Potato Wilt Disease Research Articles

Races and Biovar Characterization of Ralstonia solanacearum Causing Bacterial Wilt Disease of Potato

Ralstonia solanacearum, the causative agent of brown rot/bacterial wilt, is a major cause of severe potato illnesses in many impoverished nations located in tropical and subtropical regions of the world. When it occurs, the disease is to blame for significant losses to the potato industry. The illness has the potential to completely destroy a crop and stop using a piece of land for potato cultivation for a number of years. A survey was carried out to investigate the extent of Ralstonia solanacearum-caused bacterial wilt of potato crops in important potato-growing talukas in the Banaskantha district of Gujarat, India, including Deesa, Dantiwada, Palanpur, and Amirgadh. The frequency of bacterial wilt disease in potatoes is rather low in this region. Four talukas were utilised to identify ten isolates (RsSt1 to RsSt10) of R. solanacearum, which were then used to determine the biovar and race. Gram-negative rod-shaped cells were present in the isolates of R. solanacearum. On TZC agar medium, these isolates developed colonies that were creamy or dull white in colour with a hint of pink or red in the centre. The oxidation of disaccharides (sucrose, lactose, maltose) and sugar alcohols (manitol, sorbitol, and dulcitol) by R. solanacearum isolates was used to determine the biovar characteristics. This revealed that, of the ten isolates, eight were classified as bv2, and the two remaining isolates (RsSt5 and RsSt7) belonged to bv2T. The pathogenicity test conducted on tobacco, tomato, and brinjal allowed for the race identification of R. solanacearum isolates, which were classified as race 3 due to their limited host range and ability to exclusively elicit wilt symptoms in potatoes and tomatoes. As a result, Races 3 and bv2 and bv2T were represented among the R. solanacearum isolates that caused bacterial wilt of potatoes in the Banaskantha district.

Phylogenetic Distribution of Ralstonia solanacearum Species Complex Populations in Potato in Kenya

Ralstonia solanacearum is a pathogen causing bacterial wilt disease of potato, resulting in 70% potato production losses in Kenya. A study was conducted to determine the diversity of R. solanacearum species complex strains within the main potato-growing regions of Kenya. Potato tubers were collected in different potato-growing regions of Kenya from visibly wilted potato plants as well as samples of tomato, irrigation water, and cultures for pathogen isolation. Genomic DNA was isolated from 135 purified cultures of RSSC isolates and PCR-amplified using multiplex and sequevar primers targeting the endoglucanase (egl) partial gene sequences. Pathogenicity tests using R.solanacearum strain (phylotype II sequevar I) were done on the cultivars Kenya Karibu, Shangi, Chulu, Wanjiku, and MoneyMaker. Phylogenetic analysis of the partial egl gene identified two genospecies, R.pseudosolanacearum sp. nov. (1.5%) and R.solanacearum (98.5%). All R.solanacearum strains clustered in sequevar I and were distributed in all the potato-growing regions surveyed. The cultivars were grown in a greenhouse for two cycles in a randomized complete block design and inoculated with R.solanacearum strain. The severity scores were assessed and the area under the disease progress curve (AUDPC) was determined. All the cultivars tested for pathogenicity exhibited wilting symptoms at varying intervals after infection, with none showing complete resistance to R.solanacearum. Cultivar Shangi exhibited minimum disease severity and progression of 41.14% and AUDPC of 1041.7, respectively, while 'Kenya Karibu' was the most susceptible with a high progression rate of 68.24% and AUDPC of 1897.5, respectively. 'MoneyMaker', 'Chulu', and 'Wanjiku' showed no significant difference in disease severity, depicting a simultaneous rate of infection among them. These findings provide valuable information to better understand the pathogen genetic diversity in Kenya and how it spreads.

Role of Trehalose Synthesis in Ralstonia syzygii subsp. indonesiensis PW1001 in Inducing Hypersensitive Response on Eggplant (Solanum melongena cv. Senryo-nigou).

