Weeds In Rice Fields Research Articles

Pharmacognostic Evaluation and Pharmacological Validation of Sphaeranthus indicus DC

Sphaeranthus indicus is an important medicinal plant in Ayurveda which grows as weed in rice fields throughout India, Sri Lanka, Australia and Africa. The present study aimed for the pharmacognostical evaluation and pharmacological validation of this high-value medicinal species. All the pharmacognostical parameters were done as per the API guideline. A simple, rapid, sensitive and reproducible method was also developed for simultaneous HPTLC quantification of two bioactive compounds eugenol and β-sitosterol in S. indicus. The HPTLC was performed on silica gel 60 F254 by using toluene/ethyl acetate/glacial acetic acid (8:2:0.2) as a mobile phase for eugenol and β-sitosterol at Rf value 0.64 and 0.48, respectively. The content of eugenol (0.03%) and β-sitosterol (0.013%) was detected in dry weight per gram. In vitro activities viz. antioxidant, antidiabetic and anti-inflammatory were done to evaluate the pharmacological potential of S. indicus. Four antioxidant models viz. DPPH, ferric reducing power, 2-deoxyribose assay and antioxidant capacity were used to determine the free radical scanning. Antidiabetic and anti-inflammatory potential were determined by using starch–iodine colour assay and inhibition of protein denaturation model. IC50 value of S. indicus extract in DPPH and 2-deoxyribose assay was found (328.96 ± 0.003 µg/ml) and (30.36 ± 0.004 µg/ml), respectively. The present study will be helpful for quality check of the raw material and monitoring batch-to-batch consistency of herbal drugs, wherein S. indicus is used as an ingredient.

Performance of Dry Direct Seeded Rice and Weeds on Sesbania Brown Manuring as Compared to Farmers’ Practice and Chemical Control Method

The research was conducted to study the comparison of farmers’ weed management practice in rice with chemical control and Sesbania co-culture. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replications and five different weed management practices. The five treatments were Farmers’ practice (two hand weeding first at 28 DAS and another at 40 DAS), Chemical practice (Bispyribac sodium as post emergence @ 25 g a.i. ha-1 at 25 DAS), Sesbania co-culture (100 kg Sesbania ha-1 and knocking down at 28 DAS), Weed free (Hand removal of weeds at 10 days’ interval) and Weedy check (No weed management). The individual plot size was 5 x 4 m2. The Sesbania co-culture and farmers’ practice were found more or less similar performance for all observed parameters but as better as compared to weedy check and chemical treatment. Sesbania co-culture was found less costly than farmers’ practice for weed management. The experiment clearly demonstrated the importance of brown manuring on effective control of weeds in rice field under dry direct seeded rice.Int. J. Appl. Sci. Biotechnol. Vol 6(3): 265-269

Limnocharis flava (L.) buchenau: An emerging wetland invader-A review

Invasive alien weeds pose a serious threat to the biodiversity and are a significant constraint to agricultural production worldwide. Water cabbage (Limnocharis flava (L.) Buchenau), is one such aquatic weed, which was introduced in Asia as an ornamental species because of its attractive foliage and colorful flowers. It has subsequently naturalized and became a major weed in rice field, irrigation canals and wetlands in South-East Asia and has now attained the status as an alien invader. Developing an effective integrated management program requires a thorough understanding of the biology and ecology of the weed to identify the most vulnerable stages of its life cycle. Location-specific studies on the behavior of weeds, their population dynamics, seed bank and other features provide information on the positive or negative influence of biotic and abiotic factors on their growth and development which elaborates better control operations. Therefore literature regarding eco-biology, modes of propagation, dispersal and different methods for the sustainable management of water cabbage is reviewed in this paper.

