Characterization of twenty coconut (Cocos nucifera L.) varieties based on leaf morpho-physiological markers

The Tall varieties used in this study consisted of Bago-Oshiro (BAO), Baybay Tall (BAY), Gazelle (GPT), Karkar (KKT), Laguna Tall (LAG), Tahiti/Polynesian Tall (PYT), San Ramon Tall (SNR), Tagnanan (TAG), West African (WAT) and Zamboanga Tall (ZAM). The Dwarf varieties included Aromatic (ARO), Catigan green (CAT), Cameron Red (CRD), Galas (GAL), Kinabalan (KIN), Malayan Red (MRD), Malayan Yellow (MYD), Pilipog (PIL), Sri Lanka Green (SGD) and Tacunan (TAC). The dwarf varieties had generally reduced size than the Tall varieties. The leaf and rachis lengths were the only morphological features that provided distinct significant differences between the Tall and Dwarf varieties. Nevertheless, varieties with extreme values were identified among the Tall and Dwarf coconuts. Among the Tall varieties, KKT had the most number of distinguishing parameters namely: longest leaf and petiole lengths and smallest petiole width and thickness. Among the 20 varieties, ARO had the shortest leaf, leaflet, rachis and petiole lengths, smallest leaflet area, and least petiole width and thickness. Scanning electron micrographs showed that stomata, found only on the abaxial epidermis, were arranged in parallel rows and sunken below the epidermis. The stomatal complex is characterized by the presence of two guard cells and four subsidiary cells, two of which are roundish and the other two are lateral to the guard cells. The values of stomatal featurers were statistically significant for some Tall and Dwarf coconuts, however, they cannot be used reliably to establish differences between the two coconut types. Statistical analysis revealed important differences for some of the Tall and Dwarf varieties in terms of the physiological parameters examined. In general, wax and moisture contents, and transpiration rate could not be also utilized to classify the two coconut types. Simple correlation analysis showed significant positive relationship among leaf morphological parameters; between stomatal length and leaflet area; between total number of stomata per leaflet and leaf morphological parameters; between wax content and leaf length, rachis length, total number of leaflets and total number of stomata; and between moisture content and transpiration rate. Significant negative correlation was noted between stomatal density and stomatal length, and moisture content and stomatal density. The study confirmed that evaluation of coconut genetic diversity based on leaf morphological parameters is often inadequate. The absence of significant results on physiological characters suggests that this aspect needs further investigation