Screening of fluorescent bacteria for growth promotion and biocontrol potential against Pyricularia oryzae on aerobic rice (MARDI Aerob 1)

Aims@#This study aimed to screen the plant growth-promoting fluorescent bacteria (FLB) which isolated from the healthy rice rhizophere and to evaluate its biocontrol and growth promotion properties against Pyricularia oryzae on aerobic rice seedling of MARDI Aerob 1. @*Methodology and results@#King’s B agar with glycerol was used as the selective medium to isolate FLB from the healthy rice rhizosphere soil. All FLB obtained were in vitro screened for antagonistic activities against P. oryzae using dual culture, volatile substances and hydrogen cyanide productions. The potential FLB isolates were further evaluated on rice seedling early growth promotion before identified using 16S rRNA gene sequencing. A total of 24 FLB were isolated from the healthy rice rhizosphere soil in Setiu, Terengganu, Malaysia. Isolates: FLB4, FLB5, FLB7 and FLB10 scored the total of percentage inhibition radial growth (PIRG) values ranged 99.5-105.0%. Further seedling growth promotion screening revealed that FLB4, FLB7 and FLB10 were significantly improved seedling growth with vigor index of 378.32%, 461.53% and 335.60% over control (133.31%). 16S rRNA sequencing identified that FLB7 as Bacillus subtilis and the FLB4 and FLB10 as Pseudomonas putida.@*Conclusion, significance and impact of study@#The selected FLB isolates (FLB4, FLB7 and FLB10) are potential to be developed as biological control agents against P. oryzae with growth promoting property on aerobic rice seedling.

Candidate screening of blast resistance donors for rice breeding

Rice blast is one of the most serious diseases in the world. The use of resistant cultivars is the most preferred means to control this disease. Resistance often breaks down due to emergence of new races; hence identification of novel resistance donors is indispensable. In this study, a panel of 80 released varieties from National Rice Research Institute, Cuttack was genotyped with 36 molecular markers that were linked to 36 different blast resistance genes, to investigate the varietal genetic diversity and molecular marker-trait association with blast resistance. The polymorphism information content of 36 loci varied from 0.11 to 0.37 with an average of 0.34. The cluster analysis and population structure categorized the 80 National Rice Research Institute released varieties (NRVs) into three major genetic groups. The principal co-ordinate analysis displays the distribution of resistant and moderately resistant NRVs into different groups. Analysis of molecular variance result demonstrated maximum (97%) diversity within populations and minimum (3%) diversity between populations. Among tested markers, two markers (RM7364 and pi21_79-3) corresponding tothe blast resistance genes (Pi56(t) and pi21) were significantly associated and explained a phenotypic variance of 4.9 to 5.1% with the blast resistance. These associated genes could be introgressed through marker-assisted to develop durable blast resistant rice varieties. The selected resistant NRVs could be good donors for the blast resistance in rice crop improvement research.

Pyramiding of 3-resistant-gene to improve rice blast resistance of a restorer line, Fuhui 673 / 生物工程学报

To improve the blast resistance of elite rice restorer line Fuhui 673, 3 blast resistance genes Pi-1, Pi-9 and Pi-kh were introduced into Fuhui 673 from a good-quality restorer line Jinhui 1059 through 3 successive backcrosses followed by one selfing using the technique of marker-assisted selection. Ten near-isogenic lines (NILs) of Fuhui 673 carrying the 3 introduced resistance genes were created. Genotype analysis using 68 SSR markers evenly distributed in the genome indicated that 92.96%-98.59% of the NILs' genetic background had been recovered to Fuhui 673. Both indoor and field resistance tests indicated that the NILs and their hybrids with sterile line Yixiang A were all resistant to rice blast, with resistance levels significantly higher than those of controls Fuhui 673 and hybrid Yiyou 673 (Yixiang A  Fuhui 673). In addition, among the 10 hybrids between the NILs and Yixiang A, 2 showed significantly higher yield than and 4 displayed similar yield to that of control Yiyou 673, suggesting that most of the NILs retained the elite characteristics of Fuhui 673. Two new hybrid rice cultivars Liangyou 7283 and Jintaiyou 683 from NIL Line 9 showed high yield, good resistance to blast and moderate growth period in regional trial, suggesting that the NIL Line 9 has a good prospect for application.

