Spore Germination Of Pathogens Research Articles

Biocontrol Ability and Action Mechanism of Meyerozyma guilliermondii 37 on Soft Rot Control of Postharvest Kiwifruit.

Postharvest soft rot of kiwifruit has resulted in substantial market losses, yet there were few antagonistic yeasts reported to control the disease. This study screened 1113 yeast strains for potential antagonistic yeast to control soft rot of kiwifruit caused by Botryosphaeria dothidea and Diaporthe actinidiae, and strain 37 was selected to evaluate the control efficacy and mechanisms, which was identified as Meyerozyma guilliermondii via molecular biological identification. Our results showed that M. guilliermondii 37 effectively reduced pathogen spore germination rate to 28.52% and decay incidence of inoculated kiwifruit to 42.11% maximumly, whereas cell-free supernatant lacked antifungal activity, implying that M. guilliermondii 37 didn't produce direct antifungal compounds against the two pathogens. In addition, M. guilliermondii 37 adhered tenaciously to the pathogens' mycelium and colonized rapidly in kiwifruit flesh. Moreover, yeast strain 37 induced kiwifruit resistance by elevating the defense-related enzyme activity, increasing the antioxidant substances content, and suppressing the cell wall-degrading enzyme activity. Gene expression was consistent with the corresponding enzyme activity. Further postharvest yeast immersion treatment significantly reduced natural decay to 35.69% while maintaining soft-ripe quality. These results indicated that M. guilliermondii 37 might serve as a biocontrol agent against postharvest soft rot in kiwifruit.

A review on the potential effects of temperature on fungicide effectiveness

AbstractFungicides are one possible way to manage fungal and oomycete plant pathogens in order to safeguard yield and quality of crops and to improve shelf‐life of produce in agriculture and horticulture. However, global warming and the resulting temperature increase may affect the effectiveness of some important fungicides, including efficacy and duration of plant disease control. Nevertheless, according to our literature survey, there is little specific information available on whether and how temperature influences the effectiveness of fungicides. The very few publications that show specific data are summarized herein. Specific data are mainly gained under controlled conditions, both based on in vitro and in planta experiments. Field data are more or less missing. Most researchers assume that indirect effects of temperature on fungicide efficacy are particularly important. For example, temperature effects on pathogen spore germination and hyphal growth (optimal versus sub‐ and supra‐optimal), whereby optimal temperature conditions can improve pathogen fitness, thereby increasing the tolerance of pathogens to fungicides. Presumably, these indirect effects are often more important than the direct effects of temperature on fungicide performance. However, the data needed to prove this assumption are lacking. Therefore, it would be beneficial to conduct more in‐depth laboratory, greenhouse and field experiments in order to investigate the potential direct and indirect influence of temperature on the effectiveness of important fungicides. This would enable the establishment of appropriate recommendations for fungicide use in an increasingly warmer world and would assist the development of future fungicide solutions, based on improved knowledge.

Molecular evidence for the involvement of cotton GhGLP2, in enhanced resistance to Verticillium and Fusarium Wilts and oxidative stress

Germin-like proteins (GLPs) are a diverse and ubiquitous family of plant glycoproteins belonging to the cupin super family; they play considerable roles in plant responses against various abiotic and biotic stresses. Here, we provide evidence that GLP2 protein from cotton (Gossypium hirsutum) functions in plant defense responses against Verticillium dahliae, Fusarium oxysporum and oxidative stress. Purified recombinant GhGLP2 exhibits superoxide dismutase (SOD) activity and inhibits spore germination of pathogens. Virus-induced silencing of GhGLP2 in cotton results in increased susceptibility to pathogens, plants exhibited severe wilt on leaves, enhanced vascular browning and suppressed callose deposition. Transgenic Arabidopsis (Arabidopsis thaliana) plants overexpressing GhGLP2 showed significant resistance to V. dahliae and F. oxysporum, with reduced mycelia growth, increased callose deposition and cell wall lignification at infection sites on leaves. The enhanced tolerance of GhGLP2-transgenic Arabidopsis to oxidative stress was investigated by methyl viologen and ammonium persulfate treatments, along with increased H2O2 production. Further, the expression of several defense-related genes (PDF1.2, LOX2, and VSP1) or oxidative stress-related genes (RbohD, RbohF) was triggered by GhGLP2. Thus, our results confirmed the involvement of GhGLP2 in plant defense response against Verticillium and Fusarium wilt pathogens and stress conditions.

