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

Over two decades ago, an intercropping strategy was developed that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The push-pull strategy reportedly suppresses lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, border crop (pull). Key in the system is the intercrop's constitutive release of volatile terpenoids that repel herbivores. However, the earlier described volatile terpenoids were not detectable in the headspace of Desmodium, and only minimally upon herbivory. This was independent of soil type, microbiome composition, and whether collections were made in the laboratory or in the field. Furthermore, in oviposition choice tests in a wind tunnel, maize with or without an odor background of Desmodium was equally attractive for the invasive pest Spodoptera frugiperda. In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and no larva survived. In addition, older larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, our data suggest that Desmodium may act through intercepting and decimating dispersing larval offspring rather than adult deterrence. As a hallmark of sustainable pest control, maize-Desmodium push-pull intercropping has inspired countless efforts to emulate 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 to other cropping systems.

Therapeutic Role of Desmodium Species on its Isolated Flavonoids

Secondary metabolites are an important part to play a major role in society and it was isolated from plant flavonoids and useful in the treatment of various kinds of diseases in the human race. They are widely used as food and nutrition supplements as well as antioxidants. Traditionally, the Desmodium species are an important tool for the secondary metabolites to treat various diseases. Desmodium triquetrum (Fabaceae) one of the Indian medicinal plants is widely used in the treatment of asthma and inflammation. Three flavonoids isolated from Desmodium triquetrum Linn namely Baicalein, Naringin and Neohesperidin are useful as antioxidants, food and nutrition supplements, that help the body to function efficiently while protecting it against toxins as well stressors. The role of flavonoids may be due to the presence of the phenolic compound. Similarly, the flavonoids such as gangetin, gangetinin, desmocarpin and desmodin isolated from the species Desmodium gangeticum are responsible for antileishmanial, antioxidant, anti-arthritic, and immunomodulatory activities. Additionally, isolated flavanoids from the species Desmodium triflorum show antibacterial, antiepileptic, antifungal, and radioprotective activities. So, the aim of the present study, based on the literature miming from the desmodium species is to acknowledge the importance of flavonoids in human health as dietary food supplements and therapeutic uses.

Drought-tolerant Desmodium species effectively suppress parasitic striga weed and improve cereal grain yields in western Kenya

The parasitic weed Striga hermonthica Benth. (Orobanchaceae), commonly known as striga, is an increasingly important constraint to cereal production in sub-Saharan Africa (SSA), often resulting in total yield losses in maize (Zea mays L.) and substantial losses in sorghum (Sorghum bicolor (L.) Moench). This is further aggravated by soil degradation and drought conditions that are gradually becoming widespread in SSA. Forage legumes in the genus Desmodium (Fabaceae), mainly D. uncinatum and D. intortum, effectively control striga and improve crop productivity in SSA. However, negative effects of climate change such as drought stress is affecting the functioning of these systems. There is thus a need to identify and characterize new plants possessing the required ecological chemistry to protect crops against the biotic stress of striga under such environmental conditions. 17 accessions comprising 10 species of Desmodium were screened for their drought stress tolerance and ability to suppress striga. Desmodium incanum and D. ramosissimum were selected as the most promising species as they retained their leaves and maintained leaf function for longer periods during their exposure to drought stress conditions. They also had desirable phenotypes with more above ground biomass. The two species suppressed striga infestation, both under controlled and field conditions, and resulted in significant grain yield increases, demonstrating the incremental capability of Desmodium species in striga suppression. These results demonstrate beneficial effects of Desmodium species in enhancing cereal productivity in dry areas.

A nature-based approach for managing the invasive weed species Gutenbergia cordifolia for sustainable rangeland management

BACKGROUND

The invasive weed species Gutenbergia cordifolia has been observed to suppress native plants and to dominate more than half of the entire crater floor (250 km²) in the Ngorongoro Conservation Area (NCA). As this species has been found to be toxic to ruminants it might strongly impact animal populations in this ecologically diverse ecosystem. Hence, a nature-based approach is urgently needed to manage its spread. We tested two Desmodium spp extracts applied to G. cordifolia and assessed the latter's germination rate, height, fresh weight and leaf total chlorophyll content after 30 days in both laboratory and screen house experiments.

RESULTS

Seedling germination rate was halved by Desmodium uncinatum leaf extract (DuL), particularly under higher concentrations (≥75 %) rather than lower concentrations (≤62.5 %). Likewise, in both laboratory and screen house experiments, germination rate under DuL treatments declined with increasing concentrations. Seedling height, fresh weight and leaf total chlorophyll content (Chl) were also most strongly affected by DuL treatments rather than D. uncinatum root extract, Desmodium intortum leaf extract or D. intortum root extract treatments. Generally, seedlings treated with higher DuL concentrations were half as tall, had one-third the weight and half the leaf Chl content compared to those treated with lower concentrations.

CONCLUSION

Our study shows a novel technique that can be applied where G. cordifolia may be driving native flora and fauna to local extinction. Our data further suggest that this innovative approach is both ecologically safe and effective and that D. uncinatum can be sustainably used to manage invasive plants, and thus, to improve rangeland productivity.

in Panxi, Sichuan, China

Thirty-four rhizobial isolates were obtained from root nodules of four wild Desmodium species growing in Panxi, Sichuan, China. According to the combined ARDRA and IGS-RFLP (CACAI) cluster analysis, Rhizobium, Pararhizobium and Mesorhizobium isolates outnumbered Bradyrhizobium isolates. In general, the isolates representing the same species from the same site clustered together. Furthermore, the four Desmodium species were all nodulated by more than one rhizobial species. AFLP and phenotypic analyses showed that the 34 isolates represented at least 32 distinct strains. None of the strains were found from more than one site or host, indicating a high degree of rhizobial diversity in Panxi. In the multilocus sequence analysis, the isolates were assigned to Pararhizobium giardinii, Bradyrhizobium japonicum, Mesorhizobium septentrionale, and to undescribed species of the genera Rhizobium, Bradyrhizobium and Agrobacterium.

The enigmatic fast leaflet rotation in Desmodium motorium: butterfly mimicry for defense?

I propose that the enigmatic leaflet movements in elliptical circles every few minutes of the Indian telegraph (semaphore) plant Desmodium motorium ( = D. gyrans = Hedysarum gyrans = Codariocalyx motorius), which has intrigued scientists for centuries, is a new type of butterfly or general winged arthropod mimicry by this plant. Such leaflet movement may deceive a passing butterfly searching for an un-occupied site suitable to deposit its eggs, that the plant is already occupied. It may also attract insectivorous birds, reptiles or arthropods to the plant because it looks as if it is harboring a potential prey and while they patrol there, they can find insects or other invertebrates that indeed attack the plant. The possibility that diurnal mammalian herbivores may also be deterred by these movements should not be dismissed.