Rice Allelopathy Research Articles

Deciphering the Genetic Basis of Allelopathy in japonica Rice Cultivated in Temperate Regions Using a Genome-Wide Association Study

Allelopathy has been considered as a natural method of weed control. Despite the nature of allelochemical compounds has been studied, little is known about the genetic basis underlying allelopathy. However, it is known that rice exhibits diverse allelopathic potentials across varieties, and breeding for rice plants exhibiting allelopathic potential conferring an advantage against weeds in paddy fields would be highly desirable. Knowledge of the gene factors and the identification of the genomic regions responsible for allelopathy would facilitate breeding programs. Taking advantage of the existing genetic diversity in rice, particularly in temperate japonica rice, we conducted a comprehensive investigation into the genetic determinants that contribute to rice allelopathy. Employing Genome-Wide Association Study, we identified four Quantitative Trait Loci, with the most promising loci situated on chromosome 2 and 5. Subsequent inspection of the genes located within these QTLs revealed genes associated with the biosynthesis of secondary metabolites such as Phenylalanine Ammonia Lyase (PAL), a key enzyme in the synthesis of phenolic compounds, and two genes coding for R2R3-type MYB transcription factors. The identification of these two QTLs associated to allelopathy in rice provides a useful tool for further exploration and targeted breeding strategies.

The role of signaling compounds in enhancing rice allelochemicals for sustainable agriculture: an overview.

Plant phytotoxin synthesis is influenced by intricate signaling networks like jasmonic acid (JA) and salicylic acid (SA). These compounds not only induce allelochemical production but also aid weed suppression and plant immunity. (-)-Loliolide, JA, SA, and their derivatives trigger rice allelochemical synthesis and gene expression. Enhancing allelochemical synthesis in crops offers an alternative, reducing reliance on traditional herbicides for effective weed management. Rice (Oryza sativa L.) serves as a crucial staple food crop, nourishing over half of the global population, particularly in South Asia. Within rice plants, various secondary metabolites are produced, contributing to its nutritional value and providing energy to consumers. Over the last 5 decades, researchers have investigated 276 distinct types of secondary metabolites found in rice plants. These metabolites predominantly include phenolic acids, flavonoids, steroids, alkaloids, terpenoids, and their derivatives. The role of these secondary metabolites is to regulate the growth and development of the rice plant. In this research paper, we have focused on the allelopathic potential of rice, which involves its active defense strategy to suppress other species in its vicinity. This defense mechanism is regulated by plant signaling compounds. These signaling compounds enable rice plants to recognize and detect competitors, pathogens, and herbivores in their environment. As a response, the rice plants elevate the production of defensive secondary metabolites. One crucial aspect of rice allelopathy is the phenomenon of neighbor detection. Rice plants can sense the presence of neighboring plants and respond accordingly to establish their competitive advantage and ensure their survival. This paper specifically highlights the impact of exogenously applied signaling compounds, namely Methyl salicylate (MeSA) and Methyl Jasmonate (MeJA), on paddy rice. The aim is to provide deeper insights into the signaling mechanisms involved in rice allelopathy and how the exogenous application of signaling compounds influence the induction and regulation of defensive secondary metabolites in rice plants. Comprehensive analysis of various researchers' studies clearly reveals that the application of these elicitor compounds noticeably augments the allelopathic potential of rice, resulting in heightened accumulation of phenolic acid compounds. Expansion in more enlistment of phenolics may be because of expansion in the activities of enzymes, such as cinnamate 4-hydroxylase (C4H) and phenylalanine ammonia-lyase (PAL), the two main enzymes of the phenylpropanoid pathway, which are associated with allelopathic crop plants, and along this, they recognize the presence of weeds and react by expanding allelochemical focuses. Consequently, substantial endeavors have been dedicated in recent times to discover and characterize plant-derived signaling molecules. In bioassays conducted by Patni et al. in 2019, both competitive and non-competitive rice genotypes exhibited elevated phytotoxicity against Echino colona following treatment with MeSA. MeSA-treated rice plants displayed accelerated growth, increased yield, and concurrently demonstrated weed-suppressing properties. Published studies from 1976 to 2021 are reviewed in this paper. The study indicates that signaling compounds induce allelochemical concentrations, enhancing allelopathic activity. This insight may lead to development of novel herbicides for effective sustainable weed management.

