Biocontrol of Foliar Fungal Diseases with Compost Extracts

Compost Tea Reduces the Susceptibility of Pinus radiata to Fusarium circinatum in Nursery Production

Nutrition is one of the factors that most limits forestry plant growth; thus, current production in nurseries is based on conventional fertilization focused on enhancing vigor. However, an excessive intake of mineral nitrogen can cause morphological imbalances and the formation of more succulent tissues which, consequently, increase susceptibility to plant pathogens. Fusarium circinatum is the causal agent of pitch canker in plants of the Pinus genus, with Pinus radiata being the species most susceptible to this disease. This study compares the response of P. radiata seedlings to infection by F. circinatum as influenced by two fertilizers-conventional and aerated compost tea (ACT)-applied during the nursery phase. The potential of ACT against F. circinatum was first tested in vitro, where it was found to inhibit the pathogen's mycelial growth and conidial germination. In the greenhouse, infected plants fertilized with ACT exhibited less severe internal and external symptoms of pitch canker and lower levels of pathogen colonization of both stems and needles than with conventional fertilizer. An analysis of the hormone content and defense-related gene expression shows greater salicylic acid production and phenylalanine ammonium-lyase and chalcone synthase expression in ACT-fertilized pine. All of the parameters assessed are consistent in showing that biofertilization with ACT reduces the susceptibility of pine seedlings to the disease compared with conventional fertilization.

Development of PCR-based molecular marker for screening of disease-suppressive composts against Fusarium wilt of tomato (Solanum lycopersicum L.)

The present study was carried out to develop a PCR-based molecular marker suitable for screening of disease-suppressive composts against Fusarium wilt of tomato. An effective uncultured bacterial community was screened from our previous study on investigation of microbial communities in composts for their potential for biocontrol of Fusarium wilt. Based on available sequence information (Accession no. HQ388491) of selective community, PCR-based molecular markers were designed and tested for their specificity in different compost sample. To confirm specificity of designed marker, real-time reverse transcription-PCR (qRT-PCR) analysis was performed. Selective marker efficacy was further tested for different set of composts and results were cross-verified by conducting bioassay of same composts against Fusarium wilt in tomato crop. Results showed that out of two designed set of primers (i.e., PAC1F/PAC1R and PAC4F/PAC4R), primer set PAC4F/PAC4R resulted in successful amplification of 199 bp in highly disease-suppressive compost (i.e., CPP); however, no/below detection level amplification was observed in non-suppressive compost (JC). qRT-PCR analysis confirmed the specificity of selective marker by representing single peak in melting curve. A clear difference was observed in relative population of selective community in different set of composts. It was observed maximum in the most effective compost, i.e., CPP followed by other disease-suppressive composts. Cross-examination of results with bioassay confirmed that composts with presence of selective bacterial community having no/very less disease incidence of Fusarium. It is clearly evident from the study that such kind of molecular markers can be developed and used in future research focusing on compost-based disease suppression.

Effect of compost tea containing phosphogypsum on potato plant growth and protection against Fusarium solani infection

Three composts made of industrial wastes were prepared by mixing olive oil mill waste water (OMW), olive pomace, coffee grounds, and phosphogypsum (0, 10, and 30%). Potato plants (Solanum tuberosum) cultivated in a greenhouse were used to screen compost tea suppressive ability. All compost tea treatments inhibited Fusarium solani growth and improved plant growth and response to F. solani infection. The antagonistic effects of the different treatments were associated with a marked increase of the antioxidant enzymes and PR (pathogenesis related) protein expression and a decrease of disease severity. These results also showed that plant growth and disease suppression were improved by application of phosphogypsum-supplemented compost teas (A10 and A30). This enhancement can be attributed to the influence of phosphogypsum on nutrient elements and microbial diversity in the resulting compost teas.

Bacillus paraflexus sp. nov., isolated from compost

A Gram-stain-positive, rod-shaped, endospore-forming, aerobic bacterium capable of growing at 15–42 °C (optimum 30 °C) and at pH 5–11 (optimum pH 7) was isolated from compost. Its taxonomic position was deduced using a polyphasic approach and the strain was designated RC2T. 16S rRNA gene sequence analysis showed that the isolate belongs to the division Firmicutes , forming a clade within the cluster containing Bacillus flexus IFO 15715T, and showed highest similarity to B. flexus IFO 15715T (98.1 %). The cell wall contained meso-diaminopimelic acid as the diagnostic diamino acid. The major cellular fatty acids of the novel strain were iso-C15:0 (36.83 %), anteiso-C15:0 (49.19 %) and C16:0 (5.19 %). DNA–DNA hybridization between strain RC2T and B. flexus DSM 1320T showed a level of relatedness of 54.5 %. The polar lipid profile of strain RC2T showed the presence of phosphatidylglycerol, diphosphatidylglycerol and phosphatidylethanolamine. The predominant isoprenoid quinone was MK-7 and the G+C content of strain RC2T was 37.6 mol%. On the basis of phenotypic characteristics, phylogenetic analysis and the results of biochemical and physiological tests, strain RC2T was clearly distinguished from closely related members of the genus, and the strain is assigned to a novel species, for which the name Bacillus paraflexus sp. nov. is proposed. The type strain is RC2T ( = MTCC 9831T = MCC 2100T = KCTC 13724T = CCM 7754T).

