Minor root rot pathogens of cassava (Manihot esculenta Crantz) in Nigeria

Many different species of fungi are often isolated from rotted cassava root tubers and pathogenicity studies have often implicated Botryodiplodia theobromae and Fusarium solani as the major causal pathogens. Consequently, more attention has often been focused on Botryodiplodia theobromae and Fusarium solani with little or no attention on the other minor pathogens. Considering the increasing importance of cassava to the Nigerian economy and the fact that minor root rot pathogens of cassava today could become major tomorrow, the aim of this research is to determine the incidence, pathogenicity and symptoms of the minor root rot pathogens in cassava from cassava fields within the derived savanna and the humid forest of Nigeria. Isolation of associated fungi was done on rotted root samples and the pathogenicity of these isolates were established by inoculating them into healthy cassava tuberous roots and subsequently reisolating them from resulting rotted tissue. The less frequently isolated fungi where Macrophomina sp., Trichoderma sp., Aspergillus niger, Aspergillus flavus, Sclerotium rolfsii and Fungus ‘A’ (a yet to be identified fungus). Repeated experiments confirmed a constant relationship between inoculated fungus and the resulting rotted tissue colour. The root rot tissue colours associated with inoculated pathogens in the laboratory were identical with the pathogens colony colour on potato dextrose agar.     

Characterization of blackleg and soft rot from potato in northern Thailand

Blackleg and soft rot of potato cause economic loss through reduced yield and quality. The causal agents of bacterial blackleg and soft rot of potato were identified based on biological data and sequence analyses of the 16S rDNA gene. Between 2016 and 2018, diseased potato stems and tubers were collected in Chai Prakan District, Chiang Mai Province, and Chiang Khum District, Pa Yao Province. The symptoms included black stem lesions, soft rot on tubers, wilting, break down of the stem vascular ring and foliar yellowing. Of 13 bacterial isolates, five were identified as Pectobacterium carotovorum subsp. brasiliense, four‐Dickeya dadantii, two‐Pseudomonas putida and two‐Bacillus altitudinis. Pathogenicity tests of P. carotovorum subsp. brasiliense and D. dadantii resulted in lower leaves turning yellow and wilting followed by blackleg symptoms on lower stems and maceration of tuber tissue. Symptoms caused by P. putida were yellowing and wilting of leaves. B. altitudinis caused yellowing of the lower leaves and wilting followed by drying of leaf tissue. This is a first report of these bacterial pathogens causing blackleg and soft rot of potato in Thailand.     

Role of associative bacterial interaction in the induction of tuber rot incidence in cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz), one of the leading staples in the world, has considerable scope for integration into emerging markets through efficient and environmentally sound production of a diversified range of high quality, competitive products for food, feed and industry. One of the major reasons attributed to the low productivity of cassava in India is the incidence of tuber rot in cassava incited by Phytophthora palmivora. Usually, an array of microorganisms is involved in rotting of cassava tubers in the field and in postharvest conditions. Unfortunately, the disease management practices focus mainly on fungal pathogens. In this article, we tried to investigate the role of associative bacterial pathogens in induction of tuber rot of cassava, the potential of the bacteria with P. palmivora in causing disease incidence, spread and rotting. The bacteria and P. palmivora were originally isolated from tuber rot infected cassava from the field having a disease incidence percentage of above 40%, checked for pathogenicity and were proven for Koch postulate. The detached tubers of disease resistant (cv. Sree Pathmanabha) and susceptible cultivars (cv. M₄) of cassava were used for the study. The effect of bacterial association was studied in Cassava agar plate assay, in detached tubers and in in planta experiments in in vitro glass house conditions. The bacterial isolates were identified as Gram-negative coco bacilli of class Pseudomonas, Erwinia amylovora and Achromobacter denitrificans.     

