اولین گزارش پوسیدگی جوانه مرکزی نخل خرما ناشی از Serratia marcescens در ایران

Date palm trees (Phoenix dactylifera) in southern Iran are considered one of the most important economic resources in the region. In August 2019, symptoms such as rotting of the central bud and drying of the leaves in the central ring were observed in young palms. As the symptoms progressed, the trees eventually completely dried out and died. Samples were taken from the tips of the leaves in the central ring, where they connect to the trunk, from 85 trees showing symptoms. Samples were taken from the area between healthy and symptomatic tissues, measuring 5 mm in dimensions. They were surface disinfected with 70% alcohol and then crushed in sterile water. The resulting suspension was then cultivated in NA culture medium and kept at 28°C. After 48 hours, a bacterial isolate was chosen as a single colony and purified in a new culture medium. For the pathogenicity test, date seedlings planted in 3 kg pots with one-year-old, 2 cm crown diameter were used. A bacterial suspension with a concentration of 〖10〗^( 8)(cfu) was prepared and injected into the crown of the trees using a sterile syringe. Three replicates were done for each isolate, in three trees. For the control treatment, sterile distilled water was injected. Trees inoculated with one of the isolates showed symptoms after 4 weeks and completely dried up after 7 weeks. Symptoms were not observed in the trees of the control treatment. The inoculated bacterial isolate was re-extracted from the trees that showed symptoms. The results confirmed the pathogenicity of the bacterial isolate using Koch's method. The isolates that caused disease symptoms were gram-negative and produced red pigment. They also had the ability to cause potato soft rot. Molecular identification was performed using the PCR technique with the primer pair associated with the recombinase (recA) gene, which consisted of recA F and recA R, as well as the general 16s rRNA primer pair, which included FD1 and RD1. The analysis of the obtained sequences and BLAST in the NCBI database showed that the isolates studied in this research belong to the Serratia marcescens species with 100% similarity. The sequences are registered in GenBank with the accession numbers (OR529439, OR529477, PP763427, PP763428, PP763429, PP763430) and can be accessed. The phylogenetic tree was constructed using MEGA 11 software and the maximum parsimony method with a Bootstrap 1000. The isolates analyzed in this study were grouped together. This study represents the first report of central bud rot of dates caused by Serratia marcescens bacteria.