Fall armyworm (Spodoptera frugiperda J. E. Smith), a serious pest of maize and other cereals, recently invaded the Old World potentially threatening the food security and incomes of millions of smallholder farmers. Being able to assess the impacts of a pest on yields is fundamental to developing Integrated Pest Management (IPM) approaches. Hence, working with an early maturing, medium maturing and late maturing variety, we inoculated maize plants with 2nd instar S. frugiperda larvae at V5, V8, V12, VT and R1 growth stages to investigate the effects of FAW induced damage on yield. Different plants were inoculated 0–3 times and larvae were removed after 1 or 2 weeks to generate a wide range of damage profiles. We scored plants for leaf damage at 3, 5 and 7 weeks after emergence (WAE) using the 9 point Davis scale. While at harvest we assessed ear damage (1–9 scale), and recorded plant height and grain yield per plant. We used Structural Equation Models to assess the direct effects of leaf damage on yield and indirect effects via plant height. For the early and medium maturing varieties leaf damage at 3 and 5 WAE, respectively, had significant negative linear effects on grain yield. In the late maturing variety, leaf damage at 7 WAE had an indirect effect on yield through a significant negative linear effect on plant height. However, despite the controlled screenhouse conditions, in all three varieties leaf damage explained less than 3% of the variation in yield at the plant level. Overall, these results indicate that S. frugiperda induced leaf damage has a slight but detectable impact on yield at a specific plant developmental stage, and our models will contribute to the development of decision-support tools for IPM. However, given the low average yields obtained by smallholders in sub-Saharan Africa and the relatively low levels of FAW induced leaf damage recorded in most areas, IPM strategies should focus on interventions aimed at improving plant vigour (e.g. through integrated soil fertility management) and the role of natural enemies, as these are likely to result in greater yield gains at lower cost than a focus on FAW control.
Tag: Maize
Smoke Induced Seed Germination in Maize in Response to Self and Other Plants Biomass-derived Smoke
Fire ecology plays an important roles in germination and establishment of many plant taxa. Smoke inducedgermination and seedling vigor are well documented in many wild, crop, and weedy species. Karrikins(KAR) substances in smoke are reported to be responsible for these effects. However, only a few experimentshave been conducted on different plant-derived smoke effects on particular plant speciesâ seeds. This studywas conducted to investigate effects of self-derived and other plants biomass-derived smoke on germinationand post-germination processes in maize and its wild relative teosinte. Smoke derived from maize and alegume (Vigna unguiculata ssp. sesquipedalis) foliage burning was exposed to maize variety Guidan 162and teosinte (Zeamexicana (Schrad.) Kuntze). Germination percentage in both maize and teosinte exposedto maize smoke was found to be significantly higher than unexposed and legume smoke exposure, howevergermination in legume smoke exposure was found to slightly higher than control but not significantly so.Shoot length in maize seeds exposed to maize smoke was highest and differed significantly compared tocontrol and legume smoke exposure, while control and legume smoke exposure showed approximatelythe same shoot lengths. Coleoptile and primary root lengths showed nosignificant variation among alltreatments. Similarly, seminal root length didnâ t show much variation but legume smoke exposure seedsfound to have the lowest seminal root length. Hence direct exposure to smoke without rinsing in watermay not positively affect the shoot and root length in maize. Further studies should address morphologicaltraits, transcriptome expression, and enzyme activity to clarify effects of self-derived and other plant-derived smoke on different plant species.
