin was not affected by topping
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