Rice Infestation Research Articles

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.

Effect of rice establishment methods on weedy rice (Oryza sativa L.) infestation and grain yield of cultivated rice (O. sativa L.) in Sri Lanka

Weedy rice is a great threat to rice production in Sri Lanka. Selective herbicides to manage weedy rice in conventional rice cultivars are not available in Sri Lanka. In the absence of appropriate chemical control measures, cultural approaches may help to achieve effective control of weedy rice. A study was conducted in two consecutive seasons in farmers' fields at three sites (Atalla, Samanthurai, and Girithale villages) in Sri Lanka to evaluate the effect of different establishment methods (farmers' practice, random broadcast, row seeding, seedling broadcast, and transplanted rice) on weedy rice infestation and rice yield. The farmers' practice had a higher number of weedy rice panicles (60–80 m−2) than the random broadcast (39–48 panicles m−2), seedling broadcast (3–15 panicles m−2), and transplanted rice (1.3–3.0 panicles m−2) methods. The use of clean rice seeds in the random broadcast method reduced weedy rice seed production by 29–41% compared with the farmers' practice (0.6–2.0 t ha−1). Compared with the farmers' practice, the seedling broadcast method reduced weedy rice seed production by 71–87% and transplanted rice by 95–98%; and increased rice yield by 27–49% (7.5–9.1 t ha−1). At all three sites, the farmers' practice resulted in the lowest grain yield (5.1–6.7 t ha−1). Compared with the farmers' practice, the random broadcast and row seeding methods increased rice yield by up to 21% and 31%, respectively. The findings suggest that the use of clean rice seeds, the use of a row-seeded crop, and the adoption of different rice planting methods may help to suppress the spread of weedy rice.

A model of the relationship between weedy rice seed‐bank dynamics and rice‐crop infestation and damage in Jiangsu Province, China

A heavy infestation of weedy rice leading to no harvested rice has never been predicted in China due to a lack of knowledge about the weedy rice seed bank. We studied the seed-bank dynamics of weedy rice for three consecutive years and analyzed the relationship between seed-bank density and population density in order to predict future weedy rice infestations of direct-seeded rice at six sites along the Yangtze River in Jiangsu Province, China. The seed-bank density of weedy rice in all six sites displayed an increasing trend with seasonal fluctuations. Weedy rice seeds found in the 0-10 cm soil layer contributed most to seedling emergence. An exponential curve expressed the relationship between cultivated rice yield loss and adult weedy rice density. Based on data collected during the weedy rice life-cycle, a semi-empirical mathematic model was developed that fits well with the experimental data in a way that could be used to predict seed-bank dynamics. By integrating the semi-empirical model and the exponential curve, weedy rice infestation levels and crop losses can be predicted based on the seed-bank dynamics so that a practical control can be adopted before rice planting.

Effect of Weeding Regime on the Weed Infestation and Crop Performance of Transplant Aman Rice

An experiment was carried out at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymenshingh to study the effect of weeding regime on the weed infestation and crop performance on transplant aman rice. The treatments included 10 weeding regime - i) no weeding, ii) one hand weeding at 21 DAT, iii) two hand weeding at 21 and 42 DAT, iv) three hand weeding at 21, 42 and 63 DAT, v) Ronstar 25 EC @ 2.0 1ha-1 at pre-emergence, vi) 2, 4-D amine @ 1.84 1ha-1 at 42 DAT, vii) Ronstar 25 EC @ 2.0 1ha-1 at Pre-emergence + 2, 4-D amine @ 1.84 1ha-1 at 42 DAT, viii) Ronstar 25 EC @ 2.0 1ha-1 at Pre-emergence + one hand weeding at 42 DAT, ix) one hand weeding at 21 DAT + 2. 4-D amine @ 1.84 1ha-1 at 42 DAT and X) weed free. The experiment was laid out in a randomized complete block design with four replications. Weeding regime had significant effect on weed density and dry weight. Weed density and dry weight were significantly highest in the crop not weeded at all and lowest in Ronstar 25 EC @ 2.0 l ha -1 + one hand weeding . Plant height, total number of tillers hill-1, number of ear bearing tillers hill-1 , number of non ear bearing tillers hill-1 , number of grains panicle -1 ,number of sterile spike lets panicle -1, grain yield, straw yield, biological yield and harvest index were significantly affected by weeding regime. Ronstar 25 EC @ 2.0 1ha-1 + one hand weeding controlled the weeds to the greatest extent and produced the yield and yield attributes similar to those in weed free treatment. DOI: http://dx.doi.org/10.3329/jsf.v9i1-2.14645 J. Sci. Foundation, 9(1&2): 27-41, June-December 2011