Integrated Control against Rice Blast and Leaf Spot by Trichoderma harzianum and Two Fungicides

Integrated pest management is performed at intervals of 10 days, during all the season of rice cultivation, by the application of Trichoderma harzianum at a concentration of 108 spores/ml, in alternation with the mancozeb at 1000 ppm against rice blast and rice leaf spot and the pyrazophos at 750 ppm against blast. The assessment of symptoms is performed at the beginning of the panicles appearance, by estimating the incidence of the disease and the symptoms severity. Thus, at the end of treatment programs, the alternation of pyrazophos and T. harzianum reduced blast at a rate similar to that noted when pyrazophos is used alone (i.e. respectively 90.5 and 89.1%). This percentage is better than that recorded following treatment by T. harzianum alone (78.4%). Mancozeb alternated with T. harzianum reduced blast at a rate of (83.49%) compared with the fungicide or the antagonist alone (77 and 78.4%). The application of mancozeb alone reduced the leaf spot at a rate similar to that noted following its alternation with T. harzianum (79.2 and 75.64%) and better than that obtained after treatment with T. harzianum alone (69.5%).

The pathogen and control management of rice blast disease

Abstracts@#Outbreak of rice blast disease is a serious problem in all rice growing regions worldwide and is a threat to rice production. In Malaysia, the outbreak of rice blast is a recurrent problem where rice plant remain vulnerable to the disease. Nowadays, the generic name of rice blast pathogen is Pyricularia oryzae and Magnaporthe oryzae is the synonym. Rice pathogen infects mainly aerial parts of rice plant causing rotting and blast on the leaves, stems, peduncles, panicles and seeds leading to crop failure. Rice blast pathogen population is regarded as highly variable and consisted of multiple pathotypes which contribute to genetic diversity as well virulence diversity of the pathogen. The pathotypes can only be determined through pathogenicity test using a set of differential rice cultivars which generally differ by one or more resistance genes. Knowledge on the rice blast virulence and host resistant is important to manage the disease. Among the control methods, utilizing resistant cultivars is considered as the most effective approach to manage rice blast disease. Therefore, development of blast resistant cultivar becomes a priority.

Genomic Insights into the Rice Blast Fungus through Estimation of Gene Emergence Time in Phylogenetic Context

The rice blast fungus, Magnaporthe oryzae, is an important pathogen of rice plants. It is well known that genes encoded in the genome have different evolutionary histories that are related to their functions. Phylostratigraphy is a method that correlates the evolutionary origin of genes with evolutionary transitions. Here we applied phylostratigraphy to partition total gene content of M. oryzae into distinct classes (phylostrata), which we designated PS1 to PS7, based on estimation of their emergence time. Genes in individual phylostrata did not show significant biases in their global distribution among seven chromosomes, but at the local level, clustering of genes belonging to the same phylostratum was observed. Our phylostrata-wide analysis of genes revealed that genes in the same phylostratum tend to be similar in many physical and functional characteristics such as gene length and structure, GC contents, codon adaptation index, and level of transcription, which correlates with biological functions in evolutionary context. We also found that a significant proportion of genes in the genome are orphans, for which no orthologs can be detected in the database. Among them, we narrowed down to seven orphan genes having transcriptional and translational evidences, and showed that one of them is implicated in asexual reproduction and virulence, suggesting ongoing evolution in this fungus through lineage-specific genes. Our results provide genomic basis for linking functions of pathogenicity factors and gene emergence time.

Multifunctional cellulolytic activities from Streptomyces osmaniensis for agricultural and enzyme industry

Aims: The aims of this study were to screen for cellulose degradation activity from actinomycetes using agar plate method, detect β-glucosidase activity, morphology and molecular taxonomy study. Methodology and results: Preliminary screening for cellulose degrading Actinomycete was done on the carboxymethyl cellulose agar (CMC agar) and detected by flooding with gram iodine. It was found that 190 isolates were cellulase producing actinomycetes. Actinomycete isolate CDF2L1D13 showed maximum clear zone around the colony and the highest hydrolysis capacity value was 3.93. β-glucosidase activity was examined by measuring the amount of paranitrophenol (pNP) librated by Tako method. Study on comparison of the enzyme activity in CMC broth with alternative broth was performed. The highest β-glucosidase activity was found on alternative production medium that supplemented rice bran as a carbon source. β-glucosidase activity was 0.401 U/mL. The optimum pH of alternative production medium for producing β-glucosidase was at pH value 7 and incubated at 30 °C. Isolate CDF2L1D13 was antagonistic actinomycete against rice blast pathogen (Pyricularia oryzae). The character of this isolate was showed white color of substrate mycelium, white color of aerial mycelium, gray spore and spiral spore chain. Actinomycete isolate CDF2L1D13 was phylogenetically similar to Streptomyces osmaniensis. Conclusion, significance and impact of study: The result from this study indicated that Streptomyces osmaniensis has the potential on β-glucosidase production and it is antagonistic actinomycete against Pyricularia oryzae.