## 1 Introduction  
Pectobacteria are plant pathogens that cause soft rot, black leg and will in numerous plant species in more than 35% of angiosperm plant orders. Host specificity has never been considered to be an attribute of petobacteria, although some host specificity has been described for _Pectobacterium atrosepticum_ and _P. wasabiae_ in connection with adaptation to a cooler climate and relatively narrow (but not exclusive) host range, that is potato (_Solanum tuberosum_) and Japanese horseradish (_Eutrema japonicum_), respectively [1; 2; 3]. In terms of host range, _P. caroovorum_ probably has the widest host range and geographical distribution, with strains of this species isolated from various substrates including plant surfaces and tissues, soil, water and the gut and surfaces of invertebrates [4]. Another broad host range species is _P. brasiliense_, which is associated with potato grown in relatively warm regions in Brazil, Israel, South Africa and United States, but may also infect other crops [5]. With the ever-increasing availability of genomic sequences, several taxonomic changes have been made, including the suggestion to transfer _Pectobacterium_ and _Dickeya_ into the family Pectobacteriaceae [6]. According to the present taxonomy, the genus now includes 18 species: _P. actinidae_, _P. aquaticum_, _P. aroidearum_, _P. atrosepticum_,P. betavascalorum, P. brasiliense, P. cacticida, P. caroovorum, P. odoriferum, P. parametieri, P. parvum, P. peruviense, P. polaris, P. polonicum, P. punjabense, P. versatile, P. wasabiae and P. zantedeschiae, [4, 7, 8, 9, 10, 11]. In spite of the clarifying taxonomy, the mechanisms underlying this natural segregation are largely unexplored. The last decade, has proved that _P. caroovorum_ had been serving as a catchal designation for petobacterial isolates that did not fall within any other specific taxon [12]. The use of multi-locus sequence analyses (MLSA) revealed the heterogeneity of _P. caroovorum_, and the insufficient resolution of former taxonomic tools. One particular example was the isolates of _P. caroovorum_ obtained from monocot hosts. These were reported to be more virulent on monocot plants than on dicot plants, presented typical amplified fragment length polymorphism (AFLP) profiles and distinct banding pattern in intergenic transcribed spacer (ITS) PCR analysis [13]. The combination of molecular patterns with MLSA and recombinase polymerase amplification analyses indicated that these monocot isolates represent multiple species in the genus, _P. aroidearum, P. zantedeschiae, P. betavascalorum_, and _P. wasabiae_[12, 14, 15]. Atypical infections have also been reported in other monocots including _Allium cpa_[16], _Zantedeschia_ spp. [17, 18], _Dieffenbachia_ spp., _Scindapsus aureus_[19], _Oriithogalum dubium_[1] and _Pinellia ternate_[20]. Past studies have shown that, under laboratory conditions, a single strain may infect several plant species, including crop plants such as potato, carrot (_Daucus carota_ subsp. _sativus_), cabbage, tomato (_Solanum lycopersicum_) and peppers (_Capsicum annuum_) [1, 4]. Host adaptation (specialization) has been suggested as one of the forces underlying the course of _Pectobacterium_ evolution, but this hypothesis has not been extensively examined [13, 16, 21]. Greater fitness for infection of a host or a limited group of hosts was suggested mainly based on phylogenetic comparisons, geographical distribution and associations with the taxonomy of the hosts [22, 23]. Only a few studies have focused on physiology or virulence patterns of different strains on taxonomically diverse hosts [13, 17]. Here, host specialization was tested using two _Pectobacterium_ strains, a'monocot strain' (PC16, isolated from _Zantedeschia_) and a 'dicot strain' (WPP14, isolated from potato) on calls lily (_Zantedeschia aethiopica_) and cabbage (_Brassica oleracea_ var. _capitata_).