Abstract: The nonpathogenic Fusarium oxysporum strain Fo47 is an effective biocontrol agent against Fusarium wilt of tomato caused by F. oxysporum f. sp. lycopersici.Inoculant delivery protocols in which plants were exposed to Fo47 prior to challenge with the pathogen, so as to promote the strains ability to induce resistance to Fusarium wilt in tomato, were assessed. In rock wool microcosms, the biocontrol efficacy of Fo47 (inoculated at sowing) against F. oxysporum f. sp. lycopersici Fol8 (race O) was not improved following a second inoculation of the biocontrol strain at transplanting (i.e., when plants became exposed to the pathogen) or using inoculum levels of Fo47 higher than 104conidia/ml of nutrient solution. In natural soil microcosms (with Fo47 applied into potting mix prior to sowing and to roots at transplanting), effective control of Fusarium wilt required inoculum levels of 105conidia of Fo47/ml. Strain Fo47 was also studied in greenhouse microplots in which soil was artificially infested with the pathogenic strain Fol8. Fo47 delayed the progression of the disease in each of the two years and also improved final plant health in the second year. The protective effect of Fo47 resulted in a significant increase in the yield of first-grade tomatoes in the first year. Treatments did not influence yield in the second year. The results of this investigation illustrate how a biocontrol fungus can be used at a moderate inoculum level to obtain disease control under commercial conditions. It is hypothesized that this was achieved by making use of the ability of the biocontrol agent to induce resistance to Fusarium wilt in tomato.
Abstract: After the recent detection of serious losses caused by Fusarium wilt of lettuce, incited by Fusarium oxysporum f. sp. lactucae, in north-western Italy, thirty-two varieties of lettuce, belonging to different types and chosen among those typically grown in the affected area, were tested in order to evaluate the presence of field resistance to Fusarium wilt. Six experimental trials were carried out in glasshouse (4 trials) and growth chamber (2 trials). Roots of 15 day old plants were artificially inoculated by dipping in a spore suspension (1×106 CFU/ml) of the pathogen. One Italian isolate (FOL 4) and one American isolate (ATCC 76616) of F. oxysporum f. sp. lactucae were used. In the presence of a good level of disease incidence, a number of varieties, mostly belonging to the leaf lettuce type, were completely resistant to Fusarium wilt. All the tested varieties belonging to the butter head and most of those belonging to the Batavia types were susceptible to the disease. In the case of the romaine selections, cultivar reaction ranged from susceptible to resistant. In all experiments, the Italian and USA isolates of F. lactucae behaved similarly on all the tested cultivars.
Abstract: Acibenzolar-S-methyl (ASM) is a chemical activator of systematic resistance in many plants. The effect of preharvest and postharvest application of ASM was evaluated for its ability to induce resistance in muskmelon fruit. The results indicated that 50 and 100 mg L-1 ASM or 1 mL -1 imazalil at 1 week or 1 day before harvest were effective in reducing the lesion area with 100 mg -1 ASM the most effective. No treatment inhibited the infection rate. The postharvest results showed that 50 and 100 mg -1 ASM, and 0.1 mL -1 imazalil were effective in reducing the lesion area with 100 mg -1 ASM the most effective. No treatment inhibited the infection rate. There was a clear time-dependent response of the fruit to postharvest ASM treatment, in which treatments applied 1, 3, and 5 day before inoculation provided the best results. ASM did not demonstrate any fungicide effect in vitro and suppressed lesion area in treated muskmelons, indicating that disease resistance was induced. The protection of ASM was associated with the activation of peroxidase (POD) in treated muskmelons.
