Repeated applications of Penicillium oxalicum prolongs biocontrol of fusarium wilt of tomato plants

The suppression of fusarium wilt of tomato achieved by Penicillium oxalicum (PO) applied one or several times (up to four) was assessed during three glasshouse experiments. The first application of PO (10⁶ conidia g^-1 substrate) to the growing substrate (peat and vermiculite, 1 : 1, v : v) was performed prior to its infestation with Fusarium oxysporum f. sp. lycopersici (FOL) (10⁴–10⁶ chlamydospores g^-1). Repeated applications of PO prolonged the duration of control of fusarium wilt especially when disease incidence was high. The timing of repeated applications of PO did not affect the efficacy of the control. Disease reduction was not associated with a decrease in density of FOL in the rhizosphere, irrespective of the number of applications of PO. Density of PO in the tomato rhizosphere was higher when repeated applications were made. No relationship was observed between reduction of disease and high densities of PO. Reasons for a longer disease reduction in tomato plants following several applications with PO are discussed.     

Involvement of jasmonic acid signalling in bacterial wilt disease resistance induced by biocontrol agent Pythium oligandrum in tomato

When the biocontrol agent Pythium oligandrum (PO) colonizes the rhizosphere, it suppresses bacterial wilt disease in tomato (Solanum lycopersicum cv. Micro‐Tom) caused by Ralstonia solanacearum, and a homogenate of its mycelia exhibits elicitor activity, inducing an ethylene (ET)‐dependent defence response in Micro‐Tom. Since salicylic acid (SA) and jasmonic acid (JA) play an important role in plant defence responses to pathogens, the involvement of SA‐ and JA‐dependent signal transduction pathways in resistance to R. solanacearum was investigated in tomato roots treated with a mycelial homogenate of PO. Bacterial wilt disease was also suppressed in tomato cv. Moneymaker treated with the PO homogenate. However, the SA‐inducible PR‐1(P6) gene was not up‐regulated in either Micro‐Tom or Moneymaker. SA did not accumulate in homogenate‐treated roots in comparison with distilled water‐treated controls, even 24 h after inoculation. Induced resistance against R. solanacearum was not compromised in SA‐non‐accumulating NahG transgenic plants treated with the PO homogenate. On the other hand, the expression of the JA‐responsive gene for the basic PR‐6 protein was induced in both tomato cultivars treated with the PO homogenate. Furthermore, quantitative disease assays showed that the induced resistance against R. solanacearum was compromized in PO homogenate‐treated jai1‐1 mutant plants defective in JA signalling. These results indicated that the JA‐dependent signalling pathway is required for PO‐induced resistance against R. solanacearum in tomato.     

Compost tea-mediated induction of resistance in biocontrol of strawberry Verticillium wilt

Journal of Plant Diseases and Protection - In vitro and in vivo trials were conducted to assess the biocontrol efficacy of the tea prepared from maize straw compost against Verticillium wilt of...     

Nitric oxide-overproducing transformants of Pseudomonas fluorescens with enhanced biocontrol of tomato bacterial wilt

The relation between nitric oxide (NO) production and the protective ability of Pseudomonas fluorescens T5 against bacterial wilt disease in tomato was examined. The endogenous nitric oxide reductase gene of T5 was disrupted by homologous recombination using a suicide plasmid. Three disruptants were obtained, and all had higher levels of NO production. Infection with Ralstonia solanacearum was reduced in tomato plants treated with the NO-overproducing transformants compared with the wild type. These results suggest that the modification of pseudomonads to increase their level of NO production is a new approach to enhancing their biocontrol efficacy.     

A rapid laboratory method for assessing the biological control potential of Penicillium oxalicum against Fusarium wilt of tomato

A rapid, simple and reliable procedure was developed to evaluate biological control of Fusarium wilt of tomato by Penicillium oxalicum . The method consists in growing tomato plants in flasks with nutrient solution in a growth chamber. Plants were previously treated in the seedbed with a conidial suspension (10⁷ conidia mL⁻¹) of P. oxalicum 7 days before transplanting. Fusarium oxysporum f.sp. lycopersici (race 2) was added to the Hoagland solution just before transplanting. Different concentrations and several isolates of F. oxysporum f.sp. lycopersici were tested. Using this method, plants showed typical symptoms of the disease and the effect of the biocontrol agent was clear. Consumption of nutrient solution was reduced in diseased plants, and this reduction was diminished by treatment with P.oxalicum . Consumption of nutrient solution was correlated with other disease-related parameters (AUDPC, weight of aerial parts, stunting) and was an easy and objective parameter to measure.     

