Rice In Africa Research Articles

Nonglandular silicified trichomes are essential for rice defense against chewing herbivores.

Interspecific New Rice for Africa (NERICA) varieties have been recently developed and used in Sub-Saharan Africa but herbivore resistance properties of these plants remain poorly understood. Here we report that, compared to a local Japanese cultivar Nipponbare, NERICA 1, 4 and 10 are significantly more damaged by insect herbivores in the paddy fields. In contrast to high levels of leaf damage from rice skippers and grasshoppers, constitutive and induced volatile organic compounds for indirect plant defense were higher or similar in NERICAs and Nipponbare. Accumulation of direct defense secondary metabolites, momilactones A and B, and p-coumaroylputrescine (CoP) was reduced in NERICAs, while feruloylputrescine accumulated at similar levels in all varieties. Finally, we found that Nipponbare leaves were covered with sharp nonglandular trichomes impregnated with silicon but comparable defense structures were virtually absent in herbivory-prone NERICA plants. As damage to the larval gut membranes by Nipponbare silicified trichomes that pass intact through the insect digestive system, occurs, and larval performance is enhanced by trichome removal from otherwise chemically defended Nipponbare plants, we propose that silicified trichomes work as an important defense mechanism of rice against chewing insect herbivores.

Comparison of the penetration, development and reproduction of Meloidogyne javanica and M. graminicola on partially resistant Oryza sativa cultivars from East Africa

Summary The host response to Meloidogyne javanica infection of selected Oryza sativa and NERICA (New Rice for Africa) genotypes that are commonly grown in Tanzania and East Africa was examined. The O. sativa genotypes ‘Komboka’ and ‘Supa’ appeared to be partially resistant. A further experiment showed that both genotypes are also partially resistant to M. graminicola infection. The host response of ‘Komboka’ and ‘Supa’ to M. javanica and M. graminicola was further examined and compared in indoor growth chamber conditions. The genotypes ‘TOG5674’, ‘TOG5675’, ‘CG11’ and ‘CG14’ (both O. glaberrima) were included as the resistant reference genotypes for M. graminicola and the genotype ‘UPLRi-5’ (O. sativa) was included as the susceptible reference genotype for both species of root-knot nematodes. Meloidogyne graminicola was more aggressive on ‘Komboka’ and ‘Supa’ than M. javanica. Significantly less root galling was observed on ‘Komboka’ and ‘Supa’ than on ‘UPLRi-5’. In ‘Komboka’ and ‘Supa’ significantly fewer second-stage juveniles (J2) were able to penetrate the roots, to develop into adult females and to reproduce compared with ‘UPLRi-5’. Differential emigration of J2 from the roots of ‘Komboka’ and ‘Supa’ compared with ‘UPLRi-5’ contributed to the observed partial resistance in these genotypes to M. graminicola and M. javanica. Nematodes that successfully penetrated and developed in ‘Komboka’ and ‘Supa’ showed aberrant phenotypes. ‘Supa’ and ‘Komboka’ may be recommended for use by farmers in M. javanica and M. graminicola-infested fields.

Design of a new multiplex PCR assay for rice pathogenic bacteria detection and its application to infer disease incidence and detect co-infection in rice fields in Burkina Faso.

Crop diseases are responsible for considerable yield losses worldwide and particularly in sub-Saharan Africa. To implement efficient disease control measures, detection of the pathogens and understanding pathogen spatio-temporal dynamics is crucial and requires the use of molecular detection tools, especially to distinguish different pathogens causing more or less similar symptoms. We report here the design a new molecular diagnostic tool able to simultaneously detect five bacterial taxa causing important diseases on rice in Africa: (1) Pseudomonas fuscovaginae, (2) Xanthomonas oryzae, (3) Burkholderia glumae and Burkholderia gladioli, (4) Sphingomonas and (5) Pantoea species. This new detection tool consists of a multiplex PCR, which is cost effective and easily applicable. Validation of the method is presented through its application on a global collection of bacterial strains. Moreover, sensitivity assessment for the detection of all five bacteria is reported to be at 0.5 ng DNA by μl. As a proof of concept, we applied the new molecular detection method to a set of 256 rice leaves collected from 16 fields in two irrigated areas in western Burkina Faso. Our results show high levels of Sphingomonas spp. (up to 100% of tested samples in one field), with significant variation in the incidence between the two sampled sites. Xanthomonas oryzae incidence levels were mostly congruent with bacterial leaf streak (BLS) and bacterial leaf blight (BLB) symptom observations in the field. Low levels of Pantoea spp. were found while none of the 256 analysed samples was positive for Burkholderia or Pseudomonas fuscovaginae. Finally, many samples (up to 37.5% in one studied field) were positive for more than one bacterium (co-infection). Documenting co-infection levels are important because of their drastic consequences on epidemiology, evolution of pathogen populations and yield losses. The newly designed multiplex PCR for multiple bacterial pathogens of rice is a significant improvement for disease monitoring in the field, thus contributing to efficient disease control and food safety.

