Morphological Variation of Fruit in Mexican Populations of Cocos nucifera L. (Arecaceae) under in situ and ex situ Conditions

Morphological variation of the coconut fruit measured in situ has been used to estimate genetic diversity, and generate hypotheses about the evolutionary and geographical diffusion of coconut. Some authors have questioned the validity of this methodology due to the possibly high effect of the environment on the morphological characteristics of the fruit. The general aim of this study is to validate this methodology through: (1) characterizing the pattern of morphological variation of the fruit under homogeneous growing conditions ex situ; (2) comparing this pattern with those already reported in situ; (3) estimating the heritability values for the components of fruit in coconut. Results are also discussed in comparison with ex situ leaf variation and biochemical and molecular variation patterns previously studied. Principal components and discriminant analyses indicated that the characters that best differentiate groups are basically the same in situ and ex situ. Grouping patterns obtained with principal components and cluster analysis were similar for both growing conditions. They were also similar to the grouping pattern obtained with ex situ leaf characters. No significant differences were found in the variation coefficients of fruit characters between the same populations in situ and ex situ. Consistency was found between patterns of morphological variation of fruit ex situ and in situ, and those obtained using iso-enzymatic and molecular characteristics. The results are also consistent with hypotheses on the origin and diffusion of the germplasm introduced to Mexico. High values of heritability were found in nine characters. Weight and water percentage showed the highest values (0.88 and 0.883), with a strong correlation to the mass and the roundness of fruit and seed, suggesting that human selection of these characteristics led to the differentiation of domesticated populations. We conclude that morphological characterization of the coconut fruit in situ is useful to estimate its genetic variability because of its simplicity, speed and ease of application in the field and in remote areas.