Isolation and characterization of a quinclorac-degrading Actinobacteria Streptomyces sp. strain AH-B and its implication on microecology in contaminated soil

Quinclorac, a highly selective auxin herbicide, is widely used for controlling weeds in rice field. However, the residual quinclorac is toxic to many crops, vegetables, and aquatic animals, resulting in one of the major problems in crop rotation. Here, we investigated the degradation of quinclorac by strain AH-B, which was isolated from long-term quinclorac-contaminated soil using continuous circulating fluidized bed reactor and subjected to atmospheric and room temperature plasma mutation. Morphological examination, 16S rRNA gene sequencing, and phylogenetic analysis revealed that strain AH-B was Streptomyces sp. The quinclorac degradation efficiency of AH-B in liquid medium was 97.2% after 18 days when the initial quinclorac concentration was 20 mg L−1. The degradation products were 3-chloro-7-methoxy-8-quinoline-carboxylic, 3-chloro-7-methyl-8-quinoline-carboxylic, 3-chloro-7-oxyethyl-8-quinoline-carboxylic, and 3,7-dichloro-6-methyl-8-quinoline-carboxylic. The inoculum size, initial quinclorac concentration, pH, and temperature were found to affect quinclorac degradation efficiency of AH-B. High-performance liquid chromatography-electrospray ionization tandem mass spectrometry analysis revealed that quinclorac degradation by AH-B produced many products. In soil with initial quinclorac content of 1 mg kg−1 dry soil, addition of AH-B resulted in 87.5% quinclorac degradation after 42 days, while that in the control (without AH-B) was 22.4%. Furthermore, microecological analysis using next-generation sequencing of 16S rRNA geneshowed that some bacterial species, such as Bacterioides and Proteobacteria, could survive in quinclorac-contaminated soil, while some bacteria, such as Firmicutes, were very sensitive to quinclorac. Besides, some fungal species, such as Basidiomycota, could also survive quinclorac-contamination. After 42 days, the diversity of bacteria and fungi in soil treated with AH-B was higher than that in the control, implying that bioaugmentation with strain AH-B could reduce quinclorac toxicity to microorganisms in soil.

RGB and multispectral UAV image fusion for Gramineae weed detection in rice fields

In this paper, a new method to fuse low resolution multispectral and high resolution RGB images is introduced, in order to detect Gramineae weed in rice fields with plants at 50 days after emergence (DAE).The images are taken from a fixed-wing unmanned aerial vehicle (UAV) at 60 and 70 m altitude. The proposed method combines the texture information given by a high resolution red–green–blue (RGB) image and the reflectance information given by a low resolution multispectral (MS) image, to obtain a fused RGB-MS image with better weed discrimination features. After analyzing the normalized difference vegetation index (NDVI) and normalized green red difference index (NGRDI) for weed detection, it was found that NGRDI presents better features. The fusion method consists of decomposing the RGB image using the intensity, hue and saturation (IHS) transformation, then, a second order Haar wavelet transformation is applied to the intensity layer (I) and the NGRDI image. From this transformation, the low–low (LL) coefficients of the NGRDI image are replaced by the LL coefficients of the I layer. Finally, the fused image is obtained by transforming the new wavelet coefficients to RGB space. To test the method, a one hectare experimental plot with rice plants at 50 DAE with Gramineae weeds was selected. Additionally, to compare the performance of the method, two indices were used, specifically, the M/MGT index which is the percentage of detected weed area, and the MP index which indicates the precision of weed detection. These indices were evaluated in four validation zones using three Neural Networks (NN) detection systems based on three types of images; namely, RGB, RGB + NGRDI, and fused RGB-NGRDI. The best weed detection performance was obtained by the NN with the fused image, with M/MGT index between 80 and 108% and MP between 70 and 85%.

Floristic and Phytosociology of Weeds in Upland Rice in the Humid Tropics

ABSTRACT: Knowledge of the floristic composition and vegetation structure are essential conditions for development of more efficient and economic weed management strategies in crops in the humid tropics. The objective of the research was to carry on floristic and phytosociological surveys to know the main weeds in upland rice fields in the humid tropics of the Brazilian State of Maranhão. Weed samples were done by means of an open metal rectangle of 0.15 m2 thrown at random in the vegetative and reproductive stages of rice crop in 2009/10 and 2010/2011 harvest. A total of 65 species from 23 families was identified 35 (53.85%) from the eudicotyledons botanical group, 29 (44.06%) from the monocotyledonous and one (1.53%) belonged to the pteridophytes. The most representative families were from the monocotyledonous botanical group including Poaceae and Cyperaceae, followed by Amaranthaceae and Malvaceae, both from the eudicotyledons group. The weed species with higher importance values in the upland rice crop vegetative stage were Urochloasp., Panicumsp., C. flavus, C. benghalensis and C. argutus whereas in the reproductive stage the higher importance values were recorded for S. latifolia, C. argutus, L. octovalvis, A.tenella and P.maximum. The most important weeds in the crop vegetative phase were mainly from the monocotyledonous group, while in reproductive one they were the eudicotyledons. Weed diversity was high and the floristic similarity was lower in the vegetative one compared to the reproductive stage of upland rice cultivation in the humid tropics.

