Brenneria spp. and Rahnella victoriana associated with acute oak decline symptoms on oak and hornbeam in Iran

Abstract

Decline diseases of forest trees are complex syndromes not attributable to single causal factors. In Iran, symptoms of decline disease have been observed in a number of native forest species including Quercus castaneifolia (chestnut‐leaved oak), Q. brantii (Persian oak) and Carpinus betulus (hornbeam). The symptoms are prevalent in the northern forests and the Zagros mountain forests. There are parallels between the disease in Iran and acute oak decline (AOD) reported in the UK, specifically the presence of weeping cankers, which have been attributed to a polybacterial complex wherein Brenneria goodwinii is considered a key necrogen. Based on the AOD symptomatology, and as a first step towards discovering potential causal agents of the stem weeping symptoms of affected trees in Iran, necrotic tissues were tested primarily for the presence of B. goodwinii. Symptomatic Q. castaneifolia and C. betulus from the Mazandaran Province and symptomatic Q. brantii from Kohgiluyeh and Boyerahmad Province were sampled. Isolation and culture on a selective medium yielded uniform bacterial colonies. Isolates were characterized using phenotypic and genotypic (DNA sequencing) tests. The isolates were phenotypically identical to members of Pectobacteriaceae and Yersiniaceae, specifically Brenneria and Rahnella spp. The nucleotide sequences of the 16S rRNA and housekeeping genes gyrB, infB and atpD (MLSA) amplified via PCR demonstrated that the isolates from the trees in Iran were indeed B. goodwinii, B. roseae subsp. roseae, Rahnella victoriana and an unknown species of Brenneria. Most bacteria isolated from non‐symptomatic trees were Gram‐positive, and Pseudomonas spp. were dominant, but bacterial species isolated from the diseased trees were not detected in healthy trees. Hypersensitivity response tests were positive, but inoculation on saplings was more variable with internal necrosis developing only once in the test period. Therefore, further testing is required. This is the first report of the incidence of B. goodwinii, B. roseae subsp. roseae, R. victoriana and Brenneria sp. associated with acute oak decline‐like symptoms on Q. castaneifolia, Q. brantii and C. betulus across the western forests of Iran and in the world.

First report of bleeding canker caused by Rahnella sp. on Populus nigra in Iran

“…Samples were collected from symptomatic trees. Fifteen isolations of bacteria were made on nutrient agar (NA; Merck, Germany) from the interface between diseased and healthy tissue based on Moradi‐Amirabad et al (2019). In all cases the predominant bacteria were cream, round, convex and smooth with entire margins on NA.…”

“…DNA was extracted from a representative isolate (P1) (Moradi‐Amirabad et al ., 2019). House‐keeping genes gyrB and infB were partially sequenced (Brady et al ., 2008) (Genbank Accession Nos.…”

“…have been associated with acute oak decline symptoms (e.g. bleeding stem) on oak and hornbeam (Brady et al ., 2014; Moradi‐Amirabad et al ., 2019). This is the first report of a Rahnella sp.…”

Cultivable bacteriome dynamics in different Persian oak tissues and soil during Oak Decline Syndrome development in Iran

“…Causative agents of oak decline in Iran have not been fully determined. The possibility that a bacterial pathogen contributed to Persian oak decline had not been considered a few studies have been performed (Ahmadi et al, 2019;Moradi-Amirabad et al, 2019), although there have been previous reports of bacterial wilt of oak in other countries (Barnard et al, 1998;Scortichini et al, 1993;Brady et al, 2010;Denman et al, 2012). We explored the cultivable bacteriome of the diseased tissues in oak decline symptomatic trees vs healthy trees, in order to determine similarities and differences in the composition of bacterial communities at the site level, as well as at existing at different stages of disease (healthy vs diseased) and at the sample type levels and also in order to better characterize the distribution patterns of microbes that are pathogen and microbes that could be further exploited as biological control agents against oak diseases.…”

“…In these studies have been reportedBrenneria spp. and Rahnella victoriana (Moradi-Amirabad et al, 2019) and Bacillus pumilus andStenotrophomonas maltophilia (Ahmadi et al, 2019) as potentially causative agents involved in Persian oak decline in Zagros forests. As for the importance of fungi and bacteria as biotic factors in the phenomenon of oak decline and the lack of information in this regard, needed to further research on the effects of bacteria in this phenomenon.…”