Emergence of Two Novel <i>Pectobacterium</i> Species (<i>P. hainanensis</i> sp. nov. and <i>P. artocarpous</i> sp. nov.) Associated with Destructive Jackfruit Gummosis in Tropical China

Jackfruit (Artocarpus heterophyllus Lam.), a crucial economic crop in tropical regions, has recently been devastated by a novel gummosis disease in Hainan and Yunnan Provinces of China. This gummosis primarily affects the stems and branches of jackfruit, causing gum exudation, bark cracking, and plant death, which severely threatens the sustainable development of the industry. Although previous studies have hypothesized associations with fungi of the Fusarium genus or Pectobacterium genus, the taxonomic status of the pathogen remains controversial. This study aimed to clarify the pathogen and taxonomic classification of the gummosis. Through field investigations, seven Pectobacterium strains were isolated from diseased plants. Combining 16S rDNA, whole-genome comparisons (ANI < 95%, dDDH < 70%), and physiological-biochemical characteristics, two novel species, Pectobacterium hainanensis sp. nov (B1J-3) and Pectobacterium artocarpous sp. nov (B2J-2), were identified. Koch's postulates verified that these two species were the causative agents of gummosis, and the abundance of Pectobacterium in diseased plants was significantly higher than that in healthy ones. Notably, B1J-3 and B2J-2 lack the type III secretion system (T3SS) but carry unique virulence genes (T4SS and T6SS). Additionally, B2J-2 can infect Chinese cabbage, indicating a potential risk of cross-host transmission. This study is the first to identify novel Pectobacterium species as the pathogens of jackfruit gummosis, revealing their pathogenicity through atypical virulence factors, thus providing crucial evidence for disease control and pathogen evolution research.