Fungi associated with storage rots of cocoyams (Colocasia spp.) in Nsukka,Nigeria

Cocoyam (Colocasia spp.) corms and cormels showing spoilage symptoms were collected from many stores in Nsukka locality and examined for rot and associated fungal pathogens. Aspergillus niger, Botryodiplodia theobromae, Corticium rolfsii, Geotrichum candidum, Fusarium oxysporum, and F. solani were recovered from rotten cocoyams. The representative isolates of these species caused cocoyam rot in pathogenicity tests. The rot due to A. niger, B. theobromae and C. rolfsii was extensive resulting in complete maceration of cocoyam tissue. Potassium sorbate (0.1 mg/ml) protected cocoyams from fungal rot with the exception of C. rolfsii.     

一种由粉红粘帚霉引起的青稞根腐病

[背景]根腐病在青稞生产中的危害日趋严重,阻碍了青稞根腐病的有效防控及青海省青稞产业的发展。然而人们对青稞根腐病的研究甚少且病原菌不详。[目的]明确青稞根腐病发生的危害、病原及致病性,为青稞根腐病的防控提供理论依据。[方法]采用常规的组织分离法分离青稞根腐病病原,通过形态鉴定与分子鉴定结合的方法对病原进行鉴定,并采用烧杯水琼脂法测定其致病性。[结果]共分离得到4株青稞根腐病病原菌,鉴定为Clonostachys rosea,有较强的致病性且致病性差异显著,经柯赫氏法则验证为青稞根腐病病原菌,并且是一种新的青稞根腐病病原,该类根腐病也是一种新的根腐类病害,在国内外属首次发现。[结论]Clonostachys rosea可引起青稞根腐病且致病性强。     

Fungi associated with boll and lint rot of cotton in Southern Khorasan province of Iran

During surveys of cotton fields since 2009 in the Southern Khorasan province of Iran, symptomatic samples with lint and boll rot disease signs were collected and cultured on potato dextrose, malt extract agar and PARPH media. Several fungal isolates were obtained and identified. Among them, we found Penicillium expansum which to our knowledge is reported as a new pathogen of cotton worldwide; Fusarium semitectum and Nigrospora oryzae (associated to mite Siteroptes sp.) were also recorded as lint or boll rot pathogens for the first time from Iran. Disease symptoms and fungal characteristics of Exserohilum rostratum, which has been reported briefly as a new causal agent of boll and lint rot disease, are illustrated and presented. In addition, Aspergillus niger and Rhizopus spp. were also isolated frequently from lint parts of cotton prior to harvesting. There was a positive correlation between disease occurrence and spiny cotton bollworm damage. The pathogenicity test was characterised by inoculating the attached and detached bolls of cotton plants.     

Characterization of Bacillus altitudinis as a New Causative Agent of Bacterial Soft Rot

A total of 67 bacterial isolates were obtained from apple and pear fruits with signs of soft rot collected from Egyptian markets. Pathogenicity tests showed that 25 isolates (37%) were pathogenic to apple and pear fruits, with considerable variation of virulence. Among these isolates, 16 (64%) were Gram‐positive, motile, spore‐forming long rods and were identified as members of the genus Bacillus based on an API test. In addition, five isolates (20%) were Gram‐negative, non‐spore‐forming, motile, oxidase and catalase‐positive short rods and were identified as members of the genus Pseudomonas. Furthermore, four isolates (16%) were Gram‐negative, non‐spore‐forming, motile, catalase‐positive and oxidase negative short rods and were identified as belonging to the genus Erwinia. All selected isolates showed a wide host range and could cause soft rot of all representative fruits and vegetables tested. The three most virulent isolates, AB4, AB6 and PB6, exhibited the highest soft rot severity on different apple and pear cultivars, and apple cv. Anna (116) was the most susceptible to infection by isolates AB4 and AB6, with soft rot severities of 63.33 and 60.67%, respectively. Also, pear cv. Le‐Conte was most susceptible to infection by isolate AB6, with a soft rot severity of 89.9%. A phylogenetic tree based on 16S rRNA gene sequences indicated that strains AB4 and AB6 were very similar to one another and also showed a similarity of 99% to Bacillus altitudinis, and strain PB6 revealed a similarity of 99% to Bacillus pumilus. To our knowledge, this is the first report of B. altitudinis as a soft rot pathogen for both apple and pear fruits.     