Defensive Molecules Momilactones A and B: Function, Biosynthesis, Induction and Occurrence.

Labdane-related diterpenoids, momilactones A and B were isolated and identified in rice husks in 1973 and later found in rice leaves, straws, roots, root exudate, other several Poaceae species and the moss species Calohypnum plumiforme. The functions of momilactones in rice are well documented. Momilactones in rice plants suppressed the growth of fungal pathogens, indicating the defense function against pathogen attacks. Rice plants also inhibited the growth of adjacent competitive plants through the root secretion of momilactones into their rhizosphere due to the potent growth-inhibitory activity of momilactones, indicating a function in allelopathy. Momilactone-deficient mutants of rice lost their tolerance to pathogens and allelopathic activity, which verifies the involvement of momilactones in both functions. Momilactones also showed pharmacological functions such as anti-leukemia and anti-diabetic activities. Momilactones are synthesized from geranylgeranyl diphosphate through cyclization steps, and the biosynthetic gene cluster is located on chromosome 4 of the rice genome. Pathogen attacks, biotic elicitors such as chitosan and cantharidin, and abiotic elicitors such as UV irradiation and CuCl2 elevated momilactone production through jasmonic acid-dependent and independent signaling pathways. Rice allelopathy was also elevated by jasmonic acid, UV irradiation and nutrient deficiency due to nutrient competition with neighboring plants with the increased production and secretion of momilactones. Rice allelopathic activity and the secretion of momilactones into the rice rhizosphere were also induced by either nearby Echinochloa crus-galli plants or their root exudates. Certain compounds from Echinochloa crus-galli may stimulate the production and secretion of momilactones. This article focuses on the functions, biosynthesis and induction of momilactones and their occurrence in plant species.

Allelopathic potential in rice - a biochemical tool for plant defence against weeds.

Rice is a key crop for meeting the global food demand and ensuring food security. However, the crop has been facing great problems to combat the weed problem. Synthetic herbicides pose a severe threat to the long-term viability of agricultural output, agroecosystems, and human health. Allelochemicals, secondary metabolites of allelopathic plants, are a powerful tool for biological and eco-friendly weed management. The dynamics of weed species in various situations are determined by crop allelopathy. Phenolics and momilactones are the most common allelochemicals responsible for herbicidal effects in rice. The dispersion of allelochemicals is influenced not only by crop variety but also by climatic conditions. The most volatile chemicals, such as terpenoids, are usually emitted by crop plants in drought-stricken areas whereas the plants in humid zones release phytotoxins that are hydrophilic in nature, including phenolics, flavonoids, and alkaloids. The allelochemicals can disrupt the biochemical and physiological processes in weeds causing them to die finally. This study insight into the concepts of allelopathy and allelochemicals, types of allelochemicals, techniques of investigating allelopathic potential in rice, modes of action of allelochemicals, pathways of allelochemical production in plants, biosynthesis of allelochemicals in rice, factors influencing the production of allelochemicals in plants, genetical manipulation through breeding to develop allelopathic traits in rice, the significance of rice allelopathy in sustainable agriculture, etc. Understanding these biological phenomena may thus aid in the development of new and novel weed-control tactics while allowing farmers to manage weeds in an environmentally friendly manner.

Comparative analysis on metabolites and gene expression difference of various allelopathic potential rice under weed stress

