Molecular identification and pathogenicity of phytophthora species causing pineapple heart rot disease in Uganda

Abstract

Pineapple (Ananas cosmosus L.Merrill) has enormous potential for nutritional and health benefits, foreign exchange earnings, industrial growth and development in Uganda. The production of this crop is on the decline, because of outbreak of the pineapple heart rot disease. Therefore the objective of this study was to determine the molecular identity and pathogenicity of the phtophthora causal organism of pineapple heart rot disease. Four major pineapple growing districts in Central Uganda were surveyed for disease prevalence and samples collected for laboratory isolation and characterization between April-May 2016. Twenty one (2 1) sampies of phytophthora heart rot pathogen were isolated from diseased pineapple tissues. Pathogenicity of the pineapple heart rot causal organisms was assessed on invitro pineapple leaves and green apple fruits in laboratory following koch'spostulate. Internal transcribed spacer regions (ITSI, 5.8s !TSUrDNAs, from I I isolates of phy10phthora were analysed by polymerase chain reaction amplification and direct sequencing. The analysis of molecular variance (AMOVA) showed a significant genetic diversity within population (PhiPT= -O.Q68, P= 0.001). Intraspecific variability was detected. The genetic diversity of the population was measured by building phylogeneies based on these sequenced rDNA-ITS data using Muiltiple sequence alignment tool. The results of the pathogenicity test showed that 100% of the isolates were pathogenic apple fruits and healthy pineapple leaves with varying levels of virulence. Based on molecular identification, the sequence of amplified PCR products of DNA fragment of 850bp confined that the causal organism of pineapple heart rot disease was Pnicotianae. AMOVA indicated the variability within populations was (100%). These results also suggest that Pnicotianae has considerable evolutionary potential, which enable it to adapt to the new environment and overcome management strategies over