Allelopathic potential of indigenous Bangladeshi rice varieties

A series of experiments was conducted in the laboratory and greenhouse of the Subtropical Field Science Center, University of the Ryukyus, Japan, from April to October 2015 to assess the allelopathic potential of 50 indigenous Bangladeshi rice varieties by using the donor–receiver bioassay, equal compartment agar method (ECAM), plant residue extract method and pot culture method. Lettuce (Lactuca sativa L.), cress (Lepidium sativum L.), radish (Raphanus sativus L.), barnyard grass (Echinochloa crus‐galli L. Beauv.) and jungle rice (Echinochloa colona L.) were used as the test plants. The highest inhibition effect was given by Boterswar, while the stimulating effect was given by Kartikbalam and Panbira in the donor–receiver bioassay and ECAM tests. Boterswar, Goria, Biron and Kartiksail were selected as the highest allelopathic‐potential varieties by the donor–receiver bioassay and ECAM. In the methanol extract test, Boterswar gave the strongest inhibitory effect on both barnyard grass and jungle rice, while Kartiksail gave the highest inhibitory effect on the jungle rice shoot. The growth parameters and total dry matter of barnyard grass in the greenhouse pot experiment were significantly reduced as a result of the application of aqueous extracts of the selected rice varieties, which was similar to the results of the laboratory experiments. The varieties of Boterswar, Goria, Biron and Kartiksail were selected as the most allelopathic among the 50 indigenous Bangladeshi rice varieties. These rice varieties could be used for the isolation and identification of allelochemicals and to further develop new varieties that are tolerant to weeds.     

Genetic and morphologic diversity of <Emphasis Type="Italic">Echinochloa crus-galli</Emphasis> populations from different origins

Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass) is an annual weed that is native to Asia and found throughout the world. The broad ecological tolerance and competitive ability of E. crus-galli makes it the most important weed species in rice. Genetic studies of plants are becoming increasingly common because reliable information is necessary to better understand population dynamics, occurrence of herbicide resistance, and demographic data. Echinochloa crus-galli populations from 34 different locations in Turkey were compared with respect to morphological differences and genetic variation. For morphological variation, five seeds of each population were sown in pots and grown in a screenhouse using a randomized block design. Morphological parameters such as germination speed, flowering time, leaf area, plant height, spikelet length, above-ground biomass, root dry weight and number of seeds were measured. Distinct differences among populations with respect to hierarchical cluster analysis were observed. Genetic variations among populations were performed using random amplified polymorphic DNA (RAPD) markers. The seven RAPD primers amplified 55 bands whose molecular weight varied between 200 and 4000 bp. The percentage of polymorphic bands was 74.54%. Results showed high morphological and genetic variability among individual genotypes within geographic locations. Phenotypic and genetic variability among E. crus-galli populations would be influenced by agricultural practices, crop characteristics, geographic location and herbicide pressure. Differences between weed populations may affect response to chemical or biological control.     

Herbicidal potential and quantification of causative allelochemicals from several Compositae weeds

Compositae plants contain biologically active substances that are allelopathic to weed species. Aqueous extracts from leaves of 16 plants were bioassayed against lucerne (Medicago sativa) to determine their allelopathic effects, and the results showed the highest inhibition for the extracts from Lactuca sativa, Xanthium occidentale and Cirsium japonicum. The extracts applied to filter paper in Petri‐dish bioassay tests significantly inhibited root growth of lucerne. Extracts of 40 g dry tissue L^?1 from L. sativa, X. occidentale and C. japonicum were completely inhibitory to lucerne root growth, but hypocotyl growth of lucerne was less sensitive. Although allelopathic effects of methanol extracts were much less than those of coumarin or alachlor, early seedling growth of both lucerne and Echinochloa crus‐galli was significantly reduced by methanol extracts. Mixture of L. sativa, X. occidentale and C. japonicum extracts had more inhibitory effects on test plants than each single extract treatment. By means of high‐performance liquid chromatography, responsible causative allelopathic substances present in L. sativa, X. occidentale and C. japonicum were isolated from various fractions and identified as coumarin, trans‐cinnamic acid, o‐coumaric acid and p‐coumaric acid. These results suggest that some Compositae have various herbicidal potentials, and that their activities, types and amount of causative compounds differ, depending on the plant species.     