Ralstonia syzygii subsp. indonesiensis (Rsi, former name: Ralstonia solanacearum phylotype IV) PW1001, a causal agent of potato wilt disease, induces hypersensitive response (HR) on its non-host eggplant (Solanum melongena cv. Senryo-nigou). The disaccharide trehalose is involved in abiotic and biotic stress tolerance in many organisms. We found that trehalose is required for eliciting HR on eggplant by plant pathogen Rsi PW1001. In R. solanacearum, it is known that the OtsA/ OtsB pathway is the dominant trehalose synthesis pathway, and otsA and otsB encode trehalose-6-phosphate (T6P) synthase and T6P phosphatase, respectively. We generated otsA and otsB mutant strains and found that these mutant strains reduced the bacterial trehalose concentration and HR induction on eggplant leaves compared to wild-type. Trehalose functions intracellularly in Rsi PW1001 because addition of exogenous trehalose did not affect the HR level and ion leakage. Requirement of trehalose in HR induction is not common in R. solanacearum species complex because mutation of otsA in Ralstonia pseudosolanacearum (former name: Ralstonia solanacearum phylotype I) RS1002 did not affect HR on the leaves of its non-host tobacco and wild eggplant Solanum torvum. Further, we also found that each otsA and otsB mutant had reduced ability to grow in a medium containing NaCl and sucrose, indicating that trehalose also has an important role in osmotic stress tolerance.

Isolation and identification of endophytic bacteria from potato tissues and their effects as biological control agents against bacterial wilt

Ralstonia solanacearum, as a causative agent of potato wilt disease, is one of the deadliest diseases worldwide, and also in the Kurdistan province, Iran. Given the importance of the disease, the aim of the present study was to isolate endophytic bacteria from potato plant tissues such as the tuber, root, stem, and leaf, to investigate their antagonistic effects on R. solanacearum. In this regard, 236 endophytic bacteria were isolated and screened in vitro. As a result, 31 isolates were found as potential antagonists against potato wilt pathogen. For phenotypic and genotypic characterization, biochemical and pathogenicity tests as well as 16S rRNA gene sequence analyses were performed. 11 isolates as representatives of different taxa were selected for further investigations. These were identified as: Bacillus pumilus Bp91, B. pumilus Bp1, B. pumilus Bp49, B. licheniformis Bl17, Paenibacillus peoriae Pa86, Pseudomonas brassicacearum Psb101, P. brassicacearum Ps169, P. putida Ps52, Chryseobacterium indologenes Ch54, C. lathyri Chl98, and Microbacterium phyllosphaerae Mi41. Notably, the maximum inhibitory effects were observed by Pseudomonas brassicacearum Psb101, P. brassicacearum Ps169, Paenibacillus peoriae Pa86, Pseudomonas putida Ps52, and Bacillus licheniformis Bl17, by forming 17.6, 17.4, 17.3, 15.5, 15.2 mm diameter inhibition zones against R. solanacearum on nutrient agar medium, respectively. Based on the results of the greenhouse test, all 11 selected isolates simultaneously reduced the disease by 27–55% and also significantly increased plant growth.Among these, the five strains Pseudomonas brassicacearum Psb101, P. brassicacearum Ps169, P. putida Ps52, Paenibacillus peoriae Pa86, and Bacillus licheniformis Bl17 were introduced hereby as the most effective antagonists and growth enhancers under both laboratory and greenhouse conditions.

Detecting pathogenic bacterial wilt disease of potato using biochemical markers and evaluate resistant in some cultivars.

Bacterial wilt caused by Ralstonia solanacearum (Smith), is one of the chief severe diseases of potato in warm temperate regions, tropics and subtropics of the world. The study was conducted to isolate and identify bacterial pathogens and select the most resistant cultivars and avoid the decrease in the total value of Egyptian potato exports to the European Union (EU) due to the quarantine restrictions imposed by the EU on potato tubers exported from Egypt affected by bacterial wilt. The results of traditional identification through morphological and serological studies showed that the five isolates were isolated and identified as Ralstonia solanacearum. Furthermore, the results illustrated that RS5 isolate showed the lowest percentage of disease incidence reduction on the three tested potatoes cultivar Bellini, Spunta and Mondial recorded 9.64%, 15.41% and 34.12%, respectively. While, RS8 isolate exhibited the highest effective one the percentage of disease reduction on all tested potato cultivars. This isolate reduced disease incidence 60.60%, 63.21% and 71.66%, compering to the healthy control treatment. The result of molecular identification represent that the probe used in Taq-man (PCR) was of the type (B2) capable to detect only biovar 2 of R. solanacearum bacterial wilt. Furthermore, primer and probe are specific for detection of the race 3 biovar 2 strain. Positive results were obtained in all assays used including IFAS, protein content and SDS-PAGE with all five isolates. So the isolate (RS5) was the most virulence one, followed by RS1, RS3, RS2 and RS8, registered that the tested isolates were R. solanacearum race 3, biovar 2. Also, studies focused on the form of genetic distances and similarities based on pathogenic and plant growth parameters. The results illustrate that the highest genetic similarity (0.998) was found between Bellini and Spunta cultivars as the closest but the lowest value (0.946) was found between Mondial and Bellini as most distant. These results were similarity with genetic distances and SDS-PAGE profile of the three tested potato cultivars.