Molecular detection of Pectobacterium species causing soft rot of <Emphasis Type="Italic">Amorphophallus konjac</Emphasis>

Soft rot disease of Amorphophallus konjac is caused by Pectobacterium species. Infected corms are considered a primary and important source of inocula. Based on the 16S rDNA sequences of the soft rot pathogens, one pair of specific primers was designed to identify the soft rot disease by real-time PCR and the other two were used to identify the pathogens of Pectobacterium carotovorum subsp. carotovorum. and P. chrysanthemi respectively. According to the results, a single cell of Pectobacterium could be detected by real-time PCR with the designed primer pair, while at least 100 bacteria were required for conventional PCR. Moreover, the two special primers can directly and accurately authenticate to Pectobacterium carotovorum subsp. carotovorum and P. chrysanthemi by the conventional PCR system without testing the pathogenicity, biochemical and phenotypic characterizations and so on. In conclusion, the PCR-based techniques showed several significant advantages in identifying the soft rot pathogens from konjac, such as higher sensitivity, rapidness and precision, and it could be widely used in seed quarantine.     

Pectolytic Bacteria Associated with Soft Rot of Calla Lily (Zantedeschia spp.) Tubers

Soft rot is the most important disease on calla lily in Poland. The isolation of the presumptive pathogen from symptomatic tubers on nutrient agar yielded bacteria with different colony morphology. Of 41 isolates collected, 10 showed pectolytic activity on crystal violet pectate medium and caused soft rot on potato slices. All pectolytic bacteria appeared to be Gram‐negative rods producing typical soft rot on inoculated leaf petioles of calla lily. Bacteria with colonies which morphologically resembled those used for inoculation were re‐isolated from diseased petioles. Their identification was based on phenotypic characters and sequence of the gene fragment coding 16S rRNA. It was found that, in addition to Pectobacterium carotovorum subsp. carotovorum, soft rot of calla lily can be caused by Pectobacterium carotovorum subsp. atrosepticum, Pseudomonas marginalis, Pseudomonas veronii and Chryseobacterium indologenes. The latter two are described for the first time as plant pathogens. The pectolytic activity of all identified bacteria, except that of P. carotovorum subsp. atrosepticum, was lower than that of P. carotovorum subsp. carotovorum, but strains of P. veronii showed a higher activity than P. marginalisand C. indologenes species.     

Control of potato soft rot caused by Pectobacterium carotovorum and Pectobacterium atrosepticum by Moroccan actinobacteria isolates

Pectobacterium carotovorum and Pectobacterium atrosepticum are dreadful causal agents of potato soft rot. Actually, there are no efficient bactericides used to protect potato against Pectobacterium spp. Biological control using actinobacteria could be an interesting approach to manage this disease. Thus, two hundred actinobacteria isolated from Moroccan habitats were tested for their ability to inhibit in vitro 4 environmental Pectobacterium strains and the two reference strains (P. carotovorum CFBP 5890 and P. atrosepticum CFBP 5889). Eight percent of these isolates were active against at least one of the tested pathogens and only 2% exhibited an antimicrobial activity against all tested Pectobacterium strains. Four bioactive isolates having the greatest pathogen inhibitory capabilities and classified as belonging to the genus Streptomyces species through 16S rDNA analysis were subsequently tested for their ability to reduce in vivo soft rot symptoms on potato slices of Bintje, Yukon Gold, Russet and Norland cultivars caused by the two pathogens P. carotovorum and P. atrosepticum. This test was carried out by using biomass inoculums and culture filtrate of the isolates as treatment. Among these, strain Streptomyces sp. OE7, reduced by 65–94% symptom severity caused by the two pathogens on potato slices. Streptomyces OE7 showed a potential for controlling soft rot on potato slices and could be useful in an integrated control program against potato soft rot pathogens in the objective to reduce treatments with chemical compounds.     