Inhibition of Echinochloa crus-galli var. frumentacea seedling root elongation by chiral 1, 3, 5-triazines in the dark

2-z-Substituted benzylamino-4-substituted-amino-6-chloro-1,3, 5-triazines are herbicidal compounds showing leaf-burning and/or growth inhibition with concomitant greening and stunting. Effects of chiral 1,3,5-triazine compounds in a light-independent seedling root elongation test with Echinochloa crus-galli var. frumentacea Wight demonstrated an interaction between chirality and root growth inhibition. The test compounds inhibited root growth, and this inhibition was due to interference with a system or systems other than photosynthesis. 4-(R)-sec-butylamino-2-(α,α-dimethylbenzyl)amino-6-chloro-1,3, 5-triazine showed the highest inhibitory activity, and 4-methylamino-2-(R)-a-methylbenzylamino-6-chloro-1,3,5-triazine was second. The chiral requirement for a strong inhibition of root growth was the (R)-configuration, contrasting with the requirement for the (S)-configuration for an inhibition of photosystem II.     

Root growth and the relative importance of root and shoot competition in interactions between rice (Oryza sativa) and Echinochloa crus-galli

Competition between rice (Oryza sativa) and Echinochloa crus-galli (L.) Beauv. (barnyard-grass or cockspur) was studied experimentally in the field in Sri Lanka. By growing rice in bags sunk in the paddy soil such.that the roots of the plants were either separated from or free to mingle with those of neighbouring weeds, or by growing rice in the same bags but in the absence of weeds, it was possible to calculate the relative importance of interference below ground (root competition) and above ground (shoot competition). Three rice varieties with different above-ground morphology were inhibited to different extents by E. crus-galli but in each case root competition was more important than shoot competition. In the variety that was most sensitive to root competition, Bg 400–1, inhibition of total growth due to root competition increased with increasing weed density. When grown in monocultures in pots in the field, the two species exhibited similar growth rates whether or not the soil was fertilized, but in 1:1 mixtures growth of E. crus-galli was greater, particularly if fertilizer was added, as this promoted the growth of the weed, while having no effect on the rice. In mixture, relative yield totals were close to 1.0, with the relative yield of E. crus-galli being consistently greater than 0.5, particularly with added nutrients, while the relative yield of rice was always less than 0.5. The relative crowding coefficient for rice with respect to E. crus-galli (K_eb), when based on total plant dry weight, was lower in fertilized than in non-fertilized soil, falling in the former case from 0.4 to 0.2 during the experiments Kroot_rb, based on root dry weight, decreased with increasing soil depth and was lower in fertilized than in non-fertilized soil, most notably after 62 days of growth, when root dry weight was at its maximum. It is concluded that inhibition of root growth of rice, leading to a reduced ability to obtain resources from the soil, was the major factor contributing to the decline in the growth of rice in the presence of E. crus-galli. Croissance racinaire et importance relative de la compétition racinaire et aérienne dans les interactions entre le riz (Oryza sativa) et le panic (Echinochloa crus-galli) La competition entre le riz (Oryza sativa) et le panic (Echinochloa crus-galli) a étéétudiée dans une expérimentation de plein champ au Sri Lanka. En cultivant du riz dans des sachets immergés dans la riziére de telle façon que ses racines soient soil séparées, soil libres de se mé1anger avec celles des adventices voisines, ou en cultivant du riz dans des sachets analogues mais en 1'absence de mauvaises herbes, il est possible de calculer 1'importance relative de 1'interférence sous le sol (compétition racinaire) et de celle au dessus du sol (compétitionaérienne). 