AbstractIn this study, allelopathic rice ‘PI312777’ (PI) and non‐allelopathic rice ‘Lemont’ (LE) were used to study gene expression related to secondary metabolism and relative metabolites in soil under field conditions with and without weeding. The results showed that the inhibition rates of PI and LE soils to barnyard grass were significantly increased under weed stress. The inhibition rate of phenolic acid extracts in PI rhizosphere soils was significantly higher (p < 0.05) without the weeding treatment than with the weeding treatment; however, it was not significantly different in LE rhizosphere soils. There were no significant differences in the inhibition rates of other soil extracts (terpenoids, alkaloids and fatty acids) of PI and LE in treatments with and without weeding. Under weed stress, six genes (PAL, C4H, F5H, COMT, CCR and CAD) related to phenolic acid metabolism were upregulated in the leaves and roots of PI, while only four of the six genes were upregulated and two genes were downregulated in LE. The genes related to terpenoid metabolism (seven genes), alkaloid metabolism (three genes) and fatty acid metabolism (two genes) were upregulated in the roots and leaves of PI and LE under weed stress, but the differences were not significant. These results suggest that the increase in phenolic acids in the presence of weeds under field conditions contributed the majority of the inhibition effect in rice allelopathy.

Changxun Fang. Pioneers of Allelopathy: Wenxiong Lin

Wenxiong Lin did research for > 30 years in plant molecular ecology and agro-ecology, rice allelopathy and continuous monoculture problems/soil sickness of Chinese medicinal plants. His 20 Patents and most publications (about 100) have focussed on (i). Gene regulation of allelochemicals biosynthesis in allelopathic rice, (ii). allelopathic inhibitory effects on weeds, (iii). continuous monoculture problems/soil sickness in medicinal plants and (iv). the influence of allelochemicals and monoculture practice on the rhizospheric micro-environment. He helped in development of microbial fertilizer to alleviate the autotoxicity problem in continuous cropping of Radix pseudostellariae and Rehmannia glutinosa, etc. He had been the President of Asian Allelopathy Society, and got the outstanding achievement from the platform of International Allelopathy Foundation. His student, Dr. Changxun Fang got Rice Award and Grodzinsky Award respectively in the 6th and 8th World Congress of International Allelopathy Society. His elucidation of the molecular ecological mechanism of rice allelopathy was awarded the II Class Prize of Fujian Provincial Scientific and Technological Progress Award in 2007. His researches to find the mechanism of development of continuous cropping obstacle/soil sickness in R. pseudostellariae and its remedy was awarded the I Class Prize of Fujian Provincial Scientific and Technological Progress Award in 2020.

Allelopathy in rice: a story of momilactones, kin recognition, and weed management.

In the struggle to secure nutrient access and to outperform competitors, some plant species have evolved a biochemical arsenal with which they inhibit the growth or development of neighbouring plants. This process, known as allelopathy, exists in many of today's major crops, including rice. Rice synthesizes momilactones, diterpenoids that are released into the rhizosphere and inhibit the growth of numerous plant species. While the allelopathic potential of rice was recognized decades ago, many questions remain unresolved regarding the biosynthesis, exudation, and biological activity of momilactones. Here, we review current knowledge on momilactones, their role in allelopathy, and their potential to serve as a basis for sustainable weed management. We emphasize the gaps in our current understanding of when and how momilactones are produced and of how they act in plant cells, and outline what we consider the next steps in momilactone and rice allelopathy research.

OsPAL2-1 Mediates Allelopathic Interactions Between Rice and Specific Microorganisms in the Rhizosphere Ecosystem.

The use of plant allelopathy to control weeds in the field has been generally recognized as a win-win strategy because it is an environmentally friendly and resource-saving method. The mechanism of this natural weed-control method relies on allelochemicals, the rhizosphere microbiome, and their bio-interaction, and exploring the link between allelochemicals and specific microbes helps accelerate the application of allelopathic characteristics in farming. In this study, we used allelopathic rice PI312777 (PI), its genetically modified OsPAL2-1 repression (PR) or overexpression (PO) lines, and non-allelopathic rice Lemont (Le) as donor plants to reveal the bio-interaction between rice allelochemicals and rhizosphere specific microorganisms. The results showed a higher content of phenolic acid exudation from the roots of PI than those of Le, which resulted in a significantly increased population of Myxococcus in the rhizosphere soil. Transgenic PO lines exhibited increasing exudation of phenolic acid, which led to the population of Myxococcus xanthus in the rhizosphere soil of PO to be significantly increased, while PR showed the opposite result in comparison with wild type PI. Exogenous application of phenolic acid induced the growth of M. xanthus, and the expressions of chemotaxis-related genes were up-regulated in M. xanthus. In addition, quercetin was identified in the culture medium; according to the bioassay determination, a quercetin concentration of 0.53 mM inhibited the root length by 60.59%. Our study indicates that OsPAL2-1 is among the efficient genes that regulate rice allelopathy by controlling the synthesis of phenolic acid allelochemicals, and phenolic acid (ferulic acid, FA) induces the chemotactic aggregation of M. xanthus, which promoted the proliferation and aggregation of this microbe. The potential allelochemical, quercetin was generated from the FA-induced M. xanthus cultured medium.