Soil and landscape factors influence geospatial variation in maize grain zinc concentration in Malawi
Dietary zinc (Zn) deficiency is widespread globally, and in particular among people in sub-Saharan Africa (SSA). In Malawi, dietary sources of Zn are dominated by maize and spatially dependent variation in grain Zn concentration, which will affect dietary Zn intake, has been reported at distances of up to ~ 100 km. The aim of this study was to identify potential soil properties and environmental covariates which might explain this longer-range spatial variation in maize grain Zn concentration. Data for maize grain Zn concentrations, soil properties, and environmental covariates were obtained from a spatially representative survey in Malawi (n = 1600 locations). Labile and non-labile soil Zn forms were determined using isotopic dilution methods, alongside conventional agronomic soil analyses. Soil properties and environmental covariates as potential predictors of the concentration of Zn in maize grain were tested using a priori expert rankings and false discovery rate (FDR) controls within the linear mixed model (LMM) framework that informed the original survey design. Mean and median grain Zn concentrations were 21.8 and 21.5 mg kg−1, respectively (standard deviation 4.5; range 10.0–48.1). A LMM for grain Zn concentration was constructed for which the independent variables: soil pH(water), isotopically exchangeable Zn (ZnE), and diethylenetriaminepentaacetic acid (DTPA) extractable Zn (ZnDTPA) had predictive value (p < 0.01 in all cases, with FDR controlled at < 0.05). Downscaled mean annual temperature also explained a proportion of the spatial variation in grain Zn concentration. Evidence for spatially dependent variation in maize grain Zn concentrations in Malawi is robust within the LMM framework used in this study, at distances of up to ~ 100 km. Spatial predictions from this LMM provide a basis for further investigation of variations in the contribution of staple foods to Zn nutrition, and where interventions to increase dietary Zn intake (e.g. biofortification) might be most effective. Other soil and landscape factors influencing spatially dependent variation in maize grain Zn concentration, along with factors operating over shorter distances such as choice of crop variety and agronomic practices, require further exploration beyond the scope of the design of this survey.
Spatial approach for diagnosis of yield-limiting nutrients in smallholder agroecosystem landscape using population-based farm survey data
Adept use of fertilizers is critical if sustainable development goal two of zero hunger and agroecosystem resilience are to be achieved for African smallholder agroecosystems. These heterogeneous systems are characterized by poor soil health mainly attributed to soil nutrient depletion. However, conventional methods do not take into account spatial patterns across geographies within agroecosystems, which poses great challenges for targeted interventions of nutrient management. This study aimed to develop a novel population-based farm survey approach for diagnosing soil nutrient deficiencies. The approach embraces principles of land health surveillance of problem definition and rigorous sampling scheme. The advent of rapid soil testing techniques, like infrared spectroscopy, offers opportune avenues for high-density soil and plant characterization. A farm survey was conducted on 64 maize fields, to collect data on soil and plant tissue nutrient concentration and grain yield (GY) for maize crops, using hierarchical and purposive sampling. Correlations between soil test values with GY and biomass were established. The relationship between GY, soil NPK, and the tissue nutrient concentrations was evaluated to guide the setting up of localized critical soil test values. Diagnosis Recommendation Integrated System (DRIS) indices for total nitrogen (N), total phosphorus (P), and total potassium (K) were used to rank and map the prevalence of nutrient limitations. A positive correlation existed between plant tissue nutrient concentration with GY with R2 values of 0.089, 0.033, and 0.001 for NPK, respectively. Soil test cut-off values were 0.01%, 12 mg kg-1, 4.5 cmolc kg-1 for NPK, respectively, which varied slightly from established soil critical values for soil nutrient diagnostics. N and K were the most limiting nutrients for maize production in 67% of sampled fields. The study demonstrates that a population-based farm survey of crop fields can be a useful tool in nutrient diagnostics and setting priorities for site-specific fertilizer recommendations. A larger-scale application of the approach is warranted.
Profitability of Gliricidia-Maize System in Selected Dryland Areas of Dodoma Region, Tanzania
Declining soil fertility and climatic extremes are among major problems for agricultural production in most dryland agro-ecologies of sub-Saharan Africa. In response, the agroforestry technology intercropping of Gliricidia (Gliricidia sepium (Jacq.)) and Maize (Zea mays L.) was developed to complement conventional soil fertility management technologies. However, diversified information on the profitability of Gliricidia-Maize intercropping system in dryland areas is scanty. Using data from the Gliricidia and maize models of the Next Generation version of the Agriculture Production Systems sIMulator (APSIM), this study estimates the profitability of the Gliricidia-Maize system relative to an unfertilized sole maize system. Results show significant heterogeneity in profitability indicators both in absolute and relative economic terms. Aggregated over a 20-year cycle, Gliricidia-Maize intercropping exhibited a higher Net Present Value (NPV = Tsh 19,238,798.43) and Benefit Cost Ratio (BCR = 4.27) than the unfertilized sole maize system. The NPV and BCR of the latter were Tsh 10,934,669.90 and 3.59, respectively. Moreover, the returns to labour per person day in the Gliricidia-Maize system was 1.5 times those of the unfertilized sole maize system. Sensitivity analysis revealed that the profitability of the Gliricidia-Maize system is more negatively affected by the decrease in output prices than the increase in input prices. A 30% decrease in the former leads to a decrease in NPV and BCR by 38% and 30%, respectively. Despite the higher initial costs of the agroforestry establishment, the 30% increase in input prices affects more disproportionally unfertilized sole maize than the Gliricidia-Maize system in absolute economic terms, i.e., 11.1% versus 8.8% decrease in NPV. In relative economic terms, an equal magnitude of change in input prices exerts the same effect on the unfertilized sole maize and the Gliricidia-maize systems. This result implies that the monetary benefits accrued after the first year of agroforestry establishment offset the initial investment costs. The Gliricidia-Maize intercropping technology therefore is profitable with time, and it can contribute to increased household income and food security. Helping farmers to overcome initial investment costs and manage agroforestry technologies well to generate additional benefits is critical for the successful scaling of the Gliricidia-Maize intercropping technology in dryland areas of Dodoma, Tanzania.
