Wilt Index Research Articles

Salt stress influences the proliferation of Fusarium solani and enhances the severity of wilt disease in potato

Soil salinity has emerged as a critical abiotic stress in potato production, whereas wilt disease, caused by Fusarium solani, is the significant biotic stress. An experiment was performed to decipher the occurrence of wilt incidence by F. solani FJ1 under the influence of salinity in both in vitroand pot culture conditions. High salt concentration negatively influenced root and shoot development in the variety “Kufri Jyoti” but positively affected the mycelial growth and sporulation behaviours of F. solani FJ1. There was abundant whitish mycelial growth with enhanced biomass and high sporulation (microconidia production) in F. solani FJ1 cultured on salt-supplemented media. Moreover, under high salinity conditions (EC 2–8 dS m−1), severe wilting and rotting of vascular bundles were observed in plants artificially inoculated with F. solani FJ1. The mortality rate of potato plants was significantly higher under individual and combined stresses as compared to control. The wilt index of individual and combined stressed plants was also substantially higher compared to the control. Additionally, compared to the control, there was a significant decrease in total chlorophyll content and membrane stability index of the leaves under combined stress. However, the total phenols were increased under stress conditions. The total sugar content of potato plants decreased in infected plants, but increased when exposed to salt stress or a combination of salt stress and pathogen infection. F. solani infection also increased the activity of peroxidase (POX) and decreased the activity of phenylalanine ammonia-lyase (PAL) and catalase (CAT). These results suggest that Fusarium wilt and dry rot will be a more severe disease for potato cultivation in saline soils.

Characterization of the Endophytic Bacillus subtilis KRS015 Strain for Its Biocontrol Efficacy Against Verticillium dahliae.

Endophytes play important roles in promoting plant growth and controlling plant diseases. Verticillium wilt is a vascular wilt disease caused by Verticillium dahliae, a widely distributed soilborne pathogen that causes significant economic losses on cotton each year. In this study, an endophyte KRS015, isolated from the seed of the Verticillium wilt-resistant Gossypium hirsutum 'Zhongzhimian No. 2', was identified as Bacillus subtilis by morphological, phylogenetic, physiological, and biochemical analyses. The volatile organic compounds (VOCs) produced by KRS015 or its cell-free fermentation extract had significant antagonistic effects on various pathogenic fungi, including V. dahliae. KRS015 reduced Verticillium wilt index and colonization of V. dahliae in treated cotton seedlings significantly; the disease reduction rate was ∼62%. KRS015 also promoted plant growth, potentially mediated by the growth-related cotton genes GhACL5 and GhCPD-3. The cell-free fermentation extract of KRS015 triggered a hypersensitivity response, including reactive oxygen species (ROS) and expression of resistance-related plant genes. VOCs from KRS015 also inhibited germination of conidia and the mycelial growth of V. dahliae, and were mediated by growth and development-related genes such as VdHapX, VdMcm1, Vdpf, and Vel1. These results suggest that KRS015 is a potential agent for controlling Verticillium wilt and promoting growth of cotton.

Effects of combinations of arbuscular mycorrhizal fungal species on tomato growth and Fusarium wilt control