Assessment of resistance to bacterial wilt incited by Ralstonia solanacearum in tomato germplasm

Journal of Plant Diseases and Protection - Bacterial wilt incited by Ralstonia solanacearum has been found the most damaging and widespread diseases of tomato throughout the world and causes heavy...     

Lipid metabolism in tomato and bean as a sensitive monitor for biocontrol of wilt diseases

The lipids metabolism of tomato and bean plants during biological control of wilt pathogens (Fusarium oxysporum f.sp.lycopersici andF. oxysporum f.sp.phaseoli, respectively) byBacillus subtilis was investigated. The interaction of wilt pathogens with both tomato and bean caused an imbalance and drastic reduction in total lipids, triacylglycerol, sterol and all phospholipd fractions except phosphatidic acid. The application of a formulated biocontrol agent,B. subtilis, eliminated the detrimental effect of both wilt pathogens and consequently prevented catabolism of lipid fractions in both tomato and bean. Moreover, the changes in the lipid fractions as a sensitive monitor for biocontrol of wilt diseases suggest a positive correlation between the application ofB. subtilis and improvement in the host metabolism towards anabolism. http://www.phytoparasitica.org posting Sept. 20, 2006.     

番茄抗枯萎病I2基因的SNP分型

利用直接测序方法检测番茄抗感品种I-2基因的DNA序列,发现了2个SNPs。以其为3′端,设计等位基因特异引物及其互补引物,研究了特异引物3′端碱基错配类型和位置对等位基因特异PCR的影响,并对52份种质资源进行了SNP分型。结果表明在下游引物3′末端第1、2位引入错配碱基可以提高反应的准确性;引入C-T碱基错配的引物,退火温度在58℃时能把I-2基因的突变位点和感病品种的对应位点区分开来,为番茄抗枯萎病辅助育种提供了有力工具。     

Genetics of tomato spotted wilt virus resistance coming from Lycopersicon peruvianum

New resistance sources coming from Lycopersicon peruvianum, especially those introgressed in UPV 32 line, are studied. UPV 32 resistance is controlled by a single gene. Resistance and dominance levels of this gene are conditioned by thrips transmission and isolate aggressiveness. A partial overcoming of resistance occurs due to the incomplete penetrance of the gene. Incomplete dominance of resistance also happens, which suggests gene dosage dependence. UPV 32 gene segregates independently of both Sw-5 gene and UPV 1 resistance gene, also coming from Lycopersicon peruvianum. It is proposed to name Sw-6 this new locus from UPV 32. Sw-5 gene and UPV 1 resistance gene show higher resistance than Sw-6. Heterozygotes for UPV 1 resistance gene were more resistant than heterozygotes for Sw-5. The lower dependence of UPV 1 resistance gene on the gene dosage effect makes it very useful for the development of commercial hybrids.     

Magnesium oxide nanoparticles induce systemic resistance in tomato against bacterial wilt disease

Bacterial wilt is a serious problem affecting many important food crops. Recent studies have indicated that treatment with biotic or abiotic stress factors may increase the resistance of plants to bacterial infection. This study investigated the effects of magnesium oxide nanoparticles (MgO NP) on disease resistance in tomato plants against Ralstonia solanacearum, as well as its antibacterial activity. The roots of tomato seedlings were inoculated with R. solanacearum and then immediately treated with MgO NP; the treated plants showed very little inhibition of bacterial wilt. In contrast, when roots were drenched with a MgO NP suspension prior to inoculation with the pathogen, the incidence of disease was significantly reduced. Rapid generation of reactive oxygen species such as O₂^?˙ radicals was observed in tomato roots treated with MgO NP. Further O₂^?˙ was rapidly generated when tomato plant extracts or polyphenols were added to the MgO NP suspension, suggesting that the generation of O₂^?˙ in tomato roots might be due to a reaction between MgO NP and polyphenols present in the roots. Salicylic acid‐inducible PR1, jasmonic acid‐inducible LoxA, ethylene‐inducible Osm, and systemic resistance‐related GluA were up‐regulated in both the roots and hypocotyls of tomato plants after treatment of the plant roots with MgO NP. Histochemical analyses showed that β‐1,3‐glucanase and tyloses accumulated in the xylem and apoplast of pith tissues of the hypocotyls after MgO NP treatment. These results indicate that MgO NP induces systemic resistance in tomato plants against R. solanacearum.     