Comparison of pathogenicity of Clavibacter michiganensis subsp. insidiosus and Pseudomonas viridiflava strains on alfalfa

Hamedan province of Iran is a suitable niche for alfalfa growth but many diseases including alfalfa bacterial wilt, bacterial crown and root rot diseases cause economic crop losses. Bacterial wilt is caused by Clavibacter michiganensis subsp. insidiosus, and bacterial crown and root rot diseases are caused by Pseudomonas viridiflava. In this study, we investigated the pathogenicity of C. michiganensis subsp. insidiosus and P. viridiflava strains collected from the main alfalfa growing areas of Hamedan province. Pathogenicity of the virulent strains was tested on alfalfa and the bacterial strains caused symptoms, and data were collected about stem length, root length, wet weight and dry weight of the infected plantlets. The data about the pathogenicity of C. michiganensis subsp. insidiosus and P. viridiflava on alfalfa were compared with each other and were analysed by SAS software and Dunkan's test. Resulted data showed more pathogenicity of C. michiganensis subsp. insidiosus than P. viridiflava on alfalfa. These data also showed that both of these bacteria produced the most losses on wet weight and dry weight of alfalfa plantlets.     

花魔芋软腐病原真菌分离鉴定

魔芋软腐病是魔芋生产过程中的重要病害,也是限制魔芋产业发展的主要因素。目前,已有报道魔芋软腐病主要由细菌引起,鲜有真菌引起魔芋球茎软腐发病的报道。为明确云南曲靖市花魔芋(Amorphophallus konjac)软腐病的病原种类和侵染特征,该研究通过组织分离法,对采集自云南曲靖市的花魔芋病样进行了真菌的分离,通过形态学结合基于ITS与LSU序列分析的分子鉴定方法对分离真菌进行鉴定,并根据柯赫氏法则进行致病性测定,并对鉴定出的病原真菌同魔芋软腐病原细菌进行了双回接试验分析。结果表明:(1)从形态学和分子水平鉴定了轮纹镰刀菌(Fusarium concentricum)、尖孢镰刀菌(F. oxysporum)和F. ambrosium 3种镰刀菌,1种毛霉属真菌(Mucor sp.),1种根霉属真菌(Rhizopus sp.),1种青霉属真菌(Penicillium sp.)和1种粉红螺旋聚孢霉属真菌(Clonostachys sp.)。(2)统计分析发现,轮纹镰刀菌的相对丰度最高,为45.45%。(3)柯赫氏法则检测发现轮纹镰刀菌具有致病性。(4)轮纹镰刀菌和病原细菌胡萝卜果胶杆菌(Pectobacterium aroidearum)双接种魔芋球茎发现软腐病发病更快,病变组织重量显著高于单接种轮纹镰刀菌或果胶杆菌处理。综上表明,魔芋软腐病可能是由真菌和细菌复合侵染引发。该研究结果为魔芋软腐病的防治提供了理论依据。     

Biocontrol Potential of Soybean Bacterial Endophytes Against Charcoal Rot Fungus, <Emphasis Type="Italic">Rhizoctonia bataticola</Emphasis>

A total of 137 bacterial isolates from surface sterilized root, stem, and nodule tissues of soybean were screened for their antifungal activity against major phytopathogens like Rhizoctonia bataticola, Macrophomina phaseolina, Fusarium udam, and Sclerotium rolfsii. Nine bacterial endophytes suppressed the pathogens under in vitro plate assay. These were characterized biochemically and identified at the genus level based on their partial sequence analysis of 16S rDNA. Eight of the isolates belonged to Bacillus and one to Paenibacillus. The phylogenetic relationship among the selected isolates was studied and phylogenetic trees were generated. The selected isolates were screened for biocontrol traits like production of hydrogen cyanide (HCN), siderophore, hydrolytic enzymes, antibiotics, and plant growth promoting traits like indole 3-acetic acid production, phosphate solubilization, and nitrogen fixation. A modified assessment scheme was used to select the most efficient biocontrol isolates Paenibacillus sp. HKA-15 (HKA-15) and Bacillus sp. HKA-121 (HKA-121) as potential candidates for charcoal rot biocontrol as well as soybean plant growth promotion.     

