Abstract
Bacillus amyloliquefaciens has been widely used in the agriculture, food, and medicine industries. Isolate PP19 was obtained from the litchi fruit carposphere and showed biocontrol efficacy against litchi downy blight (LDB) whether applied preharvest or postharvest. To further understand the underlying regulatory mechanisms, the genome of PP19 was sequenced and analyzed. The genome comprised a 3,847,565 bp circular chromosome containing 3990 protein-coding genes and 121 RNA genes. It has the smallest genome among 36 sequenced strains of B. amyloliquefaciens except for RD7-7. In whole genome phylogenetic analysis, PP19 was clustered into a group with known industrial applications, indicating that it may also produce high-yield metabolites that have yet to be identified. A large chromosome structural variation and large numbers of single nucleotide polymorphisms (SNPs) between PP19 (industrial strain) and UMAF6639 (plant-associated strain) were detected through comparative analysis, which may shed light on their functional differences. Preharvest treatment with PP19 enhanced resistance to LDB, by decreasing the plant H2O2 content and increasing the SOD activity. This is the first report of an industrial strain of B. amyloliquefaciens showing a plant-associated function and with major potential for the biocontrol of LDB.
Highlights
Litchi (Litchi chinensis) belongs to Sapindaceae and is native to South China
Except for the prediction for the general function category (304 genes), the amino acid transport and metabolism (303 genes), and the transcription (279 genes) categories showed the highest percentages among 25 categories (Supplementary Figure 1)
The results demonstrated that most regions of sequence similarity fell along the diagonals of the forward strand, except for several gene sites, indicating a generally similar gene and sequence order between PP19 and DSM7 (Figures 2C,D)
Summary
Litchi (Litchi chinensis) belongs to Sapindaceae and is native to South China. It is mainly distributed in China, India, Thailand, Vietnam, South Africa, Australia, and other tropical and subtropical regions (Tindall, 1994). Litchi is known in China as the “King of fruit,” with its taste and its high nutritional value; the pulp is rich in nutrients such as sugars, organic acids, dietary. During postharvest storage of litchi, the fruit can turn brown and rot due to litchi anthracnose, sour rot, and downy blight. Among these diseases, litchi downy blight (LDB) caused by Peronophythora litchii is the most serious (Wang et al, 2013). LDB alone may destroy 20–30% of litchi fruit every year (Zheng et al, 2019)
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