Biscogniauxia mediterranea associated with cork oak (Quercus suber) in Tunisia: Relationships between phenotypic variation, genetic diversity and ecological factors

Abstract

Biscogniauxia mediterranea is a xylariaceous ascomycete responsible for ‘charcoal disease’, the most frequent disease of cork oak in the Mediterranean basin. However, little is known regarding this fungus in North Africa. This is the first report on the morphological and genetic diversity of B. mediterranea populations in Tunisia. A total of forty-eight isolates from cork oak trees, corresponding to three different sites and three tree parts, were identified as B. mediterranea based on morphological and molecular diagnosis. Variability among the isolates was evaluated using morphological traits and microsatellite-primed PCR (MSP-PCR). B. mediterranea isolates showed high variability in culture, specifically in colony color. A high level of genetic diversity within populations and within tree parts was detected (H = 0.417, I = 0.605, and H = 0.415, I = 0.601 respectively). Significant genetic differentiation among populations (G ST = 0.116 and Φ ST = 0.137; p < 0.001) was determined. However, a low genetic differentiation among tree parts (G ST = 0.066 and Φ ST = 0.018; p = 0.07) was observed. Principal coordinate analysis showed that genetic divergence was partially related to the geographical origin. Cluster analysis based on morphological traits showed that the grouping of the isolates occurs independently of the geographic location and the tree part. The effective number of alleles (Ne), the Nei's gene diversity index (H), the Shannon's information index (I), the colony color and the presence of exudates were significantly correlated with the altitude and the rainfall. The number of alleles (Na), the percentage of polymorphic loci (PPL), the texture and the density of the mycelium were significantly correlated with the temperature. These results provide a deeper understanding of population genetics of B. mediterranea and its adaptation to environmental conditions which could help to develop control strategies against charcoal canker disease.