One New Species and Two New Host Records of Apiospora from Bamboo and Maize in Northern Thailand with Thirteen New Combinations
The genus Apiospora is known as a cosmopolitan genus, found across various substrates. In this study, four Apiospora taxa were obtained from the decaying stems of bamboo and maize in northern Thailand. Apiospora collections were compared with known species based on the morphological characteristics and the DNA sequence data of internal transcribed spacer (ITS), the partial large subunit nuclear rDNA (LSU), the translation elongation factor 1-alpha gene (TEF1-α) and beta-tubulins (TUB2). Apiospora chiangraiense sp. nov. and two new host records (Ap. intestini and Ap. rasikravindra) are introduced here based on the morphological characteristics and multi-locus analyses. Additionally, thirteen species previously identified as Arthrinium are introduced as new combinations in Apiospora, viz., Ap. acutiapica, Ap. bambusicola, Ap. biserialis, Ap. cordylines, Ap. cyclobalanopsidis, Ap. euphorbiae, Ap. gelatinosa, Ap. locuta-pollinis, Ap. minutispora, Ap. pseudorasikravindrae, Ap. septate, Ap. setariae and Ap. sorghi.
Trees enhance abundance of arbuscular mycorrhizal fungi, soil structure, and nutrient retention in low-input maize cropping systems
Retaining trees in low-input agroecosystems could be key to maintain mycelia of arbuscular mycorrhizal fungi (AMF) and hence, improve soil fertility and crop performance. We assessed the impact of faidherbia (Faidherbia albida, Fabaceae) and mango (Mangifera indica, Anacardiaceae) trees on AMF and soil fertility in smallholder farmers’ maize fields. Along distance-from-tree gradients (1, 4, 10, 15 m), we collected soil to assess AMF hyphal density, soil aggregation, and aggregate-associated carbon (C), nitrogen (N), and phosphorus (P) at the end of the non-cropping season. Further, we determined maize biomass and yield. The impact of faidherbia on maize N nutrition was assessed using the 15N natural abundance methodology. Our results show that hyphal density was largest at 4 and 10 m from trees and greater around faidherbia than mango. Soil aggregation decreased with distance from mango and was greater around faidherbia than mango. Macroaggregate-associated C, N, and P decreased with distance-from-tree, due to differences in aggregate distribution. Maize biomass was smallest at 1 m from trees and did not differ when under faidherbia versus mango. On average 69 ± 14, 24 ± 9, 20 ± 6, and 12 ± 5% of total foliar N of maize grown at 1, 4, 10, and 15 m from faidherbia trees was tree-derived. Our results suggest that faidherbia and mango trees can maintain AMF mycelia and combat declining soil fertility. Faidherbia is particularly suited to enhance measured soil parameters commonly associated with soil fertility and alleviate soil mining for N via improved internal N cycling. As such, agroforestry trees can contribute to a more sustainable agriculture positively affecting the environment via mitigating soil degradation. © 2021
Maize diversity for fall armyworm resistance in a warming world
Currently, maize (Zea mays L.) production is under threat from climate change, drought, and pests such as fall armyworm (FAW) [Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)]. Since its first detection outside of its native range in 2016, FAW has spread into 76 nations across Africa and Asia adversely affecting maize production and, in turn, the livelihoods of millions of smallholder farmers. Thus, there is a strong need for the development of cost-effective and biologically based integrated pest management (IPM) practices including host-plant resistance (HPR). However, most of the commercial maize cultivars have lost some defensive traits through selective breeding for yield during domestication. The majority of the commercially cultivated hybrids and cultivars in Asia and Africa are highly susceptible to FAW. Therefore, this review summarizes information about various maize landraces, native germplasm, and crop wild relatives (CWRs) possessing FAW resistance traits and about their potential resistance mechanisms, namely antibiosis, antixenosis, and tolerance. There is clear evidence of FAW resistance acting through diverse mechanisms in several maize landraces, germplasm lines, native populations, and CWRs such as Antigua race, FAW Tuxpeno, Zapalote Chico 2451F, Doce Flor da Serra, FAWCC (C5), CMS 14C, PopG (C2), MpSWCB-4, Mp708, Mp 704, CML 67, and FAW 7050, as well as a few species of teosinte and Tripsacum L. Further, a scheme that outlines strategies and approaches for prebreeding and their introgression into elite cultivars for developing FAW-resistant maize is proposed as a possible way forward.