Assessment of bacterial diversity during composting of agricultural byproducts

Background

Composting is microbial decomposition of biodegradable materials and it is governed by physicochemical, physiological and microbiological factors. The importance of microbial communities (bacteria, actinomycetes and fungi) during composting is well established. However, the microbial diversity during composting may vary with the variety of composting materials and nutrient supplements. Therefore, it is necessary to study the diversity of microorganisms during composting of different agricultural byproducts like wheat bran, rice bran, rice husk, along with grass clippings and bulking agents. Here it has been attempted to assess the diversity of culturable bacteria during composting of agricultural byproducts.

Results

The culturable bacterial diversity was assessed during the process by isolating the most prominent bacteria. Bacterial population was found to be maximum during the mesophilic phase, but decreased during the thermophilic phase and declined further in the cooling and maturation phase of composting. The bacterial population ranged from 10⁵ to 10⁹ cfu g^-1 compost. The predominant bacteria were characterized biochemically, followed by 16S rRNA gene sequencing. The isolated strains, both Gram-positive and Gram-negative groups belonged to the order Burkholderiales, Enterobacteriales, Actinobacteriales and Bacillales, which includes genera e.g. Staphylococcus, Serratia, Klebsiella, Enterobacter, Terribacillus, Lysinibacillus Kocuria, Microbacterium, Acidovorax and Comamonas. Genera like Kocuria, Microbacterium, Acidovorax, Comamonas and some new species of Bacillus were also identified for the first time from the compost made from agricultural byproducts.

Conclusion

The use of appropriate nitrogen amendments and bulking agents in composting resulted in good quality compost. The culture based strategy enabled us to isolate some novel bacterial isolates like Kocuria, Microbacterium, Acidovorax and Comamonas first time from agro-byproducts compost. These bacteria can be used as potential compost inoculants for accelerating composting process.

Characters of compost teas from different sources and their suppressive effect on fungal phytopathogens

Compost teas (CT) are fermented watery extracts of composted materials that are used to control plant diseases and on crop fertilization. In this work, aerated (ACT) and non-aerated compost teas (NCT) were obtained from four different composts: spent mushroom substrate compost, grape marc compost, greenhouse horticultural crop residues compost, and vermicompost. Physico-chemical and microbiological analysis were carried out to determine their properties. In vitro assays were performed to assess their suppressive effect on the mycelial growth of eight fungal phytopathogens. In vivo trials aimed to assess their effect on gummy stem blight (Didymella bryonae) and powdery mildew (Podosphaera fusca) in melon plants. Results showed that ACT and NCT filtrates inhibited the in vitro growth of all tested pathogens while autoclaved CT did not completely lose their inhibitory effect, and CT sterilized by microfiltration had no effect on the pathogen growth. The severity of powdery mildew was highly reduced by ACT and NCT from all sources, though in gummy stem blight assay only a delay in disease development was observed. In general, all compost teas showed a high level of microbial populations and nutrients. Results suggest that the efficacy of ACT and NCT firstly depend on the microbiota present in them. We consider compost teas from the four tested sources as a viable way to manage plant diseases and crop fertilization, throughout its integration in pest management programs and fertirrigation systems under different dilution rates.

Phytotoxicity analysis of extracts from compost and their ability to inhibit soil-borne pathogenic fungi and reduce root-knot nematodes

Compost extracts are novel organic amendments, typically applied to suppress soil-borne diseases. This research evaluated the phytotoxicity of compost extracts and analyzed their ability to inhibit pathogenic fungal growth and reduce root-knot nematodes. The physical, chemical and biological characteristics of extracts from a pig manure and straw compost were analyzed. Three types of extracts were tested: direct extracts of compost (DEC), aerated fermentation extracts of compost (AFEC) and non-aerated fermentation extracts of compost (NAFEC). All compost extracts showed low phytotoxicity against lettuce and cress, but AFEC and NAFEC were more phytotoxic than DEC. All compost extracts significantly inhibited pathogenic fungal growth except for the fungus Rhizoctonia solania AG4. For two seasons, tomato root biomass of three compost extracts was 1.25-5.67 times greater than CK (water control), and AFEC and NAFEC showed the best tomato root growth promotion. The reduction ratio of root egg mass and density of soil nematodes were 34.51-87.77% and 30.92-51.37%, when applied with three compost extracts. The microbial population in compost extracts was considered to be the most significant factor of inhibition pathogenic fungal growth. No markedly correlations among bacterial community diversity, the inhibition of pathogenic fungal growth and the reduction of root-knot nematodes were observed. This information adds to the understanding of the growth-promoting and suppression effects of compost extracts and will help to enhance crop production.