In this study, we investigated the effects of combinations of arbuscular mycorrhizal (AM) fungal species on tomato seedling growth and Fusarium wilt control. The study was conducted in greenhouse pot experiments using the tomato (Solanum lycopersicum) variety Fusan 88 and the fungi Funneliformis mosseae, Diversispora versiformis, Claroideoglomus etunicatum, and Rhizophagus intraradices as inoculants. The results showed higher mycorrhizal root colonization rates in all inoculation mixtures than in single-inoculum treatments, while growth-promotion effects differed significantly among AM fungal species and their combinations. Except for inoculation with F. mosseae alone, other inoculation treatments significantly promoted the growth of tomato seedlings. Of all fungal species, R. intraradices had the most significant effect on promoting seedling growth, as observed in all inoculum combinations containing this species. The greatest effect on seedling growth was observed for combined inoculation with D. versiformis + R. intraradices, which led to increases in above- and belowground biomass of 67.74 % and 100 %, respectively, compared to the control (CK), followed by C. etunicatum + R. intraradices, which led to increases in above- and belowground biomass of 61.29 % and 100 % compared to CK. Redundancy analyses showed that compared to the other three species, R. intraradices had more significant effects on promoting plant nitrogen, phosphorus, and potassium uptake and increasing above- and belowground dry weight. Mycorrhizalized seedlings were more resistant to Fusarium wilt and had lower malondialdehyde content and higher catalase, superoxide dismutase, and polyphenol oxidase activity in tomato plants. The lowest Fusarium wilt disease index value was 39.96 %, for mixed inoculation with F. mosseae + D. versiformis + C. etunicatum; this was 34.28 % lower than that of CK, and the control effect was 34.27 %, followed by inoculation with C. etunicatum + R. intraradices, which had a disease index value of 41.48 %, 31.78 % lower than that of CK, with a control effect value of 31.76 %. Therefore, we transplanted tomato seedlings inoculated with C. etunicatum + R. intraradices, which had both good growth-promotion and disease-resistance effects, to a greenhouse for sand culture under conditions of high water and fertilization. The mycorrhizal relationships developed in these plants at the seedling stage remained stable throughout the tomato reproductive period. The mycorrhizal seedlings had a significantly lower incidence of Fusarium wilt and lower disease index values, indicating better disease control than observed in non-mycorrhizal seedlings. The mycorrhizal plants produced fruits with a significantly higher soluble-sugar content and sugar:acid ratio (30.8 % and 42.3 % higher, respectively, than CK) and a significantly lower organic acid content (11.5 % lower than CK). Thus, mycorrhization significantly improved tomato plants’ growth, disease resistance, and fruit quality. These findings lay a foundation for the application of mycorrhizal fungi in tomato agriculture.

Calculation method of wilting index based on fractal dimension of multispectral images for the soybean canopy

Drought stress is an important environmental factor that restricts the quality and high yield of the soybean. Rapid and nondestructive monitoring of canopy traits under drought stress is very critical to the cultivation and quality improvement of for the soybean plants. To solve the problems of traditional artificial chemical tests in determining soybean wilt index, such as cumbersome, time-consuming, and laborious, a method for calculating wilting index was proposed based on the fractal dimension of multispectral images for the soybean canopy. First, the soybean variety of Suinong 26 was chosen as the experimental subject, the multispectral images of five channels (RGB, GRE, NIR, RED and REG) of the soybean canopy were acquired. Second, the soybean canopy image was extracted by K-means clustering algorithm from the original multispectral image, with an effective segmentation rate (ESR) of 0.9729. Third, on the base of the multispectral image enhanced by the gamma transform for the soybean canopy, a method for calculating wilting index (LBC,LDBC, LDB) was constructed for the soybean canopy by using fractal dimension algorithms including box-counting (BC) dimension, differential box-counting (DBC) dimension and double blanket (DB) dimension. Finally, the proposed method was proved by using the average leaf inclination (LI) and the projected leaf area (PLA). The experimental results showed that the determination coefficients R2 were all above 0.85. The LBC got the highest correlation with LI and PLA in the RGB channel with coefficient determination R2 above 0.8729. The LDB got the highest correlation with LI and PLA in the GRE, NIR, and REG channels with determination coefficient R2 above 0.8824. The LDBC got the highest correlation with LI and PLA in the RED channel with determination coefficient R2 above 0.8857. This achievement presented that the proposed wilting index could characterize the change degree for the ecology and morphology when soybeans were affected by drought stress, which can provide the technical support to scientifically monitor the phenotypic traits in the process of variety breeding, field cultivation for the soybean plant.

Silicon Controls Bacterial Wilt Disease in Tomato Plants and Inhibits the Virulence-Related Gene Expression of Ralstonia solanacearum.

Silicon (Si) has a multifunctional role in improving plant growth and enhancing plant disease resistance, but its mechanisms are not fully understood. In this study, we investigated the impacts of silicon application on the control of bacterial wilt and elucidated the molecular mechanisms using transcriptome sequencing. Compared to non-Si treatment, Si application (0.5–2 mM) significantly reduces tomato bacterial wilt index by 46.31–72.23%. However, Si does not influence the growth of R. solanacearum. Si application negatively influences R. solanacearum exopolysaccharide (EPS) synthesis and biofilm formation. Transcriptome analysis showed that Si treatment significantly downregulates the expression of virulence genes’ transcriptional regulator (xpsR), EPS synthesis-related genes (epsD and tek), and type III effectors (HrpB2, SpaO, and EscR) in R. solanacearum. In addition, Si remarkably upregulates the expression of twitch motor-related genes (pilE2, pilE, fimT, and PilX). These findings suggest that silicon-suppressed tomato wilt incidence may be due to the regulation of the virulence-related genes of R. solanacearum by Si. Our research adds new knowledge to the application of Si in the field of disease control.

