Prevalence, Incidence And Molecular Phylogeny Of A Fungus (Phytophthora Colocasiae) Causing Taro Leaf Blight In Ghana

Abstract

Taro (Colocasia esculenta (L.) Schott) is an e staple crop for millions of citizens in some developing nations. The crop popular dish in southern Ghana because of its high carbohydrate and protein content. Taro leaf blight caused by the fungus Phytophthora colocasia is a devastating disease of taro in many parts of the world where the crop is grown. Serious outbreaks of taro leaf blight in Samoa in 1993, as well as in Cameroon, Ghana, and Nigeria in recent years, have demonstrated the disease's catastrophic impact on the livelihood and food security of small farmers and local communities that rely on the crop. In several countries, it is responsible for up to 80 % of taro yield loss. In Ghana, the disease causes a 25–50 % reduction in yield. The objective of this research was to determine the prevalence, incidence, geographical distribution and molecular diversity of the fungus causing the blight disease of taro in Ghana. A survey was conducted to examine the extent of the posed by the pathogen as well as to acertain the disease awareness level of farmers. The disease was in all taro fields surveyed, with average incidence of 79.26%. The highest disease incidence and severity on the farmer’s field was observed in Anyinam whilst the least incidence was observed in Atimpoku in the Eastern Region. Field trials were set up in an RCBD and replicated three times. Ten taro accessions namely; Adenta (AD), Akim tafo (AT), Atimpoku (AP), Fawade (FW), Gyinyasi (GY), Haatso (HT), Kumasi tafo (KT), Koforidua (KF), Kasoa (KS) and Weija (WJ) were used in the study. The taro accessions were obtained from farmers in the Ashanti, Eastern, Greater Accra and Central region. The effect of the infection was assessed by measuring disease incidence and severity. Accession FW had the highest incidence of 96.67±5.77 and the least was KS with 60±52.9. Disease severity was significantly higher in accession Gyinyasi (GY) with 1.69±0.27 and the least in accession Atimpoku (AP) with 0.70±0.27. The effect of the disease on yield was also assessed. Gyenyasi (GY) was the accession with the highest yield of 71.47 kg/ha and the least yield was recorded in accession KT with 41.00 kg/ha. The average yield of all the accessions was 56.64 kg/ha as compared to a control yield of 198.67 kg/ha. Fungal isolation was done from the diseased leaves collected during the survey and morphologically identified under the light microscope. Koch’s postulate was conducted to confirm the isolated fungus. Fungal cultures placed on healthy leaves of fifteen potted taro plants per accession resulted in 100 % infection. DNA of the P. colocasiae was successfully extracted from the different fungal isolates. Molecular detection of the pathogen using Polymerase Chain Reaction (PCR) and sequencing were also be carried out using Sanger sequencing. Nine DNA template of the P. colocasiae from the samples collected from Midie farm 1, 2 and 3 (M1, M2, M3), Kasoa farm 1, 2, and 3 (K1, K2, K3) and Akim Tafo farm 1, 2, and 3 (T1, T2, T3) were successfully amplified using ITS1/ITS4 primer which gave the expected PCR product size of ~870 bp. Nucleotide sequence alignment reveal a high degree of similarities among the isolates from the three regions. Comparison of the Ghanaian isolates to sequences of other isolates available on the NCBI revealed nucleotide sequence identities in the range of 99.27 to 100 %. Based on the current findings, accession KS was found to be moderately resistant to taro leaf blight disease and could be employed in breeding programmes for the development of resistant varieties. The current findings provide the prerequisite information needed for extensive research and development management strategies to reduce the impact of the disease.