Potential of bulb-associated bacteria for biocontrol of hyacinth soft rot caused by Dickeya zeae

Aims:  Dickeya zeae is a pectinolytic bacterium responsible for soft rot disease in flower bulb crops. In this study, the possibility of controlling soft rot disease in hyacinth by using antagonistic bacteria isolated from hyacinth bulbs was explored.
Methods and Results:  Bacterial isolates with potential for biocontrol were selected on the basis of antibiosis against D. zeae , siderophore production, and the N -acyl homoserine lactones (AHLs)-inactivation. In in vitro assays, 35 out of 565 hyacinth-associated bacterial isolates produced antimicrobial substances against D. zeae, whereas 20 degraded AHLs, and 35 produced siderophores. Isolates of interest were identified by 16S rDNA sequence analysis and reaction in BIOLOG™ tests. Twenty-six isolates that differed in characteristics were selected for pathogenicity testing on hyacinth cultivars, Pink Pearl and Carnegie. Two strains identified as Rahnella aquatilis and one as Erwinia persicinus significantly reduced tissue maceration caused by D. zeae 2019 on hyacinth bulbs, but not on leaves.
Conclusions:  Hyacinth bulbs harbour bacteria belonging to different taxonomic groups that are antagonistic to D. zeae , and some can attenuate decay of bulb tissue.
Significance and Impact of the Study:  Selected hyacinth-associated bacterial isolates have potential for control of soft rot disease caused by D. zeae in hyacinth bulb production.     

Antifungal effects of selected botanicals on fungal pathogens of watermelon fruit

This study investigates the use of botanical extracts (Piper guineense, Xylopia aethiopica and Bambusa vulgaris at 5, 10 and 15% concentration levels) for controlling deteriorating fungal pathogens in vitro. Identification of the fungal pathogens after pathogenicity test reaffirm isolates identity as Fusarium oxysporum, Fusarium solani, Macrophomina phaseolina, Fusarium verticillioides and Botryodiplodia theobromae. All the fungal pathogens induced rot in the watermelon fruit. The botanical extracts were best effective at high concentration levels (10 and 15%), though varied in their inhibitory activity. P. guineense and X. aethiopica were observed to be more effective than B. vulgaris. This study showed the efficacy of the botanical extracts on deteriorating fungal pathogens of watermelon fruit. Thus, the botanical extracts can be employed as antideteriorating biological-based fungicides for watermelon fruits.     

Characterization of Pectobacterium carotovorum subsp. carotovorum Causing Watermelon Soft Rot Disease in Iran

The aim of this study was characterized Pectobacterium carotovorum subsp. carotovorum (Pcc) the causal pathogen of watermelon soft rot disease in Iran. Of fifty bacterial isolates with white grey and convex colonies on nutrient agar obtained from symptomatic watermelon, ten isolates were selected for further tests. Pathogenicity tests results showed that all test isolates developed typical water‐soak symptoms after 2 days and signs of soft rot began 4 days after inoculation on watermelon fruits. Based on the phenotypic properties, the isolates were identified as Pectobacterium carotovorum subsp. carotovorum. The 16S rDNA sequences of isolates were 99% similar to the corresponding 16S rDNA sequence of the reference Pcc isolate. BOX and ERIC‐PCR analysis indicated that genetic diversity was present among the isolated Pcc isolates did not relate to the geographic location isolated from. To the best of our knowledge, this is the first study of biochemical and genotypic characterization of Pcc isolates the causal agents of soft rot disease on watermelon, in Iran.     