Microbial enhancement of compost extracts based on cattle rumen content compost - characterisation of a system

Microbially enhanced compost extracts ('compost tea') are being used in commercial agriculture as a source of nutrients and for their perceived benefit to soil microbiology, including plant disease suppression. Rumen content material is a waste of cattle abattoirs, which can be value-added by conversion to compost and 'compost tea'. A system for compost extraction and microbial enhancement was characterised. Molasses amendment increased bacterial count 10-fold, while amendment based on molasses and 'fish and kelp hydrolysate' increased fungal count 10-fold. Compost extract incubated at 1:10 (w/v) dilution showed the highest microbial load, activity and humic/fulvic acid content compared to other dilutions. Aeration increased the extraction efficiency of soluble metabolites, and microbial growth rate, as did extraction of compost without the use of a constraining bag. A protocol of 1:10 dilution and aerated incubation with kelp and molasses amendments is recommended to optimise microbial load and fungal-to-bacterial ratio for this inoculum source.

Managing Foliar Blights on Carrot Using Copper, Azoxystrobin, and Chlorothalonil Applied According to TOM-CAST

Alternaria dauci and Cercospora carotae cause foliar blight on carrot, causing yield reductions in severely blighted fields. Currently, fungicides are used on either a 7-day schedule or according to the TOM-CAST disease forecasting system. Organic production prohibits applications of most fungicides for blight control but does allow select copper-based products. The objective of this study was to use the TOM-CAST weather forecasting system to (i) assess the efficacy of copper hydroxide treatments for organic operations and (ii) evaluate the efficacy of reduced-risk products in an alternating spray program. Chlorothalonil, azoxystrobin, and copper hydroxide were applied alone or in alternating programs in 2001 and 2002. Reapplications were made on a 7-day schedule or according to TOM-CAST using disease severity value (DSV) thresholds of 10, 15, and 20. Area under the disease progress curve (AUDPC) data revealed that all application intervals significantly limited disease incidence on the foliage and petioles, resulting in healthier petioles at harvest compared with the untreated. The 7-day and TOM-CAST 10 DSV programs had comparable rating values for all parameters assessed and were more effective than the TOM-CAST 15 and 20 DSV programs in limiting petiole disease and maintaining overall petiole health. Copper hydroxide treatments resulted in higher AUDPC values and significantly different petiole health ratings compared with other treatments, yet P values indicated significant disease control compared with the untreated. The TOM-CAST 15 DSV program reduced sprays up to 40% compared with a 7-day interval and produced mean savings of $127/ha in 2001 and $137/ha in 2002.

Variability Associated with Suppression of Gray Mold (Botrytis cinerea) on Geranium by Foliar Applications of Nonaerated and Aerated Compost Teas

The use of compost teas in agriculture and urban landscapes is increasing, but there is conflicting information on which methods are suitable for obtaining compost teas that suppress disease when applied to plants. Numerous compost tea production parameters (compost source, aeration, nutrient additives, production duration, and use of application adjuvants) were tested for suppressing gray mold (Botrytis cinerea) on geranium. While individual compost tea batches did significantly reduce disease, the majority of compost teas did not significantly suppress gray mold of geranium. For nonaerated compost tea (NCT), the most consistent, significant disease suppression was associated with particular compost samples and increased production time, with little effect of periodic stirring or the addition of nutrients at the onset of production. Continuously aerating compost tea did not significantly increase disease suppression compared with nonaerated compost teas. Preparing aerated compost tea (ACT) with nutrient additives did not consistently increase disease suppression; however, 67% of ACT batches made with a mixture of kelp extract, rock dust, and humic acid significantly reduced disease. Applying ACT with spray adjuvants significantly reduced disease compared with ACT with no adjuvants. The variability in gray mold suppression from NCT and ACT applications indicates that disease control would not be commercially acceptable unless there are no other alternatives due to production constraints, e.g., organic standards.

