First report of latent infection of Malva nicaeensis caused by Pectobacterium carotovorum subsp. brasiliense in Israel.
To study the dissemination of Potato blackleg (Pcb) to weeds, a survey was conducted in potato fields in Israel where Pcb-infected plants were detected during the spring of 2018. Symptomless weed plants from 13 genera and 10 families, i.e. Solanum americanum (Solanaceae), Polygonum equisetiforme (Polygonaceae), Centaurea procurrens, Sonchus oleraceus (Asteraceae), Lolium rigidum, Phalaris brachystachys, Avena sterilis (Poaceae), Malva nicaeensis (Malvaceae), Amaranthus blitoides (Amaranthaceae), Chenopodium murale (Chenopodiaceae), Chrozophora tinctoria (Euphorbiaceae), Orobanche aegyptiaca (Orobanchaceae) and Erucaria rostrata (Brassicaceae), were randomly collected from areas where potato plants infected by Pcb or Dickeya solani had been identified. Roots or stems (in the case of O. aegyptiaca) of 6-15 plants of each weed were washed, surface sterilized, macerated in sterile distilled water and the suspensions were plated on crystal violet pectate medium. Cavity forming bacteria were transferred to nutrient agar for further characterization. Pcb was isolated only from latently infected Malva nicaeensis plants and with an incidence of 16.7%. DNA extracted from these colonies reacted positively in a PCR assay using BR1f/L1r specific primers and also in a TaqMan assay based on araC sequence. Sequencing the gapA gene identified the isolate as Pcb (GenBank Accession No. MK086015). A maceration assay on potato tubers at 30°C was positive. This is thought to be the first report of latent infection of Pectobacterium carotovorum subsp. brasiliensis in one of the most prevalent weeds in potato fields in Israel, Malva nicaeensis.