Gene flow from transgenic rice to red rice (Oryza sativa L.) in the field

In this study, we simulate a transgenic rice crop highly infested with red rice to examine transgene transfer from a transgenic line (A2504) resistant to glufosinate ammonium to cohabitant red rice. The red rice was sown along with the transgenic line at the highest density found in naturally infested crops in the region. Agricultural practices similar to those used to control red rice infestation in northern Italy rice fields were used to reproduce the local rice production system. During the first 2 years, the field was treated with herbicide at the appropriate time; in the first year the dosage of herbicide was three times the recommended amount. In this first year, detectable red rice plants that escaped herbicide treatment were manually removed. Nevertheless, two herbicide-resistant hybrid plants (named 101 and 104) were identified in the experimental field during the second year of cultivation. Phenotypic and molecular characterisation suggests the hybrid nature of these two plants, deriving from crossing events involving A2504, respectively, with red rice (plant 101) and the buffer cultivar Gladio (plant 104). The progeny of two subsequent generations of the two plants were examined and the presence of the transgene detected, indicating stable transfer of the transgene across generations. In conclusion, despite control methods, red rice progeny tolerant to the herbicide can be expected following use of transgenic rice and, consequently, difficulties in controlling this weed with chemicals will emerge in a relatively short time.

Spread of herbicide‐resistant weedy rice (red rice, Oryza sativa L.) after 5 years of Clearfield rice cultivation in Italy

The weedy relative of cultivated rice, red rice, can invade and severely infest rice fields, as reported by rice farmers throughout the world. Because of its close genetic relationship to commercial rice, red rice has proven difficult to control. Clearfield (Cl) varieties, which are resistant to the inhibiting herbicides in the chemical group AHAS (acetohydroxyacid synthase), provide a highly efficient opportunity to control red rice infestations. In order to reduce the risk of herbicide resistance spreading from cultivated rice to red rice, stewardship guidelines are regularly released. In Italy, the cultivation of Cl cultivars started in 2006. In 2010, surveillance of the possible escape of herbicide resistance was carried out; 168 red rice plants were sampled in 16 fields from six locations containing Cl and traditional cultivars. A first subsample of 119 plants was analysed after herbicide treatment and the resistance was found in 62 plants. Of these 119 plants, 78 plants were randomly selected and analysed at the level of the AHAS gene to search for the Cl mutation determining the resistant genotype: the Cl mutation was present in all the resistant plants. Nuclear and chloroplast microsatellite markers revealed a high correlation between genetic similarity and herbicide resistance. The results clearly show that Cl herbicide-resistant red rice plants are present in the field, having genetic relationships with the Cl variety. Finding plants homozygous for the mutation suggests that the crossing event occurred relatively recently and that these plants are in the F2 or later generations. These observations raise the possibility that Cl red rice is already within the cultivated rice seed supply.