Biological effects of two Trichoderma harzianum isolates and mint oil on some postharvest fungal pathogens of sugar beet

Abstract Sugarbeet (Beta vulgaris L.) stored in outdoor piles prior to processing, during this storage period the crop is subject to multiple postharvest rots. Some fungal pathogens (A. niger, A. flavus, Fusarium sp. and Rhizopus sp.) were isolated and identified from rotted sugarbeet. Pathogenicity test of the isolated fungi had different pathogenicity rates using different concentrations of spore suspension at different incubation periods. A. flavus showed little number of lesions and negative effect on sugarbeet when tested for pathogenicity. Two antagonists of Trichoderma harzianum were tested for their effectiveness on sugarbeet rot fungal pathogens and compared with mint oil. In dual culture, size of clear zone is not correlated with the occurrence of pathogen overgrowth by antagonists. The antagonistic action of the two tested isolates of T. harzianum against the isolated phytopathogens indicated different degrees of antagonism. The non-volatile and gaseous volatile organic compounds by the antagonists inhibited growth of phytopathogens on agar plates, and no inhibition was investigated for Rhizopus sp. and Fusarium spp. by the tested volatile and non-volatile compounds, respectively. Moreover, mint oil showed inhibition degrees as well as volatile compounds of antagonists for all of the tested pathogens except against Rhizopus. Sugarbeet treated with mint oil as well as culture filtrate of T. harzianum suppressed pathogen spore germination on the surface of sugarbeet root resulted in decreasing rot incidence. This work provides strong evidence that T. harzianum and mint oil are competitors to control sugarbeet rot.

Different Antifungal Activity of Anabaena sp., Ecklonia sp., and Jania sp. against Botrytis cinerea.

Water extracts and polysaccharides from Anabaena sp., Ecklonia sp., and Jania sp. were tested for their activity against the fungal plant pathogen Botrytis cinerea. Water extracts at 2.5, 5.0, and 10.0 mg/mL inhibited B. cinerea growth in vitro. Antifungal activity of polysaccharides obtained by N-cetylpyridinium bromide precipitation in water extracts was evaluated in vitro and in vitro at 0.5, 2.0, and 3.5 mg/mL. These concentrations were tested against fungal colony growth, spore germination, colony forming units (CFUs), CFU growth, and on strawberry fruits against B. cinerea infection with pre- and post-harvest application. In in vitro experiments, polysaccharides from Anabaena sp. and from Ecklonia sp. inhibited B. cinerea colony growth, CFUs, and CFU growth, while those extracted from Jania sp. reduced only the pathogen spore germination. In in vitro experiments, all concentrations of polysaccharides from Anabaena sp., Ecklonia sp., and Jania sp. reduced both the strawberry fruits infected area and the pathogen sporulation in the pre-harvest treatment, suggesting that they might be good candidates as preventive products in crop protection.

Combination of hot water, Bacillus amyloliquefaciens HF-01 and sodium bicarbonate treatments to control postharvest decay of mandarin fruit

An antagonistic isolate Bacillus amyloliquefaciens HF-01, sodium bicarbonate (SBC) and hot water treatment (HW) were investigated individually and in combination against green and blue mold and sour rot caused by Penicillium digitatum, P. italicum and Geotrichum citri-aurantii respectively, in mandarin fruit. Populations of antagonists were stable in the presence of 1% or 2% SBC treatment, and spore germination of pathogens in potato dextrose broth was greatly controlled by the hot water treatment of 45°C for 2min. Individual application of sodium bicarbonate at low rates and hot water treatment, although reducing disease incidence after 8 weeks or 4 weeks of storage at 6°C or 25°C respectively, was not as effective as the fungicide treatment. The treatment comprising B. amyloliquefaciens combined with 2% SBC or/and HW (45°C for 2min) was as effective as the fungicide treatment and reduced decay to less than 80% compared to the control. B. amyloliquefaciens HF-01 alone or in combination with 2% SBC or/and HW significantly reduced postharvest decay without impairing fruit quality after storage at 25°C for 4 weeks or at 6°C for 8 weeks. These results suggest that the combination of B. amyloliquefaciens HF-01, SBC and HW could be a promising method for the control of postharvest decay on citrus while maintaining fruit quality after harvest.

