Germination bioassays performed with conidia obtained from young lesions overcome most drawbacks encountered with ascospore germination bioassays and could be considered as a new reference method for fungicide resistance monitoring in this species. Different steps are proposed, from sampling to microscopic examinations, for the implementation of this technique.

Alternatives to synthetic chemicals are undertaken against phytopathogens. The aim of this work is to evaluate the effect of seed extracts of Thevetia peruviana (Pers.) K. Schum. on Mycosphaerella fijiensis Morelet, fungus responsible for banana black leaf streak disease. Five extracts of T. peruviana, hexane extract (HE), ethyl acetate extract (EAE), acetone extract (AcE), methanol extract (ME) and aqueous extract (AqE), and a fungicide, Azoxystrobin were used. GC-MS of acetone extract was performed. Fifty (50) strains of M. fijiensis per sampling site were tested. Three concentrations of extracts 6.25 (C1), 12.5 (C2), and 25 (C3) μl/ml, a negative control (0 μl/ml) and 10 ppm of azoxystrobin were used for the tests. The MIC50 and MIC90 were determined. GC-MS showed chemical compounds with different molecular height such as acids, sugars, and esters. AcE and AqE significantly reduced M. fijiensis germ tube growth at C2 and C3 concentrations and with inhibition percentage respectively ranged of 60-90% and 40-80%. The growth levels of the germ tubes were above the strobilurin resistance threshold at Njombe and peasant plantation, ranging from 77.9% to 92.3%. AcE showed the same or superior efficacy as the fungicide used on conidial germination at all tested concentrations. The MIC50 totally reducing mycelial growth and conidial germination was 6.25 μl/ml. T. peruviana seeds extracts can be exploited in integrated pests management against M. fijiensis.

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