Abstract
The efficacy of two plant growth promoting rhizobacteria (PGPR) strains including Bacillus subtilis TU-Orga1 and Pseudomonas fluorescens TU-Orga2 obtained from rice rhizosphere against naturally occurring diseases as well as their capacity to improve crop yield of sweet corn cv. Insee2 was studied. TU-Orga1 was significantly greater in inhibition of Acidovorax avenae subsp. avenae (Aaa) and Erwinia chrysanthemi pv. zeae (Ecz), caused bacterial leaf streak and stalk rot of corn, respectively by antibiosis. Greenhouse experiments using TU-Orga1 and TU-Orga2 treatments increased highest salicylic acid accumulation in corn leaves with 7.85 and 6.98 mg g-1 fresh weight, respectively to protect Ecz infection. Each PGPR strain was single applied in the field through seed treatment and 3-foliar-spray-intervals at 14, 21, and 28 days after planting. Two PGPR treatments resulted in reduced severity of all diseases and increased yields when compared with the control treatment. There were differences among the treatments in that the highest level of disease suppression of bacterial stalk rot resulted with treatments TU-Orga1 (P = 0.05), whereas TU-Orga2 showed the highest level of disease suppression of bacterial leaf streak and sugarcane mosaic virus and provided significantly greater marketable yield increases than the other treatments. This illustrates the potential of these new biocontrol agents to suppress multiple diseases. They could become a component of an integrated program or an organic farming for corn disease management. Key words: Plant growth promoting rhizobacteria (PGPR), Acidovorax avenae subsp. avenae, Erwinia chrysanthemi pv. zeae, SCMV, systemic acquired resistant.
Highlights
Corn is an economically important crop and many disease-causing organisms including several fungi, viruses, bacteria, and nematodes disseminated in the corn production system
Seed and seedling diseases caused by Pythium sp., Rhizoctonia sp. and Fusarium sp., downy mildew caused by Peronosclerospora sorghi, Northern corn leaf blight caused by Setosphaeria turcica, Southern corn leaf blight caused by Bipolaris maydis, bacterial leaf streak caused by Acidovorax avenae subsp. avenae (Aaa), and bacterial stalk rot caused by Erwinia chrysanthemi pv. zeae (Ecz) have occurred in many corn growing areas in Thailand (Prathuangwong et al, 2004)
Two new plant growth promoting rhizobacteria (PGPR) strains, Bacillus subtilis TU-Orga1 and Pseudomonas fluorescens TU-Orga2 isolated from rice rhizosphere and two commercial PGPR strains, Bacillus amyloliquefaciens KPS46 and Paenibacillus pabuli SW01/4 that have been isolated from soybean rhizosphere (Prathuangwong and Kasem, 2004) were evaluated
Summary
Corn is an economically important crop and many disease-causing organisms including several fungi, viruses, bacteria, and nematodes disseminated in the corn production system. Athinuwat et al 711 infecting corn and the symptoms include necrosis and blight on leaf, stem, flower, and ear (Li et al, 2000) These diseases are causing severe economic loss of corn production in Thailand, so effective control measures are critical. Several PGPR strain including Bacillus amyloliquefaciens KPS46 and Paenibacillus pabuli SW01/4 have been reported as offering several functions including increased plant growth by indole-3-acetic acid induction and induced plant defense by SAR against multiple diseases (caused by fungi, bacteria, and viruses) in various crops such as soybean, rice, sesame, corn, sunflower, and vegetable (Prathuangwong and Kasem, 2004; Boonnadakul et al, 2012; Sathitthampana et al, 2012; Athinuwat, 2013). Biological control using PGPR in a system of integrated control measures may provide effective and sustainable management where chemical control is not available or practical
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