Genetic diversity of African’s rice (Oryza glaberrima Steud.) accessions cultivated under iron toxicity

Iron toxicity stress is one of the most important constraints to rice production in Togo. Although several methods were explored to control this stress, the best one is still the genetic control through the use of tolerant or resistant varieties. Our hypothesis is that African’s rice, Oryza glaberrima, accessions contain sources of tolerance or resistance to the iron toxicity stress. Thus, the aim of this study was to determine the level and the structure of the African’s rice, Oryza glaberrima, genetic diversity and to identify tolerant genotypes. Two hundred and four (204) accessions obtain from Africa Rice genebank and eight control varieties were evaluated under iron toxicity conditions using alpha lattice design with three replications. There was significant variability among accessions for height of mature plants and weight of 1000 seeds. The coefficient of variation values ranged from 10.56% for the 50% flowering to 77.47% for the sterility rate. The principal component analysis (PCA) with all the measured characteristics revealed that the first four axes accounted for 59.93% of the total variability. The coordinates of the variables showed that, six (6) accessions (T30, T60, H60, Tf, yield and Tox60) are associated to the factor F1 with an eigenvalue of 2,81. A high correlation between 50% flowering and plant height, fertile tillers and number of tillers, sterility rate and total number of seeds and yield were also observed. The accessions were divided into three (3) distinct groups. Sixty (60) accessions and four (4) controls (CG14, IR64, Azucena Whyte and NERICA L-20) identified as tolerant genotypes were clustered together in Group 3. These tolerant accessions could be exploited in the rice breeding program for the tolerance to iron toxicity stress.

Resistance levels of selected rice genotypes to Sitophilus oryzae L. and Rhyzopertha dominica F. infestations

The need to screen new rice genotypes for resistance to stored product insect pests is important to boost production and availability of rice for food security. Therefore, thirteen rice genotypes and varieties included ten interspecific rice genotypes from two crossed parents Oryza sativa (WAB 56-104) and Oryza barthii (IRGC 106107), the two parents and NERICA8 variety were collected from Africa Rice Center, International Institute of Tropical Agriculture (IITA) Ibadan, to examine their resistance level to infestation by Sitophilus oryzae L. and Rhyzopertha dominica F. The resistance of the varieties were assessed by artificial infestation with 12 unsexed adults each in 10 g of the rice varieties in four replicates under laboratory conditions of 26 ± 2oC temperature and 75 ± 5% relative humidity in a completely randomized design. Number of adult insect emergent, per cent grain damage, percent weight loss of infested samples and index of susceptibility were determined. Correlation analysis between nutritional contents of the varieties and infestation variables were also obtained. Results indicate differential responses of the two insects on the rice genotypes/varieties. The O. barthii parent was resistant, while the O. sativa parent was moderately resistant using the susceptibility index. Of the ten rice genotypes, G4, G3, G1, G7, G2, G10 and G9 were resistant in descending order, while G5 and G6 were moderately resistant, whereas only G8 was susceptible. NERICA8 was also found to be susceptible to infestation. In addition, the resistant grains had lower ash content. Modification in genetic variations and nutritional contents of new rice varieties may be a critical factor in insect resistant genotype pro-grammes to reduce post-harvest losses incurred by farmers.
 Keywords: Rice resistant genotypes; Rhyzopertha dominica; Oryzae sativa; Oryzae barthii; Sitophilus oryzae; susceptibility index