Effects of farmers’ cultural practices on the weedy rice infestation and rice production

An on-farm trial was conducted at the Muda Agricultural Development Authority rice fields, Kedah, Peninsular Malaysia from November, 2003 to July, 2006 to study the impacts of farmers’ cultural practices on the weedy rice infestation and rice production. Five sample farmers (A, B, C, D and E) from five different sampling sites were selected on the basis of severity of weedy rice infestation on their fields in earlier seasons. Field observations and monitoring were carried out for collecting data and recording the agronomic practices done by the farmers from land preparation to harvesting of the crops. The number of weedy rice panicles per unit area was recorded from 50 sampling spots per plot using 1 × 1 m quadrat. Rice plants and the weedy rice within the quadrats were harvested. Data on grain yields and yield components were recorded. The collected data were analyzed statistically and mean differences in weed infestation were adjudged using standard error of means. Results revealed that the farmers used different rice varieties and applied different agronomic practices, which resulted in variable intensities of weedy rice infestations and production of variable rice grain yields. The farmers A and B, who followed transplanting and water seeding for crop establishment, applied pre-planting herbicides (2 to 3 times) during land preparation and used regular surveillance and monitoring (20 to 25 times) of their plots, had less weedy rice infestation (32.22 panicles/m2) and higher rice yields (6.70 to 8.88 t/ha). The farmers C, D and E, used wet direct seeding for crop establishment, applied no or less time of pre-planting herbicides (1 time) and had less field surveillance (10 to 15 times/season), had consequently a higher weedy rice panicle density (154.94 panicles/m2) and less rice yields (3.57 to 6.27 t/ha). Key words: Farmers’ cultural practice, weedy rice infestation, wet direct seeding, water seeding, transplanting.

Integrated management of African rice gall midge (AfRGM) (<i>Orseolia oryzivora,</i> Harris and gagné), weeds and diseases of lowland rice

Studies were conducted during the 2001 and 2002 cropping years at Edozhigi and Sachi in the Southern Guinea Savannah of Nigeria to study the effect of following rice with another crop on the next rice crop. There were twelve treatments consisting of poor, good and excellent weed management and pesticidal applications against (AfRGM and diseases set up in a randomized complete block design, in twelve plots in 3 replicates. Results showed that rice treated with gramular isazofos at 0.75 kg a.i. ha–1 and benomyl at 1.0 kg/ha at 20 and 40 days after transplanting (DAT), with good weed management and a follow up crop after rice reduced AfRGM occurrence and disease incidence with a consequent increase in yield of the next rice crop. In 2001 infestation of rice by ARGM was more at Sachi than Edozhigi, while in 2002 there was low ARGM occurrence at the two locations. Brown leaf spot was high at the two locations in the two years of the trial while leaf blast was checked by the integrated control methods used in the study. Higher yields were (1.7 - 11.9 t·ha) from treated-well weeded plots that were cropped to cowpea after the 2001 rice harvest Ludwigia decurens, Sphanoclea geylanica Cyperus difformis and Lepllocidia chinensis were the widely occurring weed species at Edozhigi site while Cyperus difformis, Ipomea mvolucrata, F. awuata and Firnbristylis litoralis were weed species prevalent at Sachi site. The rice nematode, hirschmanniella sp. was recorded at the Sachi site along with other nematodes but was absent at the Edozhigi site. The net benefit farmers would derive for following this rice-dry-season crop sequence vary from US$ 172 - 427 and US$ 175 - 265 ha–1 at Sachi and Edozhigi respectively.

EFFECT OF RICE LEAFMINER INFESTATION ON RICE YIELD, AND CORRELATION BETWEEN LEAF PLANT CHEMICAL COMPONENTS AND INSECT SEVERITY

Rice leafminer, Hydrellia prosternalis Deem. is one of important rice insects, as it causes economic yield losses, particularly in late-sown rice plantations. The current study was undertaken in 2010 rice season to monitor the population fluctuations of this insect pest. The losses resulting from the pest, in different rice plantations, were evaluated. Also, the correlations among some chemical components of rice plants and severity of the insect infestation were computed. The insect adult activity, monitored by water aluminum pan traps, exhibited five peaks from May up to September. The highest two peaks were detected during the second half of July. Yield losses due to this insect pest were negligible in rice plantations sown during the recommended duration; the first half of May. High yield losses were evaluated in rice plantations sown by late May or early June; with values of losses ranging between 21.99 and 25.24 %. Chemical analysis of rice leaves revealed a negative correlation between rice infestation by H. prosternalis and each of silica (r = - 0.605**), nitrogen (r = - 0.340) and potassium (- 0.198). However, the correlation between insect infestation and phosphorus content in rice leaves was insignificantly positive. This study show the importance of avoidance of sowing rice late in the season, otherwise chemical insecticides may be required to control the insect. The collaboration between rice breeders and entomologists is required to develop rice varieties with high silica content to reduce the infestation by H. prosternalis in rice plants.

