Characteristics and Ice Nucleation Activity of Sugarcane Epiphytic and Endophytic Bacteria and Their Role in Host Frostbite

Sugarcane is one of the most important economic plants in tropical and subtropical regions worldwide, which is exposed to damage in cold condition. This study was conducted to characterize the epiphytic and endophytic bacteria and investigation of their role in ice nucleation activity and host frostbite. During the survey in spring and summer 2015, a total of 136 Gram-negative and Gram-positive bacterial strains were isolated from main sugarcane fields, especially Ahwaz sugarcane agro-industries in the south of Iran. According to phenotypic features and sequences of 16S rRNA encoding genes of sugarcane epiphytic and endophytic bacteria, they belonged to six families including Pseudomonadaceae, Xanthomonadaceae, Enterobacteriaceae, Sphingomonadaceae, Microbacteriaceae and Bacillaceae. Representatives of these families were identified as Pseudomonas fluorescens (Epi57-A4), Pseudomonas marginalis (strain Epi48-A17), Pseudomonas putida (strain Epi57-I6), Xanthomonas axonopodis strain (Endo57-A8), Stenotrophomonas maltophilia (strain Endo69-A6), Pseudomonas geniculata strain (Epi69-A4), Pantoea stewartii (strain Epi57-I8), Sphingomonas sp. (strain Epi48-A7), Microbacterium arborescens (strain Epi69-I1) and Bacillus sp. (strain Epi48-A8). The highest frequency of the tested bacterial strains was observed for Pseudomonadaceae and Xanthomonadaceae family members. Pseudomonas fluorescens strain Epi57-A4 and Pantoea stewartii strain Epi57-I8 showed ice nucleation activity in ethanol bath and caused frost damage on sugarcane seedlings in vitro. Amplification of Ice nucleation gene using degenerate inaprimers showed that only Pseudomonas fluorescens strain Epi57-A4 was ina+ gene, suggesting the potential of this gene to accelerate frosting in sugarcane during the cold condition.