Root and shoot responses of upland New Rice for Africa varieties to fluctuating soil moisture conditions as affected by different levels of nitrogen fertilization

AbstractDrought cycling and soil re‐watering trends due to intermittent rainfall patterns are key stress factors that influence rice growth and yield under upland cultivation conditions. However, upland rice adaptation responses to fluctuating soil moisture conditions remain poorly understood. This study investigated root and shoot responses of upland New Rice for Africa (NERICA) varieties to episodic drought and re‐watering during growth. We examined root and shoot growth of NERICA 1 and NERICA 4 compared with those of IR72, an improved lowland variety, and Dular, a traditional drought‐tolerant variety, in terms of soil moisture fluctuations with different levels of nitrogen fertilization under field conditions that impeded deep root development. During soil moisture fluctuation, all varieties reduced shoot dry weight compared with well‐watered plants, regardless of nitrogen fertilization levels. However, total root length for the three upland varieties was enhanced by soil moisture fluctuations at moderate and high nitrogen fertilization, while that of the lowland variety was reduced. Comparing root development during water fluctuations revealed that NERICA 1 had a greater root system than NERICA 4, which was attributed to lateral root development. Furthermore, we found that NERICA varieties increase lateral root mass during soil desiccation under adequate nitrogen fertilization, while Dular and IR72 reduced their root growth rate during drought and increased it after re‐watering. Both root growth patterns developed, from around maximum tillering to heading. The analysis of regression between root elongation and shoot growth with fluctuating soil moisture indicated that an enhanced root system during drought, on adequate nitrogen fertilization, can contribute to shoot growth when sufficient water becomes available, specifically around the maximum tillering to the heading growth stage of rice.

Investigating the Effectiveness of Selenite on Drought Stressed Upland Rice

Water stress is an enormous problem facing food production, especially in arid and semi-arid regions. Production of free radicals during water stress has led to oxidative stress, which eventually causes death of cells in plants. Therefore, it is important to tackle this issue knowing that rice is one of the most important cereal crops largely cultivated and consumed by humans and animals. The studies aimed at the effect of selenite on physiological and biochemical activities of water-stressed upland rice. Three Upland rice cultivars namely Nerica U4, Nerica U7 and Vandana were collected in Africa Rice Centre, Ibadan. The seeds were sterilized and soaked for 10 hours in different concentrations of Selenite (Se) (0 mg/l, 50 mg/l and 100 mg/l). Primed seed were planted into sterilized-sieved top soils. Plants were subjected to 0 (irrigated) and 8 days (non-irrigated) water stress. Selenite 50 mg/l improved plant height, number of leaves, total carotene, chlorophyll contents, biomass, grain number of upland rice during water stress. Selenite increased activities of APX as water stress progressively increased consequently, low MDA content was observed in cultivar Vandana. Furthermore, selenite significantly improved total carotene, chlorophyll contents, anthocyanin, and dry shoot weight in cultivar Nerica U7 during water stress. Selenite significantly stabilized activities of anthocyanin and CAT in cultivar Nerica U4 during water stress. Hence high grain yield was recorded in Nerica U4 and U7 in selenite primed upland rice during water stress. Selenite reduced lipid peroxidation in upland rice at 100mg/l. Therefore, it can be concluded that response of rice to selenite during water stress is based on tolerance capacity of the cultivars and also, selenite 50mg/l can help to improve growth and yield of upland rice in drought-prone area.

