Evaluation of different fungicides applied as seed tuber treatments for the control of potato silver scurf

La tache argentée de la pomme de terre (Solanum tuberosum), causée par le champignon Helminthosporium solani, est une maladie affectant la qualité du tubercule. L’objectif de cette étude était d’évaluer l’efficacité de différents fongicides, appliqués sur les tubercules de semence, à contrer le développement de la tache argentée. Pour ce faire, des tubercules de semence infectés par H. solani ont été traités avec l’un des fongicides suivants : talc, fludioxonil, mancozeb, iprodione, thiabendazole, imazalil et azoxystrobin. Ils ont, par la suite, été plantés au champ. Les essais ont été réalisés au Québec sur trois sites en 1998 et deux sites en 1999. Les résultats obtenus montrent que, sous nos conditions expérimentales, ces fongicides, appliqués en traitement de semence, n’ont pas affecté significativement les rendements totaux et vendables ainsi que la sévérité de la tache argentée sur les tubercules-fils au moment de la récolte et après différentes périodes d’entreposage. D’autre part, cette étude a permis de mettre en évidence l’influence des sites expérimentaux sur le développement de la tache argentée et suggère que l’inoculum du sol joue un rôle dans l’épidémiologie de cette maladie.Silver scurf of potatoes (Solanum tuberosum), caused by the fungus Helminthosporium solani, is an important surface-blemishing disease of potato tubers. The objective of the study was to evaluate the efficacy of different fungicides applied to potato seed tubers for control of silver scurf. Field trials were conducted in Québec province in 1998 and 1999. Potato seed tubers infected with H. solani were treated with either talc, fludioxonil, mancozeb, iprodione, thiabendazole, imazalil or azoxystrobin, and planted at three locations in 1998 and two locations in 1999. The results showed that, under our experimental conditions, the fungicides tested, applied as seed treatments, did not significantly influence total and marketable yields as well as silver scurf severity on daughter tubers at harvest and after different storage periods. In addition, this study showed the influence of the experimental locations on silver scurf development and suggests that soil inoculum plays a role in the epidemiology of the disease

Water activity control: A way to improve the efficiency of continuous lipase esterification

30 ref.International audienc

Antifungal activity of aluminium-containing salts against the development of carrot cavity spot and potato dry rot

As an alternative to the use of synthetic chemical fungicides to control plant disease, aluminium-containing salts were evaluated for their effects on the mycelial growth of various fungal or fungus-like pathogens and their ability to control carrot cavity spot (Pythium sulcatum) and potato dry rot (Fusarium sambucinum). Results showed that various aluminium-containing salts provided strong inhibition of all the tested pathogens (Alternaria solani, Botrytis cinerea, F. sambucinum, P. sulcatum and Rhizopus stolonifer) with minimal inhibitory concentration of 1-10 mM. Aluminium chloride and aluminium sulphate were generally the most effective, inhibiting mycelial growth of pathogens by as much as 47% and 100%, respectively, at a salt concentration of 1 mM. Applied at 5 mM, aluminium sulphate also provided 28% and 100% inhibition of dry rot and cavity spot, respectively. Aluminium chloride (5 mM) reduced dry rot by 25% whereas aluminium lactate (5 mM) decreased cavity spot lesions by 86%. These results indicate that various aluminium-containing salts may provide an alternative to the use of synthetic fungicides to control these pathogens

Effect of chlorine atmospheres on the development of rhizopus rot [Rhizopus stolonifer] and gray mold [Botrytis cinerea] on stored strawberry fruits

Gray mold and rhizopus rot, caused by Botrytis cinerea and Rhizopus stolonifer, respectively, are major diseases of strawberry (Fragaria ×ananassa) fruits, causing significant economic losses during storage. In this study, the effect of chlorine atmospheres on spore viability and mycelial growth of B. cinerea and R. stolonifer and on the development of gray mold and rhizopus rot on stored strawberries was evaluated. The results showed that spore mortality in R. stolonifer and B. cinerea was complete following a 6 h exposure to a chlorine atmosphere of 10 mg per litre of moist air, while mycelial growth of R. stolonifer and B. cinerea was completely inhibited at concentrations of 5 and 20 mg/L, respectively. At concentrations as low as 10 mg/L, chlorine provided a marked reduction in incidence of rhizopus rot and gray mold on strawberries after a 9 h exposure period. For both diseases, a chlorine atmosphere of 20 mg/L reduced the incidence by a minimum of 60% without affecting strawberry color or firmness. The results of this study suggest that exposure of strawberries to chlorine atmospheres represents a potential method for controlling postharvest gray mold and rhizopus rot

Integrated management of potato silver scurf Helminthosporium solani

Silver scurf is a surface blemish disease of potato (Solanum tuberosum L.) tubers, caused by Helminthosporium solani Durieu & Mont., which has gained increasing economic importance in recent years. The disease develops initially in the field but fully expands in the warehouse under storage conditions favourable to the spread of the pathogen. Control of the disease, once provided by the fungicide thiabendazole, is now difficult due to the appearance of thiabendazole-resistant strains and the lack of potato cultivars with high levels of resistance to silver scurf. An integrated disease management programme including appropriate cultural methods and storage conditions along with the use at planting and/or at harvest of synthetic chemical fungicides is recommended to reduce the incidence and the severity of silver scurf. Recent studies put forth the possibility that 'generally recognized as safe' (GRAS) compounds and microbial antagonists could eventually be integrated into silver scurf management strategies

Antifungal activity of sulfur-containing salts against the development of carrot cavity spot and potato dry rot

