ABSTRACT
Seed treatment by non-sterilized powdered straw from 4 crops was tested for Pythium damping-off of squash. The tested straws including wheat, faba bean, soybean and sorghum were effective in controlling the disease in soil artificially infested with Pythium ultinum. Sterilizing straws eliminated the efficacy of these straw, faba bean and soybean straws inhibit the mycelial growth of Pythium more than wheat and sorghum on potato dextrose agar when the straws were mixed with sterilized distilled water and left to ferment for 3 days. The soil treatment by the biocontrol agent T. harzianum control the damping-off disease in artificially infested soil and combination between seed treatment by straw powder and soil treatment by T. harzianum improve the efficacy of the biocontrol agent.
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DOI: 10.3923/ppj.2007.95.98
URL: https://scialert.net/abstract/?doi=ppj.2007.95.98
INTRODUCTION
Squash (Cucurbita pepo) is susceptible to the damping-off pathogen Pythium spp. Pythium ultimum is wide spread in soil and has a wide host range (Martin and Loper, 1999). Although fungicide seed treatment remains until nowadays still the main control method for the disease, increasing evidence suggests that seeds or soil treatment with biocontrol agents could be viable alternative. For example, coating seeds with bacterial agents such as Pseudmonas fluorescens or Bacillus subtilis was effective for the control of different seed and root diseases (Campo et al., 1994; Pizzinatto and Freitas, 1996; Bardin and Huang, 2003). Also the same results were obtained when the infested soil was treated by the antagonistic fungi such as T. haezianum and Gliocladiune virens (Inglis and Kawchuk, 2002; Ding et al., 2003; Roberts et al., 2005).
Plant residues have been used as amendment to increase soil organic matter and improve plant growth (Huang and Huang, 1993). Organic soil amendment may induce chemical and physical changes that also affect soil microflora (Gamliel et al., 2000; Pascual et al., 2000; Lazarovite, 2001; Panagouleas et al., 2003; Yulianti et al., 2006). In addition some organic matter can stimulate the production of lytic enzymes involved in the degradation of plant pathogens. Degradation of Pythium ultimum cell walls was accomplished by B-glucanases and cellulose enzymes (Thrane et al., 1997; Inglis and Kawchuk, 2002). The presence of organic substances rich in cellulose was also shown to stimulate growth of organisms with cellulose activity. Microbial degradation of plant residues cane also produce secondary products with antifungal activity, for example degradation of cruciferous plants resulted in the production of sulfur containing compounds with antifungal properties (Mayton et al., 1996; Ouf et al., 2004 and Yalienti et al., 2005). Also degradation of agonic residues containing nitrogen release volatile ammonia that reduce the survival of certain pathogenic fungi (Lazarovite, 2001 and Bardin et al., 2004). The aim of this study was to find out the crop straw powders effective for control (Pythium damping-off of squash when applied as seed treatment. Also the efficacy of soil treatment by the antagonistic fungus T. harzianum with the crop straw powders was also investigated.
MATERIALS AND METHODS
Control of damping-off of squash by seed treatment with crop straw powders: Plant straws from wheat (Triticum aestivum); faba bean (Vicia faba); soybean (Glycine max) and sorghum (Sorghum vulgare) were collected after harvest, dried at 50°C oven for one week and ground to powder. Squash seeds were coated with each straw powder by the following procedure; the seeds were soaked for 15 min in 1% methyl cellulose solution (Bardin and Huang, 2003) at a concentration of 3 mL per 10 g seeds. The seeds were then removed and placed in a plastic bag containing 2 g straw powder per 20 g seeds. The bag was inflated with air and shaken vigorously. This experiment was repeated again but with sterilized straw powder. Protection of squash seedlings from pythium damping off disease by straw powder was tested by planting the coated seeds in potting soil infested artificially with P. ultimum in wheat bran preparation. The pathogenic fungi was isolated from diseased squash seedlings (Al-Sarhance, 2003). After 3 weeks from planting the percentage of healthy seedlings were estimated. T. harzianum was kindly obtained from Faculty of Agriculture, King Saud University.
Control of damping-off disease in squash seedling by soil treatment with T. harzianum with on without seeds treatment with crop straw. A Similar experiment was conducted in which soil was artificially infested with 3% inoculum level of T. harzianum and 30% P. ultimum before planting by sterilized squash seeds or seeds treated by straw powders.
