Weeds as Pathogen Hosts and Disease Risk for Crops in the Wake of a Reduced Use of Herbicides: Evidence from Yam (Dioscorea alata) Fields and Colletotrichum Pathogens in the Tropics

Abstract

The transition toward sustainable agriculture requires rethinking cropping systems in the light of less intensive and chemically reliant practices. Weed management is one of the target practices to evolve cropping systems with decreased impact on the environment. While softened management will lead to increased weeds/crops coexistence, it is of importance to assess the relative benefits and drawbacks of new practices. Among the potential drawbacks of weeds/crops coexistence, disease risk may increase if weeds are hosting pathogens. In this study, we assessed the potential of weeds for hosting pathogenic generalist fungi known to translate into disease in crops. We first describe prevalence in fields after harvest and relate prevalence to species characteristics and communities. Then, we directly test the idea that weeds serve as inoculums sources during cropping with a natural experiment. This study highlights variation in host skill among feral weeds for Colletotrichum species, including potential congeneric sub-specialization on different weeds within communities. Last, prevalence within fields was more correlated to focal crop inoculation rates compared to local weed load, but there was a significant correlation effect with prevalence on weeds in the vicinity of fields, suggesting that weeds are mediating disease levels at the local scale, too. Results pointed to the importance of weed host skill in disease risk yet open the door to the potential control of pathogens via targeted weed management.

Dynamics of Pathogenic Fungi in Field Hedges: Vegetation Cover Is Differentially Impacted by Weather

“…Leaf age was differentiated as follows: old leaves are darker green, often demonstrating traces of damage (herbivory or dry necrosis spots) and are located deeper on ramets, while young leaves are light green and fresh/recent and without signs of damage, and they are located at proximal tips of ramets. Back in the lab, leaves were rinsed in short baths of diluted bleach solution, methanol, and decontaminated water, respectively [34]. Then, three leaf areas were cut, near the stem, mid-leaf, and near the drip tip.…”

“…Then, three leaf areas were cut, near the stem, mid-leaf, and near the drip tip. For each of these leaf areas, two pieces were cut for replication, and one piece was placed on a Petri dish with simple agar media and the replication was placed on a Petri dish with S medium [34] to favor growth of Colletotrichum over other fungi; these steps were processed in sterile conditions under a laminar flow cabinet (model LRF 48). Both replicates were nevertheless recorded as either positive (one or two Colletotrichum strains identified) or negative (no Colletotrichum growth in either piece).…”

Genome Editing for Sustainable Agriculture in Africa

“…Besides, weeds could act as pathogen reservoirs, increasing the disease risk to yam plants. It is, therefore, important to develop environment friendly and economically sustainable strategies for weed management in yam plantations ( Dentika et al, 2021 ). The development of gene-edited herbicide-tolerant yam accessions can effectively alleviate the weed challenge while alleviating crop phytotoxicity due to the reduced need for repeated use of chemical herbicides.…”

Competition between Colletotrichum species reduces anthracnose symptom development in Dioscorea alata yams: Potential for biopriming and breeding

“…Indeed, weeds have proven to be an important reservoir for Colletotrichum pathogens, and they contribute to the initiation of local disease (Dentika et al, 2021). Recent findings have emphasized subspecialization of Colletotrichum congenerics on weed communities at the local level, and the potential antagonism between species of the C. gloeosporioides complex and the C. truncatum complex (Dentika et al, 2021). We therefore investigated whether C. truncatum inoculation in yams would confer a protective effect against C. gloeosporioides species and anthracnose disease development.…”

“…Studies have shown that local dispersal often plays a significant role in local disease events (Dentika et al, 2022;Penet et al, 2014), in addition to an important genetic variability even at field level (Frézal et al, 2018), possibly due to inocula from local vegetation. Indeed, weeds have proven to be an important reservoir for Colletotrichum pathogens, and they contribute to the initiation of local disease (Dentika et al, 2021). Recent findings have emphasized subspecialization of Colletotrichum congenerics on weed communities at the local level, and the potential antagonism between species of the C. gloeosporioides complex and the C. truncatum complex (Dentika et al, 2021).…”