Enterobacter species, emerging plant-pathogenic bacteria, associated with decline and offshoot rot of date palm in Iran

Date palm ( Phoenix dactylifera ), one of the oldest trees in the world, is an important fruit crop in Southwest Asia and North Africa. A severe outbreak of leaf discoloration, offshoot rot and decline was observed in palm groves in Khuzestan province during 2019–2021. The disease was characterized by severe wilt on two or three-year-old date palm offshoots which resulted in premature plant death. The lower parts of the diseased offshoots were soft, dark brown to black and extensively decayed leading to offshoot wilting. Twenty-six symptomatic samples were collected from palm groves in different regions of Khuzestan province including Ahvaz, Abadan, Khorramshahr, Hamidiyeh, Shadegan, and Karun during 2019–2021. Eighty-five strains were isolated on NA medium. The pathogenicity of strains was confirmed by inoculating petioles and rachises of young two- to three-year old date palms cv. Estameran. Fifty-two strains induced soft rot at the inoculation site on petioles and rachises after 21 days. Lesions decayed and turned dark brown over time. Pathogenic strains were Gram-negative, facultative aerobic, catalase positive, and oxidase negative. The MLSA phylogenic tree based on the concatenated sequences of two housekeeping genes, gyrB and infB revealed that strains PA5 and PA153 clustered with E. cloacae subsp. cloacae ATCC13047 T with 100% bootstrap. Strains PA192 and PA210 as well as strains PA70 and PA72 clustered with E. ludwigii EN-119 T and E. mori LMG25706 T , respectively. To the best of our knowledge, this is the first report of these three Enterobacter species as causal agents of decline and offshoot rot of the date palm in the world.