Compost Tea as a Container Medium Drench for Suppressing Seedling Damping-Off Caused by Pythium ultimum

ABSTRACT Compost tea is being used increasingly in agricultural production to control plant diseases. However, there has been limited investigation relating disease control efficacy to various compost tea production methods, particularly compost tea produced with active aeration and additives to increase microbial population densities in compost tea. Aerated compost tea (ACT) and nonaerated compost tea (NCT), produced with or without additives, was investigated for the suppression of damping-off of cucumber caused by Pythium ultimum. Compost tea was used to drench soilless container medium inoculated with P. ultimum; effect on damping-off ranged from not suppressive to consistently suppressive depending on the method used to produce the tea. The most consistent formulation for damping-off suppression was ACT produced with kelp and humic acid additives. Producing ACT with a molasses-based additive inconsistently suppressed damping-off; evidence suggests that residual nutrients can interfere with disease suppression. Heating or diluting compost tea negated suppression. Across all compost tea samples, there was no significant relationship of bacterial populations, measured as active cells, total cells, or CFU, to disease suppression. However, for all ACT produced without the molasses-based additive, there was a threshold of bacterial population density (6 log(10) active cells per ml, 7.48 log(10) total cells per ml, or 7 log(10) CFU per ml) above which compost teas were suppressive.

Suppression of Bacterial Spot of Tomato with Foliar Sprays of Compost Extracts Under Greenhouse and Field Conditions

The efficacy of foliar sprays with compost water extracts (compost extracts) in reducing the severity of bacterial spot of tomato caused by Xanthomonas vesicatoria was investigated. Extracts prepared from composted cow manure, composted pine bark, an organic farm compost, or composted yard waste, applied as foliar sprays on tomato transplants, resulted in a moderate but statistically significant reduction in the severity of bacterial spot. The population of X. vesicatoria in infected leaves was reduced significantly by extracts prepared from composted cow manure. Efficacy of the water extracts was not affected by oxygen concentrations in the suspension during extraction, compost maturity, or sterilization by filtration or autoclaving. The degree of control provided by foliar sprays with the most effective compost extracts did not differ from that obtained with the plant activator acibenzolar-S-methyl. In the field in two growing seasons, foliar sprays with compost water extracts did not reduce the severity of foliar diseases, including bacterial spot. During the 1997 season, when the severity of bacterial spot in the field was high, foliar sprays with compost water extracts significantly reduced the incidence of bacterial spot on tomato fruit. Amending plot soil with several rates of composted yard waste did not lead to additional control of fruit disease over those only sprayed with extracts. Foliar sprays with a mixture of chlorothalonil and copper hydroxide or with acibenzolar-S-methyl reduced the severity of bacterial spot as well as incidence of spot on fruit.

Compost and compost water extract-induced systemic acquired resistance in cucumber and Arabidopsis

ABSTRACT A biocontrol agent-fortified compost mix, suppressive to several diseases caused by soilborne plant pathogens, induced systemic acquired resistance (SAR) in cucumber against anthracnose caused by Colletotrichum orbiculare and in Arabidopsis against bacterial speck caused by Pseudomonas syringae pv. maculicola KD4326. A peat mix conducive to soilborne diseases did not induce SAR. The population size of P. syringae pv. maculicola KD4326 was significantly lower in leaves of Arabidopsis plants grown in the compost mix compared to those grown in the peat mix. Autoclaving destroyed the SAR-inducing effect of the compost mix, and inoculation of the autoclaved mix with nonautoclaved compost mix or Pantoea agglomerans 278A restored the effect, suggesting the SAR-inducing activity of the compost mix was biological in nature. Topical sprays with water extract prepared from the compost mix reduced symptoms of bacterial speck and the population size of pathogenic KD4326 in Arabidopsis grown in the peat mix but not in the compost mix. The peat mix water extract applied as a spray did not control bacterial speck on plants grown in either mix. Topical sprays with salicylic acid (SA) reduced the severity of bacterial speck on plants in the peat mix but did not further reduce the severity of symptoms on plants in the compost mix. The activity of the compost water extract was heat-stable and passed through a 0.2-mum membrane filter. beta-1,3-Glucanase activity was low in cucumber plants grown in either mix, but when infected with C. orbiculare, this activity was induced to significantly higher levels in plants grown in the compost mix than in plants grown in the peat mix. Similar results were obtained for beta-D-glucuronidase (GUS) activity driven by a PR2 (beta-1,3-glucanase) gene promoter in transgenic Arabidopsis plants grown in the compost or peat mix. GUS activity was induced with topical sprays of the compost water extract or SA in plants not inoculated with the pathogen, suggesting that compost-induced disease suppression more than likely involved the potentiation of resistance responses rather than their activation and that compost-induced SAR differed from SAR induced by pathogens, SA, or compost water extract.