Exogenous Melatonin Alleviates Alkaline Stress by Removing Reactive Oxygen Species and Promoting Antioxidant Defence in Rice Seedlings.

Saline-alkali stress seriously restricts rice growth, development, and production in northern China. The damage of alkaline stress on rice is much greater than that of salt due to ion toxicity, osmotic stress, and especially high pH. As a signal molecule, melatonin (N-acetyl-5-methoxytryptamine, MT) mediates many physiological processes in rice and participates in protecting rice from abiotic stress. The potential mechanism of exogenous melatonin-mediated alkaline stress tolerance is still largely unknown. In this study, the effects of melatonin on the morphological change, physiological property, and corresponding genes expression in rice seedlings were analyzed under alkaline stress (20 mmol L−1, pH 9.55). The results showed that the expression levels of MT synthesis genes (TDC2, T5H, SNAT, ASMT1, and ASMT2) were induced by both exogenous MT and alkaline stress treatment. The cell membrane was protected by MT, and the MT furtherly play role in scavenging reactive oxygen species (ROS), reducing lipoxygenase (LOX) activity, and malondialdehyde (MDA) content. The scavenging of ROS by melatonin is attributed to the coupling of the improvement of redox homeostasis and the enhancement of antioxidant enzyme activity and antioxidant content by upregulating the transcriptional levels of antioxidase genes. In the meantime, MT pretreatment promoted the accumulation of free proline, sucrose, and fructose by regulating the OsP5CS, OsSUS7, and OsSPS1 gene expression level and increased chlorophyll content upregulating the expression of chlorophyll synthesis-related genes. Ultimately, the alleviating effect of exogenous melatonin on alkaline stress was reflected in increasing the leaf relative water content (RWC) and root-shoot ratio and reducing the leaf tip wilt index (TWI) through a series of physiological and biochemical changes. Melatonin pretreatment changed the expression level of MT synthesis genes which might contribute to MT synthesis in rice, consequently, activated the ROS scavenging system and alleviating the damage of alkaline stress on rice seedlings. Our study comprehensively understands the alleviating effect of exogenous melatonin on rice under alkaline stress.

PH-Responsive On-Demand Alkaloids Release from Core-Shell ZnO@ZIF-8 Nanosphere for Synergistic Control of Bacterial Wilt Disease.

Developing an effective and safe technology to control severe bacterial diseases in agriculture has attracted significant attention. Here, ZnO nanosphere and ZIF-8 are employed as core and shell, respectively, and then a pH-responsive core-shell nanocarrier (ZnO-Z) was prepared by in situ crystal growth strategy. The bactericide berberine (Ber) was further loaded to form Ber-loaded ZnO-Z (Ber@ZnO-Z) for control of tomato bacterial wilt disease. Results demonstrated that Ber@ZnO-Z could release Ber rapidly in an acidic environment, which corresponded to the pH of the soil where the tomato bacterial wilt disease often outbreak. In vitro experiments showed that the antibacterial activity of Ber@ZnO-Z was about 4.5 times and 1.8 times higher than that of Ber and ZnO-Z, respectively. It was because Ber@ZnO-Z could induce ROS generation, resulting in DNA damage, cytoplasm leakage, and membrane permeability changes so the released Ber without penetrability more easily penetrated the bacteria to achieve an efficient synergistic bactericidal effect with ZnO-Z carriers after combining with DNA. Pot experiments also showed that Ber@ZnO-Z significantly reduced disease severity with a wilt index of 45.8% on day 14 after inoculation, compared to 94.4% for the commercial berberine aqueous solution. More importantly, ZnO-Z carriers did not accumulate in aboveground parts of plants and did not affect plant growth in a short period. This work provides guidance for the effective control of soil-borne bacterial diseases and the development of sustainable agriculture.

