GENOMIC CHARACTERIZATION OF PSEUDOPHAEMONIELLA SPECIES OCCURRING IN THE SAPWOOD OF HEALTHY AND DISEASED OLIVE TREES AFFECTED BY QUICK DECLINE SYNDROME

The new fungal species Pseudophaeomoniella oleae FV84 and Ps. oleicola M24 have been found associated with brown wood streaking and wilting symptoms of various olive varieties, either healthy or infected by Xylella fastidiosa subsp. pauca (Xfp), in Apulia (Southern Italy). Pathogenicity tests were performed in glasshouse, on young olive plantlets, cv Cellina di Nardò, indicate that fungal strain(s) alone are able to colonize the olive xylem, and to cause wood streaking. However, only few twigs, proximal to the inoculation point, showed wilting symptoms. Trials on the possible interaction among Xfp and these fungal species on aged and centenarian olive plants in the open field are currently in progress. Considering the high diffusion of Ps. oleae and Ps. oleicola over the olive growing areas in Apulia, a genomic characterization study was started, in order to investigate the biology of these fungi, and to ascertain any possible interaction with Xfp and the Olive Quick Decline Syndrome (OQDS). The two draft genomes have a total length of about 27, 44 and 26,7 Mb for Ps. oleicola and Ps. oleae, respectively. Gene annotation of Ps. oleicola M24 and P. oleae FV84 resulted in about 7,500 predicted protein-coding genes, of which about 300 resulted putative genes coding for cell wall degrading enzymes. Secondary metabolite biosynthesis gene clusters were identified for the two strains, M24 and FV84, resulting in 22 (M24) and 23 (FV84) gene clusters, some of which encoding polyketide synthetases (PKS) and nonribosomal peptide synthetases (NRPS). From the analysis, two gene clusters involved in fusaric acid and fujikurins biosynthesis, were also predicted, thus suggesting a possible role as phytopathogenic virulence determinants. Moreover, a trans-resorcylide biosynthetic gene cluster was also predicted in Ps. oleae FV84. Further researches are in progress to clarify the biology of these species, their role on aged olive plants, and to better characterize the production of secondary metabolites that can interact both with Xfp and with the microbial community into the olive xylem.