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The results of our experiments suggest that toxin(s) of Mycosphaerella fijiensis would be involved neither in infection initiation, nor in the hypersensitive reaction in highly resistant cultivars but could serve at most as secondary determinant of the pathogenicity, contributing to the lesion expansion in cultivars exhibiting partial resistance to Black Leaf Streak disease. Moreover, the effects of toxin(s) on chlorophyll fluorescence, as well as preliminary electron microscopy observation, suggest that chloroplasts could be a precocious site of action of the toxin(s). Therefore, in vitro heterotrophic tissues would not be a suitable target to perform the screening with such toxin(s). The prospects and limitations of M. fijiensis toxin(s) for screening banana for resistance to Black Sigatoka are highlighted. This revised version was published online in July 2006 with corrections to the Cover Date.     

三种猎物对小黑瓢虫成虫繁殖及寿命的影响

在实验室条件下,以自然猎物烟粉虱Bemisiatabaci为对照,研究了替代猎物红蜘蛛Tetranychusnr.fi jiensis和桃蚜Myzuspersicae(Sulzer)对小黑瓢虫成虫繁殖及寿命的影响,结果表明:(1)小黑瓢虫以蚜虫为猎物时,成虫不产卵,但可延长寿命;以红蜘蛛为猎物时,成虫可产卵。与自然猎物烟粉虱相比,小黑瓢虫取食替代猎物红蜘蛛的产卵前期延长,总产卵量及平均每雌每天产卵量减少,而两者之间的性比、产卵率及产卵期无显著差异。(2)三种猎物条件下雌虫寿命之间显著性无差异,而雄虫寿命之间的差异达显著水平,t测定法进一步表明,雄虫寿命在蚜虫与红蜘蛛之间差异显著,而在蚜虫与烟粉虱之间、以及烟粉虱与红蜘蛛之间均无显著差异。     

Analysis of the CYP51 gene and encoded protein in propiconazole‐resistant isolates of Mycosphaerella fijiensis

BACKGROUND: Mycosphaerella fijiensis Morelet causes black sigatoka, the most important disease in bananas and plantains. Disease control is mainly through the application of systemic fungicides, including sterol demethylation inhibitors (DMIs). Their intensive use has favoured the appearance of resistant strains. However, no studies have been published on the possible resistance mechanisms. RESULTS: In this work, the CYP51 gene was isolated and sequenced in 11 M. fijiensis strains that had shown different degrees of in vitro sensitivity to propiconazole, one of the most widely used DMI fungicides. Six mutations that could be related to the loss in sensitivity to this fungicide were found: Y136F, A313G, Y461D, Y463D, Y463H and Y463N. The mutations were analysed using a homology model of the protein that was constructed from the crystallographic structure of Mycobacterium tuberculosis (Zoff.) Lehmann & Neumann. Additionally, gene expression was determined in 13 M. fijiensis strains through quantitative analysis of products obtained by RT‐PCR. CONCLUSION: Several changes in the sequence of the gene encoding sterol 14α‐demethylase were found that have been described in other fungi as being correlated with resistance to azole fungicides. No correlation was found between gene expression and propiconazole resistance. Copyright © 2009 Society of Chemical Industry     

海南省香蕉褐缘灰斑病菌的鉴定及ITS序列分析

对能单独引起香蕉嫩叶的坏死反应的4个菌株的形态特征、致病性及其核糖体DNA-ITS序列进行分析。结果表明,测试菌株在PDA 平板上的菌落生长缓慢、呈圆形白色突起、分生孢子到棍棒形,有隔膜和明显孢痕。进一步克隆并分析供试菌株的DNA-ITS序列,证实了目前引起海南省香蕉叶斑病的主要病原菌为斐济球腔菌Moslarerell.fijiensis。根据Genbank上的相关序列,设计了专门检测鉴定Mfirsis的特异性引物 PFijFl∶5'CCTTTGTGAACCACAACT3';PfijR1∶5'TCCGAAGCGAATTGAAAA3',可用于香蕉褐缘灰斑病M. fijisis的分子鉴定及其辅助检测工作。