Roving Survey of Panama Wilt Disease (Fusarium oxysporum f. sp. cubense) of Banana in Bihar

A survey of Panama wilt of banana was conducted in different districts of Bihar i.e. Muzaffarpur, Vaishali, Samastipur, Darbhanga, Katihar, Purnea, Bhagalpur, Kishanganj and Saharsa. This disease was present in all the districts with different levels of percent wilt index. In the Vaishali belt (Zone–I), the maximum percent wilt index was recorded in the Vaishali district (30-45%) in cv. Malbhog (AAB) having sucker planting material in the year 2019-20. In the Koshi belt (Zone-II), the percent wilt index (External symptom) was highest in Purnea district (34-42%) in cv. Robusta (AAA) followed by district Saharsa (28-40%) and Kishanganj (25-38%). The lowest percent wilt index was found in districts Bhagalpur (22-38%) and Katihar (24-38%) in the year 2019-20. Panama wilt of banana caused by Fusarium oxysporum f. sp. cubense TR4 was recorded in the Koshi belt (Zone-II) having cv. Grand naine (AAA) and cv. Robusta (AAA) in Bihar only. While in Vaishali belt (Zone-I) was free from incidence of Fusarium wilt of banana incited by Fusarium oxysporum f. sp. cubense TR4.

Soluble Concentrate Formulation of Oxalic Acid and N-Acetyl-L-Cysteine: Potential of Use in Controlling Ralstonia solanacearum

Brown rot is a disease caused by the bacterium Ralstonia solanacearum and has the potential to cause significant losses due to tubers rotting of infected potato plants. The chemical control of R. solanacearum is ineffective and the biological control methods have not yet been developed against this organism. The antibacterial activities of a soluble concentrate (SL) formulations of oxalic acid (OXA), and N-Acetyl-L-cysteine (NAC) were tested against R. solanacearum race 3 biovar 2. Formulations of OXA SL 13%, NAC SL 10%, and OXA+NAC SL 23% showed inhibition zones against R. solanacearum. In the case of NAC SL 10%, and OXA+NAC SL 23%, the inhibition zone consisted of two regions, a clear inhibition zone, and a less clear inhibition zone. After 72 h. of incubation, the final total inhibition zone was 35.3, 33.3, and 60.0 mm for OXA SL 13%, NAC SL 10%, and OXA+NAC SL 23%, respectively. Both the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of OXA+NAC SL 23% against R. solanacearum were 62.5 μl/ml. Formulation of OXA+NAC SL 23% exhibited good stability at different storage conditions and no separation was observed during the stability test. In the pots experiment, the wilt index and the percentage of wilted plants were decreased significantly in OXA+NAC SL 23% treatments compared to the positive control (treated with R. solanacearum only) treatment. The number and weight of potato tubers were significantly increased using the concentrations 125 and 62.5 μl/ml of OXA+NAC SL 23% compared to the positive control. Field experiments are needed to confirm the results.

Zinc and Copper Enhance Cucumber Tolerance to Fusaric Acid by Mediating Its Distribution and Toxicity and Modifying the Antioxidant System.

Fusaric acid (FA), the fungal toxin produced by Fusarium oxysporum, plays a predominant role in the virulence and symptom development of Fusarium wilt disease. As mineral nutrients can be protective agents against Fusarium wilt, hydroponic experiments employing zinc (Zn) and copper (Cu) followed by FA treatment were conducted in a glasshouse. FA exhibited strong phytotoxicity on cucumber plants, which was reversed by the addition of Zn or Cu. Thus, Zn or Cu dramatically reduced the wilt index, alleviated the leaf or root cell membrane injury and mitigated against the FA inhibition of plant growth and photosynthesis. Cucumber plants grown with Zn exhibited decreased FA transportation to shoots and a 17% increase in toxicity mitigation and showed minimal hydrogen peroxide, lipid peroxidation level with the increased of antioxidant enzymes activity in both roots and leaves. Cucumber grown with additional Cu absorbed less FA but showed more toxicity mitigation at 20% compared to with additional Zn and exhibited decreased hydrogen peroxide level and increased antioxidant enzymes activity. Thus, adding Zn or Cu can decrease the toxicity of the FA by affecting the absorption or transportation of the FA in plants and mitigate toxicity possibly through chelation. Zn and Cu modify the antioxidant system to scavenge hydrogen peroxide for suppressing FA induction of oxidative damage. Our experiments could provide a theoretical basis for the direct application of micro-fertilizer as protective agents in farming.

