[en] Rice and irrigated orchards are considered as the most important food and economical sources in Mali, which watered from Niger River. However, stable productions of rice and orchards products have been limited by many disease, insects, and weeds. Recently, water hyacinth infestation in river of Niger has increased drastically and as affected by the decrease of water flow due to clogging dams and irrigation work. Biological control of weeds is an alternative approach to chemical herbicide use, focusing on the use of native fungal to control or reduce the population of water hyacinth. From 2006 to 2007, 1000 samples consisting of infected parts of water hyacinth were collected from the River Niger (District of Bamako, Segou and Niono with GPS coordinates “12° 40’ N, 7° 59’ W” ; “13° 26’ N, 6° 15’ W” and “14° 15’ N, 5° 59’ W” respectively) in Mali. Fungal belonging to seven genera (116 isolates in all) were recovered from surface-sterilized water hyacinth parts with pronounced blight symptoms. On the basis of in vivo pathogenicity tests in which the diseased leaf area percentage was estimated visually and disease severity was estimated (by calculating a disease severity index), three isolates emerged as causing severe disease: Fusarium sp. isolate Mln799 (DS = 70%), Cadophora sp. isolate Mln715 (70%), and Alternaria sp. isolate Mlb684 (71%), identified respectively as Gibberella sacchari (Anamorph. Fusarium sacchari), Cadophora malorum, and Alternaria sp. This is the first report to highlight C. malorum as a candidate biocontrol agent for water hyacinth. Influence of ecological parameter, water activity (0.880 - 0.960aw modified par glycerol) and temperature (15-35°C) on viable conidia and mycelial growth rate of Alternaria sp. (isolate Mlb684), F. sacchari (isolate Mln799) and C. malorum (isolate Mln715) were evaluated. Germination and mycelial growth dropped as aw of the medium decreased. Results showed a significant effect of aw, temperature and their interaction on mycelial growth (P < 0.0001). Growth models for F. sacchari (isolate Mln799), C. malorum (isolate Mln715) and Alternaria sp. (isolate Mlb684) differed slightly, with R2 values of 93.40, 85.89 and 77.31% respectively. Mycelial growth models, no different between predicted and experimental values was observed. Results confirm the previous finding that aw has greater influence on growth of F. sacchari (isolate Mln799), C. malorum (isolate Mln715) and Alternaria sp. (isolate Mlb684) than temperature. Analyse of 5 target regions of isolate Mlb684 genome (18 and 28S ribosomal RNA genes, Elongation factor-1 alpha gene, calmodulin gene and actin gene) allowed identifying this isolate as new specie in Alternaria genus. The strain has been deposited under accession number MUCL 53159 in the Industrial Fungal & Yeast Collection (BCCMTM/MUCL, Belgium) and DNA sequences have been deposited in GenBank. We have named it “Alternaria jacinthicola Dagno & M.H. Jijakli”. It was the first sequenced of calmodulin gene reported in Alternaria genus. Water hyacinth, paddy and wheat substrates for mass production of these biocontrol agents were evaluated. Greater sporulation of C. malorum (isolate Mln715) was observed on water hyacinth substrate (4.08 x 107 spores ml-1) following by wheat (1.06 x 107 spores ml-1). Biocontrol efficacy of fungal isolates found to be enhanced with unrefined Carapa procera (L) oil and refined palm oil supplemented with soybean lecithin in greenhouse. Applying C. malorum (isolate Mln715) and A. jacinthicola (MUCL 53159 strain) in vegetable oil emulsion [Carapa procera (L) and palm oils] caused 87.02 to 93.13% of damage severity on water hyacinth 6 weeks after treatment. Field trials showed lower efficacy control than greenhouse tests. In host specificity tests, neither C. malorum isolate Mln715 nor Alternaria sp. isolate Mlb684 showed any pathogenicity towards any member of a panel of 17 crop plants of economic importance in Mali.
Coopération Technique Belge (CTB)-Belgique ; Institut d'Economie Rurale (IER)-Mali ; Laboratoire de Phytopathologie de Gembloux Agro Bio Tech-Belgique