Effect of iron deficiency on the growth, development and grain yield of some selected upland rice genotypes in the rainforest

Iron deficiency is a major production constraint of upland rice in the tropics despite is abundance in the soil. This investigation aimed to explicate the effect of iron deficiency on the growth, development, grain yield and its attributes of some selected upland rice in the rainforest. Field experiments were established at Africa Rice sub-Station, Ibadan, Nigeria. The treatments consisted of 35 upland rice genotypes and availability of iron in the soil (Fe-sufficient and Fe-deficient). The treatments were arranged in alpha lattice design with three replications. It was observed that upland rice sown in iron (Fe) deficient soils had significantly lower growth (plant height, number of tillers and seedling vigor), flowered later, with significantly lower yield attributes (1000 grain weight, filled grain) and grain yield than those sown in Fe-sufficient soils. Conversely, the number of unfilled grains were significantly higher in upland rice sown in Fe-deficient than those in sufficient soils. Percentage yield loss was in the range 98.00% to 22.95% for China best and Faro 65 respectively. Genotypes were identified to be tolerant (Faro 65, NERICA 3 and IRAT 109) and susceptible (Ofada 2, NERICA 5 and China Best) to Fe-deficiency based on their percentage grain yield loss. These evidences suggested that despite the increased phenology of upland rice sown in Fe-deficient soils their reproductive growth was suppressed through increased number of unfilled grains as witnessed in China Best and Faro 64.

Uticaj sadržaja vlage i pozicije za utovar na mehaničke osobine nove sorte (NERICA) pirinča za Afriku

The mechanical properties of New Rice for Africa, (NERICA) were determined on different moisture content levels of 12.5, 17 and 21.5% (db), and loading positions of major, minor, and intermediate diameters using the Instron Universal Testing Machine (UTM). The mechanical properties studied were the maximum load at rupture, compressive extension at maximum load, load at bioyield point, toughness, stiffness, compressive strength, energy at maximum load, and the maximum slope. Results obtained indicated that, the loading pattern and moisture content affected the mechanical properties determined (p < 0.05). Results showed that, maximum load at rupture, compressive extension, load at bio yield point, ranged from 363.73 to 50.92 N; 0.50 to 2.79 mm; and 11.58 to 6.78 N/mm2 ; respectively for NERICA Raw-Paddy major diameter loading; and from 18.46 to 5.44 N; 0.92 to 2.52 mm; 9.01 to 4.08 N/mm2 respectively for NERICA Raw-Paddy minor diameter loading. For the NERICA Parboiled-Milled, results at both major diameter and minor diameter loading positions ranged as follows; maximum load at rupture (156.08 to 44.94 N; 94.90 to 22.05 N); compressive extension (0.59 to 1.61 mm; 0.46 to 2.67 mm). Regression analysis were carried out on the mechanical properties with moisture content, and there was positive correlation between the parameters. There were significant effects of moisture content (p < 0.05) on all parameters studied.

Impact of Rice Stem Borers and Identification of &amp;lt;i&amp;gt;Orseolia oryzivora&amp;lt;/i&amp;gt; Harris &amp;amp; Gagn&amp;#233;, 1982 (Diptera: Cecidomyiidae) Biotypes in the Southern Cameroon

The study compares the impact due to rice stem borers in two sites (Yaounde and Ntui). It also shows the diversity of the African Rice Gall Midge (AfRGM) biotypes in southern Cameroon (Santchou, Ndop, Tonga, Ebolowa, Ba?gom, Yaounde and Ntui). The New Rice for Africa (NERICA) varieties 3, 8, 9 and 13 sown in Ntui were less attacked than those sown in Yaounde. At both sites, damages ranged from 0.78% to 2.7%. In terms of diversity, the main stem-borer species were O. oryzivora, Diopsis apicalis, D. longiconis and Chilo zacconius. Molecular analyses of Orseolia oryzivora larvae collected in the localities of Santchou, Ndop, Tonga, Ebolowa, Ba?gom and Yaounde showed the existence of more than one O. oryzivora biotype in southern Cameroon’s rice basins.