Effect of calcium nutrition on resistance of tomato against bacterial wilt induced by Ralstonia solanacearum

This study investigated the effect of calcium nutrition on tomato bacterial wilt caused by Ralstonia solanacearum and the regulation of resistance mechanisms. Plants cultured in nutrient solution with calcium concentrations of 0.5, 5.0, and 25.0 mM, were inoculated with R. solanacearum by the root dip method. Severity of disease development, Ca concentration in tomato root and shoot tissues, hydrogen peroxide (H₂O₂) concentration, peroxidase (POD, EC 1.11.1.7) and polyphenol oxidase (PPO, EC 1.10.3.2) in tomato leaves were analyzed. Disease severities of low, medium and high Ca treatments were 100 %, 77.1 % and 56.8 % respectively. Plant growth in high Ca treatment was significantly better than those in low Ca treatment in height, stem diameter and biomass. Tomato plants absorbed significantly more Ca in roots and shoots as the level of Ca in the nutrient solution increased. In addition, H₂O₂ level in high Ca treatment rose faster and reached a higher peak with 10.86 μM gFW^?1(31.32 % greater than medium Ca plants). The activities of POD and PPO also have a greater increase in high Ca treatment with 99.09 U gFW^?1 and 107.24 U gFW^?1 compared to 40.70 U gFW^?1 and 77.45 U gFW^?1 in low Ca treatment. A negative correlation was found between Ca concentration, level of H₂O₂, POD, PPO in tomato, and disease severity, indicating that they played an important role in resistance of tomato to this disease. These results suggested that Ca was involved in the regulation of H₂O₂ concentration, and activity of POD and PPO in tomato.     

Evaluation of bacterial wilt resistance in tomato lines nearly isogenic for the Mi gene for resistance to root-knot

Resistance to bacterial wilt, caused by Ralstonia solanacearum , in tomato lines CRA 66 and Caraïbo is reported to be decreased by root-knot nematode galling and by introduction of the Mi gene for nematode resistance. The Mi gene is located on tomato chromosome 6, which also carries a major quantitative trait locus (QTL) for resistance to bacterial wilt. Bacterial wilt resistance was evaluated in F3-progenies derived from two crosses between near-isogenic lines, Caraïbo × Carmido and CRA 66 × Cranita, differing for small and large introgressions from Lycopersicon peruvianum that carry the Mi gene, respectively. These introgressed regions were mapped using RFLP markers. Plants homozygous Mi⁺/Mi⁺ (susceptible to the nematode) and homozygous Mi/Mi (resistant) for the Mi gene were selected in F2 and used to produce F3 progenies. Parents and F3-lines with Mi/Mi had resistance to bacterial wilt reduced by 30% in Caraïbo × Carmido and by 15% in CRA 66 × Cranita. Caraïbo and Carmido were demonstrated to be isolines and the small introgression from L. peruvianum resulted in loss of the QTL for bacterial wilt resistance, which is probably allelic or linked in repulsion to the Mi gene. In contrast, resistance to bacterial wilt segregated in the F3 lines from the cross CRA 66 × Cranita, giving families varying in resistance between the levels shown by the parents. Consequently, two hypotheses were considered: (i) after only four backcrosses, the parents were not isolines and the genes for resistance to bacterial wilt from CRA 66 were still segregating, and (ii) the parents were isolines and variation in resistance to bacterial wilt in F3 was due to recombination events among the large L. peruvianum introgressed chromosome region from Cranita.     

