Streptomyces-mediated growth enhancement and Bacterial Panicle Blight disease suppression in rice plants under greenhouse conditions.

Streptomyces corchorusii TKR8, Streptomyces corchorusii JAS2 and Streptomyces misionensis TBS5 were previously obtained from rice fields and have been studied as a biocontrol agent against the causal agent of Bacterial Panicle Blight (BPB) disease on rice, Burkholderia glumae, and rice plant growth promoter. This study evaluated the potential of plant growth-promoting Streptomyces (PGPS) to control B. glumae and promote rice plants' growth under greenhouse conditions. PGPS were further characterized based on their phenotypic and biochemical differences. Multilocus sequence analysis (MLSA) by amplifying gyrB, rpoB and trpB using PCR was conducted to identify the PGPS further. The antimicrobial activity of PGPS against B. glumae was investigated using a survival assay and microscopic analysis. Result indicates that JAS2 (61.2 %) utilized the highest number of carbohydrates tested, followed by TKR8 (53.1 %) and TBS5 (40.8 %) as analyzed using API 50 CH. Based on MLSA analysis of the concatenated partial sequences (1520 bp) from three housekeeping genes, the neighbor-joining tree identified JAS2 and TKR8 as S. corchorusii. Meanwhile, TBS5 as S. misionensis. Antimicrobial activity of PGPS against B. glumae has found that the supernatant of Streptomyces reduced the survival viability of B. glumae up to 50.7-70.3 %. SEM images showed that substantial morphological changes happened in cell membranes of B. glumae after the Streptomyces treatment. The highest vigor index of inoculated seedlings was determined when rice seeds were treated with a spore suspension of 1 × 107 spore/mL (for JAS2 and TKR8) and 1 × 106 spore/mL (for TBS5). Under greenhouse conditions, Streptomyces-treated plants showed improvement in rice plants' growth and grain yield and reduced the BPB disease severity. Results suggest that the S. corchorusii TKR8, S. corchorusii JAS2 and S. misionensis TBS5 should be promoted as biocontrol agents against B. glumae and bioformulations for rice crops.

Phylogenetic Analysis and Genetic Diversity of Colletotrichum falcatum Isolates Causing Sugarcane Red Rot Disease in Bangladesh.

Colletotrichum falcatum Went causes red rot disease in sugarcane farming in the tropical and sub-tropical regions. This disease causes significant economic loss to the sugarcane production industry. Successful disease management strategies depend on understanding the evolutionary relationship between pathogens, genetic diversity, and population structure, particularly at the intra-specific level. Forty-one isolates of C. falcatum were collected from different sugarcane farms across Bangladesh for molecular identification, phylogeny and genetic diversity study. The four genes namely, ITS-rDNA, ß-tubulin, Actin and GAPDH sequences were conducted. All the 41 C. falcatum isolates showed a 99-100% similarity index to the conserved gene sequences in the GenBank database. The phylogram of the four genes revealed that C. falcatum isolates of Bangladesh clustered in the same clade and no distinct geographical structuring were evident within the clade. The four gene sequences revealed that C. falcatum isolates from Bangladesh differed from other countries´ isolates because of nucleotides substitution at different loci. The genetic structure of C. falcatum isolates were determined using ISSR marker generated 404 polymorphic loci from 10 selected markers. The percentage of polymorphic loci was 99.01. The genetic variability at species level was slightly higher than at population level. Total mean gene diversity at the species level was 0.1732 whereas at population level it was 0.1521. The cluster analysis divided 41 isolates into four main genetic groups and the principal component analysis was consistent with cluster analysis. To the best of our knowledge, this is the first finding on characterizing C. falcatum isolates infesting sugarcane in Bangladesh. The results of this present study provide important baseline information vis a vis C. falcatum phylogeny analysis and genetic diversity study.

Induction of Systemic Resistance against Bacterial Leaf Streak Disease and Growth Promotion in Rice Plant by Streptomyces shenzhenesis TKSC3 and Streptomyces sp. SS8.

The genus Streptomyces demonstrates enormous promise in promoting plant growth and protecting plants against various pathogens. Single and consortium treatments of two selected Streptomyces strains (Streptomyces shenzhenensis TKSC3 and Streptomyces sp. SS8) were evaluated for their growth-promoting potential on rice, and biocontrol efficiency through induced systemic resistance (ISR) mediation against Xanthomonas oryzae pv. oryzicola (Xoc), the causal agent of rice bacterial leaf streak (BLS) disease. Seed bacterization by Streptomyces strains improved seed germination and vigor, relative to the untreated seed. Under greenhouse conditions, seed bacterization with consortium treatment TKSC3 + SS8 increased seed germination, root length, and dry weight by 20%, 23%, and 33%, respectively. Single and consortium Streptomyces treatments also successfully suppressed Xoc infection. The result was consistent with defense-related enzyme quantification wherein single and consortium Streptomyces treatments increased peroxidase (POX), polyphenol oxidase, phenylalanine ammonia-lyase, and ß,1-3 glucanase (GLU) accumulation compared to untreated plant. Within all Streptomyces treatments, consortium treatment TKSC3 + SS8 showed the highest disease suppression efficiency (81.02%) and the lowest area under the disease progress curve value (95.79), making it the best to control BLS disease. Consortium treatment TKSC3 + SS8 induced the highest POX and GLU enzyme activities at 114.32 µmol/min/mg protein and 260.32 abs/min/mg protein, respectively, with both enzymes responsible for plant cell wall reinforcement and resistant interaction. Our results revealed that in addition to promoting plant growth, these Streptomyces strains also mediated ISR in rice plants, thereby, ensuring protection from BLS disease.

In vitro Antimicrobial Assay of Actinomycetes in Rice AgainstXanthomonas oryzae pv. oryzicola and as Potential Plant Growth Promoter

ABSTRACT The aim of this work was to invitro assay the antimicrobial activity of actinomycetes in rice against Xanthomonas oryzae pv. oryzicola and as potential plant growth promoter. A total of 92 actinomycete strains were isolated from different rice plant components and field locations. Of these, only 21.74% showed antagonistic activity against the Xoc pathogen. Molecular identification via 16s rRNA amplification revealed that 60% of the active antagonistic strains belonged to the genus Streptomyces. Isolates that demonstrated the highest antagonistic activity were also able to produce hydrolytic enzymes and plant growth-promoting hormones. Combination of preliminary screening based on in vitro antagonistic, hydrolytic enzyme and plant growth hormone activity facilitated the best selection of actinomycete candidates as evidenced by strains classification using cluster analysis (Ward's Method). Results from the preliminary screening showed that actinomycetes, especially Streptomycetes, could offer a promising source for both biocontrol and plant growth-promotion agents against BLS disease in rice.