Natural Flora Is Indiscriminately Hosting High Loads of Generalist Fungal Pathogen Colletotrichum gloeosporioides Complex over Forest Niches, Vegetation Strata and Elevation Gradient

Abstract

Crop pathogenic fungi may originate from reservoir pools including wild vegetation surrounding fields, and it is thus important to characterize any potential source of pathogens. We therefore investigated natural vegetation’s potential for hosting a widespread pathogenic group, Colletotrichum gloeosporioides species complex. We stratified sampling in different forest environments and natural vegetation strata to determine whether the fungi were found preferentially in specific niches and areas. We found that the fungi complex was fairly broadly distributed in the wild flora, with high prevalence in every study environment and stratum. Some significant variation in prevalence nevertheless occurred and was possibly associated with fungal growth conditions (more humid areas had greater prevalence levels while drier places had slightly lower presence). Results also highlighted potential differences in disease effects of strains between strata components of study flora, suggesting that while natural vegetation is a highly probable source of inoculums for local crops nearby, differences in aggressiveness between vegetation strata might also lead to differential impact on cultivated crops.

High Genetic Diversity and Structure of Colletotrichum gloeosporioides s.l. in the Archipelago of Lesser Antilles

“…Most importantly, a low level of clonality between strains is indicative of a high prevalence of sexuality and recombination compared to asexual multiplication, despite a high capacity for multiplication via conidia from necroses. The observation would occur if broad strain reservoirs accumulating fungi diversity and local contamination dynamics co-occur, which seems to be the case with Colletotrichum as prevalence in natural flora was shown to be particularly high [ 5 ]. This pattern of diversity is at odds with most fungal diseases, where pathogenic strains are often genetically homogenous and spread regionally on susceptible cultivars.…”

“…Our results nevertheless suggest that none of morpho-species and sequencing approaches [ 56 ] would be fair enough to delimit real species entities, and will be either too liberal (morpho-species line) or possibly too conservative (sequencing/barcoding) in assessing the real diversity of Colletotrichum species (and therefore, overestimate diversity in the Genus). Our team usually favours a morpho-species approach to understand the ecology of C. gloeosporioides species complex (e.g., [ 5 , 6 , 36 ]), and we thus call for more flexibility and inclusion of a diversity of stances and viewpoints regarding the complex issue of Colletotrichum genus worldwide. Evaluating the frequency of recombination events both within species complexes and between species complexes is a promising avenue of research in our quest to understand the biology of these important crop pests.…”

“…Colletotrichum is a widespread pathogen of cultivated plants [ 1 ], causing anthracnose disease or fruit rot or stem dieback on many crops worldwide [ 2 , 3 , 4 ]. Its ubiquity in both wild [ 5 ] and cultivated environments [ 6 ] is probably increased by its relatively complex ecology, with lifestyles ranging from casual commensal endophyte [ 7 ] to parasitic pathogen, biotrophic to necrotrophic phases [ 8 ] and organizing as multiple species complexes [ 9 ] with blurring degrees of gene flow and varying levels of host ranges and agressivity on their incipient hosts [ 10 , 11 , 12 ]. It has long been regarded through the lens of pathogen–host interaction pairs, with a transient historical redefinition as morpho-species complexes (formally changing recognized species from the thousands down to twelve clearly identified morphs [ 13 ]).…”

“…This might eventually also affect global disease prevalence, as suggested for example by producers strategical shift from more sensitive species and varieties to less susceptible ones [ 33 ] or adoption of varietal admixtures as more resilient [ 34 ]. In traditional agricultural landscapes dominated by the mosaic of fields with very different, diverse and patchy feral and neighbouring [ 6 , 35 ] or even wild floras [ 5 ], the nature of pathogen intra-species diversity itself is thus expected to be dramatically high for generalists such as Colletotrichum .…”