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ARS Home » Southeast Area » Stuttgart, Arkansas » Dale Bumpers National Rice Research Center » Research » Publications at this Location » Publication #430239
Research Project: Broadening and Strengthening the Genetic Base of Rice for Adaptation to a Changing Climate, Crop Production Systems, and Markets

Location: Dale Bumpers National Rice Research Center

Title: Survey of Magnaporthe oryzae avirulence genes in Arkansas commercial rice fields

Author
item DE PAULA, SAMUEL - University Of Arkansas
item BELMAR, SCOTT - University Of Arkansas
item MARTINI, ALINE FACHIN - University Of Arkansas
item FERREIRA, ANA CARLA - University Of Arkansas
item PEREIRA, JOCILENE - University Of Arkansas
item RONNING, BRUNA - University Of Arkansas
item PEDROZO, RODRIGO - Oak Ridge Institute For Science And Education (ORISE)
item Jia, Yulin
item SHA, XUEYAN - University Of Arkansas
item NICOLLI, CAMILA - University Of Arkansas

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2026
Publication Date: 5/18/2026
Citation: De Paula, S., Belmar, S., Martini, A., Ferreira, A.B., Pereira, J., Ronning, B., Pedrozo, R., Jia, Y., Sha, X., Nicolli, C. 2026. Survey of Magnaporthe oryzae avirulence genes in Arkansas commercial rice fields. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-01-26-0015-R.
DOI: https://doi.org/10.1094/PHYTOFR-01-26-0015-R

Interpretive Summary: Rice blast disease caused by the ascomycete fungus Magnaporthe oryzae is one of the most damaging diseases globally. In the USA, this disease has been managed by the use of handful major resistance (R) genes coupled with integrated culture practices. However, the efficacy of the major R genes depends on the expression of the cognate avirulence genes in the pathogen. In this study, we purified 227 M. oryzae isolates from 15 counties of Arkansas where about 50% of the US is grown, and determined the frequency and distribution of eight AVR genes AVR-Pita1, AVR-Pik, ACE1, AVR-Pi9, AVR-Pib, AVR-Pii, AVR-Pizt, and AVR-Pia which detect corresponding R genes, Pi-ta, Pi-k,Pi33,Pi-9,Pi-b,Pii, Piz and Pia. We found that AVR-Pita1 and AVR-Pizt were present in all isolates, while AVR-Pib, AVR-Pi9, and ACE1 were detected in 226 isolates, and AVR-Pii in 225 isolates. AVR-Pik and AVR-Pia were absent. Three distinct AVR profile groups were identified: A (AVR-Pita1 and AVR-Pizt), B (AVR-Pita1, AVR-Pizt, AVR-Pib, AVR-Pi9, and ACE1), and C (AVR-Pita1, AVR-Pizt, AVR-Pib, AVR-Pii, AVR-Pi9, and ACE1), with profile C representing the predominant combination in over 99% of the isolates. These findings provided a basis for breeding for effective resistance genes to be deployed in these surveyed counties in the state of Arkansas.

Technical Abstract: Rice blast, caused by the ascomycete Magnaporthe oryzae, remains a major threat to rice production. Although major resistance (R) genes have been identified and deployed, their effectiveness depends on the presence of matching avirulence (AVR) genes in the pathogen. In this study, we surveyed Arkansas commercial rice fields to assess the frequency and distribution of eight AVR genes: AVR-Pita1, AVR-Pik, ACE1, AVR-Pi9, AVR-Pib, AVR-Pii, AVR-Pizt, and AVR-Pia. A total of 227 M. oryzae isolates were collected during the 2024 and 2025 growing seasons from 15 counties and five cultivars. Eight AVR genes were tested using PCR with gene-specific primers. AVR-Pita1 and AVR-Pizt were present in all isolates, while AVR-Pib, AVR-Pi9, and ACE1 were detected in 226 isolates, and AVR-Pii in 225 isolates. AVR-Pik and AVR-Pia were absent. Three distinct AVR profile groups were identified: A (AVR-Pita1 and AVR-Pizt), B (AVR-Pita1, AVR-Pizt, AVR-Pib, AVR-Pi9, and ACE1), and C (AVR-Pita1, AVR-Pizt, AVR-Pib, AVR-Pii, AVR-Pi9, and ACE1), with profile C representing the predominant combination in over 99% of the isolates. These results reveal a highly uniform AVR gene composition in the Arkansas M. oryzae population and provide insights into the potential effectiveness of deployed R genes, supporting breeding efforts focused on durable resistance and economically sustainable blast management in the state.