Rice Infestation Research Articles

Off-season management with herbicides as an alternative to reduce weed infestation in paddy rice production systems

Abstract Background: Weed management is a challenge in paddy rice production, mainly due to the dispersal of a population resistant to herbicides. Objective: To assess the efficacy of chemical weed control in the off-season to reduce weedy rice and other species in water-seeded or drilled rice. Methods: Two experiments were carried out in a flat field to water-seeded or drilled rice, in randomized block design. The water-seeded system treatments were organized in a split-plot design. In the plot were evaluated two water management in the off-season (with or without continuous flooding), and in the subplot nine herbicides-treatments were evaluated (Check, clomazone at 0.72 and 1.08 kg a.i. ha-1, oxadiazon at 1.00 and 1.50 kg a.i. ha-1, oxyfluorfen at 0.312 and 0.48 kg a.i. ha-1, S-metolachlor at 1.44 kg a.i. ha-1, and flumioxazin a 0.075 kg a.i. ha-1). In the drilled rice experiment, the treatments were organized in a two-factor factorial. The factor A was nine herbicides treatments (the same herbicide and rates applied in water-seeded experiment) and the factor B was two application time (73 and 43 days before of rice-sowing). Results: Off-season management was efficient to reduce weedy rice infestation only on the paddy rice system using the pre-germinated seeds. In this assay, flumioxazin was an efficient alternative to giant arrowhead control, however the selectivity of this herbicide treatment needs to be studied. In dry-seeded system, herbicide sprayed in off-season reduced barnyardgrass infestation until the paddy rice sowing. Conclusions: The off-season management was efficient to reduce weedy rice and giant arrowhead infestation in water-seeded system, and barnyardgrass infestation in drill-seeded system.

Food Specialization of the Lesser Grain Borer, Rhyzopertha Dominica F. (Coleoptera: Bostrichidae)

Observations of stored grain, products from its manufacture and materials from plant origin in the storage-silo bases in Bulgaria were conducted from 1990 till 2019 to establish the food specialization and trophic chains of Rhyzopertha dominica F. The insect was found mostly in wheat grain – 49,2% from all expected samples, followed by barley – 18,5% and maize – 15,2%. The infestation of oats, rye, rice, and sorghum was 7.3%, 5.7%, 2.6%, and 1.5%, respectively. R. dominica infested also seeds of sugar and technical cane, millet, buckwheat, ryegrass, and Dactylis glomerata L. It was established in roots and fruits of Ecbalium elaterium L., roots of wild pumpkin – Bryonia alba L., bark of Frangula alnus Mill., crashed fruits of Aesculus hippocastanum L., fruits of Paleurus aculeatus L., seeds of quinoa Chenopodium quinoa, seeds of Trigonella foenum-grecum, seeds of Hibiscus cannabinus, seeds of Beta vulgaris L. and also in grain foods like "Kus-Kus". R. dominica did not develop in dried beans, lentil, edible and forage peas, vetch, chick-peas, soy, alfalfa, and clover. It was not found in storages with sunflower, rape, and coriander, and kernels - peanuts, groundnuts, hazelnuts, almond, sesame and pumpkins seeds.

When West Meets East: The Origins and Spread of Weedy Rice Between Continental and Island Southeast Asia.

Weedy crop relatives are among the world’s most problematic agricultural weeds, and their ability to rapidly evolve can be enhanced by gene flow from both domesticated crop varieties and wild crop progenitor species. In this study, we examined the role of modern commercial crop cultivars, traditional landraces, and wild relatives in the recent emergence and proliferation of weedy rice in East Malaysia on the island of Borneo. This region of Malaysia is separated from the Asian continent by the South China Sea, and weedy rice has become a major problem there more recently than on the Malaysian peninsular mainland. Using 24 polymorphic SSR loci and genotype data from the awn-length domestication gene An-1, we assessed the genetic diversity, population structure and potential origins of East Malaysian weeds; 564 weedy, cultivated and wild rice accessions were analyzed from samples collected in East Malaysia, Peninsular Malaysia and neighboring countries. While there is considerable evidence for contributions of Peninsular Malaysian weed ecotypes to East Malaysian populations, we find that local crop cultivars and/or landraces from neighboring countries are also likely contributors to the weedy rice infestations. These findings highlight the implications of genetic admixture from different cultivar source populations in the spread of weedy crop relatives and the urgent need for preventive measurements to maintain sustainable crop yields.

