6533b828fe1ef96bd128793b

RESEARCH PRODUCT

Occurrence of tomato pith necrosis caused by Pseudomonas marginalis in Italy.

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Dipartimento di Scienze e Tecnologie Fitosanitarie. Universita` degli Studi di Catania. Via Santa Sofia 100, 95123 Catania, ItalyIn 2006, a serious outbreak of tomato pith necrosis (TPN) with approxi-mately 90% disease incidence was observed in two greenhouses in Sicily.Adult fruiting plants showed chlorosis and slight wilting of shoot apices.Internalstem browning alongthe entire length oftheplant was observed.Pith tissues were soft but not rotted or hollowed. Only fluorescent colo-nies developed on King’s B medium (KB) after isolation from infected tis-sues. Ten pure isolates were all levan, oxidase, potato soft-rotting andarginine dihydrolase positive and were negative for tobacco hypersensi-tivity; they produced 2-ketogluconate, nitrate reductase, acid fromsucroseandlecithinasefromeggyolk,andwerethusLOPATgroupIVaofthe fluorescent pseudomonads, which corresponds to Pseudomonasmar-ginalis.Tomato cv. Marmande plantlets (ten plantlets per isolate) were prickinoculated at the axil of the first true leaf with a pin coated with 24 hr-old cells grown on KB. After inoculation, plants were covered withplastic bags for 48 h, then uncovered and kept in a growth chamber at27 C with a photoperiod of 16⁄8 h. Two weeks after inoculation, allshowed extensive stem pith browning extending 2-4 cm from the inoc-ulation point. Two representative bacterial isolates were identified asP. marginalis by using the Biolog Identification System (version 4AE2;Biolog, Inc.) with a similarity of 0AE93. Their partial 16S rDNAsequences were identical and they shared 99-100% identity with otherP. marginalis strains available in GenBank. These results confirm theiridentity as P.marginalis.Pseudomonas corrugata and P. mediterranea are considered the maincausal agents of TPN (Catara, 2007) although a number of fluorescentpseudomonads have also been identified in different countries as causalagents. They include P.cichorii, P.viridiflava, P.fluorescens (Sutraetal.,1997;LoCantoreIAlippietal.,2003) andthe fluores-cent Pseudomonas strains assigned to three unnamed genomospecies bySutra et al. (1997). However, this is the first report of P. marginalis as acausalagentofTPN.References