Rice plant-hopper infestation detection and classification algorithms based on fractal dimension values and fuzzy C-means

Rice plant-hopper (RPH) (Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus) infestation is considered one of the most serious disasters in rice production in Asia. In order to use visible images to detect stress in rice production caused by RPH infestation, an algorithm based on fractal eigenvalues and fuzzy C-means (FCM) has been developed. First, an experiment was designed and many visible images of rice stems were collected. Based on the pretreatment of these visible images, such as smoothing, denoising, image color space and frequency domain transformation, the relative image fractal eigenvalues were extracted by using a box-counting dimension method, and then the linear regression model and FCM clustering algorithm were developed. Results showed that it is possible to distinguish RPH gathering areas and mouldy gray spots after RPH damage on rice plant stems from healthy rice plant stems using fractal-dimension values. Most of the fractal eigenvalues based on different-sized subregional image blocks have higher correlation coefficient with the RPH quantity, and the Dskewness (skewness), Dmean (mean) and Dmoment (moment), (where Dj is the fractal-dimension value of the j-th subregional image block), based on a 16 × 16 pixel subregional image block, have higher correlation coefficients: 0.803, 0.794, and 0.799 respectively. Using RPH infestation detection and classification based on fractal eigenvalues and the FCM algorithm, the accuracy to differentiate cases in which RPH infestation had occurred or not reached 87%. The accuracy to differentiate four groups was 63.5%. The result is expected to meet the needs of actual rice production: along with the use of a micro-sensor mobile monitoring platform, the visible-image-based method based on fractal eigenvalues and the FCM algorithm can be used to obtain redundancy information for the large area of remote sensing to the stress induced by RPHs, and then to improve the monitoring accuracy in fusion decisions of integrated pest management.

Use of electronic nose technology for identifying rice infestation by Nilaparvata lugens

Plant-emitted volatiles can change after herbivore attack. Monitoring the change in volatile profiles can offer a non-destructive method for determining plant health. An electronic nose (E-nose) equipped with a headspace sampling unit was used to discriminate between volatile profiles emitted by uninfested rice plants and those emitted by rice plants exposed to different numbers of Nilaparvata lugens adults. Principal component analysis (PCA) and linear discriminant analysis (LDA) were used to investigate whether the E-nose was able to distinguish among the different pest treatments. The results indicate that it is possible to separate differently treated rice plants using E-nose signals. The stepwise discriminant analysis (SDA) and a 3-layer back-propagation neural network (BPNN) were developed for pattern recognition models. Calculations show that the discrimination rates were over 92.5% for the training data set and 70% for the testing set using SDA. The correlation coefficient between predicted and real numbers of the pest was found to be over 0.78 using BPNN. Moreover, gas chromatography–mass spectrometry (GC–MS) analysis confirmed the E-nose results. These studies demonstrate that the E-nose technology has clear potential for use as an effective insect monitoring method.

Effects of winter flooding on weedy rice ( Oryza sativa L.)