Economic Benefits of Controlling Red Rice: A Case Study of the United States

Red rice (O. sativa) is one the most prevalent and damaging weed problems in direct seeding rice systems worldwide and can cause significant losses in rice productivity and quality. Red rice has been a problem in the United States for decades, and it is a growing problem in Asia, where 90 percent of the global rice production occurs. Unlike for other crops, where genetically engineered (GE) herbicide tolerant varieties are available, to date, Clearfield (CL) and Provisia rice are the only technologies available to selectively control red rice using chemical herbicides in commercial rice fields. We develop a counterfactual scenario without CL rice and ascertain the yield and quality losses due to red rice infestation in the Mid-South of the United States. Our findings suggest that even with the higher costs of CL rice, relative to non-CL rice, that the returns are $0.15, $0.36, and $0.54 more for every dollar invested than non-CL rice with a light, moderate, and heavy initial red rice infestation rate, respectively. These results imply that the higher upfront costs for CL rice are offset by more than proportional higher profits relative to their non-CL rice counterparts.

GRAIN YIELD OF DIFFERENT SOYBEAN GENOTYPES CULTIVATED IN LOWLAND SOILS IN THREE SOWING TIMES

<p>Soybean (Glycine max L. Merril) has been cultivated in regions of lowland soils in crop rotation with irrigated rice in order to reduce the infestation of red rice and due to the attractive soybean value in the world market. Soybean cultivation under this condition is subject to possible soil flooding, requiring recommendations of genotypes adapted to this environment. The aim of this study was to evaluate the grain yield of soybean genotypes grown in floodplain environment at three different sowing times. Cultivars used were A 6411 RG, A 7321 RG, BMX Apolo RR, BMX Ativa RR, BMX Energia RR, BMX Potência RR, BMX Turbo RR, IGRA RA 518 RR, IGRA RA 626 RR, IGRA RA 628 RR, NA 5909 RG , NS 6262 RR, NS 7100 RR, RA 728 RR and VMax RR; sown in October, November and December. The experimental design was 15 (cultivars) x 3 (times) factorial with 4 replicates. Significant differences were observed for sowing times and cultivars, as well as for the interaction between the two factors. Cultivars sown in November and December provided higher yields than those sown in October. BMX Turbo RR cultivar showed higher consistency for soybean yield in lowland, considering the sowing times evaluated. For early sowing (October and November), A 6411 RG cultivar presented higher grain yield compared to the other cultivars.</p>

Effects of Tillage System and Weed Control Method on Weed Infestation and Yield of Lowland Rice (Oryza sativa L.)

A two–year experiment was carried out to determine the effects of tillage (heap and level, hoe plough and herbicide-based zero tillage) and weed control methods (no weeding, hoe weeding at 25 days after transplanting (DAT), hoe weeding at 25 and 45 DAT, application of post-emergence herbicide propanil plus 2,4-D (Orizo Plus, Proficol Calle, Baranquilla, Colombia) at 25 DAT followed by hoe weeding at 45 DAT, and Orizo Plus® at 25 and 45 DAT) on weed infestation and performance of lowland rice in Badeggi, Nigeria. Reduced weed density and biomass, taller rice plants, and higher panicle and paddy yield were recorded in most heap and level treatments. Two hoe weedings only and Orizo Plus® at 25 DAT followed by one hoe weeding resulted in significantly lower weed density and biomass, more panicles and significantly higher paddy yield. Hoe plough in combination with two hoe weedings had the lowest weed density. Zero tillage planting in combination with two hoe weedings produced weed biomass comparable to heap and level in combination with the application of Orizo Plus® at 25 DAT followed by one hoe weeding. These results suggest that hoe plough followed by hoe weeding at 25 and 45 DAT, or heap and level tillage followed by application of Orizo Plus® at 25 DAT and hoe weeding at 45 DAT effectively controlled weeds and increased plant height, panicle number and paddy yield of transplanted rice.

