Wilt Severity Research Articles

Endophytic bacteria from Datura metel for plant growth promotion and bioprotection against Fusarium wilt in tomato

ABSTRACTNine non-pathogenic bacterial isolates, recovered from Datura metel organs and able to colonise the internal stem tissues of tomato cultivar Rio Grande, were screened for their ability to suppress tomato Fusarium wilt disease caused by Fusarium oxysporum f. sp. lycopersici (FOL), and to enhance plant growth. S33 and S85 isolates tested were found to be the most effective in decreasing Fusarium wilt severity by 94–95% compared to FOL-inoculated and untreated control. A significant enhancement of growth parameters was recorded on tomato plants inoculated or not with FOL. Both isolates were characterised and identified using 16S rDNA sequencing genes as Stenotrophomonas sp. str. S33 (KR818084) and Pseudomonas sp. str. S85 (KR818087). Screened in vitro for their antifungal activity towards FOL, these isolates led to 38.7% and 22.5% decrease in pathogen radial growth and to the formation of an inhibition zone of 12.75 and 8.37 mm respectively. Stenotrophomonas sp. str. S33 and Pseudomonas sp. str. S85 were found to be chitinase-, protease- and pectinase-producing strains but unable to produce hydrogen cyanide. Production of indole-3-acetic acid-like compounds, phosphate solubilising ability and pectinase activity were investigated for elucidating their plant growth-promoting traits and their endophytic colonisation ability.

Stem blight, foot rot and storage tuber rot of sweet potato caused by Plenodomus destruens in China

In September 2014, severe stem blight, foot rot and storage tuber rot on sweet potato were observed in experimental fields in Sanmen County, Zhejiang Province, China. The causal agent was identified as Plenodomus destruens on the basis of morphological characteristics and molecular identification. In pathogenicity tests, P. destruens caused severe wilting, stem rot, and storage tubers rot symptoms similar to those observed in the field. This is the first report of P. destruens causing stem blight, foot rot and storage tuber rot on sweet potato in mainland China where sweet potato is a main crop.

The secondary compost products enhances soil suppressive capacity against bacterial wilt of tomato caused by Ralstonia solanacearum

Composting crop residues and animal manures for CO2 fertilization of vegetable crops is popular in China, but its rapid adoption in greenhouses faces a roadblock: the public concern over the disposition of much large amounts of compost products. In the present study, we used a secondary compost process to re-use the compost products, and evaluated the effect of secondary compost products (SCP) on tomato bacterial wilt in three field trials. The results showed that SCP application had great potential for the control of tomato bacterial wilt. Compared with the control (local conventional cultivation), SCP application decreased the disease incidence by 32–81% and increased fruit yields by 59–95% across the three trials. Irrespective of treatment, significant correlations were found between Ralstonia solanacearum populations and total nitrogen, soil organic carbon and NO3−-N contents. Moreover, the severity of bacterial wilt negatively associated with the activity of phosphomonoesterase and β-d-glucosidase, FDA hydrolysis, soil respiration, microbial biomass carbon and bacterial community diversity, whereas positively related with fungal community diversity. The results indicate that the enhancement of soil suppressiveness against R. solanacearum by SCP application was likely due to the alteration of microbial community structure and increased competitive ability of beneficial microorganisms with pathogens. We concluded that SCP application, as a way of re-utilization of compost products have the ability to increase soil suppressive capacity against bacterial wilt.

The health status and yield of winter rapeseed (Brassica napus L.) grown in monoculture and in crop rotation under different agricultural production systems