Weed management in organically grown scented rice

A field experiment on evaluation of weed management practices in scented rice under organic production system was conducted during 2017–18 at All India Coordinated Research Project on Farming System, College of Agriculture, Rewa (M.P.). Fimbristylis dichotoma was the most dominating weed in rice field followed by Jussia suffurusticosa. Incorporation of mustard oil cake at 5 t/ha along with one hand weeding gave maximum weed control efficiency (68%). Growth and development of rice was better with incorporation of mustard oil cake 15 days before sowing 5 t/ha + 1 hand weeding (HW) followed by two HW at 20 and 40 days after transplanting (DAT) and locally available weed mulch Saccharum spontaneam at 3 t/ha + 1 hand weeding. These treatments gave 34 to 56% higher grain yield as compared to farmer's practice of weed control as mulching with mango leaves. Net profit of ‘ 62061/ha was maximum in mulching with locally available weeds + 1 hand weeding followed by ‘ 56695/ha in two HW at 20 and 40 DAT.

Weed management practices to control herbicide-resistant Echinochloa crus-galli in rice in Mekong Delta, Vietnam

Barnyardgrass (Echinochloa crus-galli) is one of most important weeds in rice field in Vietnam. Seventy-eight barnyardgrass seed samples were collected from rice fields in seven provinces in Mekong Delta of Vietnam. The seedlings grown from collected seed samples were evaluated to determine the level of resistance to bispyribac, penoxsulam and quinclorac. Farmers who managed the fields from which samples collected were interviewed about weed management practices and the cost of weed control per season. The average cost for weed management was 1, 980, 000 VND per hectare, the total cost included 650, 000 VND for herbicide and 1, 330, 000 VND for hand-weeding. Echinochloa crus-galli biotypes resistant to bispyribac, penoxsulam and quinclorac were found and biotypes with resistance to multiple herbicides were detected. The average resistance-score of three tested herbicides was 3.4 in the 78 samples collected. There was a correlation between field size, hand-weeding practice, and the herbicide-resistance level, herbicideresistant weeds were less common in smaller fields where hand-weeding was commonly used. The high cost and limited labour pool for hand-weeding in this region of Vietnam limits the long-term viability of this approach.

Changes in Blood Parameters of Clarias gariepinus Sub-adults Exposed to 2, 4-Dimethyl Amine

Herbicide application for the control of weeds in rice fields has come to stay in Nigeria. A herbicide commonly applied is 2, 4-Dimethyl Amine. It became pertinent to investigate its effects on the haematology and possible lethality on Clarias gariepinus . Sub-adults of Clarias gariepins measuring 906.7 ± 39.3 mg in weight 164.7 ± 10.2 mm in length were exposed to different concentration of 2, 4-Dimethyl Amine in a 96 hour bioassay. The physicochemical parameters of the water, behavioural and biological responses of the fish and the haemstological analysis of the exposed fish were evaluated. Mortalities were observed as, LC 50 in 24 hours (22.5 mg/L), 48 hours (18.0 mg/L), 72 hours (16.5 mg/L) and 96 hours (15.0 mg/L). Other results showed that temperature of the water was not influenced by the herbicide. The pH, dissolved oxygen and temperature of the water were not statistically different ( p >0.05) between control and treatment groups. The conductivity showed differences between the control and the treated groups. Total white blood cells counts and other components of the white blood cells were not significantly ( p >0.05) more populated than the non exposed groups. The red blood cells parameters like haemoglobin, mean cell volume, erythrocytes sedimentation rate and mean cell haemoglobin concentration were significantly ( p >0.05) lower in exposed groups. This showed that the herbicide had a negative impact on the oxygen carrying ability of the red blood cell.