The implications of red rice on food security

Due to its genetic similarity with commercial rice, red rice is one the most damaging weeds in direct seeding rice systems. Using an integrated approach to estimate the economic, environmental, and food security impact of red rice infestation in the U.S. as an empirical case study, we find that losses under a moderate infestation scenario from 2002 to 2014 amount to 5.7 million tons or 6%, with an environmental cost of $457 million. The resulting production loss in the U.S. is enough to feed 12 million additional people a year. We extend these findings to selected Asian countries where adoption of direct rice seeding is increasing, and estimate that red rice can have significant impacts on global food security.

Uji Fitokimia Dan Uji Toksisitas Ekstrak Daun Gamal (Gliricidia Sepium) Sebagai Insektisida Nabati

Research on phytochemical test and toxicity tests of leaf extract of Gliricidia (Gliricidia sepium) as an insecticide plant have been conducted.. Gliricidia leaves macerated dried samples using ethanol and fractionated using a solvent n-hexane and ethyl acetate. Phytochemical test showed that it contains alkaloids, steroids, triterpenoids, phenolic and flavonoid in total extract. N-hexane fraction containing steroids, triterpenoids and the phenolic. Ethyl acetate fraction containing steroids, triterpenoids, flavonoids, phenolic and saponin. Toxicity test method Brine Shrimp Lethality Test (BSLT) showed that the ethyl acetate fraction had the highest toxicity on shrimp larvae with LC50 values ​​of 49.29 ppm. Test Activity as an insecticide plant conducted in animal infestation of rice (Sitophylusorizae Leach) Value LC50 is determined using a regression line between log concentration and probit mortality, the LC50 obtained is 2.831%. Analysis of the content of chemical compounds in the ethyl acetate fraction from the leaves of Gliricidia produces 9 peak component compounds at mass spectra are shown from the results of GC-MS with 2 peaks compound dominant that serves as an insecticide plant them 2-(3H)-Benzofuranone, 3-methyl and dl-Limonene

Bacterial Community Structure in the Asian Rice Gall Midge Reveals a Varied Microbiome Rich in Proteobacteria

The Asian rice gall midge (ARGM) has emerged as a model gall forming pest of rice. The ARGM infestation of rice results in failure of panicle formation and economic loss. Understanding the molecular basis of ARGM-rice interactions is very crucial in order to control this devastating pest of rice. The current investigation was devised to identify bacterial communities present in the ARGM and in addition the bacterial diversity in the maggots during their interaction with susceptible or resistant rice varieties. Sequencing of 16S rRNA bacterial gene (V3-V4 region) revealed differences in the microflora of the ARGM maggots feeding on susceptible or resistant rice hosts. Results revealed that Wolbachia was the predominant bacterium in pupae and adults while Pseudomonas was predominant in maggots. Further, we observed that members of proteobacteria were predominant across all the samples. There was high species diversity in maggots isolated from susceptible rice and a high representation of unclassified bacteria in maggots isolated from resistant rice. This is the first study that reports variation of microbiome of the ARGM, based on host phenotype from which it was isolated, and results suggest that these variations could have an important role in host’s susceptibility.

Efficacy of different botanical and chemical insecticides against rice hispa (Dicladispa armigera)

An experiment was carried out in the Entomology Field Laboratory of Bangladesh Agricultural University (BAU), Mymensingh to determine the efficacy of six botanicals and four chemical insecticides for controlling rice hispa, Dicladispa armigera during the period of July to December 2013. In conducting the experiment BR11 rice variety was selected where ten treatments namely six botanicals such as Neem oil, Mahogany oil, Mixture of Neem and Mahogany oil, Bishkatali leaf extract, Pitraj leaf extract and Mixture of Bishkatali and Pitraj leaf extract and four chemical insecticides Sevin85SP, Advantage20EC, Cup50EC, Kinalux 25EC were laid out in the Randomized Complete Block Design (RCBD). Overall leaf infestation by rice hispa and infestation by adults and grubs separately were recorded at different time intervals. In addition to these, overall effect of pest infestation on the grain yield of rice was also examined. Among the six botanicals, Neem oil was most effective in controlling rice hispa, as overall leaf infestation was 21.20% and the infestation by adults and grubs were 14.43% and12.57%. On the other hand, among chemical insecticides, maximum efficacy was found under the treatment of Sevin 85SP where minimum leaf infestation was 9.22%, infestation by adults and grubs were 5.88% and 5.00% respectively. In case of yield, Sevin 85SP (4.62 ton/ha) showed the best efficacy in comparison to other treatments. Therefore, application of Sevin 85SP (3.46ml/L) and Neem oil (2ml/100ml) were examined as the best options in controlling rice hispa. So, it could be recommended to use Sevin 85 SP and Neem oil for the management of rice hispa.Progressive Agriculture 28 (2): 64-72, 2017

