Chlorophyll fluorescence analysis as a measure of photosynthesis is increasingly used in eco-physiological studies. It is particularly useful in investigations on the photosynthetic performance of plants in stressful environments. Chlorophyll fluorescence, which can be measured rapidly and conveniently, provides insights into a plant's ability to tolerate environmental stresses such as those of a drought. Damage to the photosynthetic apparatus due to moisture or heat stress, which would reduce photosynthetic assimilation and eventually the yield, can be detected at a very early stage of the drought. This technique is widely used to identify stress tolerant plants and crop varieties. However, this technique has not been utilized to identify putative drought tolerant coconut varieties. Hence, the objective of this study was to set out the basic principles of the technique, discuss its applications in eco-physiological studies, and evaluate its potential to screen coconut varieties for drought tolerance.
San Ramon, a tall form of coconut introduced to Sri Lanka few decades ago and a few other local tall accessions in the germplasm conservation blocks in the Coconut Research Institute of Sri Lanka appeared to possess a photosynthetic apparatus which was clearly more tolerant to moisture stress conditions than the other accessions. SRR, SRG, SA, CL PI & PW were the most drought tolerant of the 40 genotypes tested. The results generated by using Fv/Fm, were consistent with results of other important parameters such as the rate of photosynthesis and water use efficiency. Even the basic parameters of chlorophyll fluorescence, for instance the maximum quantum yield of photosystem II (Fv/Fm) measured on dark-adapted coconut leaves showed promise as a selection criterion in future screening programmes due to its quick, non-invasive and reliable nature. Similarities of fluorescence parameters observed between seedlings and adult palms enables fairly confident predictions on the performance of adult palms, based on studies with seedlings. In general, chlorophyll fluorescence appears as a promising tool for screening coconut palms for their drought tolerance.