Abstract: The strobilurins, azoxystrobin, kresoxym-methyl and trifloxystrobin, were tested in experimental trials carried out in the growth chamber or glasshouse against Fusarium wilts of carnation (Fusarium oxysporum f. sp. dianthi), cyclamen (F. oxysporum f. sp. cyclaminis) and Paris daisy (Fusarium oxysporum f. sp. chrysanthemi), in comparison with benomyl and in some experiments prochloraz. The three strobilurins controlled Fusarium wilt on carnation when applied at transplant at 1–2 g/m2 as soil drenching. Azoxystrobin, at 250 mg/l of medium controlled also Fusarium wilt on cyclamen and on Paris daisy. Kresoxim methyl at 250 mg/l controlled Fusarium wilt on cyclamen but it was phytotoxic; at the same dosage it was not effective on Paris daisy. Trifloxystrobin was only partially or not effective in controlling Fusarium wilt on cyclamen and Paris daisy. Particularly kresoxim-methyl caused chlorosis and plant stunting. This study shows the high efficacy of azoxystrobin against Fusarium wilts of three important ornamental crops. Azoxystrobin provided control similar or better to those shown by benomyl, applied at higher dosages in all trials.
Abstract: Metabolic profiles of spikelets of wheat cultivars, Roblin and Sumai3, respectively, susceptible and resistant to fusarium head blight (FHB) were analyzed using GC/MS to develop a technology to discriminate resistance. More than 700 peaks were detected and a total of 55 compounds were tentatively identified, of which 49 were induced/up-regulated following pathogen inoculation, including 23 in Roblin and 26 in Sumai3. However, only five metabolites were significantly different both between cultivars and inoculations. Metahydroxycinnamic acid, though was detected in all four treatments, exhibited a six-fold increase in abundance in Sumai3 following pathogen inoculation, with no corresponding change in Roblin. The abundance of myo-inositol in Sumai3 was higher than that in Roblin, and in both the abundance increased following pathogen inoculation. The compounds common to all treatments were subjected to factor analysis to identify groups of compounds, based on significant factor-loadings, associated with susceptibility or resistance against FHB. The treatment involving pathogen-inoculation of the resistant cv. Sumai3 was associated with the highest scores for the first and second factors that can be used for the discrimination of resistance against FHB. The first factor was associated with higher abundances of several fatty acids and aromatic compounds, while the second factor was associated with metabolites such as p- and m-coumaric acids, myo-inositol and other sugars, and malonic acid. The treatments involving pathogen-inoculation had higher factor scores for the third factor than the water inoculated, the highest being for the susceptible cultivar Roblin, and may be useful in explaining susceptibility/pathogenesis. The third factor had positive correlation with metabolites from different groups, mostly amino acids, fatty acids, and aromatics. The various compounds detected in this study are discussed, in terms of their possible roles in plant defense against pathogen-stress, their metabolic pathways of synthesis, and their potential application for screening cultivars of wheat for resistance to FHB.
Abstract: Non-host resistance is more durable than race-specific resistance and may involve more signaling systems than race-specific resistance. An array of chemicals capable of specifically inhibiting/affecting most of the vital systems of the plant cell was employed to evaluate a range of systems vital in promoting non-host resistance in the Fusarium solani f. sp. phaseoli/pea endocarp interaction. The parameters measured included pisatin synthesis, hypersensitive discoloration, fungal growth, PR gene induction, and DNA damage. Specific inhibitors of protein phosphatases 1 and 2A (calyculin A, okadaic acid, cantharidin and endothall) and two kinase inhibitors (staurosporine and K-252a from Nocardiopsis sp.) were comparable to fungal challenge in inducing pisatin accumulation. These treatments could often break non-host resistance to a bean pathogen, F. solani f. sp. phaseoli. At low concentrations the treatments transiently enhanced resistance to the pea pathogen, F. solani f. sp. pisi. Nitric oxide and superoxide-generating compounds, salicylic acid, methyl salicylate, and jasmonic acid implicated, as effectors in other systems had no major detectable effect. Thus the broad array of inhibitors delineated cellular functions associated with non-host disease resistance in pea and tentatively excluded some signaling systems reported in other systems.
Abstract: Many breeders are urgently trying to improve genetic resistance to fusarium head blight. Within a set of 17 varieties tested in 4 countries resistance seems to be stable across pathogen species and location and a reduction in disease appears to result in a proportional reduction in deoxynivale (DON) content. Breeding is a compromise between achieving improvements in yield, quality and resistance and many characters are technically difficult to handle, sometimes making progress slow. New technology is likely to increase the efficiency of this process and we hope to see better resistance to fusarium head blight in Europe within the next 10 years.