Recognition of the Duration and Prediction of Insect Prevalence of Stored Rough Rice Infested by the Red Flour Beetle (Tribolium castaneum Herbst) Using an Electronic Nose.

The purpose of this research is to explore the feasibility of applying an electronic nose for the intelligent monitoring of injurious insects in a stored grain environment. In this study, we employed an electronic nose to sample rough rice that contained three degrees of red flour beetle (Tribolium castaneum Herbst) infestation for different durations—light degree (LD), middle degree (MD), and heavy degree (HD)—and manually investigated the insect situation at the same time. Manual insect situation investigation shows that, in all three rice treatments, the insect amounts gradually decreased after infestation. When the insect population of stored rough rice was under 13 insects per 60 g of rough rice, the natural speed of decrease of the insect population became very slow and reached the best artificial insect killing period. Linear discriminant analysis (LDA) provided good performance for MD and HD insect harm duration identification, but performed poorly for LD insect harm duration identification. Both k-means clustering analysis (K-means) and fuzzy c-means analysis (FCM) effectively identified the insect harm duration for stored rough rice. The results from the back-propagation artificial neural network (BPNN) insect prevalence prediction for the three degrees of rough rice infestation demonstrated that the electronic nose could effectively predict insect prevalence in stored grain (fitting coefficients were larger than 0.89). The predictive ability was best for LD, second best for MD, and least accurate for HD. This experiment demonstrates the feasibility of electronic noses for detecting both the duration and prevalence of an insect infestation in stored grain and provides a reference for the intelligent monitoring of an insect infestation in stored grains.

A salivary EF-hand calcium-binding protein of the brown planthopper Nilaparvata lugens functions as an effector for defense responses in rice

The brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), a major pest of rice in Asia, is able to successfully puncture sieve tubes in rice with its piercing stylet and then to ingest phloem sap. How BPH manages to continuously feed on rice remains unclear. Here, we cloned the gene NlSEF1, which is highly expressed in the salivary glands of BPH. The NlSEF1 protein has EF-hand Ca2+-binding activity and can be secreted into rice plants when BPH feed. Infestation of rice by BPH nymphs whose NlSEF1 was knocked down elicited higher levels of Ca2+ and H2O2 but not jasmonic acid, jasmonoyl-isoleucine (JA-Ile) and SA in rice than did infestation by control nymphs; Consistently, wounding plus the recombination protein NlSEF1 suppressed the production of H2O2 in rice. Bioassays revealed that NlSEF1-knockdown BPH nymphs had a higher mortality rate and lower feeding capacity on rice than control nymphs. These results indicate that the salivary protein in BPH, NlSEF1, functions as an effector and plays important roles in interactions between BPH and rice by mediating the plant’s defense responses.

Morphological Characterization of Weedy Rice Populations from Different Regions of Asia

Weedy rice produces a low number of grains per plant and is considered undesirable in cultivated rice fields. It spreads rapidly because of its high phenotypic plasticity and seed shattering. We used the RID14 marker to identify the genotypes governing red and white pericarp color in weedy rice. We then evaluated 18 characters of 199 weedy rice accessions (5 rice-growing regions in Asia) and 24 of cultivated rice as control, and analyzed them using coefficients of variation, principal component analysis, and cluster analysis. Our results showed that weedy rice accessions and cultivated rice populations from different regions of Asia were significantly different in one or more of their morphological characteristics. Weedy rice significantly differed from cultivated rice in plant height at vegetative growth phase, and in pericarp color and seed shattering during the reproductive growth phase. According to principal component analysis, weedy rice populations were significantly separated from cultivated rice in North China, Korea, Southeast Asia, Korea, and South China. We used principal component analysis and cluster analysis to categorize weedy rice populations into 3 main groups: Group 1 from Korea and Northern China; group 2 from Southern China and Southeast Asia; and group 3 from Eastern China. This study established an index for morphological characteristics of weedy rice to facilitate its identification the fields, which are expected to provide a theoretical basis for weedy rice infestation control in Asia.