Removal of Imazethapyr and Imazapic from the Effluent of Aero-Agricultural Operations: Efficiency of a Treatment System Using Ozone

Imazethapyr and imazapic are widely used in South Brazil to control weeds in rice fields, mainly through agricultural aviation. The environmental legislation requires that agricultural aviation companies have environmental licensing, which implies that the effluent treatment system must be compliant with the regulations of the Brazilian Ministry of Agriculture, which advises the use of an ozone-based system. An evaluation of the efficiency of this system through the analysis of the content of imazethapyr and imazapic (from the herbicide Only®) in the treatment of effluent with two distinct rates of ozone (1.0 and 2.0 g O3/h) was performed. It was found that for each tank wash is generated an average volume of 132 L of effluent (112 L of water plus 20 L of surplus diluted spray solution). After the treatment with 1.0 and 2.0 g O3/h, imazethapyr concentration decreased − 92.4 and − 95.2%, respectively. For imazapic, the concentration in the washing effluent decreased − 69.1 and − 80.1%, respectively. The results indicate that the system was effective in the treatment of the effluent containing residues of the herbicide Only®.

Pengaruh Dosis Herbisida Ethoxysulfuron 15 WG Terhadap Gulma, Pertumbuhan Dan Hasil Tanaman Padi Varietas Ciherang

Weeds in rice fields decrease the quantity and quality of yield. One of the methods used to control weeds is chemical herbicide. The objective of this research was to find out the effective dosages of herbicide Ethoxysulfuron 15 WG on weeds growth as well as growth and yield of rice plants var. Ciherang. This experiment was used Randomized Block Design with seven treatments and four replication. The Ethoxysulfuron doses trated to rice field 6 g/ha, 9 g/ha, 12 g/ha, 15 g/ha and 18 g/ha. The two control treatments were mechanical weeding, and without weeding and herbicide. The experimental result showed that Ethoxusylfuron herbicide with the dosage of 9 g/ha could suppress the growth of weed Ludwigia adscendens, Ludwigia perrenis, Fimbristylis miliacea,other weeds, and total weeds and give a good impact on yield of rice plants.

Performance Evaluation of BRRI Power Weeder for Low Land Rice (<i>Oryza sativ</i> L.) Cultivation

Mechanical intervention in crop production is increasing rapidly in Bangladesh. Researchers are finding ways to manage weeds in rice field using suitable mechanical devices instead of conventional hand weeding. A study was conducted to evaluate the field performance of BRRI (Bangladesh Rice Research Institute) power weeder compared to BRRI weeder and hand weeding in the farmers’ field at Rashidpur in Mithapukur upazila under Rangpur district during boro season of 2014-15. Three treatments: T1 = BRRI weeder (BW), T2 = BRRI power weeder (BPW) and T3 = Hand weeding (HW) were used in the experiment. The experiment was carried out in a randomized complete block design (RCBD) and replicated in four farmers’ plots. Rice variety BRRI dhan28 was selected for the experiment. The effective field capacity of BW and BPW was found to be 0.06 and 0.09 ha hr-1, respectively. The weeding efficiency was the highest in HW (92%), followed by BPW (78%) and BW (73%). It was found that BW damaged the lowest number of plants (9%) compared to BPW (11%) during weeding operation, although the damaged plants recovered after a few days. BW and BPW reduced 74 and 85% of labor requirement in weeding operation compared to HW. The highest weeding cost was involved in HW (Tk. 4287 ha-1) compared to BW (Tk. 1103 ha-1) and BPW (Tk. 950ha-1). Weed control methods exerted insignificant effect on grain yield. BRRI power weeder and BRRI weeder reduced weeding cost, enhanced weed control and improved the labor efficiency without sacrificing grain yield. The highest BCR was obtained in BPW (1.22) followed by BW (1.16) and HW (1.11). BRRI power weeder and BRRI weeder appeared to be economic, easy and also environmentally safe weed control device in low land rice cultivation. The Agriculturists 2017; 15(1) 40-48

The Role of Leaf Volatiles of Ludwigia octovalvis (Jacq.) Raven in the Attraction of Altica cyanea (Weber) (Coleoptera: Chrysomelidae).