Abstract: Bayoud, caused by Fusarium oxysporum f. sp. albedinis (Foa), is the most damaging disease of date palm in Morocco. In the present study we have investigated the effect of jasmonic acid (JA) on two defence-related enzymes, namely peroxidases (POX) and polyphenoloxidases (PPO) in date palm seedlings root. Our data show that exogenous application of JA at a concentration of 50 μM increased the activity of both enzymes. The increase of POX activity in the presence of JA was much more important than that observed following infection with the pathogen. As compared to untreated plants, PPO activity was 2.2 and 1.3 times higher in BSTN and JHL cultivars respectively. In addition, PAGE analysis revealed increased band intensity of the major constitutive isoforms of POX and PPO in both JA-treated and Foa-treated seedlings. Close examination of symptomatic and asymptomatic plants showed that root tissues of symptomatic plants were massively colonized by Foa. Also, disease development in these plants appeared to involve a marked degradation of the host cell walls early during the process of pathogen invasion. In contrast, the presence of Foa in asymptomatic plants induced limited necrotic lesions (hypersensitive-reaction like lesions) that were probably involved in reducing the progression of the pathogen. Together, our findings indicate that JA is capable of enhancing date palm root resistance to infection by Foa via the activation of defence-related enzymes such as PPO and POX.
Abstract: Flavonoids are a group of secondary plant metabolites important for plant growth and development, and thus the regulation of their biosynthesis is of special interest. We used a transgenic approach for flavonoid content manipulation. The multigene construct contained the cDNAs for chalcone synthase (CHS), and chalcone isomerase (CHI) and dihydroflavonol reductase (DFR) were prepared. Following flax plants transformation, the levels of the products of the enzyme overproduction were assessed in leaves and seeds. The simultaneous expression of genes resulted in a significant increase in the levels of flavanones, flavones, flavonols and anthocyanins, suggesting those three overproducing enzymes efficiently control the flavonoid route of the phenylpropanoid pathway. The increase in the flavonoid content in the transgenic flax plants might be the reason for observed, enhanced antioxidant capacity of those plants. The increased antioxidative properties of transgenic plants lead to improved resistance to Fusarium, the main pathogen of flax. The changes in phenylpropanoids accumulation in transgenic plants affect cell wall carbohydrate content. Immunochemical studies revealed significant increase in carbohydrates, constituents of pectin and hemicellulose. Since pectins contribute to flax stem retting, the compounds increase might affect fibre production. An increase in pectin and hemicellulose content leads to enhanced disease resistance of those plants.
Abstract: We demonstrated that exogenous application of 200 uM salicylic acid through root feeding and foliar spray could induce resistance against Fusarium oxysporum f. sp. Lycopersici ( Fol ) in tomato. Endogenous accumulation of free salicylic acid in tomato roots was detected by HPLC and identification was confirmed by LC–MS/MS analysis. At 168 h of salicylic acid treatment through roots, the endogenous salicylic acid level in the roots increased to 1477 ng g-1 FW which was 10 times higher than control plants. Similarly, the salicylic acid content was 1001 ng g-1 FW at 168 h of treatment by foliar spray, which was 8.7 times higher than control plants. The activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.7) were 5.9 and 4.7 times higher, respectively than the control plants at 168 h of salicylic acid feeding through the roots. The increase in PAL and POD activities was 3.7 and 3.3 times higher, respectively at 168 h of salicylic acid treatments through foliar spray than control plants. The salicylic acid-treated tomato plants challenged with Fol exhibited significantly reduced vascular browning and leaf yellowing wilting. The mycelial growth of Fol was not significantly affected by salicylic acid. Significant increase in basal level of salicylic acid in noninoculated plants indicated that tomato root system might have the capacity to assimilate and distribute salicylic acid throughout the plant. The results indicated that the induced resistance observed in tomato against Fol might be a case of salicylic acid-dependent systemic acquired resistance.
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