Zinc oxide nanoparticles for the management of Ralstonia solanacearum, Phomopsis vexans and Meloidogyne incognita incited disease complex of eggplant

Two concentrations of Zinc Oxide nanoparticles (ZnO NPs) were applied using three methods i.e., spray, seed treatment and soil inoculation for the management of disease complex of eggplant caused by Ralstonia solanacearum, Phomopsis vexans and Meloidogyne incognita. The highest increase in plant growth, chlorophyll and carotenoid contents was obtained by spray of NPs followed by seed treatment and soil inoculation. Plants sprayed with 200 ppm NPs resulted in higher increase in plant growth, and higher reduction in galling and nematode multiplication. 15 and 8 days early flowering and fruiting were observed in plants sprayed with 200 and 100 ppm NPs, respectively, over seed treatments. Scanning electron microscopy revealed that ZnO NPs had an adverse effect on cell wall/body wall of test pathogens. Wilt and blight indices was three and five when inoculated with single pathogen and inoculated together, respectively. Disease index was reduced to one when plants sprayed with 200 ppm NPs.

Magnesium Oxide Nanoparticles: Effective Agricultural Antibacterial Agent Against Ralstonia solanacearum.

Magnesium (Mg) is an essential mineral element for plants and is nontoxic to organisms. In this study, we took advantage of nanotechnologies to systematically investigate the antibacterial mechanisms of magnesium oxide nanoparticles (MgONPs) against the phytopathogen Ralstonia solanacearum (R. solanacearum) in vitro and in vivo for the first time. R. solanacearum has contributed to catastrophic bacterial wilt, which has resulted in the world-wide reduction of tobacco production. The results demonstrated that MgONPs possessed statistically significant concentration-dependent antibacterial activity, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were measured as 200 and 250 μg/mL, respectively. Additional studies, aimed at understanding the toxicity mechanism of MgONPs, indicated that physical injury occurred to the cell membranes, along with decreased motility and biofilm formation ability of R. solanacearum, due to the direct attachment of MgONPs to the surfaces of the bacterial cells, which was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Reactive oxygen species (ROS) accumulation could also be an important reason for the antibacterial action, inducing DNA damage. The toxicity assessment assay under greenhouse conditions demonstrated that the MgONPs had exerted a large effect on tobacco bacterial wilt, reducing the bacterial wilt index. Altogether, the results suggest that the development of MgONPs as alternative antibacterial agents will become a new research subject.

Hyperspectral Analysis of Pine Wilt Disease to Determine an Optimal Detection Index

Bursaphelenchus xylophilus, the pine wood nematode (PWN) which causes pine wilt disease, is currently a serious problem in East Asia, including in Japan, Korea, and China. This paper investigates the hyperspectral analysis of pine wilt disease to determine the optimal detection indices for measuring changes in the spectral reflectance characteristics and leaf reflectance in the Pinus thunbergii (black pine) forest on Geoje Island, South Korea. In the present study, we collected the leaf reflectance spectra of pine trees infected with pine wilt disease using a hyperspectrometer. We used 10 existing vegetation indices (based on hyperspectral data) and introduced the green-red spectral area index (GRSAI). We made comparisons between non-infected and infected trees over time. A t-test was then performed to find the most appropriate index for detecting pine wilt disease-infected pine trees. Our main result is that, in most of the infected trees, the reflectance changed in the red and mid-infrared wavelengths within two months after pine wilt infection. The vegetation atmospherically resistant index (VARI), vegetation index green (VIgreen), normalized wilt index (NWI), and GRSAI indices detected pine wilt disease infection faster than the other indices used. Importantly, the GRSAI results showed less variability than the results of the other indices. This optimal index for detecting pine wilt disease is generated by combining red and green wavelength bands. These results are expected to be useful in the early detection of pine wilt disease-infected trees.