Effects of timing and method of application of Penicillium oxalicum on efficacy and duration of control of Fusarium wilt of tomato

The effects of timing and method of application of Penicillium oxalicum on the control of fusarium wilt of tomato were investigated. Application of P. oxalicum to tomato seedlings in seedbeds reduced disease caused by Fusarium oxysporum f.sp. lycopersici in a growth chamber by 45–49% and in glasshouse experiments by 22–69%. Disease suppression was maintained for 60–100 days after inoculation with the pathogen in the glasshouse. No disease reduction was observed in tomato plants where P. oxalicum was applied to seeds. Treatment with P. oxalicum did not affect the population of F. oxysporum f.sp. lycopersici in the rhizosphere.     

Bacterial wilt resistance in tomato associated with tolerance of vascular tissues to Pseudomonas solanacearum

High populations of Pseudomonas solanacearum were detected in some, but not all stems of bacterial wilt resistant ('CRA 66', 'Hawaii 7996' and 'Caraibo') and susceptible ('Floradel') tomatoes. Latent infection, i.e. spread of P. solanacearum into xylem vessels, was confirmed in Caraibo, Hawaii 7996 and 'CRA 66' (the resistant parent of Caraibo). None of the plants within the resistant cultivars wilted and those cultivars were characterized by tolerance of the vascular tissues to high bacterial densities. In contrast, plants of cultivar Floradel showed consistent symptoms and wilted rapidly, with higher mean bacterial density than resistant cultivars. Bacterial wilt resistance was not associated with resistance to bacterial root invasion but with the capability of the plant to limit P. solanacearum colonization in the stem. The extent of bacterial colonization is proposed as a criterion to quantify tolerance, complementary to absence of external wilt symptoms used in breeding programmes for resistance.     

Development of resistance in tomato plants grafted onto Solanum torvum against bacterial wilt disease

Journal of Plant Diseases and Protection - The bacterial wilt disease caused by Ralstonia solanacearum is a major constraint in the cultivation of tomato in Saint Lucia. The limited options and...     

Induced resistance in tomato plants against Fusarium wilt invoked by Fusarium oxysporum f.sp. dianthi

Tomato plants, susceptible toFusarium oxysporum f. sp.lycopersici, were inoculated by immersing the roots in a conidial suspension ofF. oxysporum f. sp.lycopersici race 1,F. oxysporum f. sp.dianthi race 2 or a mixture of both fungi. Plants inoculated withF. oxysporum f. sp.lycopersici showed disease symptoms after 2 weeks, whereas plants inoculated withF. oxysporum f. sp.dianthi or a mixture of both fungi remained symptomless for over 7 weeks, the duration of the experiment. In another experiment root systems of plants were split and each half was separately inoculated. One half was firstly inoculated withF. oxysporum f. sp.dianthi or treated with water, followed after a week by a second inoculation of the other half withF. oxysporum f. sp.lycopersici or by a water treatment. The disease symptoms in the half firstly inoculated withF. oxysporum f. sp.dianthi were significantly delayed, compared to plants of which that half had been treated with water. BecauseF. oxysporum f. sp.dianthi reduced disease symptoms caused byF. oxysporum f. sp.lycopersici without any direct interaction with this pathogen, it is concluded thatF. oxysporum f. sp.dianthi is able to induce resistance againstF. oxysporum f. sp.lycopersici in tomato plants.     

番茄黄萎病抗病基因Ve的AFLP和SSR分子标记

 本研究以番茄抗病品种05046与感病品种051355配制杂交组合,接种鉴定F1代及F2代分离群体的黄萎病发生情况,结果表明,番茄黄萎病属单基因显性遗传。用545对AFLP引物和101对SSR引物对两个亲本、抗感池及F2代分离群体进行AFLP和SSR分析,得到3个与番茄抗黄萎病基因Ve连锁的AFLP标记和1个SSR标记,分别是E66M84-A、E78M84-D、E66M40-A和SSR599,与抗病基因Ve的连锁遗传距离分别为10.3、14.2、30.5 和12.5 cM。     

Resistance-breaking tomato spotted wilt orthotospovirus isolates on resistant tomato in Serbia

Journal of Plant Diseases and Protection - The most effective management strategy for tomato spotted wilt orthotospovirus (TSWV) has been the use of resistant tomato (Sw-5b+) cultivars....