3.7. Plant sanitary status
In October 2014, the first symptoms of blister bark were observed on two plants from the FR location where no previous manifestation of disease had occurred in the past. The two plants belonged to the same experimental block and were separated by only two plants, which resulted as not-symptomatic. The soil substrates of the two symptomatic plants were sandy loam in one case and silt loam in the other.
The two plants showed the typical symptoms: alteration of bark colour to red-rusty and occurrence of blisters accompanied by the flaking off of the epidermis. The removal of trunk epidermis revealed extensive necrosis. In addition, premature wilting of the leaves and a general lack of vigor in plants were observed (Fig. 6).
During early spring 2015, the same symptoms appeared on 23 plants located in the SY site. Three weeks later, a 24th plant showed the symptoms, the latter cultivated on sandy loam soil. In this case,75% of plants on the peat, 40% on the sandy loam and 5% of the silt loam treatments were affected.
The isolations from all the symptomatic plants yielded the occurrence of many fluorescent colonies on KB. Representativeisolates were streaked in purity for subsequent identification.All isolates were positive for levan production as well as forhypersensitivity response on tobacco leaves, and negative for the presence of oxidase and arginine dihydrolase and for potato rot-ting (LOPAT group IA). In addition, they hydrolysed aesculin andarbutin, liquefied gelatin, utilized in ositol, quinate and sorbitol butnot anthranilate, homoserine or L(+)-tartrate, and did not producetyrosinase. Furthermore, all the isolates induced necrotic lesion on lemon fruits and were positive for the detection of the syrB gene,coding for syringomycin phytotoxin production. All isolates were identified as P. syringae pv. syringae.