ABSTRACTIn a field experiment, winter rapeseed was grown in 5-year monoculture and in crop rotation (winter rapeseed, winter wheat, field peas, spring wheat and winter rapeseed). Two open-pollinated cultivars (Californium and Castille) and one hybrid cultivar (Nelson) were compared in systems with three levels of agricultural inputs, low input, medium input and high input, characterized by different rates of nitrogen and sulfur fertilization and pesticide use. The severity of sclerotinia rot (Sclerotinia sclerotiorum) and verticillium wilt (Verticillium spp.) on plants, dark spot (Alternaria spp.) and grey mold (Botrytis cinerea) on leaves and pods, as well as dry rot (Phoma lingam) on stems was evaluated during the growing season. The yield of winter rapeseed was calculated. Rapeseed grown after a 4-year break was characterized by less severe symptoms of dark spot on leaves and dry rot on stems, but more severe symptoms of grey mold on leaves and pods. The severity of dark spots on rapeseed pods (in crop rotation) was reduced with an increase in agricultural inputs. Cultivars Californium and Nelson were generally rarely infected by Verticillium spp., their leaves were less infected by Alternaria spp. and stems by Phoma spp. Nelson was the highest-yielding cultivar.

Editorial: Control of Plant Pathogens by Biogenic Elicitors and Possible Mechanisms of Action.

Editorial: Control of Plant Pathogens by Biogenic Elicitors and Possible Mechanisms of Action.

Development of a TaqMan Real‐Time Polymerase Chain Reaction Assay for Detection and Quantification of Fusarium oxysporum f. sp. lycopersici in Soil

AbstractFusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (FOL), is an important disease of tomato. Pathogenicity and vegetative compatibility tests, although reliable, are laborious for the identification of FOL isolates and cannot efficiently quantify population densities of FOL in the soil. The objective of this study was to develop a rapid, sensitive and quantitative real‐time polymerase chain reaction (PCR) assay for detecting and quantifying FOL in soil. An inexpensive and relatively simple method for soil DNA extraction and purification was developed based on bead‐beating and a silica‐based DNA‐binding method. A TaqMan probe and PCR primers were designed using the DNA sequence of the species‐specific virulence gene SIX1, which is only present in isolates of FOL, not in isolates of other formae speciales or non‐pathogenic isolates of F. oxysporum. The real‐time PCR assay successfully amplified isolates of three races of FOL used in this study and quantified FOL DNA in soils, with a detection limit of 0.44 pg of genomic DNA of FOL in 20 μl of the real‐time PCR. A spiking test performed by adding different concentrations of conidia to soil showed a significant linear relationship between the amount of genomic DNA of FOL detected by the real‐time PCR assay and the concentration of conidia added. In addition, the real‐time PCR assay revealed a significant quadratic regression for a glasshouse experiment between disease severity and DNA concentration of FOL. The soil DNA extraction method and real‐time PCR assay developed in this study could be used to determine population densities of FOL in soil, develop threshold models to predict Fusarium wilt severity, identify high‐risk fields and measure the impact of cultural practices on FOL populations in soils.

Penyebab Penyakit Layu pada Tanaman Semangka di Karawang, Jawa Barat

Wilt disease of watermelon is an important disease in Indonesia, but determination of the causal agent has not been reported yet. Postulat Koch based approach was conducted to determine the pathogen causing wilt of watermelon from Karawang, West Java. Fungi associated with wilt symptoms were isolated from stem and root, then the fungal colonies were identified based on their morphological characters. Pathogenicity tests were performed using soil media and wet paper. Host range study involved other Cucurbitaceae plants, i.e. cucumber, melon and paria. Three species of Fusarium were successfully isolated from plants showing wilt symptom, i.e. F. oxysporum, F. solani, and F. semitectum . The fungus F. oxysporum consistently caused the most severe wilt symptom on watermelon, but developed no symptom on other tested cucurbits. The two fungi, F. solani and F. semitectum, caused necrotic on roots and stem of watermelon followed by wilting of the plant. The symptom was different than those of the initial symptoms from the field. Therefore it concluded that wilt symptom of watermelon is caused by Fusarium oxysporum f.sp. niveum. Key words: Cucurbitaceae, Fusarium oxysporum f.sp. niveum , species identification, wilt

Identification of a Novel Small Cysteine-Rich Protein in the Fraction from the Biocontrol Fusarium oxysporum Strain CS-20 that Mitigates Fusarium Wilt Symptoms and Triggers Defense Responses in Tomato.

