162 research outputs found
Push-Pull: Chemical ecology-based integrated pest management technology
Lepidopterous stemborers, and parasitic striga weeds belonging to the family Orobanchaceae, attack cereal crops in sub-Saharan Africa causing severe yield losses. The smallholder farmers are resource constrained and unable to afford expensive chemicals for crop protection. The pushâpull technology, a chemical ecology- based cropping system, is developed for integrated pest and weed management in cerealâlivestock farming systems. Appropriate plants were selected that naturally emit signaling chemicals (semiochemicals). Plants highly attractive for stemborer egg laying were selected and employed as trap crops (pull), to draw pests away from the main crop. Plants that repelled stemborer females were selected as intercrops (push). The stemborers are attracted to the trap plant, and are repelled from the main cereal crop using a repellent intercrop (push). Root exudates of leguminous repellent intercrops also effectively control the parasitic striga weed through an allelopathic mechanism. Their root exudates contain flavonoid compounds some of which stimulate germination of Striga hermonthica seeds, such as Uncinanone B, and others that dramatically inhibit their attachment to host roots, such as Uncinanone C and a number of di-C-glycosylflavones (di-CGFs), resulting in suicidal germination. The intercrop also improves soil fertility through nitrogen fixation, natural mulching, improved biomass, and control of erosion. Both companion plants provide high value animal fodder, facilitating milk production and diversifying farmersâ income sources. The technology is appropriate to smallholder mixed cropping systems in Africa. Adopted by about 125,000 farmers to date in eastern Africa, it effectively addresses major production constraints, significantly increases maize yields, and is economical as it is based on locally available plants, not expensive external inputs
Charles A. O\u27Connor, Jr. To Receive Honorary Degree of Doctor of Education, July 31, 1964
PG5-4_PressRelease_19640731_00
An indirect defence trait mediated through egg-induced maize volatiles from neighbouring plants
Attack of plants by herbivorous arthropods may result in considerable changes to the plantâs
chemical phenotype with respect to emission of herbivore-induced plant volatiles (HIPVs).
These HIPVs have been shown to act as repellents to the attacking insects as well as
attractants for the insects antagonistic to these herbivores. Plants can also respond to HIPV
signals from other plants that warn them of impending attack. Recent investigations have
shown that certain maize varieties are able to emit volatiles following stemborer egg deposition.
These volatiles attract the herbivoreâs parasitoids and directly deter further oviposition.
However, it was not known whether these oviposition-induced maize (Zea mays, L.) volatiles
can mediate chemical phenotypic changes in neighbouring unattacked maize plants.
Therefore, this study sought to investigate the effect of oviposition-induced maize volatiles
on intact neighbouring maize plants in âNyamulaâ, a landrace known to respond to oviposition,
and a standard commercial hybrid, HB515, that did not. Headspace volatile samples
were collected from maize plants exposed to Chilo partellus (Swinhoe) (Lepidoptera: Crambidae)
egg deposition and unoviposited neighbouring plants as well as from control plants
kept away from the volatile emitting ones. Behavioural bioassays were carried out in a fourarm
olfactometer using egg (Trichogramma bournieri Pintureau & Babault (Hymenoptera:
Trichogrammatidae)) and larval (Cotesia sesamiae Cameron (Hymenoptera: Braconidae))
parasitoids. Coupled Gas Chromatography-Mass Spectrometry (GC-MS) was used for volatile
analysis. For the âNyamulaâ landrace, GC-MS analysis revealed HIPV production not
only in the oviposited plants but also in neighbouring plants not exposed to insect eggs.
Higher amounts of EAG-active biogenic volatiles such as (E)-4,8-dimethyl-1,3,7-nonatriene
were emitted from these plants compared to control plants. Subsequent behavioural assays
with female T. bournieri and C. sesamiae parasitic wasps indicated that these parasitoids
preferred volatiles from oviposited and neighbouring landrace plants compared to those
from the control plants. This effect was absent in the standard commercial hybrid we tested.
There was no HIPV induction and no difference in parasitoid attraction in neighbouring and
control hybrid maize plants. These results show plant-plant signalling: âNyamulaâ maize plants emitting oviposition-induced volatiles attractive to the herbivoreâs natural enemies
can induce this indirect defence trait in conspecific neighbouring undamaged maize plants.