Rice allelopathy and momilactone B for weed management

Rice allelopathy and momilactone B for weed management

MYB57 transcriptionally regulates MAPK11 to interact with PAL2;3 and modulate rice allelopathy.

Rice allelopathy is a natural method of weed control that is regarded as an eco-friendly practice in agroecology. The allelopathic potential of rice is regulated by various genes, including those that encode transcription factors. Our study characterized a MYB transcription factor, OsMYB57, to explore its role in the regulation of rice allelopathy. Increasing the expression of OsMYB57 in rice using the transcription activator VP64 resulted in increased inhibitory ratios against barnyardgrass. The gene expression levels of OsPAL, OsC4H, OsOMT, and OsCAD from the phenylpropanoid pathway were also up-regulated, and the content of l-phenylalanine increased. Chromatin immunoprecipitation incorporated with HiSeq demonstrated that OsMYB57 transcriptionally regulated a mitogen-activated protein kinase (OsMAPK11); in addition, OsMAPK11 interacted with OsPAL2;3. The expression of OsPAL2;3was higher in the allelopathic rice PI312777 than in the non-allelopathic rice Lemont, and OsPAL2;3 was negatively regulated by Whirly transcription factors. Moreover, microbes with weed-suppression potential, including Penicillium spp. and Bacillus spp., were assembled in the rhizosphere of the rice accession Kitaake with increased expression of OsMYB57, and were responsible for phenolic acid induction. Our findings suggest that OsMYB57 positively regulates rice allelopathy, providing an option for the improvement of rice allelopathic traits through genetic modification.

(-)-Loliolide, the most ubiquitous lactone, is involved in barnyardgrass-induced rice allelopathy.

Neighbor detection and allelochemical response are important mediators in plant-plant interactions. Although there is increasing knowledge about plant allelochemicals released in response to the presence of competitors and involved in neighbor-derived signaling, less is known about which signaling chemicals are responsible for the neighbor-induced allelochemical response. Here, we experimentally demonstrate that (-)-loliolide, a carotenoid metabolite, acts as a signaling chemical in barnyardgrass-rice allelopathic interactions. The production of the rice allelochemicals momilactone B and tricin was increased in the presence of five biotypes of barnyardgrass. (-)-Loliolide was found in all the biotypes of barnyardgrass and their root exudates and rhizosphere soils. There were significant positive relationships between rice allelochemicals and (-)-loliolide concentrations across the biotypes of barnyardgrass. Furthermore, (-)-loliolide elicited the production of momilactone B and tricin. Comparative transcriptomic analysis revealed regulatory activity of (-)-loliolide on the diterpenoid and flavonoid biosynthesis pathway. The expression of key genes involved in the biosynthesis of momilactone B (CPS4, KSL4, and MAS) and tricin (CYP75B3 and CYP75B4) was up-regulated by (-)-loliolide. These findings suggest that (-)-loliolide acts as a signaling chemical and participates in barnyardgrass-rice allelopathic interactions. Allelopathic rice plants can detect competing barnyardgrass through the presence of this signaling chemical and respond by increasing levels of their allelochemicals to achieve an advantage for their own growth.