The biocontrol effect of the non-pathogenic Fusarium oxysporum strain CS-20 against the tomato wilt pathogen F. oxysporum f. sp. lycopersici (FOL) has been previously reported to be primarily plant-mediated. This study shows that CS-20 produces proteins, which elicit defense responses in tomato plants. Three protein-containing fractions were isolated from CS-20 biomass using size exclusion chromatography. Exposure of seedling roots to one of these fractions prior to inoculation with pathogenic FOL strains significantly reduced wilt severity. This fraction initiated an ion exchange response in cultured tomato cells resulting in a reversible alteration of extracellular pH; increased tomato chitinase activity, and induced systemic resistance by enhancing PR-1 expression in tomato leaves. Two other protein fractions were inactive in seedling protection. The main polypeptide (designated CS20EP), which was specifically present in the defense-inducing fraction and was not detected in inactive protein fractions, was identified. The nucleotide sequence encoding this protein was determined, and its complete amino acid sequence was deduced from direct Edman degradation (25 N-terminal amino acid residues) and DNA sequencing. The CS20EP was found to be a small basic cysteine-rich protein with a pI of 9.87 and 23.43% of hydrophobic amino acid residues. BLAST search in the NCBI database showed that the protein is new; however, it displays 48% sequence similarity with a hypothetical protein FGSG_10784 from F. graminearum strain PH-1. The contribution of CS20EP to elicitation of tomato defense responses resulting in wilt mitigating is discussed.

First report of Fusarium solani causing stem rot of Dracaena in Iran

Abstract In July 2013, symptoms of stem rot were observed in the Dracaena sanderiana cuttings in greenhouses of Mahallat County, Markazi Province, Iran. The symptoms first appeared as severe wilting. Later, leaves became brown and necrotic. Symptoms on the cuttings were observed as rotted areas on the middle of the stems. The cortical tissues of the plants showed a distinct brown discoloration. Eventually, the infected plants died. The pathogen was isolated from Dracaena stems and identified as F. solani by a fragment of the translation elongation factor 1-alpha (EF-1α) gene. Fusarium solani was confirmed by a pathogenicity test, and the causal agent was re-isolated from infected D. sanderiana plants. To the best of our knowledge, this is the first report of stem rot caused by F. solani on the cuttings of D. sanderiana.

Bio-suppression of Fusarium Wilt Disease in Potato Using Nonpathogenic Potato-associated Fungi

Ten nonpathogenic Aspergillus spp. and Penicillium spp. isolates, naturally occurring within healthy potato plants and previously selected based on their ability to suppress Fusarium dry rot disease, were evaluated for their in vitro antifungal potential against Fusarium sambucinum, F. oxysporum and F. graminearum and their effects against Fusarium wilt severity and on plant growth and production. Tested through the dual culture technique on PDA medium, all isolates tested had significantly decreased Fusarium spp. growth relative to the untreated control. Growth inhibition, achieved after 7 days of incubation at 25°C, varied from 32.3 to 42.9% using Aspergillus spp. and from 44.1 to 59.6% with Penicillium spp. The highest inhibition, by about 55-59%, was noted using isolates E.36.11 (P. chrysogenum) and E.39.11 (Penicillium sp.). Competition, mycoparasitism, hyphal lysis, early formation of resting structures and mycelial cords, and decreased sporulating ability are the main effects recorded during antagonism exerted toward targeted Fusarium species. Fusarium wilt severity, noted 75 days posy-planting, was significantly lowered by 29 to 47% on potato plants treated using 7 out the 10 isolates tested. The highest wilt severity decrease, by 41-47% over the inoculated and untreated control, was achieved using E.13.11 (A. niger), E.25.11 (A. flavus), E.36.11 (P. chrysogenum), and E.29.11 (P. polonicum) based treatments. Plant inoculated with Fusarium spp. and treated with E.29.11 (P. polonicum), E.13.11 (A. niger), E.41.11 (A. terreus), E.60.11 (A. flavus), and E.25.11 (A. flavus) showed 36-46% higher aerial part growth. The most interesting improvements of root and tuber fresh weights, achieved using the majority of isolates tested, ranged between 22-40% and 15-21%, respectively. Further investigations are needed to more elucidate the antifungal activity of the extracellular metabolites of the most effective isolates toward Fusarium species infecting potato.