In the search for alternatives to synthetic fungicides to control postharvest disease, sulfur-containing salts were evaluated for their effects on the mycelial growth of various fungal or fungus-like pathogens and their ability to control carrot cavity spot (Pythium sulcatum) and potato dry rot (Fusarium sambucinum). Results showed that metabisulfite-containing salts provided strong inhibition of all the tested fungi. Furthermore, some sulfate-containing salts were also directly inhibitory to P. sulcatum (calcium sulfate and ammonium sulfate) and to F. sambucinum (sodium sulfate). The metabisulfite salts also provided 100% inhibition of cavity spot and dry rot at concentrations of 50 and 200 mM, respectively. Calcium sulfate and sodium sulfate also significantly reduced carrot cavity spot lesions at 50 mM and ammonium sulfate, magnesium sulfate, potassium sulfate and sodium sulfate reduced potato dry rot lesions at 200 mM. These results indicate that various sulfate and metabisulfite salts could be used to control these postharvest microorganisms

Ultrastructural alterations in fusarium sambucinum and heterobasidion annosum treated with aluminum chloride and sodium metabisulfite

Aluminum chloride (AlCl3) and sodium metabisulfite (Na 2S2O5) have received increasing attention as antifungal agents for the control of plant diseases. In an effort to understand their toxic action on fungi, ultrastructural changes and membrane damage in Fusarium sambucinum (Ascomycota) and Heterobasidion annosum (Basidiomycota) in response to salt exposure was investigated using transmission electron microscopy. Conidial membrane damage was quantified using SYTOX Green stain, which only enters altered membranes. The results showed that mortality of the conidia was generally closely associated with SYTOX stain absorption in F. sambucinum treated with Na2S2O5 and in H. annosum treated with AlCl3 or Na2S2O 5, suggesting that these salts cause membrane alterations. For both fungi, ultrastructural alterations in conidia treated with AlCl3 and Na2S2O5 included membrane retraction, undulation, and invagination. At higher concentrations or exposure periods to the salts, loss of membrane integrity, cytoplasmic leakage, and cell rupture were observed. Ultrastructural alterations and increased SYTOX stain absorption in salt-treated conidia appear consistent with a mode of action where AlCl 3 and Na2S2O5 alter membrane integrity and permeability

Effect of non-aerated compost teas on damping-off pathogens of tomato

Compost teas are fermented watery extracts of composted materials that are used for their beneficial effects on plants including antimicrobial activities. Non-aerated compost teas (NCT) prepared from seaweed compost, shrimp powder compost, and chicken, bovine and sheep manure composts were tested for their effect on the in vitro growth of tomato root pathogens and for their effect on the development of damping-off diseases caused by Pythium ultimum and Rhizoctonia solani. Results showed that NCT prepared from the five types of compost had the ability to greatly reduce mycelial growth of P. ultimum, R. solani, Fusarium oxysporum f. sp. radicis-lycopersici and Verticillium dahliae in vitro. Sterilization of the NCT caused complete or partial loss of their inhibitory effect on mycelial growth of the pathogens. Application of NCT decreased the percentage of necrotic seedlings in P. ultimum-inoculated tomato seeds from 42% to 100%, but did not reduce necrosis in R. solani-inoculated seeds. When applied on tomato seedlings inoculated with damping-off pathogens, various NCT also increased seedling fresh and/or dry weights

Management of potato dry rot

Dry rot is a postharvest fungal disease affecting potato (Solanum tuberosum L.) tubers. The disease, caused by several species of Fusarium such as F. solani var. coeruleum, F. sambucinum, F. oxysporum, F. avenaceum, F. culmorum, results in significant yield losses. Some Fusarium species associated with the disease produce toxins, which are implicated in mycotoxicoses of humans and animals. The pathogens cannot penetrate the tuber through the lenticels or in the absence of wounds and cause infection only if the potato skin is ruptured. The seed tuber is considered as the main source of inoculum although soil infested by Fusarium spp. also constitutes a source of inoculum. Control of the disease, once provided by the fungicide thiabendazole, is now difficult due to the appearance of thiabendazole-resistant strains and the lack of potato cultivars with high levels of resistance to dry rot. An integrated disease management program including detection strategies, appropriate cultural practices and storage conditions (including a wound healing period) along with the use of synthetic chemical fungicides as seed tuber and/or postharvest treatment is recommended to reduce incidence and severity of dry rot. Recent studies also indicate the possibility that generally recognized as safe (GRAS) compounds and microbial antagonists could eventually be integrated into dry rot management strategies

Effect of iron and nitrogen on the development of Helminthosporium solani and potato silver scurf

Silver scurf is a surface blemish disease of potato (Solanum tuberosum L.) tubers caused by Helminthosporium solani Durieu & Mont. Silver scurf is becoming a disease of high economic impact. In this study, the effect of different iron (FeSO 4, FeCl 2) and nitrogen (NaNO 2, NaNO 3, NH 4Cl, NH 4NO 3) salts on H. solani conidial germination and on potato silver scurf development was evaluated. The results show that iron and nitrogen salts affect in vitro germination of H. solani conidia. Conidia were particularly sensitive to FeSO 4 and FeCl 2. These salts completely inhibited conidial germination and were shown to be toxic at a concentration of 0.9 mM. Among the nitrogen salts tested, conidia were most affected by NaNO 2 and NH 4Cl, which almost completely inhibited their germination at a concentration of 169.7 mM. NaNO 2 was also toxic to conidia. Among the salts tested, only FeSO 4, FeCl 2 and NaNO 2 reduced the development of silver scurf. Comparison of the effect of the different tested salts leads to the conclusion that ions Fe ++ and NO 2 - have toxic effects on the conidia and repressive effects on silver scurf development while NO 3 - and NH 4 + have no toxic effect on conidia and no repressive effect on silver scurf development