Experimental Field Study on Relationships between Rice Yield and Weather Variables of New Rice for Africa, NERICA 4 and Indica Rice Variety, IR-28

Experimental Field Study on Relationships between Rice Yield and Weather Variables of New Rice for Africa, NERICA 4 and Indica Rice Variety, IR-28

Agronomic Assessment of Upland Rice Varieties under Unpredictable Rains in the Semi-Arid Conditions of South-Western Agro-Ecological Zone of Uganda

This paper examined agronomic performance of three upland New RICE for Africa (NERICA) varieties promoted by the Government of Uganda in its efforts to improve household food and income security among smallholder farmers. Three rain-fed experimental trials were conducted on station at Mbarara Zonal Agricultural Research and Development Institute (MBAZARDI), with semi-arid climate conditions typical of more than 50% of the South-Western Agro-Ecological Zone (SWAEZ) of Uganda. The experimental trials were established in the long rain seasons that often occur in September-December period. But results for only one successful long rain seasonal trial of 2010 are presented in this paper. Successful experimental trial for upland NERICA had an average precipitation of 130 mm that was well distributed especially from booting stage, which is the most sensitive growth stage for upland NERICA. During the growth period, NERICA 1 and NERICA 4 were significantly taller (p -1. Although, NERICA 4 ranked top in terms of grain yields among the tested upland NERICA varieties and therefore, most possible candidate for smallholder rice farmers in the humid parts of the SWAEZ, it called for more breeding for upland NERICA varieties with traits that could increase their tolerance to low soil moisture most prevalent in the SWAEZ.

Evaluation of Korea Rice Germplasm for Yield and Yield Components Adaptable to Nigeria Environmental Conditions

In this current century, West Africa will continue facing major problem of food shortage. This implies increase in the rice cultivation and productivity as rice is one of their major staple crops. This study was carried out at Africa Rice Center, International Institute of Tropical Agriculture (IITA) Ibadan, Nigeria, and evaluated 30 accessions (anther culture derived) from South Korea with 10 adapted genotypes form Nigeria for their performance. The experiment was conducted in dry season using Alpha lattice design with eight blocks each planted in five entries, replicated three times. Analysis of variance revealed highly significant differences (P ≤ 0.05) among the genotypes of the studied traits. Thus, suggest the presence of wide genetic variability, which is of important, as it gives large spectrum of selection to the breeders for hybridization. Based on their means, genotypes such as FARO 67, UPN 287, FARO 66, UPN 315 and UPIA1 showed maximum tillering ability per plant, while, UPN 349, UPN 335, UPN 271, UPN 324 and UPN 300 showed the highest number of spikelets per panicle. The genotypes such as UPIA 1, SAHEL 21, UPN 301, UPN 266 and FARO 57 proved to be better for 1000_grain weight, while UPIA 1, UPN 266, UPN 349, UPN 300 and FARO 67 were better for grain yield per plant. Cluster analysis grouped the 40 genotypes into five clusters. Dendogram showed maximum genetic distance between group A and group E indicating genetic diversity among these groups. Minimum genetic diversity was observed between group B and group E. FARO 67, UPN 287, UPN 349, UPIA 1, UPN 266 and UPN 300 shown to be the most promising genotypes that could be used for rice hybridization, genetic improvement and rice hybrid programme.

Evaluation and Breeding of Lowland Rice Varieties for their Yield and Tolerance to Biotic and Abiotic Stresses in Benin and Togo: Implication for Genetic Improvement of Rice in West Africa

Evaluation and Breeding of Lowland Rice Varieties for their Yield and Tolerance to Biotic and Abiotic Stresses in Benin and Togo: Implication for Genetic Improvement of Rice in West Africa

Rice genotype and fertilizer management for improving rice productivity under saline soil conditions