Comparative Efficacy of Potassium Salts Against Soil-borne and Air-borne Fungi and Their Ability to Suppress Tomato Wilt and Fruit Rots

Potassium sorbate (PS), potassium bicarbonate (PB) and dipotassium hydrogenphosphate (DPHP) were assessed for their antifungal activity against Fusarium oxysporum f. sp. lycopersici (FOL), F. oxysporum f. sp. radicis-lycopersici (FORL), F. solani, Verticillium dahliae (VD), Rhizoctonia solani, Colletotrichum coccodes, Pythium aphanidermatum, Sclerotinia sclerotiorum, Botrytis cinerea and Alternaria solani. They were screened for their ability to suppress Verticillium and Fusarium wilts, and Fusarium Crown and Root Rot (FCRR), for their effects on tomato growth, and for their potential control of Botrytis, Alternaria, Rhizoctonia and Anthracnose fruit rots. PS (0.25-1.5%), DPHP (0.1-0.6 M) and PB (0.1-0.6 M) inhibited fungal growth in a concentration-dependent manner, with the greatest inhibition achieved using the highest concentrations. Inter specific variations in sensitivity were detected with P. aphanidermatum, S. Sclerotiorum and B. cinerea being the most sensitive to all salts. Single treatments using PS (0.25%), PB (50 mM) and DPHP (50 mM) resulted in varied degree of protection against wilts. PS led to 50, 78.26 and 65% lower wilt severity as respectively compared to VD-, FOL- and FORL-inoculated controls. PS had significantly increased plant height, root and aerial part fresh weights by 20.61, 30.76 and 33.02%, respectively, compared to FORL-inoculated plants and had improved root fresh weight by 42.18 and 32.87% compared to FOL-and VDinoculated plants, respectively. PB-based treatment led to 60.86 and 30% lower Fusarium wilt and FCRR severity but did not suppress Verticillium wilt. DPHP suppressed only Fusarium wilt by 65.21%. Used as fruit treatment, DPHP and PS significantly decreased Botrytis, Rhizoctonia, Alternaria and Anthracnose fruit rots by 46.68 and 30.81%, 14.04 and 15.74%, 20 and 31.67%, and 19.17 and 25.24%, respectively, compared to inoculated and untreated controls. PB-based treatment resulted in 12.83% significantly lower Rhizoctonia fruit rot. These results showed that PS may be used as potential abiotic agent for successfully controlling fungal tomato diseases.

Bio-Management of Fusarium Wilt Disease Complex with Pseudomonas fluorescens and Aspergillus niger

Flue Cured Virginia (FCV) tobacco is a major rain-fed crop grown in light soil regions of Karnataka. Fusarium wilt disease complex caused by Fusarium oxysporum f. sp. nicotianae in association with Root-knot nematodes, Meloidogyne incognita is a major threat to the successful production and also for its sustainability in the region. The tobacco crop affected with above malady exhibit stunted growth, severe wilt symptoms, drying of leaves on one side of the plant and with conspicuous galls on the infected roots resulted in heavy yield and quality loss. Fungicides and nematicides are being used against this wilt disease complex with limited efficacy. Extensive use of pesticides of chemical origin especially in higher doses for disaese control has to be avoided due to higher costs and associated hazards to the environment. Replicated trials were conducted with antagonistic bacterium, Pseudomonas fluorescens and antagonistic fungi, Aspergillus niger singly and in combinations against fusarium wilt disease complex in FCV tobacco under sick field conditions. Results revealed that application of P. fluorescens @ 1g/plant in combination with A. niger enriched with FYM @ 100 g /plant at the time of planting resulted in 61.0% reduction in fusarium wilt disease incidence at 70 DAT compared to untreated check. There was significant reduction in root knot nematode incidence in terms of RKI (Root- Knot Index) to 1.93 and final soil nematode population to 72.5 as compared to RKI of 3.71 and final soil nematode population of 140 in untreated check. Subsequent increase in total cured leaf and bright grade yield was 1311 kg/ha and 926 kg/ha respectively as compared to 1042 kg/ha and 615 kg/ha respectively in untreated check.

