Table of contentsMaterials and methods1. Isolation of fungi associated with cowpea damping off:2. Source of biochar, compost and mycorrhiza tested:3. Laboratory test3.1. Preparation of compost water extract (CWE)3.1.1. Effect of biochar and compost on mycelium growth of R. solani:4. Greenhouse experiments:5. Field experiences:6. Statistical analysisDiscussionImpact of certain soil amendments and mycorrhizae on cowpea damping off caused by Rhizoctonia solani.Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Adding biochar to soil improves soil fertility and plant growth, especially when combined with organic compounds such as compost. This study was carried out to examine the effect of soil amendments with biochar, compost and mycorrhiza as biofertilizer alone or in combination on certain growth parameters of cowpea plants and on the suppression of damping off caused by Rhizoctonia solani in greenhouses and in the open field. In vitro experiments have shown that biochar has no direct effect on the fungus tested, even at the highest concentrations tested. In greenhouses, Copmost has been shown to be more effective than biochar in reducing damping off. In the field, mycorrhizae alone or combined with biochar or compost gave the lowest percentages of damping off. In addition, they significantly improved plant growth parameters (plant height (cm), root length (cm), number of leaves, pods and nodules/plant, fresh weight of leaves and roots (g) and weight dry leaves and roots (g)). In addition, the treatments tested improved the ability of cowpea plants to absorb nitrogen, phosphorus and potassium from the soil. Mycorrhizae alone or combined with biochar or compost were the most effective treatments in this regard. Key words: Compost, cowpea, mycorrhiza, rice straw biochar and macronutrients. The search for new strategies to control plant diseases and improve yield has led to the discovery of various new ideas, including amendments to organic soil compounds such as biochar and compost. These compounds are well known for their suppressive effect against a wide range of soil pathogens (Coventry et. al., 2005 and Noble and Coventry, 2005). Biochar is a carbon-rich organic product, it is produced by a heating process known as pyrolysis (Sohi et. al., 2010; Elad et. al., 2011 and Sparks, 2011). The type of organic compounds and the temperature used for their production determine their nutrient content and physicochemical properties (Antal and Gronli, 2003 and Gaskin et. al., 2008). The addition of biochar to the soil improves its characterization, leading to beneficial effects on the quality and quantity of plants (Glaser et. al., 2002; Steiner et. al., 2008 and Atkinson et. al., 2010). It is very stable in soil with a half-life of up to thousands of years (Zimmerman, 2010). Recently, it has been reported that soil amended with biochar can influence the development of plant diseases caused by foliar and soil-borne pathogens (Graber et. al. 2014). Another soil amendment with suppressive effects is compost. It inhibits a wide range of plant diseases caused by various pathogens present in the soil. This could be due to increased competition and antagonism from soil biota associated with increased microbial activity in the soil (Pugliese et. al., 2011). Arbuscular mycorrhizal fungi are oneof the most important microorganisms. It establishes symbiotic relationships with plants and affects soil and leaf pathogens (Whipps, 2004 and Fritz et. al., 2006). Cowpea (Vigna sinensis Endl.) is the most important vegetable crop. Cowpea seeds contain approximately 23% protein and 57% carbohydrates (Belane and Dakora, 2009). Cowpea plants are susceptible to attack by damping off and root rot caused by Fusarium solani, Rhizoctonia solani, Macrophomina phaseolina, Sclerotium rolfsii and Pythium sp. These diseases cause considerable losses of cowpea plants around the world (Shihata and Gad El-Hak, 1989; Ushamalini et. al., 1993; Rauf, 2000; Satish et. al., 2000; El-Mohamedy et. al. , 2006). Overall study, the effect of compost, biochar and mycorrhiza, alone or in combination, on the control of cowpea damping off caused by Rhizoctonia solani and on some plant growth parameters in greenhouse and in the field were concerned. In addition, the study was expanded to evaluate the effect of these treatments on the nitrogen, phosphorus and potassium (NPK) content of plants.Materials and methods1. Isolation of fungi associated with cowpea damping off: Diseased cowpea plants, presenting typical symptoms of cowpea damping off, were collected at the Fac Experimental Farm. Agric., Univ of Cairo. For isolation, infected