Larvae and adults of Altica cyanea (Weber) (Coleoptera: Chrysomelidae) feed on the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae), commonly known as willow primrose, which is considered a biocontrol agent of the weed. Volatile organic compounds from undamaged plants, plants after 4, 12, and 36h of continuous feeding by A. cyanea larvae or adult females and after mechanical damaging were identified by GC-MS and GC-FID analyses. Twenty nine compounds were identified from undamaged plants. 2Z-Penten-1-ol, geraniol, and 1-tridecanol were present in all plants damaged by larvae. In contrast, feeding by adults caused the release of 2Z-penten-1-ol only after 12 and 36h; whereas geraniol and 1-tridecanol appeared only after 36h. Farnesyl acetone was detected after 12 and 36h of feeding by larvae and after 36h of feeding by adults. Farnesene was detected after 36h of feeding by larvae and adults. Linalool was unique after 36h of feeding by larvae. In Y-shaped glass tube olfactometer bioassays, A. cyanea females were attracted to volatiles after 36h of feeding by larvae or adults compared to volatiles released by undamaged plants. The insects were attracted to five synthetic compounds: 3-hexanol, α-pinene, linalool oxide, geraniol, and phytol. Synthetic blends were more attractive than individual compounds. Compared to undamaged plants, volatiles released by plants, damaged by conspecific individuals, were more attractive to A. cyanea females, due to elevated emissions of 3-hexanol, α-pinene, linalool oxide, geraniol, and phytol.

The climatic characteristics of Najaf province and their relationship to the growth of the bush affecting rice production

Rice is a food crop that is considered one of the mainstays of food security, so all countries seek to provide it to meet the needs of their growing population with high living standards, which increases the demand for it, and Iraq was considered one of the countries exporting rice until the end of the last century, after which its production began to decrease due to water scarcity. The problem of the spread of weeds in rice fields, which causes huge losses in its production, is exacerbated, amounting to (63%). Therefore, work must be done to increase its production by combating what grows from the bushes in the rice fields.

Non-target-site resistance to ALS-inhibiting herbicides in a Sagittaria trifolia L. population

Sagittaria trifolia L. is one of the most competitive weeds in rice fields in northeastern China. The continuous use of acetolactate synthase (ALS)-inhibitors has led to the evolution of herbicide resistant S. trifolia. A subpopulation BC1, which was derived from the L1 population, was analyzed using DNA sequencing and ALS enzyme activity assays and levels of resistance to five ALS-inhibiting herbicides was determined. DNA sequencing and ALS enzyme assays revealed no amino acid substitutions and no significant differences in enzyme sensitivity between susceptible and resistant populations. Whole-plant dose-response experiments showed that the BC1 population exhibited different levels of resistance (resistance ratios ranging from 2.14 to 51.53) to five ALS herbicides, and the addition of malathion (P450 inhibitor) to bensulfuron-methyl, penoxsulam and bispyribac-sodium strongly reduced the dry weight accumulation of the BC1 population compared with the effects of the three herbicides alone. The results of the present study demonstrated that the BC1 population has evolved non-target-site resistance to ALS-inhibiting herbicides.

Prevalence of herbicide‐resistant weed species in Malaysian rice fields: A review

The management of weeds in Malaysian rice fields is very much herbicide‐based. The heavy reliance on herbicide for weed control by many rice‐growers arguably eventually has led to the development and evolution of herbicide‐resistant biotypes in Malaysian rice fields over the years. The continuous use of synthetic auxin (phenoxy group) herbicides and acetohydroxyacid synthase‐inhibiting herbicides to control rice weeds was consequential in leading to the emergence and prevalence of resistant weed biotypes. This review discusses the history and confirmed cases and incidence of herbicide‐resistant weeds in Malaysian rice fields. It also reviews the Clearfield Production System and its impact on the evolution of herbicide resistance among rice weed species and biotypes. This review also emphasizes the strategies and management options for herbicide‐resistant rice field weeds within the framework of herbicide‐based integrated weed management. These include the use of optimum tillage practices, certified clean seeds, increased crop competition through high seeding rates, crop rotation, the application of multiple modes of action of herbicides in annual rotations, tank mixtures and sequential applications to enable a broad spectrum of weed control, increase the selective control of noxious weed species in a field and help to delay the resistance evolution by reducing the selection pressure that is forced on those weed populations by a specific herbicidal mode of action.

