Etiology of Bacterial Soft Rot and Corm Decay in Saffron

Saffron (Crocus sativus) is the world's most expensive spice. The plant is propagated vegetatively through corms. Infection of saffron corms with soil-dwelling pathogens would impact reproduction of the plant, resulting in significant yield losses. The etiology of soft rot and corm decay-inducing bacterial infections in saffron has rarely been investigated. This study aimed to isolate, identify, and characterize bacterial agents associated with saffron corm decay and soft rot in Iran. Symptomatic saffron corms were collected across the eastern, western, and central provinces of the country. Seventeen bacterial strains possessing pectinolytic activity were isolated in this study. Molecular-phylogenetic analysis using 16S rRNA and gyrA/gyrB sequences accomplished with whole-genome sequencing of the representative strains led to the identification of gram-positive species Bacillus halotolerans, Bacillus subtilis, and a Paenibacillus sp., as well as gram-negative bacteria Acinetobacter johnsonii, a Chryseobacterium sp., and a Serratia sp. Pathogenicity assays confirmed that these bacterial strains not only infected saffron plants but also had pectinolytic activity on a range of monocotyledonous and dicotyledonous plants including beetroot, carrot, cucumber, garlic, onion, potato, and turnip. Further, the Bacillus sp. and Paenibacillus sp. strains could suppress the growth of other strains isolated in this study, indicating their potential competition on the same host. Whole-genome sequence-based analyses showed that the Paenibacillus sp. and Chryseobacterium sp. strains could potentially belong to novel species. The results of the present study shed light on the etiology of soft rot, inducing bacterial infections in the hub of saffron production in the Middle East.