Maize plants growing in a field may thus benefit from this indirect defence through airborne
signalling which may enhance the fitness of the volatile-emitting plant by increasing predation
pressure on herbivores
Genetic variation and host-parasite specificity of Striga resistance and tolerance in rice: the need for predictive breeding
The parasitic weeds Striga asiatica and Striga hermonthica cause devastating yield losses to upland rice in Africa. Little is known about genetic variation in host resistance and tolerance across rice genotypes, in relation to virulence differences across Striga species and ecotypes. Diverse rice genotypes were phenotyped for the above traits in S. asiatica- (Tanzania) and S. hermonthica-infested fields (Kenya and Uganda) and under controlled conditions. New rice genotypes with either ecotype-specific or broad-spectrum resistance were identified. Resistance identified in the field was confirmed under controlled conditions, providing evidence that resistance was largely genetically determined. Striga-resistant genotypes contributed to yield security under Striga-infested conditions, although grain yield was also determined by the genotype-specific yield potential and tolerance. Tolerance, the physiological mechanism mitigating Striga effects on host growth and physiology, was unrelated to resistance, implying that any combination of high, medium or low levels of these traits can be found across rice genotypes. Striga virulence varies across species and ecotypes. The extent of Striga-induced host damage results from the interaction between parasite virulence and genetically determined levels of host-plant resistance and tolerance. These novel findings support the need for predictive breeding strategies based on knowledge of host resistance and parasite virulence
Responses of parasitoids to volatiles induced by Chilo partellus oviposition on teosinte, a wild ancestor of maize
Maize, a genetically diverse crop, is the domesticated
descendent of its wild ancestor, teosinte. Recently, we
have shown that certain maize landraces possess a valuable
indirect defense trait not present in commercial hybrids. Plants of these landraces release herbivore-induced plant volatiles (HIPVs) that attract both egg [Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)and larval [Cotesia sesamiae Cameron (Hymenoptera:Braconidae)] parasitoids in response to stemborer egg deposition.
In this study, we tested whether this trait also exists in the germplasm of wild Zea species. Headspace samples were collected from plants exposed to egg deposition by Chilo
partellus Swinhoe (Lepidoptera: Crambidae) moths and unexposed control plants. Four-arm olfactometer bioassays with parasitic wasps, T. bournieri and C. sesamiae, indicated that both egg and larval parasitoids preferred HIPVs from plants with eggs in four of the five teosinte species sampled.
Headspace samples from oviposited plants released higher
amounts of EAG-active compounds such as (E)-4,8-dimethyl-
1,3,7-nonatriene. In oviposition choice bioassays, plants
without eggs were significantly preferred for subsequent oviposition by moths compared to plants with prior oviposition.
These results suggest that this induced indirect defence trait is not limited to landraces but occurs in wild Zea species and appears to be an ancestral trait. Hence, these species possess a valuable trait that could be introgressed into domesticated maize lines to provide indirect defense mechanisms against stemborers
Removing constraints to sustainable food production: new ways to exploit secondary metabolism from companion planting and GM
The entire process of agricultural and horticultural food production is unsustainable as practiced by current highly intensive industrial systems. Energy consumption is particularly intensive for cultivation, and for fertilizer production and its incorporation into soil. Provision of nitrogen contributes a major source of the greenhouse gas, N2O. All losses due to pests, diseases and weeds are of food for which the carbon footprint has already been committed and so crop protection becomes an even greater concern. The rapidly increasing global need for food, and the aggravation of associated problems by the effects of climate change, create a need for new and sustainable crop protection. The overall requirement for sustainability is to remove seasonal inputs, and consequently all crop protection will need to be delivered via the seed or other planting material. Although genetic modification (GM) has transformed the prospects of sustainable crop protection, considerably more development is essential for the realisation of the full potential of GM and thereby consumer acceptability. Secondary plant metabolism offers wider and perhaps more robust new crop protection via GM and can be accomplished without associated yield loss because of the low level of photosynthate diverted for plant defence by secondary metabolism. Toxic mechanisms can continue to be targeted but exploiting nonâtoxic regulatory and signalling mechanisms should be the ultimate objective. There are many problems facing these proposals, both technical and social, and these are discussed but it is certainly not possible to stay where we are in terms of sustainability. The evidence for success is mounting and the technical opportunities from secondary plant metabolism are discussed here
Push-pull farming system controls fall armyworm: lessons from Africa
Fall armyworm (FAW) Spodoptera frugiperda invaded Africa, with the first detections being reported in Central and Western Africa in early 2016, and now affects at least 40 countries in Africa, causing up to total crop loss amounting to over $6.2 billion p.a. FAW is an invasive polyphagous pest that causes damage to economically important crops and has recently been reported in the Indian sub-continent. Effective control of FAW through use of synthetic chemical pesticides and genetically modified crops such as Bt maize faces challenges including improper use, unaffordability by smallholder farmers and development of resistance by the pest. Additionally, dispersal of FAW larvae into the lower maize plant canopy keeps them out of reach of topical insecticide applications. Integrated pest management (IPM) packages like the push-pull technology which eliminate pesticide use, and deploy natural processes are more suitable and cost-effective. Push-pull is a farming system intensification approach that involves attracting insect pests with trap plants (pull) such as Napier grass (Pennisetum purpureum) or Brachiaria grass, while driving them away from the main crop using a repellent intercrop (push), Desmodium spp., commonly known as desmodium, and attracting natural parasitoids and predators to the field. In the rhizosphere, chemicals secreted by desmodium roots inhibit attachment of germinated striga to maize or sorghum roots and abort germination of striga seeds which are rapidly depleted in the soil.
