Abstract
Two-different carrier formulations, kaolin and talc-based products were developed with Pseudomonas fluorescens SP007s biocontrol agent. SP007s viability in different carriers stored at room temperature (28 to 33°C) slowly declined to approximately 46.2 and 61.0% after 12-month-old shelf life. The decreased population was first found in five and month months of storage for kaolin and talc-based formulations, respectively. Field experiment with 6-foliar spray intervals (1 × 108 cfu/ml) of SP007s was conducted against naturally-occurred dirty panicle disease caused by a multiplex fungus at Suphanburi. The two bioformulations significantly reduced pathogen colonization on rice panicle and exhibited the greatest yield that correlated with increased defense-related enzyme accumulation in treated plants, compared to 4-fungicide spray intervals and nontreated control. Protection of seeds collected from colonized and noncolonized plants of dirty panicle treated with bioformulations (1 × 106 cfu/ml) and fungicides (copper hydroxide) was further determined for 12 months of storage at room temperature. The best results in reducing 6-causal fungi including Alternaria padwickii, Cercospora oryzae, Curvularia lunata, Fusarium semitectum, Helminthosporium oryzaeqe and Sarocladium oryzae; and induced seedling vigor (35%) were obtained from SP007s kaolin-based formulation evaluated at 8-month storage, but not at 12 months which indicated that these causal pathogens totally recovered their colonization except S. oryzae. In 8-month trials, control efficacy with dose of 1 × 106 cfu/ml SP007s seed treatment, the increase in SP007s populations relatively with the decreased colonization of pathogens could be found. SP007s in kaolin-based formulation increased GABA in SP007s treated seeds suggesting this plant bioactivator may involve plant’s defense against stress conditions also. Key words: Biocontrol, multiplex fungus causes, induced systemic resistance, protective enzymes, reduced chemical application.
Highlights
Dirty panicle of rice (Oryza sativa L.), one of the most important diseases in Thailand can cause great losses in grain and seed production which makes it unacceptable for consumption and seeding
The bioproduct must be quickly dissolved in water in order to activate its bacterial activity and eliciting properties that kaolin-based powder formulation dissolved in water is a faster alternative compared to talc-based
The results reveal in this study corroborate earlier studies and indicate a future possibility that plant growth promoting rhizobacteria bioformulations can be used to promote growth and health of economic crops (Raj et al, 2003; Chuaboon and Prathuangwong, 2007)
Summary
Dirty panicle of rice (Oryza sativa L.), one of the most important diseases in Thailand can cause great losses in grain and seed production which makes it unacceptable for consumption and seeding. The disease caused by multiplex fungi includes Alternaria padwickii, Cercospora oryzae, Curvularia lunata, Fusarium semitectum, Helminthosporium oryzae and Sarocladium oryzae. They favor to infect plants at panicle forming stage under high temperature (28 to 33°C) and humidity (>80% RH). Biological control of plant pathogen is becoming an important component of plant disease management practices This alternative control strategy can solve many persistent problems in agriculture including fungicide residues causing environmental pollution and human health hazard, and inducing pathogen resistance (Commare et al, 2002; Cook, 2002; Bharathi et al, 2004; Chaluvaraju et al, 2004; Anitha and Rabeeth, 2009; Chen et al, 2009; Ardakani et al, 2010, 2011; Haggag and Wafaa, 2012)
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