Weedy rice ( Oryza sativa L.), characterised by competitiveness, seed longevity, and dormancy is a troublesome weed to rice fields. Furthermore, its close botanical affinity to cultivated rice makes its control particularly difficult. However, winter flooding of rice fields can be an efficient technique to control weedy rice infestation by promoting weed seed decay, animal predation, or germination. The effects of winter flooding on weedy rice plant and seed densities were assessed via two methods: field study of plant densities and laboratory study of germination behaviour. In the field experiment, weedy rice plant density decreased following application of winter flooding. In fact, winter flooding resulted in more than a 95% reduction in the number of viable weedy rice seeds on the soil surface as compared to reductions in the range of 26–77% on fields left dry between rice crops. The laboratory study showed that weedy rice germinability was affected by storage duration, moisture condition, and thermal regimen. In general, seed germinability increased with storage duration. Both awnless and awned populations displayed poor germinability under low temperature seed storage, but displayed differences when moisture content varied. At −20 °C, we observed, on average, 58% of seeds to be non-viable when stored for 248 days in water. At +5 °C the awnless population showed higher germination percentages following shorter storage durations, particularly water stored seeds. At +25 °C, the highest germination values were recorded in both populations after dry storage, whereas in water, total germination of the awnless population was inversely related to storage duration. Under typical field temperatures, in dry conditions germination behaviour was intermediate between that displayed at +5 °C and +25 °C, while storage in water resulted in a faster dormancy breaking in both populations. The results suggest that winter flooding can be a useful practice to mitigate weedy rice infestations as it promotes germination already in the autumn, before rigorous winter conditions, and favours the decay of non-germinated seeds under low temperature conditions.

Genetic diversity of weedy red rice (Oryza sativa) in Arkansas, USA

Shivrain VK, Burgos NR, Agrama HA, Lawton‐Rauh A, Lu B, Sales MA, Boyett V, Gealy DR & Moldenhauer KAK (2010). Genetic diversity of weedy red rice (Oryza sativa) in Arkansas, USA. Weed Research50, 289–302.SummaryWeedy red rice (Oryza sativa) is a problematic weed in cultivated rice. About 50% of US rice is produced in Arkansas and 60% of these fields have some red rice infestation. Red rice populations are morphologically and phenologically diverse. We hypothesise that red rice in Arkansas has high genetic diversity, which underlies its wide phenotypic diversity, and that some alleles from cultivated rice have been introgressed into red rice during more than a century of coexistence. We tested 137 red rice accessions from four ecological zones in Arkansas and 36 cultivars that have been grown in Arkansas in the past century. Twenty‐seven rice microsatellite primers, distributed across 12 chromosomes, were used to generate molecular markers. The overall Nei’s genetic distance (GD) of red rice accessions was 0.70. Rice grown in the last century had an overall GD of 0.26. The awnless strawhull red rice was genetically distant from blackhull (GD = 0.55) and brownhull (GD = 0.60) red rice types. Nei’s GD between blackhull and brownhull red rice was 0.42. Brownhull and blackhull formed one genotypic cluster, whereas the majority of strawhull red rice formed another cluster. Within blackhull red rice, the GD was 0.76, whereas for awnless strawhull it was 0.68, 0.75 for awned strawhull and 0.80 for brownhull types. The gene diversity of blackhull and strawhull correlated with zone of origin. A quarter of the red rice accessions share common alleles with cultivated rice. A diverse complex of weedy populations has evolved in a region devoid of other weedy and wild Oryza species.

Diâmetro do trado e número de amostras para quantificação do banco de sementes de arroz-vermelho do solo

Com o objetivo de determinar o diâmetro ideal do trado e o número de amostras necessárias para quantificar o banco de sementes de arroz-vermelho, foram realizados levantamentos em lavouras de arroz irrigado, no Município de Santa Maria, Rio Grande do Sul (RS), Brasil. O experimento foi conduzido em três áreas de 400m² (20x20m), com diferentes níveis de infestação, sendo considerado nível baixo, médio e alto, respectivamente, 71, 282 e 498 sementes de arroz-vermelho por m², coletadas com trados de 5, 10 e 15cm de diâmetro. Os resultados mostraram que, quanto maior o diâmetro do trado, menor foi o CV entre as amostras. O trado com 10cm de diâmetro foi mais funcional e necessitou de 280, 55 e 31 (D=20%); 33, nove e seis (D=60%); e 13, quatro e três (D=100%) amostras de solo, respectivamente, para as infestações de 71, 282 e 498 sementes de arroz-vermelho por m². O número de amostras de solo necessário para melhor estimar populações de sementes de arroz-vermelho é variável com o número médio de sementes no solo e com a precisão desejada.