Effect of simultaneous and sequential inoculations of Meloidogyne incognita, Ralstonia solanacearum and Phomopsis vexans on eggplant in sand mix and fly ash mix soil

Effects simultaneous and sequential inoculations of Meloidogyne incognita, Ralstonia solanacearum and Phomopsis vexans were studied on the growth, chlorophyll and carotenoid contents of eggplants grown in 25% fly ash and 25% sand mix soil. Plants grown in 25% fly ash mix soil had lesser plant growth than grown in 25% sand ash mix soil. Inoculation of M. incognita / R. solanacearum or P. vexans caused reduction in plant growth, chlorophyll and carotenoid contents in both types of soils but these pathogens in combination caused a greater reduction in than individual inoculation. Inoculation of M. incognita 20 days prior to R. solanacearum caused a greater reduction in plant growth than inoculation of M. incognita prior to P. vexans. Inoculation of P. vexans prior to R. solanacearum caused a lesser reduction in plant growth, chlorophyll and carotenoid contents than inoculation of P. vexans prior to M. incognita. Inoculation of R. solanacearum 20 days prior to M. incognita caused a greater reduction in plant growth, chlorophyll and carotenoid contents than inoculation of R. solanacearum prior to P. vexans. Galling and multiplication of M. incognita was higher in plants grown in 25% sand amended soil than with 25% fly ash soil. R. solanacearum and P. vexans had adverse effects on galling and nematode multiplication. Wilt and blight indices caused by R. solanacearum and P. vexans were 3 respectively. Wilt and blight indices were 4 when two pathogens were inoculated together.

Interactions of Meloidogyne incognita, Ralstonia solanacearum and Phomopsis vexans on eggplant in sand mix and fly ash mix soils

Interactions of Meloidogyne incognita, Ralstonia solanacearum and Phomopsis vexans were studied on the growth of eggplant, chlorophyll and carotenoid contents of plants grown in 25% fly ash and 25% sand mix soil. Plants grown in 25% sand mix soil had greater plant growth compared to plants grown in 25% fly ash mix soil. Inoculation of plants with M. incognita, R. solanacearum or P. vexans reduced plant growth, chlorophyll and carotenoid contents in both types of soils. Combined inoculation of these pathogens caused a greater reduction in plant growth, chlorophyll and carotenoid contents than single inoculation. Inoculation of M. incognita 20days prior to R. solanacearum and P. vexans caused a greater reduction in plant growth than inoculation of R. solanacearum plus P. vexans prior to M. incognita. Plants inoculated in combination with 2 or more pathogens suffered greater plant growth reduction in 25% sand amended soil than in 25% fly ash amended soil. Nematode multiplication and galling were higher in plants grown in 25% sand amended soil than with 25% fly ash soil. R. solanacearum and P. vexans had adverse effects on galling and nematode multiplication. Inoculation of R. solanacearum plus P. vexans prior to M. incognita caused maximum reduction in galling and nematode multiplication. Wilt and blight indices caused by R. solanacearum and P. vexans were 3 respectively. Wilt and blight indices were 5 when R. solanacearum and P. vexans were inoculated together or these were inoculated with M. incognita.

Potassium deficiency and root exudates reduce root growth and increase Fusarium oxysporum growth and disease incidence in continuously cultivated strawberry

ABSTRACTStrawberry fruits are increasingly produced under continuous cultivation and K deficiency, but the response of strawberry to this combination of stresses has not been extensively studied. Pot and tissue culture grown strawberry (Fragaria ananassa Duch.) plants were used to determine the effect of strawberry root exudates on the growth of strawberry plants and Fusarium oxysporum under continuous cultivation and potassium (K) deficiency. The pot experimental results showed that the Fusarium wilt disease rating and index were very high (62% and 86, respectively), and the lateral roots of strawberry plants were significantly restricted under the continuous cultivation and K deficiency treatment. The growth of tissue culture plantlets was inhibited by a high concentration (4%) and promoted by a low concentration (1%) of root exudates from the replanted pot strawberries. The number of lateral roots of tissue culture plantlets was significantly lower in the 4% root exudate treatment. Growth of F. oxysporum was promoted by the relatively high concentration of root exudates of the replanted pot strawberry under continuous cultivation and K deficiency. Total phenolics and three individual phenolics (ferulic acid, p-coumaric acid and cinnamic acid) were detected in the rhizosphere soil of replanted pot strawberries and were higher in the K-deficiency treatments. Fusarium oxysporum growth was promoted by the addition of exogenously added phenolic acids. A positive relationship was observed between the growth of F. oxysporum and the higher concentration ranges of ferulic acid and p-coumaric acid.

