Amare Ayalew

Molecular characterization of Xanthomonas strains responsible for bacterial spot of tomato in Ethiopia

Bacterial spot of tomato (BST) is a major constraint to tomato production in Ethiopia and many other countries leading to significant crop losses. In the present study, using pathogenicity tests, sensitivity to copper and streptomycin, and multilocus sequence analysis (MLSA), we identified a diverse group of Xanthomonas strains isolated from central Ethiopia. None of the strains were sensitive to copper or streptomycin. Multilocus sequence analysis was used to compare Ethiopian strains with representative Xanthomonas strains from a worldwide collection based on DNA sequences of six housekeeping genes (lacF, lepA, gyrB, fusA, gltA and gapA) and hrpB genes. Phylogenetic analysis of the concatenated sequences showed that X. gardneri, X. vesicatoria and X. perforans were associated with BST in Ethiopia, whereas Xanthomonas euvesicatoria was absent from the Ethiopian sample. There was no genetic diversity among the isolated strains belonging to X. gardneri and X. perforans. However, two X. vesicatoria haplotypes were identified indicating at least two different sources of introduction of X. vesicatoria to Ethiopia. All of the X. perforans strains were only pathogenic on tomato and were T3 strains with the exception of one identified as tomato race 4 (T4). The X. gardneri and X. vesicatoria strains were tomato race 2 (T2), but were variable in pepper race determinations indicating variation in effectors among strains.

Antifungal Activity of Some Plant Extracts against (Colletotrichum Musae) the Cause of Postharvest Banana Anthracnose

The present study was conducted to determine the efficacy of extracts of some plant species against Colletotrichum musae. Methanolic extracts of 21 plant species were screened for their inhibitory effect against C. musae using paper disc method and spore germination assay. Among them, extract of Prosopis juliflora exhibited superior antifungal activity (30.7 mm), followed by Acacia albida (19 mm) as compared to nill in the control. On the other hand, carbendazim, which was used as a standard chemical check, demonstrated by far the highest inhibition zone of 51.7 mm diameter. Extracts from A. albida, Dovalis abyssinica and P. juliflora reduced conidial germination to 0.2, 0.5 and 0.3%, respectively, which didn’t vary statistically from 1.2% in Carbendazim. Six plant species, viz., A. albida, Azadirachta indica, Argemone mexicana, D. abyssinica, P. juliflora and Vernonia amygdalina, that showed high to moderate antifungal activity in the preliminary screening, were further tested for their thermal stability at 60°C and for the efficacy of their aqueous extracts against C. musae. Extracts of the tested plant species were found to be heat stable and aqueous extracts of A. albida showed the highest antifungal activity (18 mm), followed by P. juliflora (12.3 mm). Further studies need to be undertaken to isolate the active compounds from those extracts with fungicidal potential.

Evaluation of Antifungal Activity of Plant Extracts against Papaya Anthracnose (Colletotrichum gloeosporioides)

Antifungal activities of nineteen plant extracts were tested in 2010 with the objectives of screening potential plant extracts against Colletotrichum gloeosporioides under in vitro and anthracnose caused by Colletotrichum gloeosporioides, on papaya (Carica papaya L.) during storage. Ethyl acetate extracts of Lantana camara resulted in the highest inhibition (with inhibition zone of 35.3 mm) and showed strong activity against C. gloeosporioides. Inhibition levels of spore germination that reached 88.7, 85.8, 85.1 and 84.6% were recorded over the control by extracts of Lantana camara, Lantana viburnoides, Echinops sp. and Ruta chalepensis. Four aqueous extracts were evaluated for control of anthracnose under in vivo for 14 days, and Echinops sp. (25%) was found to be most effective in the reduction of disease development and maintaining the overall quality of papaya fruit. Further studies on isolation and characterization of the active (antifungal) compounds are needed.