Evaluation of antibacterial activity of extract and essential oil of Tagetes patula L. in vitro against Ralstonia solanacearum biovar 2

This work aims to assess the in-vitro antimicrobial activity of the essential oil and hydroalcoholic extract of Tagetes patula against Ralstonia solanacearum the causal of potato wilt disease. Providing necessary information on the antimicrobial activity of the extract and essential oil on this phytopathogen, also contributing to knowledge in the phytopathology area. The antimicrobial activity was carried out through dilution both liquid medium and agar (perforation in well) at different concentrations. The content of flavonoids, polysaccharides, tannins and phenols present in the extract was quantified, and the oil was characterized through gas chromatography–mass spectrometry. The majority compound identified in the oil were piperitone (42.95%) and the extract mostly had polysaccharides (1.54 ± 0.18 mg EG/g DE). Both registered a minimum inhibitory concentration bacteriostatic of 50 μg/mL and the half maximal effective concentrations were 306 μg/mL (oil) and 352 μg/mL (extract). The oil had better yield through the dilution method in liquid medium at concentration of 500 μg/mL, and the hydroalcoholic extract had better bactericide yield of 200 μg/mL. It was concluded that the essential oil and hydroalcoholic extract with further applied studies could be a viable and environmentally friendly alternative to control R. solanacearum.

Spread of bacterial wilt disease of potato in the highlands of Fouta Djalon, Republic of Guinea

Bacterial wilt in potato (Solanum tuberosum) is caused by Ralstonia solanacearum in the highlands of Fouta Djalon in Guinea. The disease causes 50-70% loss of potato in Guinea. The bacterium is transmitted either by imported tuber seeds or through seed exchanges between the farmers themselves from a contaminated area to bacteria-free areas or through irrigation waters along the fields. This is mainly a consequence of the informal potato seed system that prevails in Guinea. Because of the high price of seeds, farmers use several sources of supply. However, potato is an attractive cash crop in Guinea and the most important economic crop in Fouta Djalon. Most populations in the middle Guinea utilizes potato. The potato farmer's organization in Guinea, FPFD (Fédération des Producteurs du Fouta Djalon), is a model in West African sub-region because of its dynamism and organization with its 500 groups, 25 unions and more than 25,000 members. Training of potato growers in certified seed production techniques remains a major problem in Guinea that needed to be solved. This information is important for developing bacterial wilt disease management strategies through the training of farmers and state support for research.

Management of Ralstonia solanacearum (potato wilt disease) virulence by using bioactive compounds

Potato is an important vegetable crop of Bangladesh which is facing challenges worldwide due to a quarantine pathogen, Ralstonia solanacearum. It is a very successful bacterial pathogen against most of the traditional management practices. Suspension of ten bioactive compounds viz. propolis, honey, turmeric powder+oil, turmeric powder, magnesium chloride, boiled rice fluid, boiled rice fluid+iodine, sun dried cow dung powder, honey+iodine and sodium bicarbonate were evaluated and compared with control (sterile water), commercial bactericide (Krosin AG) and farmers practice (stable bleaching powder). In vitro assessment was done by comparing the inhibition zones produced on TZC (tetrazolium chloride) solid medium in disc diffusion method. All of those compounds produced larger inhibition zones as compared to control which indicated the effectiveness of the test compounds against the bacteria. To screen out the performances of those compounds in vivo, potato seedlings were inoculated in sterilized soil by soil soak method. Later, mature plants were inoculated in unsterilized soil to find the better resulting compound(s) in field soil condition against the disease. Finally, suspension of cow dung (@25%), propolis (@ 6mg/ml) and turmeric powder (@25%) were selected for trial as soil and seed treatment against the pathogen. It was found that, cow dung reduced 28.89% disease severity index which was followed by 26.67% in propolis and 22.22% in turmeric powder as compared to control (84.44%) in artificially inoculated potato plants against R. solanacearum.
 J. Biodivers. Conserv. Bioresour. Manag. 2020, 6(1): 65-76

