SUMMARY

Burkholderia glumae causes bacterial panicle blight of rice, which is an increasingly important disease problem in global rice production. Toxoflavin and lipase are known to be major virulence factors of this pathogen, and their production is dependent on the TofI/TofR quorum-sensing system, which is mediated by N-octanoyl homoserine lactone. Flagellar biogenesis and a type III secretion system are also required for full virulence of B. glumae. Bacterial panicle blight is thought to be caused by seed-borne B. glumae; however, its disease cycle is not fully understood. In spite of its economic importance, neither effective control measures for bacterial panicle blight nor rice varieties showing complete resistance to the disease are currently available. A better understanding of the molecular mechanisms underlying B. glumae virulence and of the rice defence mechanisms against the pathogen would lead to the development of better methods of disease control for bacterial panicle blight.



Taxonomy:Bacteria; Proteobacteria; Betaproteobacteria; Burkholderiales; Burkholderiaceae; Burkholderia.



Microbiological properties: Gram-negative, capsulated, motile, lophotrichous flagella, pectolytic.



Disease symptoms: Aborted seed, empty grains as a result of failure of grain filling, brown spots on panicles, seedling rot.



Disease control: Seed sterilization, planting partially resistant lines (no completely resistant line is available).



Known virulence factors: Toxoflavin, lipase, type III effectors.

/pdf/burkholderia-glumae-next-major-pathogen-of-rice-1vubz72r4v.pdf

Burkholderia glumae: next major pathogen of rice?

Potential biological control agents for two major rice diseases, sheath blight and bacterial panicle blight, were isolated from rice plants in this study. Rice-associated bacteria (RABs) isolated from rice plants grown in the field were tested for their antagonistic activities against the rice pathogens, Rhizoctonia solani and Burkholderia glumae, which cause sheath blight and bacterial panicle blight, respectively. Twenty-nine RABs were initially screened based on their antagonistic activities against both R. solani and B. glumae. In follow-up retests, 26 RABs of the 29 RABs were confirmed to have antimicrobial activities, but the rest three RABs did not reproduce any observable antagonistic activity against R. solani or B. glumae. According to16S rDNA sequence identity, 12 of the 26 antagonistic RABs were closest to Bacillus amyloliquefaciens, while seven RABs were to B. methylotrophicus and B, subtilis, respectively. The 16S rDNA sequences of the three non-antagonistic RABs were closest to Lysinibacillus sphaericus (RAB1 and RAB12) and Lysinibacillus macroides (RAB5). The five selected RABs showing highest antimicrobial activities (RAB6, RAB9, RAB16, RAB17S, and RAB18) were closest to B. amyloliquefaciens in DNA sequence of 16S rDNA and gyrB, but to B. subtilis in that of recA. These RABs were observed to inhibit the sclerotial germination of R. solani on potato dextrose agar and the lesion development on detached rice leaves by artificial inoculation of R. solani. These antagonistic RABs also significantly suppressed the disease development of sheath blight and bacterial panicle blight in a field condition, suggesting that they can be potential biological control agents for these rice diseases. However, these antagonistic RABs showed diminished disease suppression activities in the repeated field trial conducted in the following year probably due to their reduced antagonistic activities to the pathogens during the long-term storage in -70C, suggesting that development of proper storage methods to maintain antagonistic activity is as crucial as identification of new biological control agents.

/pdf/biological-control-activities-of-rice-associated-bacillus-sp-5380htupqs.pdf

Biological Control Activities of Rice-Associated Bacillus sp. Strains against Sheath Blight and Bacterial Panicle Blight of Rice

The members of the Burkholderia genus are characterized by high versatility and adaptability to various ecological niches. With the availability of the genome sequences of numerous species of Burkholderia, many studies have been conducted to elucidate the unique features of this exceptional group of bacteria. Genomic and metabolic plasticity are common among Burkholderia species, as evidenced by their relatively large multi-replicon genomes that are rich in insertion sequences and genomic islands and contain a high proportion of coding regions. Such unique features could explain their adaptability to various habitats and their versatile lifestyles, which are reflected in a multiplicity of species including free-living rhizospheric bacteria, plant endosymbionts, legume nodulators, and plant pathogens. The phytopathogenic Burkholderia group encompasses several pathogens representing threats to important agriculture crops such as rice. Contrarily, plant-beneficial Burkholderia have also been reported, which have symbiotic and growth-promoting roles. In this review, the taxonomy of Burkholderia is discussed emphasizing the recent updates and the contributions of genomic studies to precise taxonomic positioning. Moreover, genomic and functional studies on Burkholderia are reviewed and insights are provided into the mechanisms underlying the virulence and benevolence of phytopathogenic and plant-beneficial Burkholderia, respectively, on the basis of cutting-edge knowledge.

https://www.mdpi.com/1422-0067/20/1/121/pdf

Genomic Features and Insights into the Taxonomy, Virulence, and Benevolence of Plant-Associated Burkholderia Species

Research Status and Prospect of Burkholderia glumae, the Pathogen Causing Bacterial Panicle Blight☆

In rice (Oryza sativa L.), damage from diseases such as brown spot, caused by Bipolaris oryzae, and bacterial seedling rot and bacterial grain rot, caused by Burkholderia glumae, has increased under global warming because the optimal temperature ranges for growth of these pathogens are relatively high (around 30 °C). Therefore, the need for cultivars carrying genes for resistance to these diseases is increasing to ensure sustainable rice production. In contrast to the situation for other important rice diseases such as blast and bacterial blight, no genes for complete resistance to brown spot, bacterial seedling rot or bacterial grain rot have yet been discovered. Thus, rice breeders have to use partial resistance, which is largely influenced by environmental conditions. Recent progress in molecular genetics and improvement of evaluation methods for disease resistance have facilitated detection of quantitative trait loci (QTLs) associated with resistance. In this review, we summarize the results of worldwide screening for cultivars with resistance to brown spot, bacterial seedling rot and bacterial grain rot and we discuss the identification of QTLs conferring resistance to these diseases in order to provide useful information for rice breeding programs.

/pdf/qtls-for-resistance-to-major-rice-diseases-exacerbated-by-3thn8e7s53.pdf

QTLs for Resistance to Major Rice Diseases Exacerbated by Global Warming: Brown Spot, Bacterial Seedling Rot, and Bacterial Grain Rot.

To confirm the causal agent of the disease, infected grains were collected. Two botanic parasitic bacteria were isolated and identified in the laboratory. One had a yellow colony and the other, a creamy white colony. Seedborne fungi Cercospora, Helminthosporium, and Curvularia were also isolated. Variety CR203, which is widely grown in the Red River Delta was artificially inoculated at the heading stage. Only the bacterium with the creamy white colony at 10 to the 8th cfu/ml concentration produced symptoms similar to the disease observed in the field; it was designated as isolate no. 18. The method of Matsuida et al was used to detect Pseudomonas glumae using a CaC204 crystal. Isolate no. 18 was cultured in a potato-peptone-glucose-agar (PPGA) mixed medium and with 0.1% CaCl2 at 38 deg C. The color of the PPGA turned a pale greenish yellow, and the CaC204 crystal on the colony was observed under the microscope. P. glumae was identified as the causal organism

Occurrence of rice grain rot disease in Viet Nam

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Occurrence of rice grain rot disease in Viet Nam