Effect of Rate of Growth and Development on Needle Photosynthate and Phloem Transport in Caribbean Pine (Pinus caribaea Mor.)

Plants of Pinus caribaea var. hondurensis raised from seeds obtained from a general collection from one seed source (Peten, Guatemala) were categorized into fast and slow growing individuals to study the relationship of growth rate with needle soluble sugars, starch content and velocity of phloem transport. Soluble sugar levels in the slow growing plants were significantly higher than the levels seen in the fast growing individuals. There was no difference between the levels of starch in plants of the two growth types during the day, but starch concentration remained signiftcantly higher in needles of the slow growing plants during the dark period. Results of phloem transport studies, using a fluorescence tracing technique on forest trees, reveal a 3-fold faster velocity of phloem translocation in plants of the fast growth catego~y. Rapid removal of soluble carbohydrates and rapid conversion of starch to soluble carbohydrates in pine needles were highly correlated with rapid growth of the seedlings while starch accumulation and inefficient removal of photosynthate from the needles were characteristic of the slow growing plants. These results are useful in evaluating seedlings, trees and tissue culture plantlets in tropical forest reforestation and afforestation programs.