Bacteriostatic stimulus of meropenem on allelochemical-metabolizing Burkholderia sp. LS-044 mitigates ferulic acid autotoxicity in rice (Oryza sativa ssp. japonica cv. Tainung 71)

To screen plant-associated Burkholderia strains for plant probiotic traits including allelochemical metabolism and understand their role on rice allelopathy using a bacteriostatic-dose of antibiotic. Burkholderia sp. LS-044, CC-Al74 and CC-3XP9 were screened for plant probiotic traits. Rice (Oryza sativa ssp. japonica cv. Tainung 71) root endophytic isolate LS-044 was subjected to multilocus sequence typing, antibiotic assay, and seed germination bioassay under ferulic acid (FA; 0–200 ppm) and bacteriostatic-dose of meropenem (4 ppm). FA metabolism and cell viability were assessed through alamarBlue (AB) assay. All tested Burkholderia strains exhibited multiple plant probiotic traits. LS-044, a meropenem-sensitive novel member of Burkholderia cepacia complex displayed rapid metabolism of multiple allelochemicals. Bacteriostatic-dose of meropenem improved germination index (GI) of inoculated seed under FA treatments. Meropenem promoted GI by controlling bacterial FA metabolism and prolonging the cell viability, as evident through AB assay. Uncontrolled bacterial growth under high-dose FA found to be phytotoxic to rice than FA alone. Burkholderia sp. LS-044 is a potential allelochemical-metabolizing bacterium, which possibly plays a key role in rice allelopathy. Bacteriostatic-dose of meropenem mitigates autotoxicity by controlling and prolonging allelochemical metabolism of rice-associated LS-044.

Fine-root traits of allelopathic rice at the seedling stage and their relationship with allelopathic potential.

BackgroundAllelopathic rice releases allelochemicals through its root systems, thereby exerting a negative effect on paddy weeds. This research aimed to evaluate the relationship between fine-root traits and the rice allelopathic potential at the seedling stage.MethodsTwo allelopathic rice cultivars, ‘PI312777’ and ‘Taichung Native1,’ and one non-allelopathic rice cultivar, ‘Lemont,’ were grown to the 3–6 leaf stage in a hydroponic system. Their fine roots were collected for morphological trait (root length, root surface area, root volume, and root tips number) in smaller diameter cutoffs and proliferative trait (root biomass) analysis. Their root-exudates were used for quantitative analysis of phenolic acids contents and an evaluation of allelopathic potential. Correlation analysis was also used to assess whether any linear relationships existed.ResultsOur results showed that allelopathic rice cultivars had significantly higher fine-root length having diameters <0.2 mm, more root tips number, and greater root biomass, coupled with higher allelopathic potential and phenolic acid contents of their root exudates, comparing with non-allelopathic rice cultivar. These fine-root traits were significantly-positively correlated to allelopathic inhibition and total phenolic contents in rice root-exudates. However, there were not significant correlations among the rice allelopathic potential and total phenolic acid contents of rice root-exudates with the root length, root surface area, and root volume of fine root in diameter >0.2 mm.DiscussionOur results implied that fine-root traits appears to be important in understanding rice allelopathy at the seedling stage. The high allelopathic potential of rice cultivars might be attributed to their higher length of fine roots <0.2 mm in diameter and more number of root tips of fine root, which could accumulate and release more allelochemicals to solutions, thereby resulting in high inhibition on target plants. The mechanisms regulating this process need to be further studied.

Transcriptome analysis reveals that barnyard grass exudates increase the allelopathic potential of allelopathic and non-allelopathic rice (Oryza sativa) accessions