Use of silicon for reducing the severity of bacterial wilt of sweet pepper

Bacterial wilt of sweet pepper, caused by Ralstonia solanacearum (Rs) race 1, is a limiting disease in northern and northeastern Brazil. The present study evaluated the effect of silicon (Si) on the disease in the sweet pepper cv. Enterprise, which was grown in a substrate containing 0.00, 0.25, 0.50, 1.50, or 3.00 g SiO2 kg-1and was subsequently transplanted into soil infested with Rs CGM-8. The following variables were evaluated: latency period (LP50); incidence; bacterial wilt index (BWI); area under the disease progress curve (AUDPC); biomass; accumulation of Ca+2, Mg+2, and Si; total protein and enzymatic activity; chemical characteristics of the substrate; and in vitro bacterial growth. A dose of 2.95 g Si kg-1substrate increased the LP50 (33.6%) and reduced the BWI (98%) and AUDPC (93.7%); this treatment also increased Ca+2 levels in the shoots and reduced Mg+2levels in the shoots and the roots. Supplementation with various doses of Si yielded maximum increases in the shoot fresh biomass (121.8%), the root fresh biomass (83.6%), and the shoot dry biomass (84.9%); increased the concentrations of total protein, catalase, ascorbate peroxidase, and chitinase; caused the accumulation of Si in the shoots and substrate; increased the pH, Na+, and K+; and decreased P in the substrate. The putative mechanisms of action of Si included a direct effect on colonization of the pathogen, an indirect effect on the plant’s development, increased Ca+2 absorption, and signaled for the production of plant defence enzymes. Therefore, the production of sweet pepper seedlings in a substrate containing calcium silicate (2.95 g SiO2 kg-1) could be utilized as an alternative cultivation practice for the management of bacterial wilt disease. More research is needed to elucidate the exact mechanisms of silicon and its effects on latent infections and on bacterial cells and population.

Modes of action of the protective strain Fo47 in controlling verticillium wilt of pepper

The protective fungus Fusarium oxysporum Fo47 reduces the severity of wilt caused by the soilborne pathogen Verticillium dahliae in pepper. Modes of action responsible for the biocontrol activity were studied. Microscopic observations of fluorescent protein‐transformed strains colonizing the root surface show that the colonization patterns of Fo47 and V. dahliae were similar. Pixel counting of the images obtained by confocal microscopy showed that Fo47 reduces colonization of the root surface by V. dahliae, suggesting a possible role of competition for nutrients at the root surface. Besides these effects on surface colonization, the hormonal pathways activated during priming of plant defence responses were identified by measuring the amount of some phytohormones and their derivatives in roots and stems of pepper. Results showed an early, slight increase of jasmonyl isoleucine, followed by a transient increase of salicylic acid during the pre‐challenged phase of priming and an increase of 12‐oxo‐phytodienoic acid during the challenge phase of priming. The caffeic, ferulic and chlorogenic acids, known to play a role in plant defence reactions, showed a strong antimicrobial activity against V. dahliae in vitro. In pepper roots, Fo47 stimulated the biosynthesis of caffeic acid and primed that of chlorogenic acid. These results demonstrated that the effective control of V. dahliae provided by Fo47 is based on different but complementary mechanisms.

A rice mutant defective in antioxidant-defense system and sodium homeostasis possesses increased sensitivity to salt stress

Screening salt-sensitive mutants is a powerful method to identify genes associated with salt tolerance. We used forward genetic screening with sodium azide-mutated rice (Oryza sativa L. cv. Tainung 67) to identify mutants showing hypersensitivity to salt stress. A new mutant line, named salt hypersensitive 1 (shs1) and exhibiting a severe salt-sensitivity when grown under a high NaCl concentration, was identified; the salt hypersensitivity was caused by duplicate recessive epistasis with mutations likely in two different loci. The shs1 salt sensitive phenotypes included a decreased seed germination rate, reduced shoot height and root length, severe and quick wilting, and overaccumulation of sodium ions in shoots as compared with wild-type plants. In addition, shs1 showed a decreased photosynthetic efficiency and enhanced hydrogen peroxide (H2O2) production under the salt stress. An increased superoxide dismutase activity and decreased catalase activity were responsible for the hyperaccumulation of H2O2 in shs1. The hypersensitivity of shs1 to the salt stress might be caused by an impaired antioxidant machinery and cellular Na+ homeostasis.

