Rahnella spp. are commonly isolated from onion ( Allium cepa ) bulbs and are weakly pathogenic

Abstract

Aims: Bacterial decays of onion bulbs have serious economic consequences for growers, but the aetiologies of these diseases are often unclear. We aimed to determine the role of Rahnella, which we commonly isolated from bulbs in the United States and Norway, in onion disease. Methods and Results: Isolated bacteria were identified by sequencing of housekeeping genes and/or fatty acid methyl ester analysis. A subset of Rahnella spp. strains was also assessed by multilocus sequence analysis (MLSA); most onion strains belonged to two clades that appear closely related to R. aquatilis. All tested strains from both countries caused mild symptoms in onion bulbs but not leaves. Polymerase chain reaction primers were designed and tested against strains from known species of Rahnella. Amplicons were produced from strains of R. aquatilis, R. victoriana, R. variigena, R. inusitata and R. bruchi, and from one of the two strains of R. woolbedingensis. Conclusions: Based on binational testing, strains of Rahnella are commonly associated with onions, and they are capable of causing mild symptoms in bulbs. Significance and Impact of the Study: While Rahnella strains are commonly found within field-grown onions and they are able to cause mild symptoms, the economic impact of Rahnella-associated symptoms remains unclear.

Rahnella perminowiae sp. nov., Rahnella bonaserana sp. nov., Rahnella rivi sp. nov. and Rahnella ecdela sp. nov., isolated from diverse environmental sources, and emended description of the genus Rahnella

“…A study by Asselin et al . [13] indicated the existence of several potential novel Rahnella species, isolated over a number of years from onion bulbs with signs of bacterial decay in the United States and Norway, and from creek water in the United States. Multilocus sequence analysis (MLSA) of a selection of onion isolates placed them in four separate clusters without reference strains in the genus Rahnella , suggesting they belong to four novel taxa [13].…”

“…[13] indicated the existence of several potential novel Rahnella species, isolated over a number of years from onion bulbs with signs of bacterial decay in the United States and Norway, and from creek water in the United States. Multilocus sequence analysis (MLSA) of a selection of onion isolates placed them in four separate clusters without reference strains in the genus Rahnella , suggesting they belong to four novel taxa [13]. A further potential novel Rahnella taxon was identified in this study following gyrB gene sequencing of a strain previously isolated from a Quercus species displaying symptoms of acute oak decline (AOD) in the Netherlands.…”

“…Bacterial strains were previously isolated from onion bulbs in the United States (New York State and Oregon) and Norway (Vestfold, Østfold, Oppland and Hedmark) as described in Asselin et al . [13], either directly from onion tissue or following soaking and crushing in buffer or sterile water. Strain FC061912-K T was isolated from creek water following high-speed centrifugation and culturing.…”

The Effect of Gaseous Ozone Generated by Surface Dielectric Barrier Discharge on the Decay and Quality of Stored Onion Bulbs

“…The results of this study indicate that the reduction of rotten onion bulbs might be a result of the reduced counts of R. aquatilis by the ozone treatment during the two months of storage. It was previously found that scale discoloration and shrinkage appear when R. aquatilis is present with other pathogens in onion bulbs [3]. About 30% of onion bulbs are reported to be rotten due to pathogen invasion, suggesting that synthetic fungicides, bio fungicides or other novel methods should be used to reduce postharvest loss of onion bulbs [29].…”

“…However, their decay often occurs due to postharvest pathogens and results in serious economic loss [2]. Some bacterial pathogens including Rahnella strains are able to cause disease symptoms such as discoloration and softening of the onion bulbs at 5 °C [3], and other pathogens including fungi cause severe disease such as black mold, blue mold and neck rot in onion bulbs [4]. To prevent these diseases during cold storage, the practical use of sulfur fumigation has been carried out in storage rooms [5].…”