Biological control of damping-off caused by Rhizoctonia solani using chitinase-producing Paenibacillus illinoisensis KJA-424

A bacterium having strong chitinolytic activity was isolated from a coastal soil in Korea and identified as Paenibacillus illinoisensis KJA-424 on the basis of the nucleotide sequence of a 16S rRNA gene. By activity staining after SDS-PAGE, three major chitinase bands with chitinolytic activity, approximate molecular weight of 63, 54 and 38 kDa were detected. On co-culture Rhizoctonia solani with KJA-424, abnormal swelling and deformation of R. solani hyphae were observed, where the release of N-acetyl-d-glucosamine was detected. The bacterium suppressed the symptom of damping-off cucumber seedlings caused by R. solani, in greenhouse trial.     

Suppression of damping-off of cucumber caused by Pythium ultimum with live cells and extracts of Serratia marcescens N4-5

Environmentally friendly control measures are needed for the soil-borne pathogen, Pythium ultimum. This pathogen can cause severe losses to field- and greenhouse-grown cucumber and other cucurbits. Live cells and ethanol extracts of cultures of the bacterium Serratia marcescens N4-5 provided significant suppression of damping-off of cucumber caused by P. ultimum when applied as a seed treatment. Live cells of this bacterium also suppressed damping-off caused by P. ultimum on cantaloupe, muskmelon, and pumpkin. Culture filtrates from strain N4-5 contained chitinase and protease activities while ethanol extracts contained the antibiotic prodigiosin, the surfactant serrawettin W1, and possibly other unidentified surfactants. Production of prodigiosin and serrawettin W1 was temperature-dependent, both compounds being detected in extracts from N4-5 grown at 28 °C but not in extracts from N4-5 grown at 37 °C. Ethanol extracts from strain N4-5 grown at 28 °C inhibited germination of sporangia and mycelial growth by P. ultimum in in vitro experiments. There was no in vitro inhibition of P. ultimum associated with ethanol extracts of strain N4-5 grown at 37 °C. Prodigiosin, purified from two consecutive thin-layer chromatography runs using different solvent systems, inhibited germination of sporangia and mycelial growth of P. ultimum. Another unidentified compound(s) also inhibited germination of sporangia but did not inhibit mycelial growth. There was no in vitro inhibition associated with serrawettin W1. These results demonstrate that live cells and cell-free extracts of S. marcescens N4-5 are effective for suppression of damping-off of cucumber caused by P. ultimum possibly due in part to the production of the antibiotic prodigiosin.     

Multiple statistical approaches of community fingerprint data reveal bacterial populations associated with general disease suppression arising from the application of different organic field management strategies

Multiple statistical analyses of terminal restriction fragment length polymorphism (T-RFLP) data were used to screen and identify bacterial populations involved in general disease suppression in an organically managed soil. Prior to sampling three different management strategies (i.e. mixed hay (H), tilled fallowing and open-field vegetables production) were used during the transition from conventional to organic farming, with and without compost amendment. The H transition strategy consistently led to the lowest damping-off disease incidence on two different crops in separate greenhouse and field experiments. Bacterial population structure in bulk soil and the rhizosphere of both crops was characterized using T-RFLP analyses of amplified 16S rDNA sequences. First, principal component analysis (PCA) revealed changes in the relative abundance of bacterial terminal restriction fragments (TRF) in response to transition strategy and/or compost amendment in eight different experimental contexts. In each context, a different subset of TRF substantially contributed to the variation along the first two principal components. However, terminal restriction fragment M148 contributed significantly to the observed variation in 6 out of the 8 experiments, and moderately in the remaining 2 experiments. As a second approach, nonparametric analyses of variance revealed that the relative abundance of TRF differed among treatments. While the responsive subsets identified varied somewhat by experimental context, M137, M139 and M141 were more abundant in samples from the H transition strategy in multiple experimental contexts. Subsequent correlation analyses revealed that TRF associated with disease suppressive treatments (i.e. H with and without compost) were frequently negatively correlated with damping-off disease incidence. As a group, these TRF were disproportionately associated with lower disease levels further indicating their role in disease suppression. Interestingly, in silico analysis of the bacterial 16S rDNA sequence database revealed that the TRF identified in this study (e.g. M137, M139, M141, and M148) might correspond to well-characterized genera of bacterial biological control agents.     