Efficacy of the antagonist Aureobasidium pullulans PL5 against postharvest pathogens of peach, apple and plum and its modes of action

The efficacy of Aureobasidium pullulans PL5 against different postharvest pathogens of fruits ( Monilinia laxa on plums and peaches, Botrytis cinerea and Penicillium expansum on apples) were evaluated under storage conditions when applied at 10 8 cells ml −1 and their interactions were studied in vitro and in vivo to discover the possible modes of action. Under 1.2 °C and 95% relative humidity (RH) for 28 days, the efficacy of PL5 against M. laxa on plums was 45%, reducing disease incidence from 78% to 43%. Under 1 °C and 95% RH for 21 days, the efficacy against M. laxa on peaches was 63%, reducing disease incidence from 79% to 29%. Under 4 °C and 95% RH for 45 days, the efficacy against B. cinerea and P. expansum on apples was 56% and 46%, respectively. In Lilly–Barnett minimal salt medium with the fungal cell walls of pathogens as sole carbon source, PL5 produced β-1,3-glucanase, exo-chitinase and endo-chitinase. Nutrient concentrations had significant effect on pathogen growth reduction by PL5. No attachment was observed in antagonist–pathogen interactions in vitro or in vivo. PL5 completely inhibited pathogen spore germination in PDB at 10 8 cells ml −1, whereas at 10 6 cells ml −1 the efficacy was significantly decreased. However, inactivated cells and culture filtrate of PL5 had no effect on pathogen spore germination and germ tube elongation. Our results showed that A. pullulans PL5 could be introduced in commercial formulations to control postharvest pathogens on fruits and its activity was based on secretion of lytic enzymes and competition for nutrients.

THE SENSITIVITY OF ASPERGILLUS NIGER AND FUSARIUM OXYSPORUM f. sp. CEPAE TO FUNGISTASIS IN ONION-GROWING SOILS

SUMMARY Twenty-seven soil samples were collected from the onion (Allium cepa L.) fields of Tekirdag province, Turkey. These samples were investigated for the sensitivity of Aspergillus niger V. Tieghem (AN) and Fusarium oxysporum Schlechtend.: Fr. f. sp. cepae (H. N. Hans.) W. C. Snyder H. N. Hans (FOC), known as the causal agents of black mould and basal rot of onion, respectively, to soil fungistasis. Fungistasis was evaluated using two methods: inhibition of pathogen spore germination by volatile compounds from the soil and determination of the antagonistic fungal population of soil samples. Volatile compounds in twelve of the soil samples strongly (>70%) inhibited spore germination of only AN. Inhibition rates of volatile compounds were not correlated with physical and chemical characters of the soils. Fungi isolated from soil samples were evaluated for their antagonism to both pathogens using dual cultures. The population of species causing over 70% inhibition of radial growth on pathogens was calculated in soil samples. The presence of both volatile compounds inhibiting spore germination of AN and populations of fungi antagonistic for AN and FOC were observed in six of the soil samples. The possible effects of two fungistatic mechanisms in soils on disease development by these pathogens are discussed.

Control of postharvest pear diseases using Rhodotorula glutinis and its effects on postharvest quality parameters

Rhodotorula glutinis was evaluated for its activity in reducing postharvest gray mold decay and blue mold decay of pear caused by Botrytis cinerea and Penicillium expansum respectively, and in reducing natural decay development of pear fruits, as well as its effects on postharvest quality of fruits. There was a significant negative correlation between concentrations of the yeast cells and infectivity of the pathogens. At concentrations of R. glutinis at 5 × 108 CFU/ml, the gray mold decay was completely inhibited after 7 days incubation at 20 °C, while the control fruit had 100% disease incidence and 2.15 cm lesion diameter respectively, at challenged with B. cinerea spores suspension of 1 × 105 spores/ml; No completely control was got to blue mold, when pear fruits stored at 20 °C for 7 d (challenged with P. expansum spores suspension of 5 × 104 spores/ml), but the decay was distinctly prevented with 20% and 0.60 cm of disease incidence and lesion diameter respectively, while the control fruits were 100% and 2.74 cm, respectively. Rapid colonization of the yeast in wounds was observed during the first 1 d at 20 °C, and then the populations stabilized for the remaining storage period. On pear wounds kept at 4 °C, rapid colonization of the yeast in wounds was observed during the first 3 d, and then the increase in population density of R. glutinis turned slow, which continued over 6 d after application of the antagonist until it reached a high level. Then, the populations stabilized for the remaining storage period. In the test on PDA plates, R. glutinis significantly inhibit the growth of B. cinerea and P. expansum. Spore germination of pathogens in PDB was greatly controlled in the present of living yeast cell suspensions. R. glutinis significantly reduced the natural development of decay of pear following storage at 20 °C for 7 days or at 4 °C for 30 days followed by 20 °C for 5 days, and did not impair quality parameters, including mass loss, firmness, TSS, ascorbic acid or titratable acidity. Thus, the application of R. glutinis can be an alternative to chemicals for control of postharvest diseases on pear fruits.

