Effectiveness of some Bio-control Agents and Chemical Resistance Inducers Against Brown Stem Rot in Soybean (Glycine max (L.) Merrill)

Document Type : Original Article

Authors

1 Plant Pathology Research Institute, Agricultural Research Center, 12619, Giza, Egypt.

2 Soils, Water and Environment Research Institute, Agricultural Research Center, 12619 Giza, Egypt.

Abstract

Brown stem rot (BSR) [Phialophora gregata (Allington & Chamberlain) Gams.] is a widespread and significant disease in all over world’s soybean-growing regions. In isolation trials, eight isolates associated to soybean stem rot symptoms were collected from various governorates in Egypt. All the tested isolates could attack soybean plants of the cv. Giza 22 variety and cause brown stem rot. The results of pathogenicity tests showed that isolate of Mallawi from Minia governorate was the most virulent isolate. The isolates were identified as Phialophora gregata. Efficacies of some bio-control agents viz. Trichoderma harzianum and Bacillus subtilis in addition to chemical resistance inducers viz. salicylic acid (SA), humic acid (HA) and hydroquinone (HQ) compared with Topsin M-70 % tested individually or in combinations as seed treatments showed antifungal activities against P. gregata in vitro and in vivo. Linear growth P. gregata in vitro was severely reduced by chemical inducers and antagonistic bacteria to varying degrees as compared to the control. The combination of B. subtilis + SA was most efficient in inhibiting mycelial growth of P. gregata.  In vivo, the application of all treatments used as seed soaking showed significantly reduced the percentage of internal stem discoloration (PISD). Employing chemical resistance inducers and bio-control agents together was more efficient than using each of them alone. Additionally, in two growing seasons after one another, biocontrol agents, chemical inducers and their mixtures significantly raised soybean growth and yield parameters. The best control of brown stem rot disease and the highest growth and yield parameters values was observed under combination of B. subtilis + SA. In soil analysis and biochemical changes in soybean plants, all treatments showed significantly increased in dehydrogenase (DHA), photosynthetic pigment content, total protein, total carbohydrate, total oil contents and nitrogen (N), phosphorus (P), and potassium (K) contents in yielded seeds, meanwhile the total phenols significantly increased in all treatments compared with untreated control treatment. In general, utilizing biotic inducers appears to be one of the solutions to replace, or to reduce, fungicides usage in the management of plant diseases.

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