roots were washed thoroughly with tap water and cut into small fragments (0.5–1.0 cm), superficially sterilized with 1% sodium hypochlorite for 3 min, then rinsed several times in sterilized water, blotted dry. dry between the folds of sterilized filter paper. Small pieces were transferred to PDA medium in Petri plates and incubated at 26 ± 2°C for 7 days. Observations were recorded daily and emerged fungi were collected and cultured on PDA medium slopes and their frequencies were calculated. Fungal growth was examined microscopically and purified using single spore and/or hypha tip techniques (Dhingra and Sinclair, 1985). The purified fungi were identified based on their morphological characteristics, either at the generic or species level, according to Booth and Waterston (1964) and Barnett and Hunter (1972). The most common fungus was used in vitro and in vivo (pot experiments) after confirmation of its pathogenicity.2. Source of biochar, compost and mycorrhiza tested: Rice straw biochar and commercial compost were kindly obtained from Soil, Water and Environ. Res. Inst., Agric. Res. Center, Giza, Egypt. The characteristics of compost and rice straw biochar are mentioned in table (1). For mycorrhiza inoculation, Mycorrhizen was used as a commercially available inoculum. This mycorrhiza product was purchased from Soil, Water and Environ. Res. Inst., Agric. Res.Center, Giza, Egypt.3. Laboratory test3.1. Preparation of compost water extract (CWE) CWE was prepared by vigorously shaking mature compost, at a ratio of 1:2 (w/v) compost (500 g) in sterile water (1 000 ml), for 20 min. To be deletedTable 1. Selected characteristics of compost and rice straw biochar used in the present studyTested compound pH Total carbon (%) Total N (%) Total P (%) Total K (%)Biochar 9.0 36.60 0 .52 0.54 0.88Compost 8.19 25.05 1.31 1.65 -the large particles of the compost mixture, a 250 ml aliquot of the mixture was filtered by passing through 3 layers of sterile cheese cloth , then the filtrate was centrifuged at 500 rpm for 10 min to obtain an active supernatant as a stock solution. Four different concentrations, namely 0, 5, 10 and 15%, werebeen tested against the tested fungus.3.1.1. Effect of biochar and compost on the mycelium growth of R. solani: The inhibitory effect of the tested compost in the form of aqueous extract (CWE) was examined in vitro against the tested pathogenic fungus using the well diffusion method. according to El-Masry et. al. (2002). The CWE was filtered through a sterilized 0.22 µm Millipore membrane filter. Fifteen ml of sterile PDA medium was used for each plate, a well was then drilled on one side of the plate using a sterile 0.5 cm cork borer and the bottom of the well was sealed with two drops of sterile PDA medium. One hundred ml of each concentration of CWE was transferred separately to each well. Sterile water was used as a control. Five petri dishes were used as replicates for each treatment as well as the control. All plates were incubated at 25°C for 7 days, then the reduction in mycelium growth was recorded. The direct toxicity of biochar was investigated using an in vitro contact assay to assess the reduction in growth of R. solani. PDA medium was amended with different concentrations of biochar, i.e. 0, 5, 10 and 15%, w:v before autoclaving, then distributed in Petri dishes (9 cm in diameter). Agar plugs (5 mm in diameter), coated with actively growing mycelium, were transferred to the center of Petri dishes amended with one of four concentrations of biochar and then incubated at 25°C for 7 days, followed by growth. fungal was calculated. Inhibition of fungal growth was calculated using the following formula: I = CT/CX100Where; I = Reduction (%) in fungal growth; C = Fungal growth in the control treatment and T = Fungal growth in the treatment4. Greenhouse experiments: Effect of compost and biochar at different concentrations on damping off of cowpea under greenhouse conditions: To determine the most effective concentrations of the tested compost and biochar, cowpea seeds (cv. Tiba) , obtained from Agric, Res. Center, Giza, Egypt, were surface disinfected in 2% sodium hypochlorite, rinsed with sterile distilled water, and then 5 seeds were sown in each plastic pot (40 cm3) filled with a mixture sterilized sand and clay (2:1, v/v) containing compost at 0, 5, 10 and 15% w/w or biochar at 0, 5, 10 and 15%, w/w. One day later, the treated soil was individually infested with the tested fungal inoculum at a rate of 3% w/w, previously cultivated on a sandy barley substrate (1/1, w/w and 40% water). ) at 25 ± 1°C for two weeks. . Five randomly replicated