Companion cropping with potato onion enhances the disease resistance of tomato against Verticillium dahliae.

Intercropping could alleviate soil-borne diseases, however, few studies focused on the immunity of the host plant induced by the interspecific interactions. To test whether or not intercropping could enhance the disease resistance of host plant, we investigated the effect of companion cropping with potato onion on tomato Verticillium wilt caused by Verticillium dahliae (V. dahliae). To investigate the mechanisms, the root exudates were collected from tomato and potato onion which were grown together or separately, and were used to examine the antifungal activities against V. dahliae in vitro, respectively. Furthermore, RNA-seq was used to examine the expression pattern of genes related to disease resistance in tomato companied with potato onion compared to that in tomato grown alone, under the condition of infection with V. dahliae. The results showed that companion cropping with potato onion could alleviate the incidence and severity of tomato Verticillium wilt. The further studies revealed that the root exudates from tomato companied with potato onion significantly inhibited the mycelia growth and spore germination of V. dahliae. However, there were no significant effects on these two measurements for the root exudates from potato onion grown alone or from potato onion grown with tomato. RNA-seq data analysis showed the disease defense genes associated with pathogenesis-related proteins, biosynthesis of lignin, hormone metabolism and signal transduction were expressed much higher in the tomato companied with potato onion than those in the tomato grown alone, which indicated that these defense genes play important roles in tomato against V. dahliae infection, and meant that the disease resistance of tomato against V. dahliae was enhanced in the companion copping with potato onion. We proposed that companion cropping with potato onion could enhance the disease resistance of tomato against V. dahliae by regulating the expression of genes related to disease resistance response. This may be a potential mechanism for the management of soil-borne plant diseases in the intercropping system.

Mefenoxam Sensitivity, Aggressiveness, and Identification of Pythium Species Causing Root Rot on Floriculture Crops in North Carolina.

Herbaceous ornamental plants exhibiting symptoms of Pythium root rot were collected from 26 greenhouses in 21 counties in North Carolina (NC) from 2010 to 2012. Plant symptoms ranged from mild stunting to severe wilting, root rot, and death. Roots were plated on selective media, and 356 isolates of Pythium were recovered from 34 host species. Selected isolates were identified by sequencing of the internal transcribed spacer (ITS) rDNA gene region. Seventeen Pythium species were identified, with P. aphanidermatum, P. irregulare, and P. myriotylum comprising 75% of the 320 isolates sequenced. Twelve of the 26 greenhouses had more than one species present. Mefenoxam sensitivity was tested in vitro by growing isolates in wells of microtiter plates containing clarified V8 agar amended with 100 µg a.i./ml mefenoxam. Colonization was scored after 24 to 48 h using a scale of 0 (no growth) to 5 (entire well colonized). Fifty-two percent of the isolates were resistant to mefenoxam (mean score ≥4). All 32 isolates of P. myriotylum were sensitive, whereas sensitivity varied among isolates of P. aphanidermatum and P. irregulare. Resistant and sensitive isolates of the same species were found within the same greenhouses. The aggressiveness of P. aphanidermatum and P. irregulare isolates was evaluated on poinsettia, Gerbera daisy, and petunia. P. aphanidermatum was more aggressive than P. irregulare on poinsettia and petunia; symptoms were mild and no differences in aggressiveness were observed on Gerbera daisy. Sensitivity to mefenoxam was not related to aggressiveness.

