Assessing the extent of diversity among noni (Morinda citrifolia L.) genotypes of Morobe Province, Papua New Guinea

Abstract

The extent of morphological variation among extant noni (Morinda citrifolia: Rubiaceae) genotypes was assessed using 58 polymorphic traits. A total of 39 mature noni trees were sampled from five sites within the vicinity of Lae, Morobe Province, Papua New Guinea. Cluster analysis identified five homogenous clusters, and was able to separate the three known botanical varieties namely, M. citrifolia var. citrifolia, M. citrifolia var. bracteata and M. citrifolia var. potteri as distinct morphotypes. Ordination of the data revealed traits such as young shoot pigmentation, stem diameter, angle of insertion of primary branch on main stem, stipule shape, heterostyly, occurrence of pistillate florets, fruit shape, occurrence of floral bracts, fruit width, and peduncle positioning at maturity as having greater contributions to the observed variation. Although the genetic nature of these traits is yet to be elucidated, occurrence of floral bract and fruit branching were observed to be transitional between the botanical varieties, and may shed light on their origins. The 58 descriptor states showed varying levels of polymorphism, however, the significant (P<0.01) correlations observed between numerous traits provide an element of caution in the development of a descriptor list, particularly when considering stability of the traits and the sample size. The results obtained in this study provided useful information for the standardisation of the developed descriptor list comprising of 49 polymorphic descriptor states, and for future diversity studies in noni.