Effect of yeast antagonist in combination with heat treatment on postharvest blue mold decay and Rhizopus decay of peaches

The potential of using heat treatment alone or in combination with an antagonistic yeast for the control of blue mold decay and Rhizopus decay of peaches caused by Penicillium expansum and Rhizopus stolonifer respectively, and in reducing natural decay development of peach fruits, as well as its effects on postharvest quality of fruit was investigated. In vitro tests, spore germination of pathogens in PDB was greatly controlled by the heat treatment of 37 °C for 2 d. In vivo test to control blue mold decay of peaches, heat treatment and antagonist yeast, as stand-alone treatments, were capable of reducing the percentage of infected wounds from 92.5% to 52.5% and 62.5%, respectively, when peach fruits stored at 25 °C for 6 d. However, in fruit treated with combination of heat treatment and Cryptococcus laurentii, the percentage of infected wounds of blue mold decay was only 22.5%. The test of using heat treatment alone or in combination with C. laurentii to control Rhizopus decay of peaches gave a similar result. The application of heat treatment and C. laurentii resulted in low average natural decay incidences on peaches after storage at 4 °C for 30 days and 20 °C for 7 days ranging from 40% to 30%, compared with 20% in the control fruit. The combination of heat treatment and C. laurentii was the most effective treatment, and the percentage of decayed fruits was 20%. Heat treatment in combination with C. laurentii had no significant effect on firmness, TSS, ascorbic acid or titratable acidity compared to control fruit. Thus, the combination of heat treatment and C. laurentii could be an alternative to chemicals for the control of postharvest decay on peach fruits.

Postharvest biological control of gray mold decay of strawberry with Rhodotorula glutinis

Rhodotorula glutinis was evaluated for its activity in reducing postharvest gray mold decay of strawberry caused by Botrytis cinerea in vitro and in vivo. In the test on PDA plates, R. glutinis significantly inhibit the growth of B. cinerea. Spore germination of pathogens in PDB was greatly controlled in the presence of living cell suspensions. Rapid colonization of the yeast in wounds was observed during the first 3 days at 20 °C, and then the populations stabilized for the remaining storage period. On strawberry wounds kept at 4 °C, the increase in population density of R. glutinis was lower than those kept at 20 °C, but continued over 8 days after application of the antagonist until it reached a high level. Number of inoculated strawberry fruit treated with 1 × 108 CFU/ml washed cell suspension of R. glutinis was 10% after 2 days at 20 °C, compared to 100%, respectively, in the control. Washed cell suspensions of yeast controlled gray mold better than yeast in culture broth. Treatment of wounds with autoclaved cell cultures or cell-free culture filtrate did not prevent decay. The concentrations of antagonist had significant effects on biocontrol effectiveness: the higher the concentrations of the antagonist, the lower the disease incidence regardless of whether the fruit was stored at 20 °C for 2 days or 4 °C for 7 days. At concentrations of R. glutinis 1 × 109 CFU/ml, the incidence of gray mold was reduced by 94.7 or 95%, respectively, compared with control, after storage at 20 °C for 2 days or 4 °C for 7 days, respectively. R. glutinis significantly reduced the natural development of decay of fruit following storage at 20 °C for 3 days or 4 °C for 5 days followed by 20 °C for 3 days.