Impact of volunteer rice infestation on yield and grain quality of rice.

Volunteer rice (Oryza sativa L.) grains may differ in physicochemical traits from cultivated rice, which may reduce the quality of harvested rice grain. To evaluate the effect of volunteer rice on cultivated rice, fields were surveyed in Arkansas in 2012. Cropping history that included hybrid cultivars in the previous two years (2010 and 2011) had higher volunteer rice infestation (20%) compared with fields planted previously with inbred rice (5.5%). The total grain yield of rice was reduced by 0.4% for every 1% increase in volunteer rice density. The grain quality did not change in fields planted with the same cultivar for three years. Volunteer rice density of at least 7.6% negatively impacted the head rice and when infestation reached 17.7%, it also reduced the rice grain yield. The protein and amylose contents of rice were not affected until volunteer rice infestation exceeded 30%. Crop rotation systems that include hybrid rice are expected to have higher volunteer rice infestation than systems without hybrid rice. It is predicted that, at 8% infestation, volunteer rice will start to impact head rice yield and will reduce total yield at 18% infestation. It could alter the chemical quality of rice grain at >30% infestation. © 2016 Society of Chemical Industry.

Effect of Nitrogen on Weed Infestation and Performance of Boro Rice Under Two Selected Herbicides

A field experiment was conducted at the experimental farm of Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Salna, Gazipur from November 2013 to May 2014 to determine the effect of nitrogen and herbicide on weed infestation and performance of Boro rice (cv. BRRIdhan28). Five nitrogen doses i.e. 0 , 50.6 , 101.2 , 151.8 and 202.4 kg ha-1 under selected pre-emergence and post-emergence herbicides along with one weed free and control (unweeded) treatment were imposed in the experiment. Nine weed species was found to dominate in the experimental plots where Scirpus maritimus L. showed the maximum visual abundance (58%) followed by Leersia hexandra sw., Paspalam distichum L. and Fimbristylis miliacea L. Post-emergence herbicide contributed to higher control efficiency than that in pre-emergence herbicide. Post-emergence herbicide without receiving nitrogen showed the highest weed control efficiency (97.39) at 60 days after transplanting. Treatment receiving N @ 200.4 kg ha-1 under post-emergence herbicide showed the highest number of tiller per hill (13.00), total dry matter (1568.6 g m-2), panicles per hill (10.60), filled grains per panicle (125.20) and grain yield (6.46 t/ha). N-dose 151.8 kg ha-1 under postemergence herbicide contributed to the second highest grain yield (6.41 t ha-1) with the highest benefit cost ratio of 1.60 but 50.6 kg N ha-1 under post-emergence herbicide showed the maximum Nitrogen use efficiency of 0.49. The study revealed that nitrogen dose up to 151.8 kg ha-1 might be increased above the recommended dose under coverage of a suitable post-emergence herbicide for profitable rice production.Bangladesh Agron. J. 2015, 18(2): 53-63