Approving the biocontrol method of potato wilt caused by Ralstonia solanacearum (Smith) using Enterobacter cloacae PS14 and Trichoderma asperellum T34

This study aimed to evaluate the efficiency of Enterobacter cloacae PS14 and Trichoderma asperellum T34 in the control of potato wilt, caused by Ralstonia solanacearum (Smith), under greenhouse and field conditions. In vitro, the endophyte E. cloacae PS14 caused the highest reduction of the pathogen growth among 7 screened bacteria. It produced an inhibition zone as 16.9 mm compared to a specific antibiotic (20.0 mm). E. cloacae PS14 was selected as an effective antagonistic bacterium to be compared to T. asperellum strain T34 for reduction of the disease as well as increasing the crop yield of potato plants. Both E. cloacae and T. asperellum reduced the disease severity up to 10.7–26.5%, respectively, under greenhouse and up to 26.6–36.6%, respectively, under field conditions. The results approved that both E. cloacae and T. asperellum increased the yield of the crop by 20.44–40.96%, respectively. Their mode of action was indicated by suppression of the pathogen as well as induction of plant systemic resistance. The induction of systemic resistance was confirmed by increasing the total phenol and salicylic acid contents as well as increasing the activities of peroxidase, lipoxygenase, and polyphenol oxidase in potato plants than the healthy or only infected plants. Production of siderophore, indole-3-acetic acid (0.577–0.884 μM), hydrogen cyanide (2.34–3.61 μg/ml), and salicylic acid (0.436–1.488 μg/ml) was confirmed by E. cloacae PS14 and T. asperellum T34, respectively, in vitro. The study recommends the new strain E. cloacae PS14, as new endophytic effective bacteria, in the control of R. solanacearum causing the potato wilt disease.

The Effect of a combination of growing media and biological agents to control bacterial wilt disease of potato (Ralstoniasolanacearum) in greenhouse

Potato (Solanumtuberosum L.) in Indonesia is a commodity that priorities todeveloped, and has the potential to be marketed in the domestic as well as export. One of the obstacles is important that faced is pathogen soil-borne which is caused by the Ralstoniasolanacearum. This pathogen can causing loss of yield of potato 40-100%. Bacillus sp. and Pseudemonas fluorescens are antagonistic microbes that are proven to be able to control bacterial wilt disease by 69,95 % and 61,67%. This study aimed to determine the effect of the comparison composition of growing media and the ability of some agents of biological within suppress the growth of the disease wilt bacteria of potatoes which is caused by R. solanacearum.This research using completely randomized design (CRD) nonfactorial with 10 treatments, namely: M0(top soil), M1(top soil, R. solanacearum), M2(top soil, R. solanacearum, P.fluorescens), M3(top soil, R. solanacearum, Bacillus subtilis), M4(top soil, Chicken manure, R. solanacearum, P.fluorescens), M5 until M9 are combination of them. The results showed that the application of biological agents was able to suppress the growth of the pathogen R. solanacearum, as well as significantly affect plant height, number of shoots, and production.

Synergistic effect of Bacillus subtilis and boric acid on management of bacterial wilt disease of potato caused by Ralstonia solanacearum in coastal plains of Odisha under field conditions

Field trial were conducted following split plot design in the year 2008–2009 and 2009–2010 under All India Co-ordinated Potato Research Project, Orissa University of Agriculture &Technology, Bhubaneswar with chemical soil amendments in main plots followed by individual and combine treatment of chemical and bio-agent treatments in the sub plots to study synergistic effect of Bacillus subtilis and boric acid on management of bacterial wilt of tomato caused by Ralstonia solanacearum (Smith) Yabuuchi. Combined potato seed treatment with B. subtilis BS-5 (6 × 106 CFU /ml) and 3% boric acid coupled with soil application of bleaching powder showed lower wilt incidence (9.55%) and enhanced yield (17.31 t/h) over control after 75 days of sowing under field conditions which is economical and also eco-friendly. With single application of boric acid (3%) or B. subtilis BS-5 (6 × 106 CFU /ml), wilt incidence were significantly higher 11.82 and 17.06% and yielded less healthy tubers 15.49 and 13.65 t/h, respectively. Though, the tubers treated with antibiotic streptocycline (150 ppm) followed by application of the same antibiotic at 10 days interval for four times after planting resulted in minimum wilting (3.83%) of plant and maximum of tuber yield (18.21 t/h) however it is more expensive and perilous.

