Agrophysiological characterisation and parametrisation of Andean tubers: Potato ( Solanum sp.), oca ( Oxalis tuberosa), isaño ( Tropaeolum tuberosum) and papalisa ( Ullucus tuberosus)

Abstract

Bolivia is part of the eight most important centres of biodiversity and domestication of plants in the world, including a broad diversity of Andean grains, roots and tubers. A study was implemented to obtain the quantitative information to develop and validate, a simple growth potential model of Andean tubers in production areas located above 3000 m altitude, and to analyze the difference between species in growth attributes and the resulting tuber production. Three potato species and sub-species ( Solanum tuberosum ssp. andigenum and ssp. tuberosum, and Solanum juzepczukii) as well as Oca ( Oxalis tuberosa), Isaño ( Tropaeolum tuberosum) and Papalisa ( Ullucus tuberosus) were studied. Trials were conducted under normal field conditions prevailing in Bolivia but with the best cropping techniques available locally to obtain optimal growing conditions. Data on dry weight (of leaves, stems, tubers and roots) and leaf area were taken at several dates in five trials conducted between 1993 and 2003. The percentage of ground cover was also measured. Beta functions were fitted to data of dry weight and leaf area to establish growth curves. The potato groups have a smaller cycle duration than other Andean tubers. The Crop Growth Analysis indicated three important characteristics differentiating Andean tubers: the S. juzepczukii potato has a high Relative Growth Rate (RGR) and a higher leaf mass ratio but a smaller tuber yield, due to a smaller harvest index (HI) and a very low Net Assimilation Rate (NAR). S. tuberosum ssp. tuberosum potatoes have smaller Leaf Area Index (LAI), and RGR than juzepczukii, but their NAR and HI are higher. S. tuberosum potatoes are quite productive for the size of their LAI. The Tropaeolum tuberosum or Isaño has a great capacity of Ground Cover (GC) or a great LAI that is not translated into a greater tubers yield. It has low RGR, NAR and HI compared to all the other species studied. The crop growth was interpreted in Light Use Efficiency (LUE) and evolution of light interception through a linear model. The LUE of potato group is more elevated than the LUE of the other Andean tubers. Within each group there is no statistical difference for the LUE value. The relationship of LAI with GC or fraction of light interception was determined with both linear and exponential relations. The low slope value for the relationship between LAI and GC characterises all Andean tubers studied compared to results reported for potato under other latitudes.