Biology subjects

Dodhia, K. N.

Publications and source records attributed to Dodhia, K. N..

5 recordsLinked to original sources

bioRxiv2025

Evidence of a distinct Blumeria graminis f. sp. tritici pathotype structure in Australian wheat powdery mildew: implications for resistance breeding.

The obligate biotrophic fungus Blumeria graminis f. sp. tritici (Bgt) is the causal agent of wheat powdery mildew. To investigate virulence diversity, 30 Australian Bgt isolates collected between 2020 and 2024 were screened against a panel of 24 wheat lines carrying defined resistance (R) genes. Pathotyping analysis indicated that the Australian Bgt population is diverse in its virulence profile. Non-metric multidimensional scaling analysis of disease phenotyping revealed evidence of six distinct Bgt pathotype groups. In addition, we identified wheat varieties carrying defined R genes and their combinations that remain effective against the contemporary Australian Bgt. Notably, wheat cvs Khapli and Tabasco, possessing Pm4a and Pm2, respectively, in addition to unknown R gene(s), were highly resistant to all the isolates tested. Furthermore, elite European varieties that possess durable resistance, such as Alchemy and Cordiale, display complete to moderate resistance against all selected isolates representing the Australian pathotype groups.

microbiology↗

bioRxiv2025

Monitoring fungicide resistance frequencies -- a case study of barley net blotch

Decreased sensitivity to fungicides impacts the effectiveness of fungicide applications for managing plant disease. Knowledge of the frequency of decreased sensitivity in field populations is critical for evaluating risks for disease control. This study has applied a droplet digital PCR detection approach to assess pathogen populations and quantify the frequencies of alleles associated with decreased sensitivity to either demethylation inhibitor or succinate dehydrogenase inhibitor fungicides in Pyrenophora teres causing net blotch on barley in Western Australia. Pyrenophora teres f. maculata was the most frequent form of the pathogen in the sampled region. Frequencies of decreased fungicide sensitivity alleles varied, being as great as 92% for the PtTi insertion in the CYP51A promoter, 88% for C-S75 and 28% for L489-2. Impacts of cultivar selection and weed hosts on the presence and survival of decreased fungicide sensitivity were observed. Determining the dynamics of alleles within different field populations of P. teres provides an important perspective on the impact of fungicides, the fitness associated with decreased fungicide sensitivity alleles and the susceptibility of barley cultivars.

pathology↗

bioRxiv2023

Workflows for detecting fungicide resistance in net form and spot form net blotch pathogens

Fungicide resistance in Pyrenophora teres f. maculata and P. teres f. teres has become an important disease management issue. Control of the associated barley foliar diseases, spot form and net form net blotch, respectively, relies on three major groups of fungicides, demethylation inhibitors (DMI), succinate dehydrogenase inhibitors (SDHI) and quinone outside inhibitors (QoI). However, resistance has been reported for the DMI and SDHI fungicides in Australia. To enhance detection of different resistance levels, phenotyping and genotyping workflows were designed. The phenotyping workflow generated cultures directly from lesions and compared growth on discriminatory doses of tebuconazole (DMI) and fluxapyroxad (SDHI). Genotyping real-time PCR assays were based on alleles associated with sensitivity or resistance to the DMI and SDHI fungicides. These workflows were applied to a net blotch collection from 2019 consisting predominantly of P. teres f. teres from South Australia and P. teres f. maculata from Western Australia. For South Australia the Cyp51A L489-3 and SdhC-R134 alleles, associated with resistance to tebuconazole and fluxapyroxad, respectively, were the most prevalent. These alleles were frequently found in single isolates with dual resistance. This study also reports the first detection of a 134 base pair insertion located at position -66 (PtTi-6) in the Cyp51A promoter of P. teres f. maculata from South Australia. For Western Australia, the PtTi-1 insertion was the most common allele associated with resistance to tebuconazole. These workflows will be valuable for screening P. teres populations for fungicide resistance, and informing appropriate management strategies.

pathology↗

bioRxiv2023

Emergence of resistance to succinate dehydrogenase inhibitor fungicides in Pyrenophora teres f. teres and P. teres f. maculata in Australia

The net blotches are among the most economically significant diseases of barley worldwide. There are two forms of the disease: net-form net-blotch (NFNB, causal agent Pyrenophora teres f. sp. teres [Ptt]) and spot-form net blotch (SFNB, causal agent Pyrenophora teres f. sp. maculata [Ptm]). Alongside varietal choice and cultural practices, fungicides form an important part of the regime for net blotch control. The succinate dehydrogenase inhibitors (SDHIs) are a key class of fungicides used in net blotch management. However, resistance to this group of compounds has emerged in the net blotches in recent years. Here, we describe the first cases of resistance to SDHIs in Australian populations of net blotches. This study was prompted by reports of field failures of SDHI fungicides in controlling NFNB in South Australia and SFNB in Western Australia. Target site mutations in the Sdh complex genes, previously associated with reduced sensitivity in European net blotch populations, were found in Australian isolates, and two mutations which have not been previously observed in P. teres, are also described. The mutations found in Ptt included H134R and S135R in SdhC; and H134Y and D145G in SdhD; the SdhC-H134R mutation was the most frequently observed. In Ptm, the mutations found included H277L in SdhB; S73P, N75S, H134R and S135R in SdhC; and D145G in SdhD; the SdhC-N75S mutation was the most common. These mutations were correlated with reduced in vitro SDHI fungicide sensitivity by microtiter assay. The highest resistance factors to fluxapyroxad and bixafen, the most important SDHI fungicides for net blotch control in Australia, were associated with the SdhC-H134R and SdhC-S135R mutations in Ptt, and with the SdhB-H277L, SdhC-H134R, and SdhC-S135R mutations in Ptm. Modelling of the P. teres Sdh complex showed that the two novel mutations, H277L in SdhB and H134Y in SdhD, result in a highly altered binding mode and lower binding affinity of the SDHI compound compared to the wild-type.

microbiology↗

bioRxiv2020

When time really is money: in situ quantification of the strobilurin resistance mutation G143A in the wheat pathogen Blumeria graminis f. sp. tritici

BackgroundThere has been an inexorable increase in the incidence of fungicide resistance in plant pathogens in recent years. Control of diseases and the management of resistance would be greatly aided by rapid diagnostic methods. Quantitative allele specific PCR (ASqPCR) is an ideal technique for the analysis of fungicide resistance in the field as it can both detect and quantify the frequency of mutations associated with fungicide resistance. We have applied this technique to the fungal pathogen Blumeria graminis f. sp. tritici (Bgt), an obligate biotrophic fungus that causes wheat powdery mildew and is responsible for up to 25% yield loss annually. In Australia, strobilurin resistant Bgt was first discovered in samples from Tasmania and Victoria in 2016. Molecular analysis revealed a nucleotide transversion in the cytochrome bc1 enzyme (cytb) complex, resulting in a substitution of alanine for glycine at position 143 (G143A) in Cytb. ResultsWe have developed an in-field ASqPCR assay that can quantify both the resistant (A143) and sensitive (G143) cytb alleles down to 1.67% in host and Bgt DNA mixtures within 90 min of sample collection. The in situ analysis of field samples collected during a survey in Tasmania revealed A143 frequencies ranging between 9-100%. We validated the analysis with a newly developed laboratory based digital PCR assay and found no significant differences between the two methods. ConclusionWe have successfully developed an in-field quantification method, for a QoI resistant allele, by pairing an ASqPCR assay on a lightweight qPCR instrument with a quick DNA extraction method. The deployment of this type of methodologies in the field can contribute to the effective in-season management of fungicide resistance.

molecular biology↗