Soil salinity is a threat to crop production in the Senegal River Delta where salt intrusion increases soil electrical conductivity and most of farmers had abandoned their rice farms. The objective of this study was to evaluate an integrated management to improve rice productivity under saline soil condition in the Senegal River Delta. Field experiments were conducted during four rice-growing seasons from July 2014 to July 2016 at Africa Rice Center research station at Ndiaye, Senegal. The performance of five rice genotypes (IR63275-B-1-1-3-3-2, WAS73-B-B-231-4, NERICA-L9, FL478, and IR29) was evaluated under three salinity levels (0.5–0.8 dS m−1, 2.0 dS m−1, 3.5 dS m−1) and two fertilizer management options (basal dressing at 100 kg ha−1 of N–P–K (15–15–15) only and basal dressing at 200 kg ha−1 of N–P–K (15–15–15) + 50 kg N ha−1 urea at panicle initiation and at booting. Rice seedlings were raised at nursery for 21 days and transplanted at the density of 20 cm × 20 cm around March 15 and August 15 and harvested around July 15 and early December. The plots were drained canal when soil EC increased 0.1 dS m−1 above the designed EC levels. The results showed that rice yield decreased with the increasing soil salinity and were season dependent. Rice grain yield varied from 0.9 to 8 tons ha−1. Rice grain yield was 20% higher during the hot and dry seasons than the wet season. The application of the recommended fertilizer improved rice yield by 52% compared to the basal fertilizer application only. Nitrogen application at panicle initiation and at booting stages in addition to the basal fertilizer application doubled rice grain yield and should be adopted under salinity condition across the Senegal River Delta. The analysis of the combination of yield index, yield stability index, stress susceptibility index and the stress tolerant index indicated that the newly developed rice genotypes IR63275-B-1-1-3-3-2 and WAS73-B-B-231-4 showed high salt tolerance with better yield stability and low stress susceptibility and constitute good candidate to be adopted under the best fertilizer management option in the Senegal River Delta climate, soil salinity and similar environmental conditions.

Predicting Rice Yield Under Salinity Stress Using K/Na Ratio Variable in Plant Tissue

ABSTRACTEstimation of yield reduction in crop caused by the salinity stress is mostly based on variations of soil electrical conductivity and the severity of water stress. Crop response curves to salinity were developed without considering ion toxicity and nutritional imbalance in the plant. The objective of this study was to explore the possibility of using the ratio of the concentration of potassium by sodium in rice leaf (leaf-K/Na) to predict yield under the salinity stress. The rice (Oryza sativa L.) yield under fresh and saline condition and the leaf-K/Na related database was created. Data were collected from consecutive three seasons of a field experiment in the Africa Rice Center experimental farm in Senegal (16° 11ʹ N, 16° 15ʹW). We studied the relationship between the relative yield (Yr), a ratio of yield under the salinity stress to the potential yield and the leaf-K/Na (x). Furthermore, we did regression analyses and F-test to determine the best fitting function. Results indicate that the exponential function [i.e. Yr = 100 exp (-b x)] was the best fitting model with the lowest root mean square error (9.683) and the highest R2 value (0.90). Example applications on independent data from published papers showed relatively good predictions, suggesting that the model can be used to predict rice yield in saline soils.

Productivity of new rice for Africa under different contour patterns in northern Guinea Savanna of Kaduna State, Nigeria

This study investigated productive and profitability capacities of contour farming technologies in rice production in Barangwaje, Ikara Local Government Area and Dutsen Abba in Zaria Local Government Area of Kaduna State. In Barangwaje, 36 and 28 farmers from Dutsen Abba were selected based on interest for the trials. To compare the profitability, seeds, land preparation, fertilizer application and use of family labour, among others were used. Stochastic frontier model was employed to determine the efficiencies of contour rice farmers. Data were analysed using descriptive statistics, gross margin analysis and stochastic frontier model. The results showed that almost all (96%) of the respondents had annual income between ₦ 100, 000 and ₦150,000. High proportion (76%) of the respondents had extension contact and all the farmer had access to agricultural credit. In Barangwaje, the gross margin for one hectare of land cultivated was ₦420,253.75 for contour, ₦88,508.75 for contour + ridge-tie, N1,791.25 for flat land and ₦45,357.50 for farmer’s practice (up-down slope). In Dutsen Abba, gross margin obtained shows that contour + ridge tie had ₦34,978.56, flat land had ₦26,132.06, contour had ₦2,313.00 and farmer’s practice (up-down slope) had ₦114.31. Investment in rice cultivation was profitable as indicated by return per Naira invested. Stochastic frontier model shows that contour rice farmers were highly efficient as indicated by the value of gama (0.99), which implies that 99% of the variation of output from frontier was due to technical efficiency of the farmers. It concluded that rice production was highly profitable. Measures should be in place to reduce importation of rice in order to encourage local production. Constraints faced by farmers were not indicated in the abstract. Keywords: Rice, contour, contour + tie, profitability, allocative, efficiency

Survey of potential insect vectors of Rice Yellow Mottle Virus in the Southern and Central rice basin of Benin

