Diversity, Antagonistic Potential of Endophytes, Phytochemicals and Antimicrobial Activity of Selected Agroforestry Trees Against Xanthomonas Campestris Pv. Musacearum and Cercospora Zeae-Maydis

Abstract

Maize and banana yields have continued to decline due to pests and diseases such as grey leaf spot (GLS) of maize and Xanthomonas wilt of bananas caused by Cercospora zeae-maydis and Xanthomonas campestris pv. musacearum respectively. Plants contain endophytes that protect them against pests and diseases. There is paucity of information regarding the diversity of endophytes of Calliandra calothyrsus, Leucaena diversifolia and Sesbania sesban are important biocontrol agents. Endophytes have antagonistic effects against plant pathogens. However, there is inadequate information on the antagonistic potential of endophytes from these plants against C. zeae-maydis and X.c. pv. musacearum. These pathogens have continued to lower yield of maize and bananas hence compromising food security. Plants contain phytochemical compounds with antimicrobial activity. There is lack of information on the phytochemical compounds of these plants which are vital in identifying antimicrobial properties of the plant extracts to control GLS and Xanthomonas wilt diseases. Moreover, there is little information on the antimicrobial properties of these plants extracts against C. zeae-maydis and X.c. pv. musacearum important in improving yield of maize and bananas. The objective of the study was to determine diversity, phylogeny, antagonistic potential of endophytes, phytochemical compounds and antimicrobial activity of C. calothyrsus, L. diversifolia and S. sesban extracts against C. zeae-maydis and X.c pv. musacearum. Nine plants of C. calothyrsus, L. diversifolia and S. sesban were collected randomly from an agroforestry based system comprising of maize and banana at Maseno University farm located 0° 10' 0" South, 34° 36' 0" East. Three leaves, stems and roots were surface sterilized in 4% NaOCl, rinsed with sterile water and plated on potato dextrose agar and nutrient agar for growth of endophytes. Leaf samples were dried and ground for extraction in ethanol and aqueous solvents. Test pathogens were isolated from diseased maize and banana leaves and their pathogenicity determined. Endophytes were isolated in pure cultures, characterized morphologically and molecularly and their phylogenetic relationships determined. Antagonistic potential of endophytes and activity of leaf extracts against C. zeae-maydis and X.c pv. musacearum was determined in dual culture, disc diffusion and food poison techniques. Treatments of 12.5, 25, 50 and 75% aqueous extracts and, 12.5, 25, 50, and 75mg/ml ethanol extracts were used. Plates were arranged in a completely randomized design. Qualitative phytochemical analysis of the extracts’ compounds was determined. Morphological and molecular data was subjected to cluster analysis. Data on growth was subjected to analysis of variance and means separated using Least Significant Differences (P ≤ 0.05). Morphological and molecular data revealed that there were Gram positive and Gram negative cocci and bacilli belonging to ten genera, while fungal endophytes belonged to four genera. Fungal endophytes clustered in three orders, and bacteria endophytes clustered in six orders. Morphological dendograms clustered isolates in two groups at 75% similarity level. Phylogenetic tree grouped the isolates into two clades at 99% similarity level. The results revealed that most of the isolates had a common ancestor. Thirteen fungal isolates showed growth inhibition against X.c pv. musacearum while twenty four inhibited growth of C. zeae-maydis. Nineteen bacterial isolates inhibited the growth of X. campestris pv. musacearum while eleven inhibited growth of C. zeaemaydis. Tannins, steroids and saponins were detected in the three plants. Terpenoids, flavonoids and alkaloids were not all present in the three plants. Leaf extracts showed significant differences in growth inhibition among the treatments and plant species. The findings revealed that endophytes and extracts from C. calothyrsus, L. diversifolia and S. sesban have the potential to control GLS and Xanthomonas wilt in maize and bananas. The study recommends the use of endophytes and extracts from these plants in control of GLS and Xanthomonas wilt.