Offshoot Decline and Bud Rot of Date Palm Caused by Three Species of Enterobacteriaceae

Abstract

Date palm (Phoenix dactylifera) considered a main income and food source for local individuals in producing countries. However, palm offshoot decline and bud rot disease was observed in some palm groves in Khuzestan province as a major date producer in Iran. Thirty-five samples with rot and decline were collected from diseased offshoot from palm groves of six cities of Khuzestan during 2019–2021. Yellowing in outer leaves, black, brown or reddish brown spots were observed on petioles at the early stage, which gradually continues to rot. Seventy-nine were isolated from symptomatic samples among which 38 strains caused rotting in the inoculated site and emission of a foul odour 3 weeks after inoculation on petioles and rachises of young offshoots. Based on the phenotypic characters, pathogenic strains categorised in three groups including Klebsiella oxytoca with 15, Kosakonia radicincitans with 12 and Citrobacter koseri with 11 strains. The phylogenic tree based on analysis of the concatenated partial sequences of two housekeeping genes, gyrB and infB, revealed that six representative strains clustered with the type strains of K. oxytoca and K. radicincitans. Furthermore, two strains were clustered with the type strain of C. koseri based on concatenated partial sequences of gyrB, fusA and pyrG genes. This is the first report of K. oxytoca, K. radicincitans and C. koseri, as agents of date palm offshoot decline and bud rot. The inundation of palm groves due to massive flood during 2019 and 2020 in Khuzestan province may intensify the outbreak of decline and offshoot rot disease.