PHYSIOLOGICAL-RESPONSES OF BANANA (MUSA-AAA, CAVENDISH SUBGROUP) IN THE SUBTROPICS .3. GAS-EXCHANGE, GROWTH ANALYSIS AND SOURCE-SINK INTERACTION OVER A COMPLETE CROP CYCLE

Gas-exchange readings as well as dry-matter production and distribution measurements were taken for determining optimum source-sink interactions of 'Williams' tissue culture banana plants over a whole crop cycle. Net assimilation rate (NAR), crop growth rate (CGR) and relative growth rate (RGR) were calculated. The results were supported by carbohydrate analysis and the monitoring of C-14-assimilates translocated throughout the plant. High NAR, CGR, RGR and photosynthesis rates (A) were measured during summer and low rates during winter. Growth parameters and CO, assimilation increased. into the second summer growing season, but quickly declined during the last three months prior to harvest. This was attributed to an aging and rapidly depleting leaf area after flowering. Changes in the sink strength of the leaves and pseudostem during vegetative growth were shown, as with the rhizome during flowering, and the bunch before harvest. The most important sinks for C-14-assimilates during vegetative growth were leaf1, together with the rhizome of the plant crop (P) cycle and the sucker of the first ratoon (R1) cycle. After flowering, the developing bunch was the primary sink for C-14-assimilates. R1 sucker dry-matter accumulation was slow until its own leaf area developed, thus increasing the capacity to assimilate and especially when suitable climatic conditions for A were present. Therefore, in terms of photosynthetic efficiency, optimum source/sink interaction and seasonal effects, R1 sucker selection during the early vegetative development phase of the P Crop is recommended, when primary assimilates are mainly being translocated to the rhizome. This would lead to a larger R1 sucker leaf area in spring, with better light interception, higher A and an increased capacity to utilize favourable climatic conditions during the second summer after planting. This in turn leads to a rapid increase in R1 sucker dry matter production reduced cycle time and avoidance of sink competition between sucker and bunch.