Barrage formation is independent from heterokaryon incompatibility in Verticillium dahliae
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Barrage formation has been traditionally used for the assessment of mycelial compatibility in many fungi and has often been assumed to represent a non-self recognition phenotype that is directly associated with vegetative incompatibility in these organisms. In this work, the optimal growth conditions for large-scale studies of barrage formation in the asexual fungus Verticillium dahliae were determined, and they were used for the analysis of a diverse collection comprising 69 isolates of V. dahliae and related species. Barrage formation was very frequent on a defined complete agar medium within V. dahliae and between species of the genus. However, it was not correlated with the classification of V. dahliae isolates into Vegetative Compatibility Groups (VCGs) (based on the standard method using complementary nit mutants), as it was recorded at high frequencies both within and between V. dahliae VCGs. The high overall frequency of barrage formation demonstrated the presence of a higher level of mycelial incompatibility in V. dahliae than heterokaryon incompatibility assessed by forcing complementary nit mutants to form heterokaryons under selective conditions. The possible association of barrage formation with morphological characteristics of the fungal colonies was investigated, and a negative correlation of frequency and intensity of barrages with the isolates’ capacity for pigment production was detected.
KeywordsBarrage formation Heterokaryon incompatibility Mycelial compatibility groups Mycelial interactions Non-selective compatibility tests Vegetative compatibility
The authors would like to thank all individuals listed in the footnote of Table 1 who provided fungal isolates that were used in this study. Furthermore, Prof. P. Apostolakos and Dr. P. Livanos (Faculty of Biology, National and Kapodistrian University of Athens) are gratefully acknowledged for their valuable help with live-cell imaging and fluorescent staining techniques. I. A. Papaioannou and this research have been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF)—Research Funding Program: Heracleitus II. Investing in knowledge society through the European Social Fund.
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