Evaluating Grafted Watermelon for Verticillium Wilt Severity, Yield, and Fruit Quality in Washington State

Verticillium wilt caused by Verticillium dahliae is a serious disease for watermelon growers in Washington State. Grafting represents a possible alternative disease management strategy, but little is known about rootstock resistance to verticillium wilt or the performance of grafted watermelon in the different production regions of the state. In this study, verticillium wilt severity, yield, and fruit quality were evaluated at three contrasting field sites in Washington using verticillium wilt-susceptible ‘Sugar Baby’ (diploid) watermelon grafted onto four commercial rootstock cultivars (Marvel, Rampart, Tetsukabuto, and Titan); nongrafted ‘Sugar Baby’ was included as the control. Verticillium dahliae soil densities varied at each site (<1.0, 5.7, and 18.0 colony-forming units (cfu)/g soil at Othello, Eltopia, and Mount Vernon, respectively). Area under disease progress curve (AUDPC) values differed significantly among treatments at Eltopia and Mount Vernon. Nongrafted ‘Sugar Baby’ had the highest AUDPC value at all three sites, while ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had the lowest AUDPC value at Eltopia and Mount Vernon. Nongrafted ‘Sugar Baby’ also had the lowest fruit weight per plant at all sites, but ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had the highest fruit weight per plant at Eltopia and Mount Vernon. Marketable fruit weight per plant did not differ among treatments at Othello. Yield was negatively correlated with AUDPC values at both Eltopia and Mount Vernon. Fruit number per plant was only significantly impacted at Eltopia, where ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had more fruit per plant than all other treatments except ‘Sugar Baby’ grafted onto ‘Rampart’. Fruit quality (flesh firmness, total soluble solids, and lycopene content) was unaffected by grafting at either Othello or Eltopia, except for increased flesh firmness for ‘Sugar Baby’ grafted onto ‘Marvel’ and ‘Titan’ as compared with nongrafted ‘Sugar Baby’ at Eltopia. At season’s end, plants were sampled from all treatments at Eltopia and Mount Vernon and assayed for V. dahliae. Microsclerotia typical of this organism were observed in all samples. Results from this study indicate that verticillium wilt of watermelon can be successfully managed by grafting when the V. dahliae soil density exceeds 5.0 cfu/g in Washington. In addition, grafting does not reduce fruit quality and using certain rootstocks can improve the quality of flesh firmness at certain locations.

Rhizoctonia blight of turnip green caused by Rhizoctonia solani AG-4 HG-III

Severe wilt was found on seedlings of turnip green (Brassica rapa L., perviridis group) in Ibaraki Prefecture, Japan, from May to September 2013. A fungus repeatedly isolated from diseased plants was identified as Rhizoctonia solani AG-4 HG-III based on culture morphology, anastomosis and sequencing of the internal transcribed spacer region on ribosomal DNA (rDNA-ITS region). Pathogenicity of this isolate to turnip green was confirmed based on inoculation test. Because Rhizoctonia blight of turnip green by AG-4 HG-III has not been reported so far, we propose including it as one of the pathogens causing this disease.

Effects of Bio-organic Fertilizers Produced by Four Bacillus amyloliquefaciens Strains on Banana Fusarium Wilt Disease

ABSTRACTContinuous planting of banana disrupts the micro-ecological balance, resulting in severe fusarium wilt disease caused by Fusarium oxysporum f. sp. cubense (FOC). In this study, fifty-eight antagonistic bacterial strains were isolated from the rhizosphere soils in fields with different soil types and cropping histories, four bacterial strains among which identified as Bacillus amyloliquefaciens, based on 16S rRNA analysis combining with morphological, physiological, and biochemical properties and possessing best survival and antibiotic abilities were further selected. Greenhouse experiments showed that these four bacterial strains were found to observably decrease the fusarium wilt incidence and promote the growth of banana plants when combined with organic fertilizers, demonstrating an effective management strategy. An in vitro assessment using cell-free extracts of liquid culture validated that the four Bacillus antagonists possessed the ability to produce antifungal compounds, including iturin, surfactin, fengycin, and bacillomycin families, all of which were identified by liquid chromatograph-mass spectrometer (LC-MS) analysis during the growth of the antagonists. In addition to lipopeptides, these bacterial strains could also produce volatile antifungal compounds with significant antagonistic effect against FOC. Thus, the work described herein highlights the possibility for using the novel bio-organic fertilizers to control fusarium wilt of banana in the field in the future.