BackgroundAllelopathy in rice (Oryza sativa) is a chemically induced response that is elevated by the exogenous application of chemical compounds and barnyard grass root exudates. An in-depth understanding of the response mechanisms of rice to chemical induction is necessary for the identification of target genes for increasing the allelopathic potential of rice. However, no previous studies have evaluated the transcriptomic changes associated with allelopathy in rice in response to barnyard grass exudates treatment. Thus, the aim of the present study was to reveal differentially expressed genes (DEGs) in allelopathic and non-allelopathic rice seedlings treated with barnyard grass exudates to identify target allelopathy genes.ResultsThe inhibitory effect of the culture solutions on the allelopathic rice accession PI312777 (PI) and the non-allelopathic rice accession Lemont (LE) significantly increased (P < 0.05) after treatment with barnyard grass root exudates. The RNA sequencing results revealed that 14,891 genes in PI(+B) vs. LE(+B), 12,505 genes in PI(+B) vs. PI(−B), and 5857 genes in LE(+B) vs. LE(−B) were differentially expressed following root exudates treatment. These DEGs were classified into three categories and 32 functional groups, i.e., 12 groups in the biological process category, 12 groups in the cellular component category, and eight groups in the molecular function category. There were 5857 and 2846 upregulated genes and 135 and 50 upregulated Gene Ontology terms (P < 0.05) in the biological process category in PI(+B) vs. PI(−B) and LE(+B) vs. LE(−B), respectively. These results indicated that the allelopathic accession PI is more sensitive than the non-allelopathic accession LE to exogenous root exudates treatment. Genes related to rice allelochemical-related biosynthesis pathways, particularly the shikimic acid and acetic acid pathways, were significantly differentially expressed in both rice accessions. These findings suggested that phenolic acids, fatty acids, and flavonoids, which constitute the downstream metabolites of the shikimic acid and acetic acid pathways, are significantly expressed in response to root exudates of barnyard grass.ConclusionsThe allelopathic potential of both rice accessions could be significantly enhanced by barnyard grass root exudates application. Furthermore, genes related to the biosynthesis pathways of reported rice allelochemicals were significantly differentially expressed in both accessions. Phenylalanine ammonia lyase was determined to be a potential target for the regulation of chemical induction.

Rice allelopathy in weed management – An integrated approach

The intensive use of pesticides with low biodegradability and high persistence in soil, surface and ground waters, represents a considerable environmental risk, especially under high weed pressure conditions. Furthermore, the number of herbicide-resistant weeds is increasing. Against this background, the investigation of alternative weed control strategies has taken on considerable importance. Among these, allelopathy as a negative effect of one plant on another due to the direct or indirect (including microorganisms) release of chemicals in the environment can be a useful tool for the integrated management of weeds in agroecosystems. In particular, the paddies have been considered in this work by reviewing the data both on rice allelopathy and rice weed agronomic control methods developed to improve the crop yield.

Review of the biotechnological applications of rice allelopathy in agricultural production

An improvement in the allelopathic potential of rice will have a great impact on both low‐input and high‐input management systems. Allelopathy alone is not likely to replace other weed control practices, but it surely functions as a component of integrated weed management technology. Allеlораthу is thе рrосеѕѕ whеrеbу аn organic сhеmісаl (аllеlосhеmісаl) that is rеlеаѕеd from one рlаnt influences the growth and dеvеlорmеnt of other plants. Allelochemical biosynthesis, release, environmental fate and action on other plant species can depend on genetic factors or on the environment and their interaction. As a result of these interactions, allelopathy is a complex phenomenon with limited repeatability. The term “allelopathy” has undergone several changes and it has been defined as any direct or indirect harmful or beneficial effect of a plant on another through the production of chemical compounds that it releases into the environment. Rice allelopathy is one of the modes of interaction between receptor and donor plants and could exert either positive effects or negative effects. The development of genetic modification by enhancing crops with allelopathic traits should be done cautiously, given the ecological risk (untoxic and safe for humans and the ecosystem, crop productivity, the ratio of benefit and cost etc.). Finally, this article reviews the agricultural production system allelopathy of novel applications, including the role of allelochemical consortia and their potential use in no‐tillage cropping systems, cover crops or mulches.

Relationship Between Allelopathic Effects and Functional Traits of Different Allelopathic Potential Rice Accessions at Different Growth Stages