Molecular Dissection of Extracellular Matrix Proteome Reveals Discrete Mechanism Regulating Verticillium Dahliae Triggered Vascular Wilt Disease in Potato.

Plants exposed to patho-stress mostly succumb due to disease by disruption of cellular integrity and changes in the composition of the extracellular matrix (ECM). Vascular wilt, caused by the soil borne hemibiotrophic filamentous fungus Verticillium dahliae, is one of the most significant diseases that adversely affect plant growth and productivity. The virulence of the pathogen associated with the ECM-related susceptibility of the host plant is far from being understood. To better understand ECM-associated disease responses that allow the pathogen to suppress plant immunity, a temporal analysis of ECM proteome was carried out in vascular wilt susceptible potato cultivar upon V. dahliae infection. The proteome profiling led to the identification of 75 patho-stress responsive proteins (PSRPs), predominantly involved in wall hydration, architecture, and redox homeostasis. Two novel clues regarding wilt disease of potato were gained from this study. First, wall crosslinking and salicylic acid signaling significantly altered during patho-stress. Second, generation of reactive oxygen species and scavenging proteins increased in abundance leading to cell death and necrosis of the host. We provide evidence for the first time that how fungal invasion affects the integrity of ECM components and host reprogramming for susceptibility may function at the cell surface by protein plasticity.

Quantitative Gene Expression of Peroxidase, Polyphenoloxidase and Catalase as Molecular Markers for Resistance against <i>Ralstonia solanacearum</i>

Brown rot or bacterial wilt of potato caused by Ralstonia solanacearum, is an economically important disease. Potato, cv. Nicola, was found to be relatively highly resistant to the infection with R. solanacearum and showed 15.12% wilt disease index, meantime, cv. Kara showed intermediate resistance with 37.40% disease index while, cv. Spunta was susceptible and showed 80.33% disease index. The role of defense-related enzymes in imparting resistance in potato against R. solanacearum was investigated by quantifying enzymes activity and gene expression of three defense- related enzymes, peroxidase, polyphenol oxidase and catalase. Peroxidase showed maximum activity 0.488 min-1&middotg-1 early at 12 h after pathogen inoculation in the cv. Nicola, whereas in susceptible cultivar Spunta showed lower activity of maximum 0.226 min-1&middotg-1 later at 48 h after inoculation. While, the moderately resistant cultivar Kara showed intermediate activity for the peak and its time. Meanwhile, polyphenol oxidase showed similar trends to that of peroxidase. On the contrary, catalase showed the highest activity values in the susceptible, cv. Spunta, while, in relatively highly resistant (cv. Nicola) and the moderately resistant (cv. Kara) showed lower values of activity and up to 96 h after inoculation. Meanwhile, gene expression of related enzymes the RT-PCR was used. At zero time, the relatively highly resistant potato cultivar, Nicola, showed the highest values of gene expression for both Peroxidase (POD) and Poly Phenol Oxidase (PPO). While, the susceptible potato cultivar, Spunta showed the lowest values. On the contrary, Catalase (CAT) gene expression was the highest in the susceptible, cv. Spunta, and was the lowest in the relatively highly resistant, cv. Nicola, while, was of intermediate values in the intermediate resistance, cv. Kara. Results show that peroxidase and polyphenol oxidase activities can be used as biochemical markers to reveal the resistance and susceptibility nature of potato cultivars against bacterial wilt disease of potato caused by R. solanacaerum.

English

Twenty (20) of Verticillium dahliae were isolated from wilted potato specimens collected from six districts in Guizhou, China. All the isolates were evaluated for pathogenicity on two potato cultivars, Favorita (susceptible) and Hui-2 (resistant) using the root dip inoculation (RDI) and microsclerotia inoculation (MI). All of the V. dahliae isolates appeared to be pathogenic on both cultivars but VGZ-HZ-4 isolate gave the highest wilt incidence comparing to the others, seconded by VGZ-SC-1 and VGZ-XW-1. Combined analysis of wilt incidence resulting from using two inoculation methods for VGZ-HZ-4 and VGZ-XW-1 isolates on the two potato cultivars showed that the MI gave a higher wilt incidence than that of the RDI and cultivar Favorita had a higher wilt incidence than that of Hui-2. These two V. dahliae isolates were further used as representative isolates for mycelial inhibition (MyI) test with 33 Trichoderma isolates under a dual culture condition on potato dextrose agar plate. The 33 Trichoderma isolates consisting of 21 isolates isolated from potato soils from seven districts of Guizhou, 11 isolates from single spore isolates of the TGZ-150 isolate preserved at Guizhou Institute of Plant Protection (GZIPP) and one isolate TGZ-OLD-81 also preserved at the GZIPP. Most of the single spore isolates and TGZ-SC-4 were found to have higher MyI efficiency than that of the rest. The results indicate that the Trichoderma isolates in this study have initial modes of action of biological control to protect potato crop against V. dahlia.   Key words: Trichoderma, potato wilt disease, growth inhibition, Verticillium dahliae, antagonistic fungi.

