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Although lupin anthracnose caused by Colletotrichum lupini is a significant threat for spring and winter lupin crops, it has been poorly studied so far. This study aimed at characterizing the (i) phylogenetic, (ii) morphological, and (iii) physiological diversity of collected isolates from anthracnose-affected lupins. The genetic identification of representative isolates (n = 71) revealed that they were all C. lupini species, further confirming that lupin anthracnose is caused by this species. However, multilocus sequencing on these isolates and 16 additional reference strains of C. lupini revealed a separation into two distinct genetic groups, both of them characterized by a very low genetic diversity. The diversity of morphological characteristics of a selected subset of C. lupini isolates was further evaluated. To the best of our knowledge, microsclerotia production observed for some isolates has never been reported so far within the Colletotrichum acutatum species complex. Finally, the modeling of growth responses of a subset of C. lupini strains revealed the capacity of some strains to grow in vitro at 5°C. This ability was also evidenced in planta, because C. lupini DNA was detectable in plants from 14 days postinoculation at 5°C onward, whereas symptoms began to appear a week later, although at a very low level. Since lupin crops are planted during winter or early spring, growth studies in vitro and in planta demonstrated the capability of the species to grow at temperatures ranging from 5 to 30°C, with an optimum close to 25°C. In this study, C. lupini-specific primers were also designed for real-time quantitative PCR on fungal DNA and allowed the detection of C. lupini in asymptomatic field samples. These results open perspectives to detect earlier and limit the development of this pathogen in lupin crops.

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Lupin anthracnose is a major threat caused by the filamentous fungus Colletotrichum lupini. The genus Colletotrichum includes a wide number of phytopathogen species distributed worldwide. They were classified into 14 species complexes, with C. lupini belonging to the C. acutatum species complex. To date, studies performed on C. lupini, aimed at better understanding its phylogenetic classification and infectious lifecycle. But additional studies seemed necessary to increase our knowledge on (i) intraspecific diversity within the C. lupini species and (ii) the molecular determinants of pathogenicity. To address the first objective, a study was performed on strains from official collections and from isolates recently collected in the west of France. A low intra-specific phylogenetic diversity was found compared to the phenotypic diversity, notably characterized by contrasted aggressiveness between strains. The second objective was evaluated by determining fungal gene expression and protein synthesis during lupin infection by C. lupini using, respectively, a RNAseq-based transcriptomic approach and a mass spectrometry-based proteomic approach with a nLC Q-exactive Orbitrap. Taken together, our results highlighted that the dynamics of symptoms, gene expression and protein synthesis shared similarities to those of hemibiotrophic pathogens. In addition, few genes of unknwown or poorly-described functions were found to be specifically associated to the early or late stages of infection, suggesting that they may be of importance for pathogenicity. Functional validation will be discussed to confirm their role in promoting C. lupini pathogenicity.