Evaluation of Local Isolates of Trichoderma Spp. against Black Root Rot (Fusarium solani) on Faba Bean

Faba bean (Vicia fabae L.) is one of the most important pulse crops in Ethiopia and is now cultivated on large areas in many countries. In most growing areas, however, the production of the crop is constrained by several disease infections, including fungal diseases. Black root rot caused by Fusarium solani is the most destructive disease of faba bean. The antagonistic potentials of locally isolated Trichoderma spp. from rhizosphere soils of faba bean plants in the highlands of northeastern Ethiopia were evaluated against F. solani, responsible for black root rot. All isolates of Trichoderma spp. had strong biological control activity against F. solani in vitro as well as in vivo pot experiment. Under dual culture, the percentage of mycelial growth inhibition of F. solani by the Trichoderma ranged from 33.9 to 67.0%. The highest (67.0%) inhibition was obtained from isolate TS036, while the lowest (33.9%) by isolate TS015. Pathogen-inoculated faba bean plants grown in pots that were treated with antagonists had taller plant heights and biomass than the Trichoderma untreated control inoculated with F. solani. The Trichoderma isolates significantly reduced black root rot severity on faba bean seedlings with disease reduction ranging from 64.4 to 74.6% over control. Use of Trichoderma species can be a potential source of biological control agents for the management of black root rot in faba beans grown in the region. Hence, the potential Trichoderma isolates under field condition might used as a components in the integrated management of F. solani that caused faba bean black root rot in the highlands of northeastern Ethiopia.

In Vitro and In Vivo Activity of Selected Plant Extracts against Papaya (Carica papaya L.) Anthracnose (Colletotrichum gloeosporioides)

Anthracnose is the major postharvest disease of papaya wherever the fruit crop is grown. The present investigation was conducted with the objectives of evaluating plant extracts for their activity against Colletotrichum gloeosporioides in vitro and for controlling anthracnose on artificially inoculated ‘solo’ papaya fruit. Plant specimens were collected from Ambo and Haramaya, Ethiopia, dried under shade and extracted using methanol. Out of 18 plant extracts tested, nine of them showed activity against C. gloeosporioides. Methanol extract of Echinops sp. of 10 μL from the concentration of 50 mg/ml resulted in the highest inhibition zone of 13.5 mm against mycelial growth of C. gloeosporioides. Spore germination of C. gloeosporioides was reduced by 98.7%, 97.7% and 97.3% over the control by extracts of Echinops sp., Thymus serrulatus and Ocimum lamifolium, respectively. Among four botanicals evaluated in vivo as 10% and 25% aqueous extracts, Echinops sp. at 25% concentration kept disease severity score at 1.3 out of 5 (i.e. less than 1% fruit surface affected) and maintained quality of papaya fruit during 14 days experimental period. Further study is necessary on sensory analysis and developing botanicals as natural fungicides.

The Mycotox Charter: Increasing Awareness of, and Concerted Action for, Minimizing Mycotoxin Exposure Worldwide

Mycotoxins are major food contaminants affecting global food security, especially in low and middle-income countries. The European Union (EU) funded project, MycoKey, focuses on “Integrated and innovative key actions for mycotoxin management in the food and feed chains” and the right to safe food through mycotoxin management strategies and regulation, which are fundamental to minimizing the unequal access to safe and sufficient food worldwide. As part of the MycoKey project, a Mycotoxin Charter (charter.mycokey.eu) was launched to share the need for global harmonization of mycotoxin legislation and policies and to minimize human and animal exposure worldwide, with particular attention to less developed countries that lack effective legislation. This document is in response to a demand that has built through previous European Framework Projects—MycoGlobe and MycoRed—in the previous decade to control and reduce mycotoxin contamination worldwide. All suppliers, participants and beneficiaries of the food supply chain, for example, farmers, consumers, stakeholders, researchers, members of civil society and government and so forth, are invited to sign this charter and to support this initiative.

Effect of hot-water treatments in vitro on conidial germination and mycelial growth of Colletotrichum musae isolates

Anthracnose caused by Colletotrichum musae is the most important postharvest disease of banana fruit. The present study was conducted to evaluate the sensitivity of C. musae isolates to hot water treatment in vitro. The effect of hot water treatment (HWT) in vitro was determined by placing conidial suspensions and plugs of agar with mycelia of 12 single spore isolates of C. musae in hot water bath at 45, 50 and 55°C for 2, 5, 8, 11, 14 and 17 min. Percent inhibition of conidial germination and colony growth increased with increased temperature and time combinations. HWT at 55°C for 5 min had an equivalent inhibition of conidial germination and reduction of mycelial growth to that of HWT at 50°C for 17 min in the 12 C. musae isolates. Remarkable variability in thermo-tolerance was found among 12 isolates of C. musae and isolate HC2 and HC3 were found to be the most sensitive, while DL1 and DL2 were comparatively heat tolerant isolates. Key words: Banana anthracnose, Colletotrichum musae, hot water treatment, sensitive, tolerant.