ECONOMIC THRESHOLD AND ECONOMIC INJURY LEVELS FOR RICE STEM BORER, USING SIMULATED WHITE HEADS IN RICE

Rice (Oryza sativa L.) ranks second to wheat in area and production on the global level. Unfortunately, it is attacked by several insect pests. The rice stem borer, Chilo agamemnon Bles. is the most important in Egypt. The current investigation was carried out at the Experimental Farm of Sakha Agricultural Station, Kafr EL-Sheikh Governorate in 2013 and 2014 rice seasons using two cultivars, Giza 178 (high tillering capacity) and Egyptian Jasmine (medium tillering capacity) to establish the correlation between borer infestation as white heads and rice yield losses to determine the economic threshold and injury levels of C.agamemnon infestation in rice fields. Due to the great difficulty to use the technique of artificial infestation by the rice stem borer, the simulated technique (panicle removal) was applied to induce different levels of simulated white heads. The panicles were removed by hand to get gradual levels of stimulated white heads; 0, 2, 4,6, 8, 10, 12, 14 and 16%. Yield components (panicle weight, 1000-grain weight and filled grain %) increased at the higher levels of panicle removal. This could be interpreted in the light of phenomenon compensation. This phenomenon suggests that the nutrients going to removed panicles are translocated to the adjacent ones. Consequently, the panicles adjacent to the removed ones become healthier than normal, and compensate, to a certain extent, the removed ones. The final grain yield was negatively affected, in the current study, by high levels of panicle removal. In Giza 178 rice cultivar (high tillering), the grain yields were 2315, 2295 and 2311, match to 1815, 1755 & 1781 g/ 2 m2 at 0, 2 & 4% panicle removal, respectively. However, in both cultivars, the lowest grain yields were at 12, 14 1nd 16 % simulated white head (panicle removal). Considering the cost of chemical control against the rice stem borer, and obtained grain yield at different levels of simulated white heads, economic threshold and economic injury levels were estimated. In Giza 178, the economic threshold was determined as 10 and economic injury as 12 % white heads (panicle removal), while the economic threshold level of Egyptian Jasmine cultivar was determined as 8% white heads, and economic injury as 10% white heads. These results are important to the decision makers and rice growers to avoid using insecticides before the rice stem borer infestation reaches the economic threshold. On the other hand, economic threshold level should be assessed under several circumstances, e.g. location, cultivar, cultural practices, prices of insecticides and prices of rice.

Herbicide and winter flood treatments for controlling volunteer rice off-season

Field experiments were conducted to study the efficacy of 12 herbicide treatments for volunteer rice control with, or without, winter-flooding in Stuttgart and Rohwer, Arkansas, USA over two years (2012–13 and 2013–14). Herbicides were applied either in the fall or at 35 d prior to planting rice in the spring. Commercially harvested Clearfield™ long-grain inbred rice 'CL152' was used as volunteer rice seed, broadcasted and lightly incorporated in October, 2012 and 2013. 'Jupiter' (medium-grain inbred, conventional rice) was planted in May as the rice crop. Winter-flood was initiated soon after the fall herbicide treatments were applied and terminated in February. Winter-flood reduced volunteer rice germination by 34% in 2013 and by 40% in 2014. Some fall herbicide treatments, without winter flood, generally caused more injury to the rice crop planted in the spring than the winter-flooded treatments. Fall application of pyroxasulfone (0.12 kg ha−1), flumioxazin (0.14 kg ha−1), and sulfentrazone (0.34 kg ha−1) as well as pre-plant application of pyroxasulfone (0.12 kg ha−1) and 2,4-D (2.24 kg ha−1), resulted in lower volunteer rice infestation, averaged over flood treatments. Pre-plant application of 2,4-D (2.24 kg ha−1), sulfentrazone in the fall (0.34 kg ha−1) and pyroxasulfone pre-plant (0.12 kg ha−1) injured the rice crop by 20%, 23%, and 47%, respectively. Fall application of pyroxasulfone (0.12 kg ha−1) followed by a lower rate of 2,4-D (1.12 kg ha−1) 35 d pre-plant caused minimal (6%) crop injury and did not reduce yield. This treatment provided better volunteer rice control (73%) than pyroxasulfone alone at 0.12 kg ha−1 applied in the fall (64%). To evaluate the overwintering potential of hybrid and non-hybrid volunteer seeds, these seed types were planted at three depths (0, 7.5, 15 cm) in flooded and non-flooded conditions in a buried-pot experiment at Stuttgart and Rohwer over 2 years. Winter-flood reduced rice germination by 50% in 2013–14 and 40% in 2014–15 (averaged over seed type and burial depth), after 160 d and 130 d of burial, respectively. After the winter, the viability of hybrid seed (germinable + dormant) was higher (13 and 53%) than that of non-hybrid seed (8 and 27%) in both years.

