Characterization of Bacillus altitudinis as a New Causative Agent of Bacterial Soft Rot

A total of 67 bacterial isolates were obtained from apple and pear fruits with signs of soft rot collected from Egyptian markets. Pathogenicity tests showed that 25 isolates (37%) were pathogenic to apple and pear fruits, with considerable variation of virulence. Among these isolates, 16 (64%) were Gram-positive, motile, spore-forming long rods and were identified as members of the genus Bacillus based on an API test. In addition, five isolates (20%) were Gram-negative, non-spore-forming, motile, oxidase and catalase-positive short rods and were identified as members of the genus Pseudomonas. Furthermore, four isolates (16%) were Gram-negative, non-spore-forming, motile, catalase-positive and oxidase negative short rods and were identified as belonging to the genus Erwinia. All selected isolates showed a wide host range and could cause soft rot of all representative fruits and vegetables tested. The three most virulent isolates, AB4, AB6 and PB6, exhibited the highest soft rot severity on different apple and pear cultivars, and apple cv. Anna (116) was the most susceptible to infection by isolates AB4 and AB6, with soft rot severities of 63.33 and 60.67%, respectively. Also, pear cv. Le-Conte was most susceptible to infection by isolate AB6, with a soft rot severity of 89.9%. A phylogenetic tree based on 16S rRNA gene sequences indicated that strains AB4 and AB6 were very similar to one another and also showed a similarity of 99% to Bacillus altitudinis, and strain PB6 revealed a similarity of 99% to Bacillus pumilus. To our knowledge, this is the first report of B.altitudinis as a soft rot pathogen for both apple and pear fruits.