Biocontrol: Endophytic bacteria could be crucial to fight soft rot disease in the rare medicinal herb,Anoectochilus roxburghii

Microbial destabilization induced by pathogen infection has severely affected plant quality and output, such as Anoectochilus roxburghii, an economically important herb. Soft rot is the main disease that occurs during A. roxburghii culturing. However, the key members of pathogens and their interplay with non-detrimental microorganisms in diseased plants remain largely unsolved. Here, by utilizing a molecular ecological network approach, the interactions within bacterial communities in endophytic compartments and the surrounding soils during soft rot infection were investigated. Significant differences in bacterial diversity and community composition between healthy and diseased plants were observed, indicating that the endophytic communities were strongly influenced by pathogen invasion. Endophytic stem communities of the diseased plants were primarily derived from roots and the root endophytes were largely derived from rhizosphere soils, which depicts a possible pathogen migration image from soils to roots and finally the stems. Furthermore, interactions among microbial members indicated that pathogen invasion might be aided by positively correlated native microbial members, such as Enterobacter and Microbacterium, who may assist in colonization and multiplication through a mutualistic relationship in roots during the pathogen infection process. Our findings will help open new avenues for developing more accurate strategies for biological control of A. roxburghii bacterial soft rot disease.     

Bacterial Stem Rot in Greenhouse Pepper (Capsicum annuum L.) in Sardinia (Italy): Occurrence of Erwinia carotovora subsp. carotovora

An unusual bacterial disease was observed in pepper plants during research carried out in greenhouses in central‐north Sardinia. The characteristics were: the presence of lesions and exudates on stems, soft rot of the pith, and a brownish‐black colour in the petioles and leaf‐veins. Only two isolates of 21 were pathogens. One was obtained from exudate present on the stem and the other from pith. Experimental infections revealed that the bacterial isolates were particularly aggressive in the stems and fruit of pepper and tomato. Biochemical, physiological and serological tests in conjunction with fatty acid profile analysis confirmed that they were Erwinia carotovora subsp. carotovora (Jones) Bergey et al. The product of 434 bp polymerase chain reaction (PCR) enabled a preliminary identification of isolates to be made. Restriction fragment length polymorphism (RFLP) analysis of amplification products showed that the isolates DPP 23_ef and DPP 24_m, strain type CFBP 2046 and DPP 28₁, isolated from pepper fruit, belonged to the RFLP group 12, whereas DPP 29, also isolated from pepper fruit, was included in RFLP group 1. Measures to prevent and control this recently introduced disease are suggested in the conclusion of this paper.     

Preliminary report on the study of postharvest fruit rot bacteria and yeasts in Lanzhou Lily (Lilium davidii var. unicolor) in China

Fruit rot is one of the most important factors affecting the postharvest quality and shelf life of Lanzhou Lily fruits. The aims of this study were to characterize different isolates from Lanzhou Lily using morphological and molecular approaches and to test their pathogenicity in Lanzhou Lily fruit. Different isolates were collected from decayed Lanzhou Lily fruits in Lanzhou in Gansu Province in China during 2016 and 2017. In total, four isolates were obtained and identified based on their DNA sequences of the 16S rDNA and 26S rDNA genes in combination with the morphological characteristics of the cultures and sporulation. Of the four isolates, one was identified as Bacillus safensis, one was Stenotrophomonas maltophilia and the other two isolates were Metschnikowia pulcherrima. The pathogenicity tests showed that all four isolates were pathogenic in Lanzhou Lily fruit. Previously Fusarium tricinctum has been reported to be the primary cause of fruit rot in Lanzhou Lily throughout the world. Our report is the first to show results that indicate that B. safensis, S. maltophilia and M. pulcherrima are pathogenic in Lanzhou Lily in China. This is the first report on the bacteria and yeast that infect Lanzhou Lily fruits.