Assessment of the severity of bacterial leaf blight in rice using canopy hyperspectral reflectance

Bacterial leaf blight (BLB) is an important vascular disease of irrigated rice and serious infestations may cause a significant loss of yield. This study analyzed hyperspectral canopy reflectance spectra of two rice cultivars with different susceptibilities to BLB to establish spectral models for assessing disease severity for future site-specific management. The results indicated that wavebands from 757 to 1039 nm were the most sensitive region of the spectrum for the moderately susceptible cultivar TNG 67, whereas most narrow bands showed a significant relationship for the highly susceptible cultivar TCS 10. All the spectral indices (SIs) calculated had significant relationships with proportions of infested area in cultivar TCS 10, but only two SIs correlated significantly with cultivar TNG 67. The relation between the severity of the disease and spectral reflectance for the less susceptible cultivar TNG 67 can be improved by using a multiple linear regression approach.

Red Rice (Oryza sativa) Emergence Characteristics and Influence on Rice Yield At Different Planting Dates

Cultivated rice yield losses due to red rice infestation vary by cultivar, red rice density, and duration of interference. The competition effects of red rice could be influenced further by emergence characteristics, red rice biotype, and planting time of cultivated rice. We aimed to characterize the emergence of red rice biotypes at different planting dates and evaluate the effect of red rice biotype, rice cultivar, and planting date on cultivated rice yield loss. Field experiments were conducted at the Southeast Research and Extension Center, Rohwer, AR, and at the Arkansas Rice Research and Extension Center, Stuttgart, AR, in the summer of 2005 and 2006. The experimental design was a split-split plot with three or four replications. Planting time, ClearfieldTM(CL) rice cultivar, and red rice biotype were the main plot, subplot, and sub-subplot factors, respectively. There were three planting times from mid-April to mid-May at 2-wk intervals. CL rice cultivars, CL161 and hybrid CLXL8, and 12 red rice biotypes were planted. The emergence rate and coefficient of uniformity of germination differed among some red rice biotypes within a planting time. Planting date affected the emergence characteristics of red rice biotypes. The mean emergence rate of red rice was 0.043 d−1in the mid-April planting and 0.058 d−1in the late April planting. For the mid-April planting, 50% of red rice biotypes emerged in 20 ± 2 d compared with 15 ± 2 d for CL rice cultivars. Yield losses due to red rice biotypes generally increased in later planting dates, up to 49%. Yield losses due to interference from red rice biotypes ranged from 14 to 45% and 6 to 35% in CL161 and CLXL8, respectively. Cultivated rice became less competitive with red rice in later plantings, resulting in higher yield losses.

Effect Of Planting Time And Nitrogen Levels On Infestation Of Rice By African Rice Gall Midge Orseolia Oryzivora Harris And Gagné In Southeastern Nigeria

Field experiments were conducted to evaluate the effect of time of planting (July 14, August 11 and September 8) and varying nitrogen levels (0, 80 and 160 N/ha) on infestation of rice by African rice gall midge and grain yield. The experiments were conducted at West African Rice Development Association (WARDA) research farm at Ogidiga near Abakaliki during the wet seasons of 2002 and 2003 farming seasons. The rice variety used for the experiments was ITA 306. Percentage infestations of rice by African rice gall midge were significantly highest on rice planted on July 14. Percentage infestations by African rice gall midge also significantly increased with the increasing levels of nitrogen up to 160 kg N/ha irrespective of time of planting. Results show that grain yields were highest on rice planted on August 14 for both seasons. However, the response of grain yield to nitrogen was optimum at 80 kg N/ha. Further increase in nitrogen did not cause any significant different in grain yield for both seasons. Keywords : Time of planting, Nitrogen levels, Infestation, Rice, African Rice Gall Midge Journal of Technology and Education in Nigeria Vol. 10 (1) 2005: pp. 39-45

Effect Of Dates Of Transplanting, Plant Spacing And Nitrogen Levels On The Incidence Of African Rice Gall Midge Harris And Gagné (Diptera: <i>Cecidomyiidae</i>) In Southeastern Nigeria