Weedy rice: A threat to rice production in Sri Lanka

Weedy rice (Oryza sativa L. f. spontanea), one of the four most significant weeds, is globally well known as a problem in the rice industry. The economic and environmental problems they pose include those related to rice crop production, milling for commerce, quarantine regulations and seed trade. Weedy rice possesses a number of common features with other weeds and distinctive characteristics such as phylogenetic and morphological resemblance to cultivated rice. Weedy rice is a difficult-to-manage weed when coexists in rice ecosystems causing economic losses to rice. Currently, weedy rice has been found in nearly all the rice growing regions in Sri Lanka. The estimated rice yield losses caused by the infestation of weedy rice varied largely from 40% to 90%, depending on its density and degree of shattering in rice fields. Effective control of weedy rice must be taken into immediate consideration to secure rice production in the country. The promotion of the use of certified seed paddy without weedy rice contamination should be the immediate and key step in the implementation of efficient control mechanism followed by other integrated weed control measures to reduce the proliferation and limiting its distribution to non-contaminated areas. However, the outcome will be limited except all parties in the rice industry are unified and committed to control weedy rice. In contrary to all unfavorable impacts of weedy rice on rice production, high heritability values coupled with high genetic variability of its favorable characteristics could be considered in rice improvement programs and in broadening the rice gene pool. Journal of the University of Ruhuna 2015 3(1): 2-13

Seed-mediated gene flow promotes genetic diversity of weedy rice within populations: implications for weed management.

Increased infestation of weedy rice—a noxious agricultural pest has caused significant reduction of grain yield of cultivated rice (Oryza sativa) worldwide. Knowledge on genetic diversity and structure of weedy rice populations will facilitate the design of effective methods to control this weed by tracing its origins and dispersal patterns in a given region. To generate such knowledge, we studied genetic diversity and structure of 21 weedy rice populations from Sri Lanka based on 23 selected microsatellite (SSR) loci. Results indicated an exceptionally high level of within-population genetic diversity (He = 0.62) and limited among-population differentiation (Fst = 0.17) for this predominantly self-pollinating weed. UPGMA analysis showed a loose genetic affinity of the weedy rice populations in relation to their geographical locations, and no obvious genetic structure among populations across the country. This phenomenon was associated with the considerable amount of gene flow between populations. Limited admixture from STRUCTURE analyses suggested a very low level of hybridization (pollen-mediated gene flow) between populations. The abundant within-population genetic diversity coupled with limited population genetic structure and differentiation is likely caused by the considerable seed-mediated gene flow of weedy rice along with the long-distance exchange of farmer-saved rice seeds between weedy-rice contaminated regions in Sri Lanka. In addition to other effective weed management strategies, promoting the application of certified rice seeds with no weedy rice contamination should be the immediate action to significantly reduce the proliferation and infestation of this weed in rice ecosystems in countries with similar rice farming styles as in Sri Lanka.

An Appraisal of Insect Pests Associated with Cereal Grains Traded in Maiduguri, Borno State, Nigeria

This study investigated insect pest infestation of maize, millet, sorghum, rice and wheat grains traded in the three main markets namely Monday, Baga-Road and Custom-Park markets in Maiduguri, Borno state, Nigeria. Sampling lasted from January to June 2012. Samples per grain type, each weighing one kilogram, were obtained every two weeks from ten randomly selected traders per market. Each sample was sieved in the laboratory to recover all adult insects present, both at sampling and also after one month stay (laid out in a completely randomized design). In each market, Sitophilus zeamais Motschulsky and Rhyzopertha dominica (F.) followed by Tribolium castaneum Herbst, Sitophilus oryzae (Linnaeus), Trogoderma granarium (Everts) or Cryptolestes sp. were the insect pests commonly found attacking more (between two to five) grain types. Observed highest and lowest mean insect numbers were respectively by S. zeamais in maize grains (12.13 individuals in Monday market) and T. granarium in wheat grains (0.13 individuals in Baga-Road market). Results unveil that among three markets, higher mean total numbers of insects were present in maize, rice or wheat (18-33). For all grain types, the mean numbers of damaged grains were significantly higher in Monday (53-357) and Custom-Park (46-302) than in Baga-Road (17-109) markets. Furthermore, the mean total number of damaged grains across markets was significantly higher maize, followed by rice and wheat (55-231) than in other grain types (37-41). The implications of all these results on insect infestation of different cereal grain types sold in these markets are discussed.