Morphological and genetic characterization of jackfruit (Artocarpus heterophyllus) in the Kayunga and Luwero districts of Uganda

Abstract

Background: Jackfruit (Artocarpus heterophyllus) is an economically valuable fruit tree in Uganda. However, the production of jackfruit in Uganda is low. Additionally, because of deforestation, genetic erosion of the resource is predicted before its exploitation for crop improvement and conservation. As a prerequisite for crop improvement and conservation, 100 A. heterophyllus tree isolates from the Kayunga and Luwero districts in Uganda were characterized using 16 morphological and 10 microsatellite markers.

Results: The results from the morphological analysis revealed variations in tree height, diameter at breast height (DBH), and crown diameter, with coefficient of variation (CV) values of 20%, 41%, and 33%, respectively. Apart from the pulp taste, variation was also observed in qualitative traits, including tree vigor, trunk surface, branching density, tree growth habit, crown shape, leaf blade shape, fruit shape, fruit surface, flake shape, flake color, flake flavor and pulp consistency/texture. Genotyping revealed that the number of alleles amplified per microsatellite locus ranged from 2 to 5, with an average of 2.90 and a total of 29. The mean observed (H_o) and expected (H_e) heterozygosity were 0.71 and 0.57, respectively. Analysis of molecular variance (AMOVA) indicated that 81% of the variation occurred within individual trees, 19% among trees within populations and 0% between the two populations. The gene flow (Nm) in the two populations was 88.72. The results from the 'partitioning around medoids' (PAM), principal coordinate analysis (PCoA) and genetic cluster analysis further revealed no differentiation of the jackfruit populations. The Mantel test revealed a negligible correlation between the morphological and genetic distances.

Conclusions: Both morphological and genetic analyses revealed variation in jackfruit within a single interbreeding population. This diversity can be exploited to establish breeding and conservation strategies to increase the production of jackfruit and hence boost farmers' incomes. However, selecting germplasm based on morphology alone may be misleading.

Keywords: Artocarpus heterophyllus; Conservation; Crop improvement; Microsatellite markers; Morphological markers.

Fig. 1

Morphological relationships of jackfruit accessions from the Kayunga and Luwero districts of Uganda. The relationships of 100 jackfruit accessions were derived based on Gower distances. The color intensity is proportional to the distance measure, with the lightest intensity representing the minimum distance and hence close relationships and the deepest intensity representing the maximum distance and therefore distant relationships. The scale on the right side of the plot shows the distance measured with the corresponding colors. The L and K prefixes on the sample identification numbers represent Luwero and Kayunga, respectively

Fig. 2

The two clusters of jackfruit accessions from the Kayunga and Luwero districts of Uganda. The clusters were identified via the PAM method [48]. The L and K prefixes on the sample identification numbers represent Luwero and Kayunga, respectively

Fig. 3

Allele frequency by population across all ten loci. The alleles are coded with numeric names such as “170”, “200”, and “250”. N = 100, n (Luwero) = 50, n (Kayunga) = 50

Fig. 4

Genetic relationships of jackfruit accessions from the Luwero and Kayunga districts of Uganda. The relationships were determined using 10 microsatellite markers via PCoA. N = 100

Fig. 5

Genetic clustering of jackfruit accessions from the Luwero and Kayunga districts of Uganda. The dendrogram was derived from ten microsatellite loci based on Provesti’s genetic distance [57] and UPGMA [58] with 100 bootstraps. Bootstrap values above 90% are shown. The L and K prefixes on the sample identification numbers represent Luwero and Kayunga, respectively