Biological control of postharvest green mold decay of oranges by Rhodotorula glutinis

The biocontrol activity of Rhodotorula glutinis on green mold decay of oranges caused by Penicillium digitatum was investigated in vitro and in vivo. Significant control was achieved with a washed cell suspension and an unwashed cell culture mixture of R. glutinis. Treatment of wounds with autoclaved cell cultures or cell-free culture filtrate did not prevent decay. The protection provided by the washed yeast cells was dose-dependent. The higher the concentration of R. glutinis, the better the effect of the biocontrol capacity. At concentrations of yeast of 1×109 colony-forming units per milliliter or higher and pathogen spore suspensions of 5×104 spores per milliliter, green mold was almost inhibited after 4-days incubation at 20 °C. The interval between the pathogen inoculation and the antagonist application significantly influenced the biocontrol ability. The biocontrol efficacy of R. glutinis applied before the pathogen was better than that of applied after the pathogen. Surprisingly, R. glutinis was also effective in controlling green mold at low temperature (4 °C). Rapid colonization of the yeast in wounds was observed during the first 3 days at 20 °C, and remained stable after 5-days incubation. On fruits stored at 4 °C, even after 21 days, the population of R. glutinis in wounded fruits was more than 1,600-fold of what it was just prior to storage. In the test on potato dextrose agar plates, agar disks of R. glutinis nutrient yeast dextrose agar cultures placed on PDA plates seeded with pathogens did not inhibit the growth of P. digitatum. Spore germination of pathogens in potato dextrose broth was greatly controlled in the presence of living cell suspensions.

Effect of salt compounds on mycelial growth, sporulation and spore germination of various potato pathogens

Post-harvest potato diseases are responsible for significant economic loss. Tuber infection may occur naturally through lenticels and eyes or mechanically through wounds incurred during harvest. There are few fungicides approved for use on human foodstuffs and there is a necessity to evaluate and screen the efficacy of alternative compounds against pathogens responsible for post-harvest disease in potatoes. In vitro trials were conducted to evaluate the effect of several organic and inorganic salt compounds and two commercial fungicides on mycelial growth, sporulation and spore germination of Alternaria alternata, Botrytis cinerea, Fusarium solani var. coeruleum, Phytophthora erythroseptica, P. infestans, Verticillium albo-atrum, and V. dahliae. The effects of various salt compounds on these fungi were evaluated at three concentrations: 0.002, 0.02 and 0.2 M. Overall, mycelium growth and spore germination of all pathogens were strongly inhibited by sodium metabisulfite and propyl-paraben. Spore germination in most pathogens was consistently inhibited by the aluminum compounds (aluminum chloride, aluminum acetate and alum) and the commercial fungicides mancozeb and copper sulfate. Information gathered from this study provides an important basis for further study into the uses of salt compounds for control of post-harvest diseases of potato.

Effects of Ca2+ and Mg2+ on Botrytis cinerea and Penicillium expansum in vitro and on the biocontrol activity of Candida oleophila

Calcium salts have been reported to play an important role in the inhibition of postharvest decay of apples and in enhancing the efficacy of postharvest biocontrol agents. Therefore, the present study was conducted in order to examine and compare the effects of calcium and magnesium salts on the germination and metabolism of the postharvest pathogens Botrytis cinerea and Penicillium expansum, and to determine the effects of these salts on the biocontrol activity of two isolates (182 and 247) of the yeast Candida oleophila. Increasing concentrations of CaCl2 (25–175 mM) resulted in decreased spore germination and germ‐tube growth of both pathogens. The greatest effect was observed in the case of B. cinerea. The inhibitory effect could be overcome by the addition of glucose to the germination medium. MgCl2 (25–175 mM) had no effect on germination or germ‐tube growth of either pathogen, indicating that the calcium cation rather than the chloride anion was responsible for the inhibition. The pectinolytic activity of crude enzyme obtained from the culture medium of both pathogens was also inhibited by 25–175 mM CaCl2, with the greatest effect on the crude enzyme from P. expansum. Biocontrol activity of isolate 182 was enhanced by the addition of 90 or 180 MM CaCl2, whereas there was no effect on the biocontrol activity of isolate 247. This was apparently due to the inability of isolate 247 to proliferate in apple wounds. It is postulated that enhanced biocontrol activity of isolate 182 of the yeast C. oleophila in the presence of Ca2+ ions is directly due to the inhibitory effects of calcium ions on pathogen spore germination and metabolism, and indirectly due to the ability of isolate 182 to maintain normal metabolism in the presence of“toxic” levels of calcium.