Characterization of Burkholderia gladioli strains causal agents of saffron (Crocus sativus L.) bacterial rot

Burkholderia gladioli is the causal agent of a bacterial disease recently reported in saffron (Crocus sativus L.) grown in central Sardinia (Italy). The symptoms were rot of emerging flowers and shoots, and spots on leaves. In the last two years the disease has been particularly harmful, reducing flowering by some 80%. Isolations on nutrient glucose agar from symptomatic plants produced two types of colony. The first type (ten isolates) was round, wrinkled, and yellowish. The second type (fifteen isolates) was round, smooth and colourless. In pathogenicity tests, the twenty five isolates reproduced symptoms on saffron plants, while only the first type of isolate was pathogenic on gladiolus leaves. The twenty five isolates were analyzed with the computerised BIOLOG system, conventional tests and genomic tests such as PCR and PCR-RFLP. BIOLOG, conventional tests and PCR using LP1 and LP4 primers, identified all isolates as Burkholderia gladioli. PCR-RFLP analysis using three restriction enzymes (AluI, DdeI and BssKI), identified only ten of the isolates (nine wrinkled and one smooth) as B. gladioli pv. gladioli. Our evidence indicates that other B. gladioli forms are also involved in this bacterial rot of saffron, and further studies are under way to verify this.