Effect of straw powders on the radial growth of P. ultimum and the total nitrogen content in straws: The powdered straws were tested for the production of volatile substances suppressive to the growth of P. ultimum in plate assay. The plate assay consisted in forming a paste of the non sterilized or sterilized straw powder. The paste was made by mixing 2.0 g of each straw powder with about 5 mL sterile distilled water. The paste of each straw was spread on the bottom of each Petri dish (9 cm diameter). A disc of 5 mm diameter of P. ultimum was taken from the periphery of 5 days old culture and placed at the center of the bottom of another plate containing Potato Dextrose Agar (PDA) medium the lids of the straw-containing and Pythium-inoculated plates were removed, the Pythium inoculated plate was inverted on the top of the straw containing plate and the two plates were sealed with parafilm. Mycelium growth of P. ultinum was measured after 3 days of incubation at 25°C±2 and was compared to the control which was the growth of P. ultimum on a PDA plate in the absence of a straw paste. The treatment of each experiment was replicated three times.
The total nitrogen content in each straw powder was determined according to Nagiub et al. (1983) .
RESULTS AND DISCUSSION
The data in Table 1 revealed that there was significant decrease in disease incidence by P. ultimum when seeds were treated by non-sterilized straw powders especially the straw powder of both soybean and faba bean than of wheat and sorghum. The data also showed that sterile straw powders have low ability to protect squash seedling from Pythium damping-off when coated on seeds. Also, when soil was treated by T. harzianum there was significant decrease in disease incidence. When seeds were treated with crop straw powder and the soil was treated with T. harzianum, this condition was more effective for the control of damping-off disease in squash, than, soil treatment with biocontrol agent alone.
Table 2 showed that the growth of P. ultimum on the solid media was reduced in the presence of non-sterilized straw powdered especially these of faba bean and soybean than wheat and sorghum straw. In the case of sterilized powders the rate of inhibition was very low in comparison with growth on sterilized powder. Still faba bean and soybean straw powders were more effective than wheat and sorghum straw.
The data in Table 3 revealed that the amount of total nitrogen in straw powders varied by the kind of the crop. Dicot crops especially leguminosae contains nitrogen more than monocot.
In this investigation the crop straws was used as seed coating material for the protection of squash seeds against Pythium damping-off disease the pots experiment revealed that straw powder of faba bean and soybean were effective for the control of damping-off of squash caused by P. utimum Previous studies (Huang and Huang, 1993; Gamliel et al., 2000) indicated that soil amendments with organic wastes for the control of plant disease often requires high amount of organic matter and thus is not cost-effective. However the present study demonstrated that by coating certain types of straw into squash seeds, only very small amount of the straw was needed to protect the seeds from the disease, possibly by changing the chemical properties of the soil at the interface with the seed.
Table 1: | Control of Pythium damping-off in squash seedling by seed treatments with sterile and non-sterile straw powders with or without the presence of T. harzianum as biocontrol agent (% of healthy seedling, Means±SE) |
***Significant at 5 and 1%, respectively |
Table 2: | Effects of straw powder paste on the radial growth and growth rate of P. ultimum (mm/disc, means±SE) |
*Significant at 5% *significant at 1% *** Significant at 5 and 1%, respectively |
Table 3: | The total nitrogen content in straw powders of wheat, faba bean, soybean and sorghum as mg N/1 g dry straw (means±SE) |
Faba bean and soybean straws were effective in controlling damping off disease in squash, more than coating wheat or sorghum straw powder on squash seeds (Table 1). This might be explained on the basis that both faba bean and soybean non-sterilized straw powders when fermented by the accompanied microorganisms which suppressed the incidence of disease and at the same time the sterilized straws were unable to suppress the disease. This was confirmed by the effects of straw powders paste on the radial growth of P. ultimum on PDA media (Table 2). Both faba bean and soybean straw powders contain a large amount of nitrogen than the nitrogen content of wheat and sorghum straw powders (Table 3). It also appears from the results in this study that the antagonistic fungus T. harzianum suppressed the damping-off disease in green houses experiments. Many researches suggested that T. harzianum can produce lytic enzymes which analyze mycelium of the pathogenic fungi (Viterbo et al., 2004; Wen et al., 2005). Also T. harzianum secreted some metabolites as mycotoxins and antibiotics which inhibited the pathogenic fungi found in the rhizrosphere of the plant (Benhamou and Chet, 1993; Pristchepa and Voitka, 1999; Jones, 2002; Harman et al., 2004; Chung et al., 2005). The combination between straw powders and T. harzianum improved the efficacy of biological control might be explained on the basis that straw produced volatile ammonia and T. harzianum also produced some secondary product which suppressed the growth of the pathogenic fungus P. ultimum.
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