Monitoring the Occurrence and Distribution of Stewart's Wilt of Maize in Iran

Stewart's wilt of maize, caused by the gram-negative bacterium Pantoea stewartii subsp. stewartii, is one of the economically important diseases of the crop around the globe. The disease has not yet been reported in Iran. Following preliminary observation of suspected symptoms on maize plants in Southeastern Iran in 2019, a 4-year comprehensive field survey and sampling program was initiated across maize-growing areas in the country to monitor the occurrence and distribution of the disease. During 2019 to 2022, 180 maize fields were surveyed, from which 400 symptomatic and asymptomatic maize samples were collected. Among dozens of bacterial strains isolated from leaves and stems of maize plants, 22 strains phenotypically resembled those of Pantoea spp. Species-specific PCR and multilocus phylogenetic analyses using the sequences of atpD, gyrB, infB, and rpoB genes showed that P. stewartii subsp. stewartii is the causal agent of Stewart's wilt in Iran. All strains induced leaf chlorosis and plant stunting on maize plants under greenhouse conditions 7 to 15 days postinoculation, confirmed with accomplishment of Koch's postulates. These 22 strains were isolated in Bushehr, Fars, Hormozgan, Kermanshah, Khuzestan, Kohgiluyeh-Boyer Ahmad, and Sistan-Baluchistan provinces. Results of the present study confirmed the occurrence of P. stewartii subsp. stewartii causing Stewart's wilt of maize in Iran. The occurrence of Stewart's wilt on maize in Iran can lead to yield reduction, trade restrictions, increased control costs, and threats to food security. Considering the quarantine status of the pathogen in Iran, strict inspections are warranted to combat potential threats due to Stewart's wilt epidemics in the country.