First Report of Dickeya fangzhongdai Causing Peduncle Soft Rot of Banana in China

Abstract

Banana (Musa spp.) is a popular fruit all over the world, and it’s also an important cash crop with a planting area of 358,924 ha in southern China. In July 2020, a peduncle soft rot disease occurred on dwarf banana (Musa sp. cv. Guangfen) in Guigang city (N22°50'29″, E109° 43'34″), Guangxi province, China. More than 20% plants were infected in the banana plantation. The first external sign of the disease appeared on the incisional wound after the flower bud was cut off from the peduncle. The symptom initially appeared as a black lesion on the wound, then extended into the internal tissue of the whole peduncle. In the later stages, the internal tissue became soft and rot, occasionally formed a necrotic cavity, and eventually led to the black rot of the whole peduncle with a foul smell. To isolate the pathogen, the internal lesion tissues of 5 mm × 5 mm were collected between the border of symptomatic and healthy tissue, treated with 75% ethanol for 10 s, and 0.1% HgCl2 for 3 min, then rinsed with sterile water for three times. Sterilized tissue fragments were cut to pieces with sterilized surgical shears and soaked in 5 mL sterile water, then shaken for 10 min in a vortex oscillator. The suspension was diluted 1000 times with sterilized water，then plated on nutrient-agar medium and incubated at 28℃ in darkness for 24 h. Among the 32 isolates, 23 pure bacterial cultures with similar morphology were predominantly obtained from the samples. These bacteria were gram-negative, and their colonies were initially yellowish white with irregular edges and smooth surfaces, then turned to grayish blue after 72 h incubated at 28℃. The representative isolates GZF2-2 and GZF1-8 were selected for further identification. Genomic DNA was isolated from the bacteria and the 16S rDNA was amplified with primers 27F/1492R (Weisburg et al. 1991) and sequenced. The obtained sequences (GenBank Accession No. MZ768922 and OK668082) showed >99% identities to several records of Dickeya fangzhongdai deposited in NCBI GenBank (1400/1404 bps for GZF2-2 to KT992690, 1409/1417 bps for GZF1-8 to MT613398) based on BLAST analysis. In addition, the recA, fusA, gapA, purA, rplB, dnaX genes and the 16S-23S intergenic spacer (IGS) regions of the two isolates were also amplified and sequenced (GenBank Accession Nos. OK634381-OK634382, OK634369- OK634370, OK634373-OK634374, OK634377-OK634378, OK634385-OK634386, OK634365- OK634366 and OK631722-OK631723) as described by Tian et al. (2016). All the DNA sequences matched that of D. fangzhongdai strains JS5T (percent identities>99.06%), PA1 and ECM-1 in GenBank. Neighbor-joining phylogenetic analysis by software MegaX (Kumar et al. 2018) based on the 16S rDNA sequences revealed that the two isolates were in the same clade with reported D. fangzhongdai strains. Multilocus sequence analysis of the other seven regions also showed the two representative isolates were belong to D. fangzhongdai. Therefore, the isolates were identified as D. fangzhongdai. Pathogenicity of isolate GZF2-2 was investigated to demonstrate Koch’s postulate. The end of the banana peduncles of 6 healthy plants were cut off, and 10 mL bacterial suspension (108 CFU/mL) was inoculated to the fresh wound on the plants using sterile brushes. Six control plants were inoculated with sterilized water. All the inoculated peduncles were covered with plastic bags to maintain high humidity. After 28 days, all the peduncles inoculated with strain GZF2-2 showed soft rot symptoms similar to those observed in the field, while the controls remained symptomless. The same bacteria were re-isolated from the symptomatic peduncles and confirmed by sequencing the 16S rDNA. D. fangzhongdai has been reported to cause soft rot on onion (Ma et al. 2020) and bleeding cankers on pear trees (Chen et al. 2020). To the best of our knowledge, this is the first report of D. fangzhongdai causing peduncle soft rot on banana in China.

Field surveys indicate taxonomically diverse Pectobacterium species inducing soft rot of vegetables and annual crops in Iran

“…For instance, D. fangzhongdai was isolated from banana, banxia ( Pinellia ternata ), Belamcanda chinensis syn. Iris domestica , jackfruit, onion, orchids, pear, potato and taro ( Colocasia esculenta ) (Ma et al, 2020; Tian et al, 2016; Yang et al, 2022; Zhou et al, 2021). E. mori was isolated from peach fruits (Ahmad et al, 2021), E. persicina was isolated from lettuce, Phaseolus vulgaris and Pisum sativum (Canik Orel, 2020; González et al, 2005, 2007).…”

Polyamine signaling communications play a key role in regulating the pathogenicity of Dickeya fangzhongdai

“…D. fangzhongdai is a newly emerged and defined plant pathogen which was found capable of infecting numerous host plants ( 5 , 13 – 15 , 18 – 22 ), but its pathogenic and corresponding regulatory mechanisms are mostly unknown. In this study, we used the D. fangzhongdai strain ZXC1 isolated from taro, as a model organism to investigate the role of putrescine in D. fangzhongdai physiology and virulence.…”

“…To date, about 27 D. fangzhongdai strains have been isolated and identified, infecting both monocotyledonous and dicotyledonous plants, including pear trees, taro [ Colocasia esculenta (L.) Schott], Allium cepa L , Allium fistulosum L., Phalaenopsis orchid , Aglaonema sp., Artocarpus heterophyllus Lam., Dendrobium nobile , Banxia ( Pinellia ternata ), and banana ( Musa spp.) ( 11 – 22 ). These findings suggest that D. fangzhongdai might have formidable virulence and corresponding regulatory mechanisms to outperform and infect a wide range of host organisms.…”

Retrospective survey of Dickeya fangzhongdai using a novel validated real-time PCR assay

“…However, based on the outbreak reports, it has a more significant impact on agriculture in Asia. While data on losses is limited, several authors report outbreaks on various economically important plants such as orchids ( Shen et al, 2019 ; Balamurugan et al, 2020 ; Wei et al, 2021 ; Chi et al, 2022 ), banana ( Yang et al, 2022 ), onion ( Tsai et al, 2019 ; Wei et al, 2021 ), jack fruit ( Jaffar et al, 2019 ), Asian pear ( Tian et al, 2016 ; Choi et al, 2021 ), and even staple food crops such as taro ( Dobhal et al, 2020 ; Huang et al, 2021 ; Hugouvieux-Cotte-Pattat et al, 2022 ). Based on the reports, it can be surmised that D. fangzhongdai is well established in Asia.…”

“…Multiple D. fangzhongdai outbreaks ( Tian et al, 2016 ; Jaffar et al, 2019 ; Shen et al, 2019 ; Tsai et al, 2019 ; Balamurugan et al, 2020 ; Ma et al, 2020 ; Choi et al, 2021 ; Zhou et al, 2021 ; Chi et al, 2022 ; Yang et al, 2022 ) in recent years suggest that the pathogen is present and spreading in Asia and also other continents. It was indicated before that trade plays can promote the spread of the Dickeya disease ( Toth et al, 2011 ).…”