Field experiments were conducted to evaluate the effect of dates of transplanting (July 31, August 14 and August 28), plant spacing (10 cm x 10 cm, 20 cm x 20 cm and 30 cm x 30 cm) and nitrogen levels (0 kg ha-1, 80 kg ha-1 and 160 kg ha-1) on infestation of rice by African rice gall midge. The experiments were conducted at West African Rice Development Association (WARDA) research farm at Ogidiga near Abakaliki during the 2002 and 2003 farming seasons. The experiments were laid out in split-split- plot in randomized complete block design. The rice variety used for the experiments was ITA 306 a susceptible variety to African rice gall midge. Percentage infestation of rice by African rice gall midge were most severe (47. 5% and 41.32%) on earliest transplanted rice (July 31) irrespective of plant spacing and nitrogen levels for all the experimental years. Similarly rice plants on plots with the least plant spacing (10 cm x 10 cm) had the highest infestation of 40.6% and 33.40 % by African rice gall midge for 2002 and 2003 respectively. Severity of infestation was found to decline with the increasing plant spacing. Percentage infestation increased significantly (P=O.05) with the increasing levels of nitrogen with 34. 3% and 25.75 % infestation recorded in plots treated with 160 kg ha –1. Date of transplanting, plant spacing and nitrogen level significantly influenced the grain yield of rice with highest grain yield of 188.9 g, 307. 9 g and 198. 9 g for the second planting date, 30 cm x 30 cm plant spacing and 80 kg ha -1 nitrogen levels respectively. Keywords: Dates of transplanting, plant spacing, nitrogen levels, African rice gall midge and grain yield,Journal of Technology and Education in Nigeria Vol. 10 (2) 2005: pp. 30-37

Red Rice (Oryza sativa) Status after 5 Years of Imidazolinone-Resistant Rice Technology in Arkansas

Certified Crop Advisors of Arkansas and members of the Arkansas Crop Consultants Association were surveyed in fall 2006 through direct mail to assess the current situation of the red rice problem and early impact of imidazolinone-resistant (IMR) rice technology on red rice infestation. The information generated represented 40% (226,800 ha) of rice production areas in Arkansas. Barnyardgrass and red rice were the most problematic weeds, with 62% of fields infested with red rice. The estimated economic loss due to red rice averaged $274/ha. Red rice infestation was prevented mostly by crop rotation (96%) and use of certified seed (86%). Of the red rice–infested fields, 38% had light infestation and 26% had severe red rice problems before adopting IMR rice. Thirty-seven percent of infested fields had been planted with IMR rice once and 43% at least twice. Approximately 85% of the consultants reported > 90% red rice control when using IMR rice. The majority (92%) of IMR rice growers rotate to other crops, mostly soybean. Unsuitable field condition was the main reason for growing only rice. After 3 seasons, the consultants perceived that red rice infestation level declined by 77% on average. The herbicide-resistance gene had escaped to red rice in some fields, and 90% of growers are exerting effort to mitigate outcrossing.Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, red rice, Oryza sativa L. ORYSA, rice, Oryza sativa L, soybean, Glycine max (L.) Merr

Origins and population genetics of weedy red rice in the USA

Weedy red rice (Oryza sativa spontonea) is a persistent and problematic weed of rice culture worldwide. A major hypothesis for the mechanism of production of this weed in South and Southeast Asia is hybridization between cultivated rice (Oryza sativa) and wild rice (Oryza rufipogon). However, weedy red rice can often be found outside the range of O. rufipogon leaving questions on the origin and process behind weedy rice infestations. In the USA, weedy red rice was first documented as early as 1846 and has continued to affect rice production areas. In this study, we attempt to identify the origin and population structure of weedy red rice sampled from the USA using both DNA sequence data from a neutral nuclear locus as well as microsatellite genotype data. Results suggest that two major accessions of weedy rice exist, strawhull and blackhull, and these forms may both hybridize with the cultivated rice of the USA, O. sativa japonica. Using population assignment of multilocus genotype signatures with principal component analysis and structure, an Asian origin is supported for US weedy rice. Additionally, hybridization between strawhull and blackhull varieties was inferred and may present the opportunity for the production of new weedy forms in the future.