A bacterial disease of saffron caused by Burkholderia gladioli and Pseudomonas spp.

Symptoms of a disease of possible bacterial origin were observed in the leaves and corms of some saffron plots in Sardinia since October 2003. The leaves had reddish brown spots, that were either isolated or coalescing and were surrounded by a large chlorotic halo. The corms had yellowish-brown rounded spots, which tended to become black with time. Isolation on nutrient agar from corms and leaves produced numerous cream to yellowish- brown and white-cream bacterial colonies mixed with others characterized by a yellow hue. Based on their frequency, ten colonies were selected, four of which were cream to yellowishbrown, four white-cream, and two yellowish. In pathogenicity tests, only four of ten isolates reproduced the symptoms on saffron leaves and corms, and three could also infect tomato plants. These four virulent isolates were identified with conventional tests and the computerised system BIOLOG. One isolate was identified as Burkholderia gladioli, one as Pseudomonas corrugata while the remaining two were P. fluorescens biotype F. The latter three isolates reacted positively with a serum to P. corrugata anti IPVSS-6FP. Fatty acid profiles of two representative isolates confirmed that one was Burkholderia sp., and the other Pseudomonas sp. (P. fluorescens/P. marginalis/P. putida). We suggest that isolates of B. gladioli and Pseudomonas spp. are responsible for the saffron disease found in Sardinia. B. gladioli has only been reported once in the literature. Genomic characterization of the other three pseudomonads is underway.