In this study, effects of temperature, light and their interactions on allelopathic effects and the functional traits specific leaf area (SLA) and stem mass fraction (SMF) of different allelopathic potential rice accessions at different growth stages were analyzed. The main results were as follows: Allelopathic responses to temperature and light varied with different allelopathic potential rice accessions at different growth stages. With the rise of temperature and the extension of photoperiod, allelopathic effect increased firstly and then decreased at 2–3 leaf stage, but increased constantly at the 4–5 and 7–8 leaf stages in strong allelopathic rice accessions [O. longistaminata, F1 (O. longistaminata × RD23), F2 (RL159 and RL169)]. Temperature had significant impact on allelopathic effect without considering light factors, but light showed little effect on rice allelopathy at the same temperature conditions. The greatest allelopathic effect was attained with moderate temperature and long photoperiod at 2–3 leaf stage in strong allelopathic rice accessions, but all the rice accessions showed weak allelopathic effects at the low temperature condition (15°C/10°C), and the influence of different factors on allelopathy followed a general trend as temperature > leaf stage > light, indicating that among the multiple factors impacting rice allelopathy, temperature was the main factor. Allelopathic characteristics of F1 and F2 to various temperature and light were similar to O. longistaminata, showing that allelopathic genes from wild rice can be expressed in its descendants. Temperature and light also had significant effects on SLA and SMF, and rice allelopathy was closely correlative to SLA in strong allelopathic rice accessions at the 4–5 and 7–8 leaf stages, but there was no correlation between rice allelopathy and SMF at different growth stages. These results suggested that rice adjust the relationship between allelopathy and SLA and adapt to the varied environments, and that high temperature and long photoperiod can enhance rice allelopathic activity.

Increasing Rice Allelopathy by Induction of Barnyard Grass (Echinochloa crus-galli) Root Exudates

An allelopathic rice PI312777 and a non-allelopathic rice Lemont were hydroponically cultured and treated with extracts of seeds and tissues and root exudates of barnyard grass (Echinochloa crus-galli, BYG) to induce an allelopathic response. The results of bioassays showed that the % inhibition of two rice leaf extracts was significantly (p < 0.05) increased by treatment with BYG root exudates. This induced trait was dosage- and time-dependent. The highest % inhibition for both PI312777 and Lemont was obtained following treatment with 15 mL of BYG root exudates for 2 days. Under these conditions, total allelopathy (TA) values of PI312777 on root length, plant height, and plant dry weight of BYG were 73.39, 68.01, and 70.42%, respectively, and induced allelopathy (IA) values were 21.53, 17.04, and 16.62%, respectively, accounting for 24–29% of TA. Correspondingly, TA values of Lemont were 28.38, 21.38, and 23.38%, respectively, and IA values were 14.49, 11.37, and 12.11%, respectively, accounting for 51–53% of TA. The % inhibition of two rice culture solutions was in agreement with the results of their leaf extracts. The total contents of 7 phenolic acids in the culture solutions of PI312777 and Lemont were 2.18 and 1.47 times, respectively, as much as those in the control solutions. The phenylalanine ammonia-lyase (PAL) gene in PI312777 leaves was significantly up-regulated after induction treatments. The results indicated that rice allelopathy is a chemical induction mechanism, and confirmed that chemical induction to raise rice allelopathy is a practical and feasible method.

Allelopathic potential of plant residues of thirty Sri Lankan traditional rice (Oryza sativa L.) varieties on Barnyardgrass (Echinochloa crusgalli)

The use of rice (Oryza sativa L.) allelopathy for weed management could reduce the need for applying herbicides to the crop. In this study a pot experiment and a laboratory bioassay were conducted to assess the allelopathic potential of residues of 30 traditional rice varieties in Sri Lanka on seed germination and seedling growth of barnyardgrass (Echinochloa crus-galli). All seeds were collected from “Farmer Federation for Conservation of Traditional Seeds and Agri Resources”. Rice residues were incorporated with silica sand (1% w/w) in small pots to prepare residue mixture and ground rice residues mixed with water (2.5g/100ml) were used to prepare residue extract for laboratory bioassay. Rice varieties exhibited marked differences in the inhibition of barnyardgrass growth and development. In the bioassay, residue extract of rice variety Herathbanda exhibited the greatest activity on the weed seedling growth, reducing dry weight by 30.7%, while Gonabaru residue extract exhibited the greatest inhibition on seed germination, reducing germination by 29.6%. In the pot experiment of residue mixture, Batapola el and Sula varieties showed the greatest inhibition percentage on germination (48.4%). However, Godaheenati showed the greatest inhibition % on plant height (27.4%) and dry weight (45.6%). These results suggest that incorporation of rice residues of tested varieties has influence on controlling barnyardgrass seedling growth.

Anne Osbourn.

Anne Osbourn.