Application method and rate of Trichoderma species as a biological control against Pythium aphanidermatum (Edson) Fitzp. in the production of microgreen table beets (Beta vulgaris L.)

Seed balls of ‘Early Wonder Tall Top’ table beet (Beta vulgaris L.) were incubated for 2 days at 21 °C in moist exfoliated grade 3 vermiculite (3 g seed balls [168 seed balls] and 1.1 g vermiculite) containing equal weights of Trichoderma harzianum Rifai strain KRL-AG2 G41 and T. virens strain G-41 (ThTv) at 0, 0.25, 0.50, 0.75 or 1.00 mg ThTv per seed ball. ThTv also was applied to the peat-lite growth medium 14 days before planting, at the same rates per seed ball as the seed ball treatments. Four days before planting, the peat-lite was inoculated with Pythium aphanidermatum (Edson) Fitzp. (Pa) at 0, 0.5 and 1.0× the rate that resulted in 96% damping-off when non-ThTv-treated dry seed balls were sown in peat-lite containing 1.0 Pa. Increasing ThTv level per seed ball decreased percentage damping-off, with 1.0 Pa giving greater percentage damping-off than 0.5 Pa. At 1 mg ThTv per seed ball, damping-off was 5% and 19% at 0.5 and 1.0 Pa, respectively. Including Agro-Lig UF (mostly humic acids) in the incubating seed-ball-ThTv mixture further decreased damping-off by an average 13 and 10 percentage points in 0.5 and 1.0 Pa, respectively. Increasing ThTv per seed ball in growth media decreased percentage damping-off, but not to the extent achieved with seed ball treatment, with 1 mg ThTv per seed ball giving 20% and 55% damping-off in 0.5 and 1.0 Pa, respectively. Decreasing incidence of damping-off with increasing ThTv application to seed balls or growth media was associated with increasing shoot fresh weight m⁻² at 14 days after planting, a response attributable to increased percentage plant survival and not to a ThTv growth-promoting effect.     

落叶松幼苗立枯病的田间药剂防治实验

立枯病是落叶松苗期常见的一种病害,其危害严重,我圃在2007-2009年,采用多菌灵、甲醛托布津、敌克松、乙磷铝4种内吸杀菌剂土壤消毒和药剂苗期喷雾相结合的方法,防治效果均在81.6%-90.3%,防治效果显著。     

水稻有机育苗关键技术研究

防治水稻苗期恶苗病、立枯病和杂草是目前水稻有机栽培急需解决的关键技术。利用物理方法(温汤处理)和微生物技术(有机育苗生物调理剂)进行防治苗期恶苗病、立枯病和杂草控制试验,并研发了有机育苗生物调理剂。研究结果表明,温汤处理采用58℃温度处理15 min或60℃温度处理10 min,能够有效控制恶苗病和立枯病的发生;有机育苗生物调理剂具有杀灭病原菌、抑制立枯病及杂草发生,并提高秧苗素质等功能。     

Evaluation of soil solar heating for control of damping-off fungi in two forest nurseries in France

Field experiments were carried out at two different forest nurseries during the summer of 1994 to examine the efficacy of soil solarization for the control of damping-off. Both soils hosted Pythium spp., Fusarium spp. and Rhizoctonia solani as damping-off agents. Soil samples from solarized, steamed, fumigated and untreated plots were periodically collected and assayed for soil infectivity. Solarization with a double layer of polyethylene film was as effective as steaming or fumigation in reducing soil infectivity in the uppermost layer. During July the temperature of covered beds rose as high as 50°C at a soil depth of 5cm. The method achieved good control of Pythium spp., the main cause of damping-off at both nurseries, whereas Fusarium spp. were more tolerant. The association of Trichoderma spp. with a reduction of soil infectivity at the last sampling date strongly suggested that biocontrol processes were induced after solarization. Soil solarization provides a suitable method for control of damping-off. Received: 29 October 1996     

