David, A. B. | Search bioRxiv

bioRxiv2023

A comparative study on the impact of five Desmodium species on soil microbiome reveals enrichment of selected bacterial and fungal taxa

IntroductionSeveral Desmodium spp. are used as intercrops in push-pull pest management systems to repel insect herbivores. In addition, Desmodium suppresses the parasitic weed Striga, and diversifies the soil microbiome with negative impacts on fungi. We investigated the impact of a 2-year cropping of five Desmodium species on soil microbiome populations. MethodologyTotal DNA was obtained from root zone soil samples collected from a two-years-old common garden experiment with replicated plots of five Desmodium spp. at the international centre for insect physiology and ecology (ICIPE), Mbita, Kenya. Subsequently, 16S and ITS DNA sequencing were performed and the data was analysed by using QIIME2 and Calypso. ResultsOur findings show significant differences in composition and abundance of specific microbial taxa among the Desmodium plots and the bulk soil, with a stronger shift observed for fungal community profiles than bacteria. There was, however, no significant difference in overall diversity, richness and evenness of microbial communities among the Desmodium plots and the bulk soil. Similarly, beta diversity analysis did not reveal a significant association of variation to specific Desmodium spp. plots. Discussion and conclusionThis is the first study to compare impact and association of whole soil microbiomes to different Desmodium species. Whereas long-term Desmodium cropping clearly shifts whole microbiome communities, no significant difference in overall diversity and richness of microbial populations was observed among the studied plots. However, there was a divergence of individual taxa reflected on their increased abundance in association to specific Desmodium spp., pointing towards potential impact on ecosystem services. These findings indicate that significant shifts in whole microbial populations due to Desmodium spp. and thus potentially provision of associated ecosystem services require longer cultivation periods to solidify. Future studies should focus on techniques that monitor real-time changes in microbial populations such as RNA-seq to ascertain live and dead microbes, and thus infer ecological services.

ecology↗

bioRxiv2022

The push-pull intercrop Desmodium does not repel, but intercepts and kills pests

Over two decades ago, scientists developed a push-pull intercropping strategy that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The strategy suppresses Lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, dead-end border crop (pull). Key is the intercrops constitutive release of volatiles that repel herbivores. Surprisingly, however, we found that Desmodium does not constitutively release volatiles, and only minimally upon herbivory. Further, in oviposition choice settings, Spodoptera frugiperda, a devastating invasive pest, was not repelled by Desmodium volatiles. In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and none survived. In addition, larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, entirely different from repelling adult moths, Desmodium intercepts and decimates dispersing offspring. As a hallmark of sustainable pest control, maize-Desmodium intercropping has inspired countless efforts trying to emulate a stimulo-deterrent diversion in other cropping systems. However, detailed knowledge of the actual mechanisms is required to rationally improve the strategy, and translate the concept into other cropping systems.

ecology↗