Cultural studies on Ustilaginoidea virens, the incitant of false smut of rice (Oryza sativa)

A study was carried out to find out the favourable culture media for mass multiplication and the effect of carbon sources and duration on chlamydospore germination of Ustilaginoidea virens (Cook.) Tak. Different synthetic and semi synthetic solid, liquid media, substrate media were evaluated for mass multiplication of U. virens. Potato sucrose broth was the best medium for fast mycelia growth (104.80 mg) and sporulation (6.78 × 105 spores/ml), potato dextrose broth also favored mycelial growth, whereas corn meal dextrose broth was not suitable. Out of four solid media tested, maximum colony diameter (68.74 mm) and sporulation (6.86 × 105 spores/ml) was produced by potato sucrose agar followed by potato dextrose agar. Maximum sporulation was produced on substrate media based on barley seeds (5.54 × 105 spores/ml) followed by rice seeds (3.72 × 105 spores/ml) whereas rice husk based media produced minimum sporulation. Higher concentration of sucrose and dextrose at 2 per cent supported maximum germination of spores of U. virens and sucrose was found superior in inducing germination than dextrose. The results of this study help to understand the physiological and biochemical requirements for the growth and development of the pathogen, which could serve as an input in disease management to minimize the effect of false smut disease on rice

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Not AvailableWild relatives of rice (Oryza sativa) are important sources for rice improvement under both biotic and abiotic stress. Sheath blight caused by Rhizoctonia solani [Teleomorph - Thanatephorus cucumeris (Frank) Donk.] is major rice (Oryza sativa L.) disease and cause significant losses up to 69% under favourable environmental conditions worldwide. Four hundred five accessions of Oryza rufipogon were screened to identify resistance against sheath blight during the year 2015.There was not a single accession which showed complete resistance. Out of 405, 22 were found to be moderately resistant which were further evaluated during the years 2016 and 2017. Finally 19 accessions were identified as promising one which showed continuously moderately resistant reaction for three years. Correlation study revealed that the different disease variables such as lesion height, relative lesion height and disease score measured were significantly (P<0.05) correlated. All the genotypes and genotype*experiment interaction had a significant (P < 0.001) effect on all the disease variables. Cluster analysis showed that all the accessions were clustered into 4 groups during the year 2015. These groups showed moderately resistant, moderately susceptible and susceptible reaction. The results of present study showed the promising accessions viz., IRGC80600, IRGC80762, IRGC104404A, CR100036 and CR100436 can be utilized in the sheath blight resistance breeding programme.Not Availabl

A Strain of an Emerging Indian Xanthomonas oryzae pv. oryzae Pathotype Defeats the Rice Bacterial Blight Resistance Gene xa13 Without Inducing a Clade III SWEET Gene and Is Nearly Identical to a Recent Thai Isolate

<p>The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) injects transcription activator-like effectors (TALEs) that bind and activate host “susceptibility” (S) genes important for disease. Clade III SWEET genes are major S genes for bacterial blight. The resistance genes xa5, which reduces TALE activity generally, and xa13, a SWEET11 allele not recognized by the cognate TALE, have been effectively deployed. However, strains that defeat both resistance genes individually were recently reported in India and Thailand. To gain insight into the mechanism(s), we completely sequenced the genome of one such strain from each country and examined the encoded TALEs. Strikingly, the two strains are clones, sharing nearly identical TALE repertoires, including a TALE known to activate SWEET11 strongly enough to be effective even when diminished by xa5. We next investigated SWEET gene induction by the Indian strain. The Indian strain induced no clade III SWEET in plants harboring xa13, indicating a pathogen adaptation that relieves dependence on these genes for susceptibility. The findings open a door to mechanistic understanding of the role SWEET genes play in susceptibility and illustrate the importance of complete genome sequence-based monitoring of Xoo populations in developing varieties with effective disease resistance.</p

Data_Sheet_1_RETRACTED: A Strain of an Emerging Indian Xanthomonas oryzae pv. oryzae Pathotype Defeats the Rice Bacterial Blight Resistance Gene xa13 Without Inducing a Clade III SWEET Gene and Is Nearly Identical to a Recent Thai Isolate.PDF

The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) injects transcription activator-like effectors (TALEs) that bind and activate host “susceptibility” (S) genes important for disease. Clade III SWEET genes are major S genes for bacterial blight. The resistance genes xa5, which reduces TALE activity generally, and xa13, a SWEET11 allele not recognized by the cognate TALE, have been effectively deployed. However, strains that defeat both resistance genes individually were recently reported in India and Thailand. To gain insight into the mechanism(s), we completely sequenced the genome of one such strain from each country and examined the encoded TALEs. Strikingly, the two strains are clones, sharing nearly identical TALE repertoires, including a TALE known to activate SWEET11 strongly enough to be effective even when diminished by xa5. We next investigated SWEET gene induction by the Indian strain. The Indian strain induced no clade III SWEET in plants harboring xa13, indicating a pathogen adaptation that relieves dependence on these genes for susceptibility. The findings open a door to mechanistic understanding of the role SWEET genes play in susceptibility and illustrate the importance of complete genome sequence-based monitoring of Xoo populations in developing varieties with effective disease resistance.</p