Arbuscular mycorrhizal fungi potentially regulate N2O emissions from agricultural soils via altered expression of denitrification genes
Agricultural soils are an important source of nitrous oxide (N2O), a potent greenhouse gas involved in the destruction of the protective ozone layer that contributes to global warming. During N2O production, soil microorganisms play important driving and regulating roles. A few recent studies have revealed the potential effects of arbuscular mycorrhizal fungi (AMF), a widely distributed soil fungi, on controlling N2O emissions. However, how AMF regulate N2O production from soils remains poorly understood. To address the knowledge gap, we manipulated two independent soil environments, which were either allowed (AM) or prevented (NM) access by AMF hyphae in a microcosm experiment (n = 5). Soil physicochemical properties, N2O flux, the diversity of bacterial communities, and the abundance of key genes responsible for N2O production were assessed in both treatments over three months. Results showed that the presence of AMF significantly decreased N2O emissions from agricultural soils in the 1st month, and the abundance of key genes responsible for denitrification (nirK and nosZ) significantly decreased in AM treatments, indicating that the regulation of N2O emissions is transmitted by AMF-induced changes in the denitrification process. A structural equation model further revealed that AMF indirectly influenced N2O emissions by altering the abundance of N metabolism-related genes, rather than by altering soil chemical properties or the diversity of bacterial communities. Thus, we proposed a possible mechanism by which AMF can regulate denitrification activities and therefore N2O emissions from agricultural soils.
Conservation agriculture improves adaptive capacity of cropping systems to climate stress in Malawi
Context: Adaptation to climate stress is an unprecedented challenge facing cropping systems. Most adaptation assessments focus on how adaptation options affect yields of a single crop under different weather or climate conditions. Yet, cropping systems often comprise more than one crop, and holistic assessments should consider all crops grown in a cropping system. One adaptation option is Conservation Agriculture that is commonly defined around a set of three principles: minimum mechanical soil disturbance, permanent soil organic cover, and crop species diversification. Objective: Here we estimated the statistical effect of Conservation Agriculture on cropping-system yields under historical climate conditions. Methods: The cropping-system yields considered all crops grown including maize (Zea mays L.) and legumes in intercropping or rotation, or both. The climate conditions included conditions of heat stress for maize and precipitation balances during the maize growing season. Heat stress for maize was studied using growing degree days over 30 °C. Precipitation balance was the difference between precipitation and reference evapotranspiration. Data included 6296 yield observations from on-farm trials in farmer plots conducted over 14 seasons (2005–2006 to 2018–2019) in ten communities in Malawi. These yield data were coupled with daily weather data. We studied three treatments: (1) a Control Practice treatment where the soil was tilled, crop residues were removed, and there was no crop species diversification, (2) a No-Tillage treatment where the soil was not tilled, crop residues were retained, and there was no crop species diversification, and (3) a Conservation Agriculture treatment where the soil was not tilled, crop residues were retained, and there was crop species diversification through legume intercropping. The use of maize varieties and legume rotation changed over time; however, the treatments studied remained the same over the entire length of the on-farm trials period in all individual communities. Results and conclusions: Results of our study showed that heat stress for maize had a negative effect on cropping-system yields for non-stress-tolerant maize varieties and no legume rotation, although the Conservation Agriculture treatment reduced this negative effect compared with the Control Practice treatment. With the use of stress-tolerant maize varieties and legume rotation and Conservation Agriculture, our results suggest that heat stress for maize did not have a negative effect on cropping-system yields. Significance: Our results demonstrate how Conservation Agriculture can improve the adaptive capacity of cropping systems and this provides urgently needed evidence on how farmers can adapt to climate stress.