Bahasa Indonesia

Rhizosphere is an ideal area for growth and development of microbial antagonists, because it is a nutrition rich area. Nutrients that secreted in the rhizosphere are influenced by many environmental factors which in turn effect the diversity and abundance of microbial community. Based on these facts, the research were aimed to isolate bacteria from the rhizosphere and organic materials in Tana Toraja, and determine their role as biological control agents for potato wilt disease. Antagonistic test was conducted in order to determine the ability of each bacterial isolate to inhibit the growth of Ralstonia solanacearum and Fusarium oxysporum. The results showed that from totally 74 bacterial isolates, only 10 and 4 bacterial isolates were able to inhibit the growth of R. solanacearum and F. oxysporum in vitro, respectively.

Bacterial Antagonist Isolates in Controlling Bacterial Wilt Disease of Potato (Ralstonia solanacearum) in Aeroponic Cultivation System

The growing of potato plants in aeroponics system is considered as safe and ecologically friendly for producing natural, healthy plants and crops. However, it often faces with several constraints. Infection of bacterial wilt caused by Ralstonia solanacearum in the aeroponics cultivation system can spread rapidly through the nutrition flow and lead to plant death and crop failure. The objective of this study was to evaluate bacterial antagonist isolates belonging to Clostridium sp in reducing bacterial wilt disease of potato caused by Ralstonia solanacearum in aeroponic system and its effect on increasing the weight and number of potato tubers. The results showed that of the seven treatments tested on potato aeroponic system, treatment with a combination of isolates NS01 + G06 + S06 tend to be more effective in suppression of bacterial wilt disease (85%), increase the amount of seed tubers (162.5 tubers/treatment) and increase the average of tuber weight as much as 311.25 gr/treatment. It can therefore be concluded that a combination of three isolates of Clostridium sp i.e: NS01 + G06 + S06 had some synergic activities in potato aeroponic cultivation system.

Determination of Races and Biovars of Ralstonia solanacearum Causing Bacterial Wilt Disease of Potato

A survey was carried out in some selected potato growing districts of Bangladesh during December to February 2011 to know the status of bacterial wilt of potato caused by Ralstonia solanacearum in terms of its incidence and severity. The results showed that the highest wilt incidence was recorded in Munshigonj (22.65%), followed by Nilphamari (19.98%) and the lowest incidence was recorded in Jamalpur (9.07%). The highest bacterial wilt severity was recorded in Munshigonj (3.80), while the lowest wilt severity was recorded in Jamalpur (2.90). A total of 44 isolates (R. solanacearum) were obtained from the wilted potato plant samples i.e. 20 from Munshigonj, 17 from Nilphamari and 7 from Jamalpur and the isolates were divided into three groups. The production of pink or light red colour with whitish margin on TZC medium by the bacterial isolates indicated all groups of R. solanacearum isolates were virulent. The results of pathogenicity test revealed that all groups of R. solanacearum isolates were able to cause wilt symptoms in potato plants and brown rot symptoms in potato tuber. On the other hand, all biochemical tests were used for the identification of R. solanacearum isolates. The biovar test using the oxidization of disaccharides (sucrose, lactose, maltose) and sugar alcohols (manitol, sorbitol and dulcitol) by R. solanacearum isolates confirmed that all groups of R. solanacearum isolates belong to biovar III. The race identification of R. solanacearum isolates by pathogenicity test on brinjal, tomato, tobacco and chilli indicating a narrow host range (only in potato) and were categorized in race 3. Therefore, the R. solanacearum isolates causing bacterial wilt of potato in Bangladesh were belonging to Biovar III and Race 3.