Moreover, it improves soil fertility by fixing nitrogen, improving carbon sequestration, organic matter, moisture retention, and soil biota, and prevents further degradation of soil. The climate-adapted push-pull technology significantly reduces plant damage by FAW and is the first IPM management tool for the pest in Africa, and is well suited to agro-ecosystem intensification needs of smallholder mixed farming systems in Africa and beyond. Both the African and the Asian continents provide favourable climatic conditions for sustained reproduction of the FAW, which is expected to result in severe damage to crops; and being a new pest in both continents, it might have few natural enemies. Conventional control methods have limited effectiveness, as explained above. Therefore, an IPM approach that is compatible with mixed cropping farming systems of small and medium scale farmers is necessary. The climate adapted push-pull is the first demonstrated IPM management tool for the FAW in Africa. The technology combines this with other concomitant benefits including control of stemborers and the parasitic striga weeds, improvement of soil health through factors such as nitrogen fixation by desmodium, natural mulching, moisture retention and improvement of soil organic matter and soil biota. The combined benefits, including control of FAW, result in ecologically sustainable higher crop yields, and well suited to agro-ecosystem intensification needs of smallholder mixed farming systems in Africa and beyond
Field evaluation of a new third generation push-pull technology for control of striga weed, stemborers, and fall armyworm in western Kenya
Production of cereal crops in sub-Saharan Africa is threatened by parasitic striga weeds and attack by stemborers and the invasive fall armyworm (FAW), compounded by increasing hot and dry conditions. A climate-smart push-pull technology (PPT) significantly reduces effects of these biotic challenges. To improve further resilience of the system to climate change, more adapted and suitable companion plants were identified and integrated in a new version of PPT, termed âthird generation PPTâ. Our study evaluates field performance and farmer opinions of this new version in comparison with the earlier version, climate-smart PPT, and farmersâ own practices of growing maize in controlling stemborers, FAW, and striga weeds. Trials were conducted across five locations in western Kenya for two cropping seasons in the year 2019 following a one-farm one-replicate completely randomized design. We assessed infestation on striga, stemborers, and FAW, and yield performance of the three cropping systems. We also sought the opinions of the hosting farmers through semi-structured questionnaires that were administered through individual interviews. Both PPT plots recorded significantly (P < 0.05) lower striga count, FAW, and stemborer damage, and higher grain yield than in plots that followed farmersâ own practices. There was no statistically significant difference between the two PPT plots except for stemborer damage for which the third generation PPT recorded higher damage than the climate-smart PPT. However, farmers preferred the third generation PPT for important traits possessed by its companion plants which their counterparts in climate-smart PPT are deficient. The cultivar Xaraes was rated as âvery goodâ for resistance to spider mites, biomass yield, and drought tolerance while Desmodium incanum was rated âvery goodâ for seed production and drought tolerance. The third generation PPT is based on companion crops that are more resilient to hot and dry conditions which are increasing rapidly in prevalence with climate change. This version therefore presents a better option to upscale the technology and meet different needs of farmers especially in arid and semi-arid conditions
Ecological management of cereal stemborers in African smallholder agriculture through behavioural manipulation
1. Africa faces serious challenges in feeding its rapidly growing human
population owing to the poor productivity of maize and sorghum, the most important
staple crops formillions of smallholder farmers in the continent,with yields being among
the lowest in the world.
2. A complex of lepidopterous stemborers attack cereals in Africa. However, their
effective control is difficult, largely as a result of the cryptic and nocturnal habits of
moths, and protection provided by host stem for immature pest stages.Moreover, current
control measures are uneconomical and impractical for resource-poor farmers.
3. An ecological approach, based on companion planting, known as âpushâpullâ,
provides effective management of these pests, and involves combined use of inter- and
trap cropping systems where stemborers are attracted and trapped on trap plants with
added economic value (âpullâ), and are driven away from the cereal crop by antagonistic
intercrops (âpushâ).
4. Novel defence strategies inducible by stemborer oviposition have recently been
discovered, leading to the attraction of egg and larval parasitoids, in locally adapted
maize lines but not in elite hybrids. We also established that landscape complexity did
not improve the ecosystem service of biological control, but rather provided a disservice
by acting as a âsourceâ of stemborer pests colonising the crop.
5. Here we review and provide new data on the direct and indirect effects of the
pushâpull approach on stemborers and their natural enemies, including the mechanisms
involved, and highlight opportunities for exploiting intrinsic plant defences and natural
ecosystem services in pest management in smallholder farming systems in Africa
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