Biology subjects

Ermel, M.

Publications and source records attributed to Ermel, M..

5 recordsLinked to original sources

bioRxiv2022

Identifying fungal leaf spots on oilseed rape: could pictures help?

From sowing in late summer until harvest in following summer, oilseed rape can be infected by several fungi, which foliar symptoms (leaf spots) coexist on the crop. Training an expert at their identification is quick for the typical symptoms with characteristic appearance. However, in many cases the size, colour and morphology are similar and for the atypical symptoms, there is a risk of confusion or in-decidability. Also, scouting the fields for expert training is not possible at all seasons and all diseases might not be seen in all years and all places. The aim of our study was to produce large sets of pictures annotated by several experts, from which tables illustrating the diversity of symptom appearance were chosen. These tables will enable assistance to diagnostic and expert training.

ecology↗

bioRxiv2020

Influence of the culture media on the aspect and growth of oilseed rape fungal pathogens

While culturing fungal pathogens on artificial media, the phenotype, i.e. colony aspect, growth kinetics and in some case the pigment production can be used as discrimination criteria. Our aim was to enable the comparison between the growth kinetics of 8 fungal species, cultured simultaneously on 3 different media, and imaged under standardised conditions. Using a camera stand, taking pictures was quick and easy, producing homogeneous pictures, facilitating their comparison. The colony growth kinetics varied widely across the 8 species. The mycelium aspect and pigment production depended on the media and changed over time. Having standardised the imaging setup and grown species simultaneously allows proposing reference sets of pictures.

microbiology↗

bioRxiv2020

A Leptosphaeria maculans set of isolates characterised on all available differentials and used as control to identify virulence frequencies in a current French population

The characterization of virulence frequencies has to be regularly updated to identify which genes are currently efficient and use this information to advise gene deployment by choosing varieties depending on the current composition of local pathogen population. In L. maculans on Brassica napus, because different genes were characterized by different teams, because new interactions are continuously identified and seed of differentials are difficult to obtain, we today still lack isolates characterized on all current resistance genes. On the one hand, we assembled a set of 12 isolates characterized on 13 of the 17 described resistance genes, having clearly compatible and clearly incompatible isolates for each interaction. This set can be used to characterize the L. maculans - B. napus interaction at cotyledon stage. Expanding the set of isolates with clearly virulent ones allowed us to detect inconsistent behaviour or intermediate (avirulent) phenotypes. On the other hand, we used this set of isolates as controls to identify virulence frequencies in a current French L. maculans population sampled in 2018 at Le Rheu. We provide the current status for 13 avirulence frequencies, including LepR1, LepR2 and LepR3 available in near isogenic lines of spring canola but not yet documented in France. Avirulence frequencies on the genes Rlm1, Rlm2, Rlm3, Rlm4, Rlm7, Rlm9 and LepR3 were low, indicating the lack of efficacy of these genes against the current population. In the opposite, all or most of isolates were avirulent for the genes Rlm5, Rlm6, Rlm10, Rlm11, LepR1 and LepR2. An optimistic point of view could conclude that there are ample resources for oilseed rape breeding. However, as compared to previous studies, so far all the resistance genes used on significant acreage without additional management practices have lost efficacy and only avirulences corresponding to resistance genes not deployed in France retain efficacy. While the call to wisely manage the available host resistance genes is not recent, it is still relevant. Adding, management practices to the deployment of resistance genes in order to reduce inoculum carry-over from one growing season to the next and to lower population sizes is key to maintain their efficacy over time.

pathology↗

bioRxiv2018

Fungal growth is affected by and affects pH and redox potential (Eh) of the growth medium

Fungal plant pathogens live in the specific environment of plants. Understanding of the interaction between pathogens and their host plants might open new ways to control plant diseases. Yet, the specificities of the plant environment and its effects on fungal growth are not yet fully explored. Both pH and Eh play a key role during the interaction between the fungus and its host plants, but often studied independently or at different scales. To decipher the interrelation between plant growth and their soil environment, recent theoretical and methodological advances have been made through the joint characterization of the pH and Eh. This opens the prospect to develop similar methods for fungi. The aim of our study was to investigate whether the methods developed for soil could be transposed to fungi. We first worked on artificial media, assessing the impact of fungal growth on the media in cultures. The growth of all 16 species tested significantly altered either Eh, pH or both in agar media. Measuring Eh reveals that even the species not modifying pH can have an impact on the surrounding environment. Reciprocally, altered media were used to characterize sensitivity of fungal growth to both pH and Eh parameters. The response of the six fungi tested to the modified media was quantitative with a decrease in colony diameter. In addition, colony aspect was repeatedly and thoroughly modified. As a first step towards the same studies in conditions matching the natural environment of fungal pathogens, we tested how the measurement can be performed with fungi growing on oilseed rape plants. In infected plant stems, pH and Eh were significantly altered, in opposite directions for L. maculans and S. sclerotiorum. The observed alcalinisation or acidification correlates with canker length. Our series of experiments indicate that the procedure published for Eh and pH in soil can be extended for measurement in agar media and in infected plants. Further, the joint characterization of both parameters opens the way to a more precise understanding of the impact of fungi on their environment, and conversely, of the environment on fungal growth. The availability of methods for measurement opens the prospect to study combinations of stresses, either on agar media or in plants, and get an understanding of the involvement of pH and Eh modifications in these interactions.

microbiology↗

bioRxiv2018

Careful deployment of oilseed rape crops with Rlm6 resistance gene against L. maculans is recommended to prevent the loss of efficacy of this resistance gene in French condiment mustard.

Breeding varieties for increased disease resistance is a major means to control epidemics. However, the deployment of resistance genes through space and time drives the genetic composition of the pathogen population, with predictable changes in pathotype frequencies. In France, Leptosphaeria maculans causes disease on Brassica napus oilseed rape crops but not on B. juncea condiment mustard. Prior to the deployment of winter B. napus varieties with Rlm6 resistance gene introduced from B. juncea, the aim of our study was to investigate if this deployment could impact disease control in condiment mustard. We assessed the presence of resistance genes against phoma stem canker in a set of current French B. juncea varieties and breeding lines. Rlm6 was detected in all the 12 condiment mustard varieties. Rlm5 was also detected in 8 varieties. No additional resistance genes were detected with the set of isolates used. Because frequency of isolates virulent on Rlm6 is very low, these results indicate that Rlm6 gene is a major component of disease control in the French B. juncea mustards tested. Using Rlm6 in oilseed rape varieties will very likely induce an increase in frequency of Rlm6 virulent isolates. This raises the acute concern of a wise deployment of oilseed rape around the condiment mustard growing area. Scientific knowledge on adaptation dynamics, spatial segregation of crops and cooperation between actors is currently available in order to mitigate the risk and advert negative consequences of the introduction of Rlm6 resistance gene in oilseed rape varieties.

epidemiology↗