Assessing the morphological characteristics of elite Cocoa accessions (Theobroma cacao L.) in Makira Island, Solomon Islands

Abstract

Based on the suggested Australian Center for International Agricultural Research (ACIAR) guidelines the characterization in Theobroma cacao L., is observed to be important to encourage fine quality Cocoa production, and to realize remunerative income. Each nine quantitative and qualitative morphological traits were used to characterize 40 Cocoa accessions collected from fields distributed under different wards of Makira Island of the Solomon Islands.

Among the identified Cocoa accessions, Principal Component Analysis (PCA) characterized traits into three major Principal Components (PC) responsible for 46.2 percent of total variation. PC axis one accounted for 23.1 percent of total variation explained by pod weight, pod circumference, cotyledon length, pod length, cotyledon width, pod external thickness, mature pod ridge color (anthocyanin), pod surface texture, pod surface shape and pod shape. The 12.2 percent of total variation in PC axis two was considerably attributed by the qualitative traits cotyledon color, pod surface texture , mature pod ridge color (anthocyanin), pod surface shape, cotyledon width, pod shape and tree vigor. While, PC axis three amounted for 10.9 percent of total variation referred to traits pod neck, pod surface shape, pod surface texture, pod length, tree vigor, pod internal thickness, weight of the bean per pod, pod external thickness, number of beans per pod, pod weight and reaction to black pod.

Unweighted Pair Group Mean with Arithmetic Average (UPGMA) classified the 40 accessions in to three clusters. Under Cluster 1, 95.5 percent of identified accessions were characterized by traits such as cotyledon length and cotyledon width, red pods tree. While, Cluster 2 made up of 5 percent of total number of accessions with traits least pod weight, least pod external thickness, least cotyledon length and red podded trees. A single accession in Cluster 3 characterized by longest pod and constituted only 2.5 percent of the total accession.

The frequency distribution of the nine qualitative traits confirmed that, 90 percent of identified accessions exhibited pod surface texture as smooth and slightly rough, 97 percent with pod surface shape as slightly furrowed with medium furrows and 85 percent with Amelonado pod shape. Most of the identified Cocoa accessions, grouped into three pod apex shapes traits such as Mammelate, Acute and Obtuse, accounting for 44 percent, 25 percent and 20 percent, respectively. Of the total accessions studied, 63 percent had no anthocyanin on the mature pod ridge. Each of 72 percent measured as the strength of the accessions to withstand Phytophthora palmivora , and  vigorous.The Shannon Weaver Diversity Index characterized and suggested that the Cocoa accessions in Makira Island mainly resemble to Amelonado (bulk) type, usually classified as Forasterio variety.