Development of new bioformulations using Trichoderma and Talaromyces fungal antagonists for biological control of sugar beet damping-off disease

The aims of this study were to develop new bioformulations using Trichoderma harzianum, Trichoderma asperellum, and Talaromyces flavus and some organic and inorganic carriers and evaluate their effects against Rhizoctonia solani, the fungal causal agent of sugar beet seedling damping-off disease. Selected fungal isolates were first re-cultured and maintained on potato dextrose agar (PDA) culture medium. Antagonistic effects of eight isolates of the above-mentioned antagonistic fungi were then evaluated against R. solani, through volatile metabolites and non-volatile metabolites production mechanisms under laboratory conditions. In volatile and non-volatile metabolite experiments, five and seven isolates caused significant reduction in R. solani growth respectively. Based on the results of laboratory experiments, the most effective antagonistic isolates (one isolate from each species) were selected for development of nine bioformulations using peat, rice bran and talc as carriers. The effectiveness of developed bioformulations was then evaluated in controlling sugar beet damping-off disease in a greenhouse experiment where sugar beet seeds were coated with bioformulations and were sown in pasteurized field soil pre-inoculated with R. solani. Results of the greenhouse experiment 60 days after sowing showed that all bioformulations increased the number of healthy seedlings significantly (compared to the untreated control) with different rates. According to the results, the most effective bioformulation was Talc-T. harzianum followed by Peat-T. flavus, Talc-T. flavus and Rice bran-T. harzianum. In general, in both laboratory and greenhouse experiments, T. flavus was the most effective fungal antagonist followed by T. harzianum and T. asperellum. Based on the results of this study it is concluded that Trichoderma and Talaromyces employing different mechanisms might be potential biocontrol agents for controlling R. solani-induced sugar beet damping-off disease.     

Effectiveness of plant extracts on suppression of damping-off and wilt diseases of lupine (Lupinus termis Forsik)

The aim of this study was to evaluate water and organic solvent of plant extracts for protection of lupine plants against damping-off and wilt diseases caused by Fusarium oxysporum f. sp. lupini, F. oxysporum f. sp. lupini Snyder & Hansen was isolated from diseased lupine roots collected from different locations of Minia, Assiut and New Valley governorates. Water leaf extracts of Calotropis procera, Nerium oleander, Eugenia jambolana, Citrullus colocynthis, Ambrosia maritime, Acacia nilotica and Ocimum basilicum and fruit extracts of C. colocynthis, C. procera and E. jambolana reduced damping-off and wilt diseases caused by F. oxysporum f. sp. lupini. Water extracts of E. jambolana leaves, C. colocynthis fruits and N. oleander leaves were the most effective ones for controlling such diseases. In contrast, A. nilotica and O. basilicum extracts were the least effective ones. Organic solvent extracts of tested plants reduced damping-off and wilt diseases than water extracts. Butanolic and ethereal extracts were highly effective in reduction of diseases than the other tested extracts. Under field conditions, during winter growing seasons 2008/09 and 2009/10, ethereal and butanolic extracts of N. oleander and E. jambolana leaves and C. colocynthis fruits significantly reduced the percentage of wilt severity as well as improved growth parameters (plant height, number of branches, pods and seeds per plant) and increased seed index, total seed yield/hectare compared with control treatment, while protein content in seeds was not effected. In conclusion, our study demonstrated that some plant extracts can be used for biocontrol of lupine damping-off and wilt diseases.     

Identification and pathogenicity of Pythium species causing damping-off of kidney bean

Five Pythium species (Pythium irregulare, P. mamillatum, P. myriotylum, P. spinosum and P. ultimum var. ultimum) were isolated from the hypocotyls and roots of kidney bean plants with damping-off from a commercial field and from experimental plots that have undergone either continuous cropping with kidney bean or rotational cropping with arable crops. In inoculation tests, all five Pythium species were pathogenic to kidney bean. This is the first report of damping-off of kidney bean caused by Pythium species; we named this disease damping-off of kidney bean. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB291811, AB291944 and AB291945.