Biology subjects

Adhikari, T. B.

Publications and source records attributed to Adhikari, T. B..

2 recordsLinked to original sources

bioRxiv2025

Real-Time Quantitative PCR Method for Assessing Wheat Cultivars for Resistance to Zymoseptoria tritici

Septoria tritici blotch, caused by Zymoseptoria tritici (formerly Mycosphaerella graminicola), is an economically significant disease of wheat (Triticum aestivum) worldwide. However, there is little understanding of the fungus growth dynamics during the 14- to 18-day latent period between penetration and symptom expression, making it challenging to develop wheat cultivars resistant to Z. tritici Furthermore, environmental factors and variations in disease-scoring systems among evaluators add to the complexity. To address these issues and quantify the fungus growth during the initial stages of infection, we developed a real-time quantitative polymerase chain reaction (real-time PCR) method to monitor the T. aestivum - Z. tritici pathosystem. The assay used specific primers designed from {beta}-tubulin gene sequences of Z. tritici to quantify fungal DNA in susceptible and resistant wheat cultivars and segregating recombinant-inbred lines (RILs) that were inoculated at seedling and adult-plant stages with low or high concentrations of inoculum. The real-time PCR method was compared with visual disease assessment for 0 to 27 days after inoculation (DAI). The results showed that fungal DNA increased more quickly in two susceptible cultivars than in resistant cultivars with the Stb4 or Stb8 genes for resistance. In the susceptible cultivars, the amount of fungal DNA remained low until symptoms became visible at around 18 DAI. Disease severity and fungal DNA in the two resistant cultivars were less than in either susceptible cultivar, starting at 12 DAI. The differences in fungal DNA between resistant and susceptible cultivars were more significant in adult plant tests that used a higher concentration of inoculum. The data analyses showed that the fungus was not eliminated during resistant interactions but could persist throughout the 27 days. Our results suggest that the real-time PCR method can distinguish between resistant and susceptible cultivars starting at 12 DAI and can be used to evaluate early-stage breeding materials for both quantitative and qualitative resistance to Z. tritici.

plant biology↗

bioRxiv2024

Intercontinental dissemination and diversification of Xanthomonas perforans in tomato production

Emerging and re-emerging plant diseases continue to present multifarious threats to global food security. Considerable recent efforts are therefore being channeled towards understanding the nature of pathogen emergence, their spread and evolution. Xanthomonas euvesicatoria pv. perforans (Xep), one of the causal agents of bacterial spot of tomato, rapidly emerged and displaced other bacterial spot xanthomonads in tomato production regions around the world. In less than three decades, it has become a dominant xanthomonad pathogen in tomato production systems across the world and presents a model for understanding diversification of recently emerged bacterial plant pathogens. Although Xep has been continuously monitored in Florida since its discovery, the global population structure and evolution at the genome-scale is yet to be fully explored. The objectives of this work were to determine genetic diversity globally to ascertain if different tomato production regions contain genetically distinct Xep populations, to examine genetic relatedness of strains collected in tomato seed production areas in East Asia and other production regions, and to evaluate variation in type III effectors, which are critical pathogenicity and virulence factors, in relationship to population structure. We used genome data from 270 strains from 13 countries for phylogenetic analysis and characterization of Xop effector gene diversity among strains. Our results showed notable genetic diversity in the pathogen. We found genetically similar strains in distant tomato production regions, including seed production regions, and diversification over the past 100 years, which is consistent with intercontinental dissemination of the pathogen in hybrid tomato production chains. Evolution of the Xep pangenome, including the acquisition and loss of type III secreted effectors, is apparent within and among phylogenetic lineages. The apparent long-distance movement of the pathogen, together with variants that may not yet be widely distributed, poses risks of emergence of new variants in tomato production.

microbiology↗