Antifungal and defense elicitor activities of pyrazines identified in endophytic Pseudomonas putida BP25 against fungal
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ORIGINAL ARTICLE
Antifungal and defense elicitor activities of pyrazines identified in endophytic Pseudomonas putida BP25 against fungal blast incited by Magnaporthe oryzae in rice Asharani Patel1 · Aundy Kumar1 · Neelam Sheoran1 · Mukesh Kumar1 · Kuleshwar Prasad Sahu1 · Prakash Ganeshan1 · Mushineni Ashajyothi3 · Subbaiyan Gopalakrishnan2 · Robin Gogoi1 Received: 10 April 2020 / Accepted: 27 August 2020 © Deutsche Phytomedizinische Gesellschaft 2020
Abstract Black pepper-associated endophytic Pseudomonas putida BP25 displayed volatile-mediated antagonism against rice blast fungus Magnaporthe oryzae 1637. The major chemical fraction identified in the volatiles of Pseudomonas putida BP25 was 2-methylpyrazine and 2-ethyl-3,6-dimethylpyrazine; both of them inhibited all developmental stages such as conidial germination, mycelial growth, and sporulation of M. oryzae. To validate the antifungal activity of 2-methylpyrazine and 2-ethyl-3,6-dimethylpyrazine on blast disease, in planta experiments were conducted on rice seeds and seedlings. Blast disease incidence and disease severity on volatile-treated seedlings were significantly reduced as compared to mock. Seedlings that emerged from volatile-exposed seeds were analyzed for expression of candidate defense gene, OsPAD4, OsEDS1, OsPDF2.2, OsPR3, and OsPR1.1 by quantitative real-time PCR (qPCR). Seedlings exposed to volatiles showed significant induction of the OsPAD4 gene with both 2-ethyl-3,6-dimethylpyrazine and 2-methylpyrazine. Direct antifungal activity of pyrazine coupled with its defense elicitation capability can be harnessed for rice seed disinfection to ensure healthy, vigorous, and disease-free transplants. Keywords Volatile metabolites · Endophytic Pseudomonas putida BP25 · Magnaporthe oryzae · Elicitor · Defense genes · Blast disease · Rice · Pyrazine
Introduction Rice is one of the major staples for over half of the world’s human population, especially in Asia. Rice blast disease caused by a filamentous fungus Magnaporthe Electronic supplementary material The online version of this article (https://doi.org/10.1007/s41348-020-00373-3) contains supplementary material, which is available to authorized users. * Aundy Kumar [email protected] 1
Division of Plant Pathology, ICARIndian Agricultural Research Institute, New Delhi 110012, India
2
Division of Genetics, ICAR-Indian Agricultural Research Institute, New Delhi 110012, India
3
Seed Pathology, ICAR-Indian Institute of Seed Science, Mau, Uttar Pradesh 275103, India
oryzae (Hebert) Barr (anamorph: Pyricularia grisea) (Cavara 1891) is a major constraint leading to a loss in the production and productivity of rice. (Dean et al. 2012). All foliar parts of rice are susceptible to infection; however, infection on panicle and grain can lead to the total loss. Seed-borne latent infection of M. oryzae can lead to rapid transboundary movement of pathogen and the consequent introduction of disease as witnessed in wheat blast outbreak in Bangladesh in 2016 (Ceresini et al. 2018). The inadvertent
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