In vitro and greenhouse evaluations of Trichoderma isolates for biological control of potato wilt disease (Fusarium solani)

The biological efficacy of Trichoderma species may differ due to variations in ecosystems. This study was conducted to assess the biocontrol efficacy of some native Trichoderma isolates against Fusarium solani, an important causal agent of potato wilt disease under laboratory and greenhouse conditions at Shahrood Agricultural Research Centre, Shahrood, Iran, during 2006–2007. Fourteen isolates were collected among which eight showed promising ability in inhibiting the growth of the pathogen through dual culture and production of volatile and non-volatile inhibitors but T. brevicompactum (T1), T. longibrachiatum (T5) and T. asperellum (T2) were almost better than other isolates in inhibiting the mycelial growth of the pathogen in comparison to control in the above three tests (p ≤ 0.01). Isolates performing mycoparasitism under in vitro condition were evaluated against the disease in pot culture under greenhouse condition. In all treatments in which Trichoderma isolates + F. solani were involved lower disease incidence was noticed in comparison to Fusarium-infested control (p ≤ 0.05). Best disease control was observed in potted plants treated with F. solani + T. longibrachiatum (T5) with 6.25% disease incidence in comparison to Fusarium-infested control, in which disease incidence was observed to be 75%. Interaction of T. brevicompactum (T1) and F. solani also indicated good control of the disease by 12.50% of disease incidence.

Study on antagonistic effects of Talaromyces flavus on Verticillium albo-atrum, the causal agent of potato wilt disease

Talaromyces flavus a fungal antagonist, was isolated from soil samples collected from potato fields in Varamin and Karaj districts, Tehran province, Iran. Antagonistic effects of T. flavus isolates against Verticillium albo-atrum, the causal agent of potato wilt disease were investigated in the laboratory and greenhouse conditions. T. flavus colonies were recovered after three weeks from soil samples cultured on selective medium. Antagonistic effects of volatile and non-volatile extracts of T. flavus isolates on V. albo-atrum growth were investigated in the laboratory and five that caused higher growth inhibition of V. albo-atrum, were selected for greenhouse experiments. Infection index was compared in the greenhouse in a split plot trial with five isolates applied to soil, seed, or both arranged in a randomized complete block design with four replications. The minimum infection index was observed when seed were treated with T. flavus with the most effective isolate being Tf-Po-V-52. On seed, the minimum infection index was observed with Tf-Po-V-50. The most effective T. flavus isolate was also evaluated in a field experiment. Results indicated that infection index in seed treatment contained this isolate was 0.15 whereas that of control was 3.5. The overall results of this study showed that it may be possible to manage potato Verticillium wilt disease effectively by using T. flavus, a biocontrol fungus.

Mapping genes for resistance to Verticillium albo-atrum in tetraploid and diploid potato populations using haplotype association tests and genetic linkage analysis

Verticillium wilt disease of potato is caused predominantly by Verticillium albo-atrum and V. dahliae. StVe1 -a putative QTL for resistance against V. dahliae -was previously mapped to potato chromosome 9. To develop allele-specific, SNP-based markers within the locus, the StVe1 fragment from a set of 30 North American potato cultivars was analyzed. Three distinct and highly diverse haplotypes can be distinguished at the StVe1 locus. These were detected in 97%, 33%, and 10% of the cultivars analyzed. We tested for haplotype association and for genetic linkage between the StVe1 haplotypes and resistance of tetraploid potato to V. albo-atrum. Moreover, field resistance was assessed in diploid populations with known molecular linkage maps in order to identify novel QTLs. Resistance QTLs against V. albo-atrum were detected on four chromosomes (2, 6, 9, and 12) at the diploid level, with one QTL on chromosome 2 contributing over 40% to the total phenotypic variation of the trait. At the tetraploid level, a significant association between the StVe1-839-C haplotype and susceptibility to the disease was detected, suggesting that resistance-related genes directed against V. albo-atrum and V. dahliae are located in the same genomic region of chromosome 9. However, on the basis of the present analysis, we cannot determine whether these genes are closely linked or if a single gene provides resistance against both Verticillium species. To assess the usefulness of the StVe1-839-C haplotype for marker-assisted selection, we subjected the resistance data to Bayesian analysis, and calculated positive (0.65) and negative (0.75) predictive values, and overall predictive accuracy (0.72). Our results indicate that tagging of additional genes for resistance to Verticillium with molecular markers will be required for efficient marker-assisted selection.