pots were used for each treatment.5. Field experiments: Effect of compost, biochar and mycorrhiza alone or in combination on damping off of cowpea plants under field conditions during the 2013 and 2014 growing seasons: The most effective concentrations of compost and biochar tested were selected to study their effect on disease suppression when mixed in the presence or absence of mycorrhizae. Sterilized cowpea seeds were covered with mycorrhiza inoculum before sowing. The following treatments were used in the experimental setup: Compost; Biochar; Mycorrhizene; Compost + Biochar; Compost + Mycorrhizene; Biochar + Mycorrhizene; Compost + Biochar + Mycorrhizene; Rhizolex-T; Control. The experiment was carried out in the experimental unit of Department of Plant Pathology, Faculty of Agriculture, Cairo University, Giza, Egypt during two successive seasons of 2013 and 2014. The land was divided into ridges (70 cm width). Seeds were sown 15 cm apart in a row on the ridge, two seeds in each location. The seeds were sown on April 15, 2013 seasons and2014. All agricultural practices were carried out in accordance with the recommendations of the Egyptian Ministry of Agriculture. The experimental treatments were organized according to a randomized complete block design with three replications. The plot area was 4.2 m2 (6 m length and 0.7 m width). The percentages of damping off before and after emergence as well as healthy surviving plants were measured at 15, 21 and 45 days after sowing, respectively, using the formula described by Mikhail et. al. (2005) and Abd El-Moneim, et. al. (2012) as follows: Pre-emergence (%) = Number of ungerminated seeds / Total number of seeds sown × 100 Post-emergence (%) = Number of plants dead after emergence / Total number of seeds sown × 100 Surviving plants (% ) = Number of surviving plants / Total number of seeds sown × 100 Survival efficiency (%) = D1-D2 / D1 × 100 Where: D1 = Damping off (%) in the control treatment and D2 = Damping off (%) in treatment5. Effect of compost, biochar and mycorrhiza alone or in combination on certain parameters of cowpea plants in greenhouse during the 2013 and 2014 growing seasons: The vegetative growth parameters of cowpea plants, namely plant height (cm ), root length (cm), number of leaves, pods and nodules/plant, fresh weight of leaves and roots (g) and dry weight of leaves and roots (g), were determined 90 days after sowing. Five random samples of cowpea plants representing each treatment were carefully removed from the soil and then washed under running tap water to remove adhering particles.6. Effect of compost, biochar and mycorrhiza alone or in combination on the nitrogen, phosphorus and potassium contents of cowpea plants under field conditions during the 2013 and 2014 growing seasons: The nitrogen and phosphorus contents were analyzed according to Jackson (1973), where the potassium content was determined using atomic absorption spectrophotometer (Barkin Elmer, 3300) according to (Chapman and Pratt, 1961), the results were calculated as g/100 g of dry weight.6. Statistical analysis Most data were statistically evaluated according to Snedecor and Cochran (1967). Means were compared with a probability level of 5% using least significant differences (LSD), as mentioned by Fisher (1948). On the other hand, the percentage data were arcsine transformed and then subjected to statistical analysis to determine the least significant differences (LSD) to compare the variance between treatments (Gomez and Gomez, 1984). Discussion Biochar not only improves crop yield (Kloss and Gomez, 1984). . al., 2014), but also has the ability to control diseases caused by different pathogens (Matsubara et. al. 2002; Nerome et al. 2005; Elmer and Pignatello 201; Zwart and Kim 2012; Graber et al., 2014 Jaiswal). et al. 2014), but there is no information available on the impact of biochar on cowpea damping-off caused by Rhizoctonia solani. On the contrary, many authors have reported a suppressive effect of organic amendments such as compost against R. solani and other soil pathogens (Borrero et. al., 2004; Bonanomi et. al., 2007). This study is the first report on the effects of compost and biochar alone or in combination with mycorrhizae on cowpea plant growth and the incidence and development of damping off caused by R. solani. In the presented investigation, the in vitro study indicated that biochar has no direct effect on the tested fungus, while the compost extract had a greater effect on reducing the growth of the mycelium of the fungus. These results are, to some extent, consistent with those reported by Bonanomi et al.,.