Genetic analyses of the major and minor locus groups of bacterial wilt resistance in tobacco using a diallel cross design.

Tobacco germplasm samples with various levels of resistance to bacterial wilt were selected to construct F1 combinations of parental inbred lines and orthogonal diallel crosses using samples collected in 2009 (15 germplasms), 2010 (15 germplasms), and 2011 (16 germplasms). A total of 1/2P (P + 1) experimental materials were used for analysis. Based on the analyses of major and minor locus groups, genetic effects on the incidence rate and index of bacterial wilt in tobacco were investigated on the 15th and 25th day during the early stage. Significant effects were observed in major locus groups, but not in minor locus groups. Specifically, adjacent major locus groups (J1 = 13,056 and J1 = 13,055; J1 = 14,080 and J1 = 14,079) were detected in both the first and second analyses with considerable effects. Based on the additive effects of minor locus groups on the rate and index of bacterial wilt, the effects on the incidence rates of Yunyan 85, DB101, and RG11 as well as the effects on the disease index of the latter two germplasms reached the maximum. This was consistent with the disease resistance indicators of these tobacco varieties in the field (corresponding broad heritability >20%). Genetic homozygous dominant loci (+ +) increased the rate of bacterial wilt (susceptible), whereas homozygous recessive loci (- -) reduced the index of bacterial wilt (resistant) with considerable additive effects and low dominant effects, suggesting that the inheritance of the bacterial wilt rate and index in tobacco mainly relies on additive inheritance.

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.

Drought Resistance Identification of Mungbean Germplasm Resources at Seedlings Stage

It is significant to identify and screen drought resistant mungbean germplasm resources at seedling stage for mungbean cultivars improvement and production in China, at same time, which could provide some reference methods and basic information for developing the technical specification of identification and evaluation for drought resistance in mungbean. The indices including survival rate of seedlings, wilt index, plant height, weight of fresh and dry leaf, relative water content, biomass weight and stress index were measured with method of repeat drought stress in 70 accessions of mungbean resources. The survival rate of seedlings had significantly positive correlation between first and second drought stress, both wilt index and plant height had significantly negative correlation with survival rate. The survival rate of seedling under first drought stress, wilt index and plant height were selected as suitable indices for drought resistance identification and evaluation based on correlation analysis. The various resistant accessions of mungbean germplasm resources screened by subordinative function analysis included 16 highly resistant, 20 resistant, 23 moderately resistant, eight susceptible and three highly susceptible. The drought resistance was evaluated based on survival rate of seedling under first drought stress, wilt index and plant height with concordance rate of 70.0%, 58.6%, and 51.4% respectively as compared to comprehensive evaluation. The survival rate of seedling under first drought stress was recommended as a drought resistance index in screening a large number of germplasm resources ofmungbean.

Rhizobacteria induces resistance against Fusarium wilt of tomato by increasing the activity of defense enzymes

Fusarium wilt, caused by Fusarium oxysporum f.sp. lycopersici (Fol), is one of the most important diseases that affect tomato yield worldwide. This study investigated the potential of three antagonists, Streptomyces setonii (UFV 618), Bacillus cereus (UFV 592) and Serratia marcescens (UFV 252), and as positive control the hormone jasmonic acid (JA), to reduce Fusarium wilt symptoms and to potentiate the defense enzymes in the stem tissues of tomato plants infected by Fol. The seeds were microbiolized with each antagonist, and the soil was also drenched with them. The plants were sprayed with JA 48 h before Fol inoculation. The area under the Fusarium wilt index progress curve was reduced by 54, 48, 47 and 45% for the UFV 618, JA, UFV 592 and UFV 252 treatments, respectively. The three antagonists, and even the JA spray, efficiently reduced the Fusarium wilt symptoms on the tomato plant stems, which can be explained by the lower malondialdehyde concentration (an indication of oxidative damage to lipids in the plasma membranes) and the greater activities of peroxidases, polyphenoloxidases, glucanases, chitinases, phenylalanine ammonia-lyases and lipoxygenases, which are commonly involved in host resistance against fungal diseases. These results present a novel alternative that can be used in the integrated management of Fusarium wilt on tomatoes.