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 distributio n measurements were taken for determining optimum source-sink interact ions of 'Williams' tissue culture banana plants over a whole crop cycl e. Net assimilation rate (NAR), crop growth rate (CGR) and relative gr owth rate (RGR) were calculated. The results were supported by carbohy drate analysis and the monitoring of C-14-assimilates translocated thr oughout the plant. High NAR, CGR, RGR and photosynthesis rates (A) wer e measured during summer and low rates during winter. Growth parameter s and CO, assimilation increased. into the second summer growing seaso n, 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 flower ing, and the bunch before harvest. The most important sinks for C-14-a ssimilates during vegetative growth were leaf1, together with the rhiz ome of the plant crop (P) cycle and the sucker of the first ratoon (R1 ) cycle. After flowering, the developing bunch was the primary sink fo r C-14-assimilates. R1 sucker dry-matter accumulation was slow until i ts 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 prima ry assimilates are mainly being translocated to the rhizome. This woul d lead to a larger R1 sucker leaf area in spring, with better light in terception, higher A and an increased capacity to utilize favourable c limatic conditions during the second summer after planting. This in tu rn leads to a rapid increase in R1 sucker dry matter production reduce d cycle time and avoidance of sink competition between sucker and bunc h.