Objectives : Insects are considered as the main vectors of Rice Yellow Mottle Virus (RYMV) in Africa. However, in Benin, little is known about the abundance and diversity of potential insect vectors of RYMV in rice fields to prevent and manage disease impact on rice production. Methodology and Results : The inventory of the potential insect vectors of this disease was carried out in the rice basin of the Southern and Central of Benin where three sites namely Africa Rice station, Koussin and Ouedeme, were prospected. The sweep net technique, visual observation and yellow plates trap were used to conduct the surveys. Eighty insect species belonging to 28 families and 8 orders were recorded at rice tillering, booting, heading and maturation stages. Variation of insect diversity was low among the sites. The shorthorned grasshopper Oxya hyla (Serville) , the ladybird beetle Chnootriba similis (Mulsant) , the rice white leafhopper Cofana spectra (Distant) and the stalk-eyed fly Diopsis thoracica (Westwood) were the most important species considering their relative abundance (10.62%, 5.19%, 7.99% and 7.01%, respectively) and frequency of occurrence (90%, 80%, 73.33% and 80%, respectively). These insects were mostly present at tillering and booting stages. Conclusion and application of results : Seventy-five (75 %) of the recorded species were not identified as RYMV vectors before. Special attention must be paid to the distribution and importance of these insects in the fields. Studies on their ability to transmit RYMV according ecological conditions should be done to know high-risk production areas and to prevent large epidemics of RYMV. Keywords : Rice-feeding insects, West Africa, virus transmission, relative abundance, occurrence, rice ecology

Optimization of pyrolysis conditions for char production from rice husks and its characterization as a precursor for production of activated carbon

Response surface methodology was employed to optimize pyrolysis conditions for production of char with maximum yield, fixed carbon content, and with minimum ash content from Uganda’s New Rice for Africa (NERICA) 1 rice husk variety. The aim was to obtain rice husk char with more suitable properties as an activated carbon precursor. Mathematical models were developed to explain the relationships between the experimental responses and the pyrolysis parameters of temperature (400–600 °C), heating rate (10–25 °C min−1), and heating period (60–120 min). The optimized rice husk char was further characterized for elemental and proximate compositions, thermal behavior, specific surface area, as well as surface functional groups. Results from the analysis of variance (ANOVA) revealed that the quadratic model best fits each of the responses. Pyrolysis temperature had the greatest influence on each of the responses, followed by heating period, and lastly heating rate. Optimum pyrolysis conditions were found to be temperature (406 °C), heating rate (10 °C min−1), and heating period (60 min), resulting in char yield, fixed carbon, and ash contents of 35.26, 55.39, and 35.01% dry basis, respectively. Compared to raw rice husk, the resulting rice husk char was found more suited as activated carbon precursor, due to its enriched carbon content (60.35%) and specific surface area (123.9 m2 g−1). Thermogravimetric analysis of the rice husk char revealed that thermal activation temperatures higher than 400 °C may be required to considerably devolatilize the char, forming a more porous activated carbon.

Complete mitochondrial genomes of three Oxya grasshoppers (Orthoptera) and their implications for phylogenetic reconstruction

Oxya is a genus of grasshoppers (Orthoptera: Acridoidea) attacking rice and other gramineous plants in Africa and Asia. In the present study, we characterized complete mitochondrial genomes (mitogenomes) of three species, Oxya japonica japonica (15,427 bp), Oxya hainanensis (15,443 bp) and Oxya agavisa robusta (15,552 bp) collected from China. The three mitogenomes contained a typical gene set of metazoan mitogenomes and shared the same gene order with other Acridid grasshoppers, including the rearrangement of tRNAAsp and tRNALys. Analyses of pairwise genetic distances showed that ATP8 was the least conserved gene, while COI the most conserved. To determine the position of Oxya grasshoppers in the phylogeny of Acrididae, we reconstructed phylogenetic trees among 64 species from across 11 subfamilies using nucleotide sequences of mitogenomes. While the tree confirms traditional classifications of Acrididae at major higher-levels, it suggests a few modifications for classifications at lower-levels.