Long-chain alkanes and fatty acids from Ludwigia octovalvis weed leaf surface waxes as short-range attractant and ovipositional stimulant to Altica cyanea (Weber) (Coleoptera: Chrysomelidae).

The importance of leaf surface wax compounds from the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae) was determined in the flea beetle Altica cyanea (Weber) (Coleoptera: Chrysomelidae). Extraction, thin layer chromatography and GC-MS and GC-FID analyses of surface waxes of young, mature and senescent leaves revealed 20, 19 and 19 n-alkanes between n-C15 and n-C35, respectively; whereas 14, 14 and 12 free fatty acids between C12:0 and C22:0 fatty acids were identified in young, mature and senescent leaves, respectively. Tricosane was predominant n-alkane in young and mature leaves, whilst eicosane predominated in senescent leaves. Heneicosanoic acid, palmitic acid and docosanoic acid were the most abundant free fatty acids in young, mature and senescent leaves, respectively. A. cyanea females showed attraction to 0.25 mature leaf equivalent surface waxes compared with young or senescent leaves in a short glass Y-tube olfactometer bioassay. The insects were attracted to a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml-1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively, comparable with the proportions as present in 0.25 mature leaf equivalent surface waxes. A. cyanea also laid eggs on a filter paper moistened with 0.25 mature leaf equivalent surface waxes or a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml-1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively. This finding could provide a basis for monitoring of the potential biocontrol agent in the field.

Evaluation of bioethanol production from rice field weed biomass

Evaluation of bioethanol production from rice field weed biomass

Biology of Galerucella placida Baly (Coleoptera: Chrysomelidae) on the Rice-Field Weed Polygonum orientale L. (Polygonaceae)

Galerucella placida Baly (Coleoptera: Chrysomelidae) is a promising biocontrol agent of the rice-field weed Polygonum orientale L. (Polygonaceae) in India and Bangladesh. The longevity of G. placida adults was related with nutrients and antinutrients of young, mature and senescent leaves of P. orientale. Mature leaves of P. orientale had higher level of nutrients (carbohydrates, proteins, lipids, nitrogen and amino acids) and lower level of antinutrients (phenols and flavonols) compared to young and senescent leaves. Higher level of carbohydrates, proteins, lipids, nitrogen, amino acids including water content, and lower phenol and flavonol content of mature leaves had influenced higher survival of G. placida. Total larval developmental and pupal periods were 26.27 ± 0.45 SE and 7.06 ± 0.17 SE days on mature weed leaves, respectively; whilst adult males and females lived for 52.15 ± 0.33 SE and 58.0 ± 0.38 SE days on mature leaves, respectively. Fecundity of individual G. placida was 133.3 ± 3.2 SE eggs during life time. The net reproductive rate, generation time, intrinsic rate of increase, finite rate of increase and doubling time were 66.675, 27.5376, 0.1525, 1.2502 and 4.5452 days, respectively, under laboratory conditions (27 ± 0.5 °C, 12L:12D photoperiod, 65 ± 5% RH).

Population genomics identifies the origin and signatures of selection of Korean weedy rice.

SummaryWeedy rice is the same biological species as cultivated rice (Oryza sativa); it is also a noxious weed infesting rice fields worldwide. Its formation and population‐selective or ‐adaptive signatures are poorly understood. In this study, we investigated the phylogenetics, population structure and signatures of selection of Korean weedy rice by determining the whole genomes of 30 weedy rice, 30 landrace rice and ten wild rice samples. The phylogenetic tree and results of ancestry inference study clearly showed that the genetic distance of Korean weedy rice was far from the wild rice and near with cultivated rice. Furthermore, 537 genes showed evidence of recent positive or divergent selection, consistent with some adaptive traits. This study indicates that Korean weedy rice originated from hybridization of modern indica/indica or japonica/japonica rather than wild rice. Moreover, weedy rice is not only a notorious weed in rice fields, but also contains many untapped valuable traits or haplotypes that may be a useful genetic resource for improving cultivated rice.