3 variétés de riz ayant une morphologie aérienne différente ont été inhibées par le panic à des niveaux différents mais chaque fois la compétition racinaire a été plus importante que l'aérienne. Chez la variété la plus sensible à la compétition racinaire, Bg 400–1, le ralentissement de la croissance totale due à la compétition racinaire augmenta avec l'augmentation de la densité de mauvaises herbes. Quand elles sont cultivées en pots dans les champs, les deux espèces ont des taux de croissance similaires que le sol soit ou non fertilisé, mais dans un mélange 1/1 la croissance du panic est plus forte surtout si l'on ajoute de l'engrais puisque celui-ci favorise la croissance de l'adventice sans avoir d'effet sur le riz. En mélange, le total des poids relatifs était très proche de 1, avec un poids relatif de panic conséquemment plus grand que 0,5, surtout dans le cas d'adjonction d'engrais, tandis que celui du riz était toujours inférieur à 0,5. Le coefficient de tassement relatif du riz en regard du panic (K_rb), basé sur le poids sec de la plante entière était plus faible dans les sols fertilisés que dans les autres, tombant de 0,4 à 0,2 pendant l'expérimentation. KracinC_rb, basé sur le poids sec de racine, diminue avec l'augmentation de la profondeur du sol et est plus bas dans les sols fertilisés que dans les autres, surtout après 62 jours de croissance quand le poids sec de racine est à son maximum. Il est conclu que le ralentissement de la croissance des racines de riz, aboutissant à une capacité moindre à prélever les ressources du sol, était le facteur principale de la réduction de la croissance du riz en présence de panic. Wurzelwachstum von und Wurzel- sowie Sproßkonkurrenz zwischen Reis (Oryza sativaj und Echinochloa crus-galli In Freilandversuchen in Sri Lanka zur Wurzelund Sproßkonkurrenz zwischen Reis (Oryza sativa L.) und Hühnerhirse (Echinochloa crus-galli (L.) Beauv.) wurde Reis so in Beuteln gepflanzt, daß seine Wurzeln sich entweder getrennt oder mit denen des Unkrauts zusammen wachsend entwickeln konnten. Andere Parzellen blieben unkrautfrei. E. crus-galli konkurrierte mit 3 Reissorten von unterschiedlicher Sproßmorphologie verschieden stark, doch die Wurzelkonkurrenz war immer bedeutender als die Sproßkonkurrenz. Bei der gegen Wurzelkonkurrenz empfindlichsten Sorte “Bg 400–1” war die Gesamthemmung auf die mit der Unkrautdichte zunehmende Wurzelkonkurrenz zurückzuführen. In Monokultur hatten beide Arten unabhängig von der Düngung ähnliche Wachstumsraten, aber in l:l-Mischkulturwuchs E. crus-galli stärker, besonders bei Düngung, die auf den Reis wirkungslos blieb. In Mischkultur lag der relative Gesamtertrag nahe 1,0, wobei der Ertrag von E. crus-galli stets über 0,5, der des Reises jedoch immer unter 0,5 lag. Für die Wechselbeziehung zwischen Reis und E. crus-galli auf die Gesamttrockenmasse wurde ein ‘crowding coefficient’ (K_rb) für Reis berechnet, der mit Düngung kleiner war als ohne. K_rb nahm während des Versuchs von 0,4 auf 0,2 ab. Der auf die Wurzeltrockenmasse bezogene ‘crowding coefficient’ (Kroot_rb) nahm mit zunehmender Bodentiefe ab. Kroot_rb war niedriger in gedüngtem verglichen mit ungedüngtem Boden. Dieser Unterschied war nach 62 Tagen Wachstum besonders deutlich, als die Wurzeltrockenmasse ein Maximum erreichte. Die Hemmung des Wurzelwachstums des Reises wurde als wichtiger Faktor für seine Wachtum-shemmung in der Gegenwart von E. crus-galli angesehen, weil sie die Fähigkeit des Reises zur Nährstoffaufnahme aus dem Boden verringert.     

Performance of Bangladesh indigenous rice in a weed infested field and separation of allelopathy from resource competition

This study aimed to identify the potential allelopathic indigenous rice (Oryza sativa L. ssp. indica) varieties from Bangladesh using a performance study in a weed‐infested field and to assess the extent of allelopathic interference relative to resource competition in a glasshouse experiment. Six varieties – namely, “Boterswar,” “Goria,” “Biron” and “Kartiksail” as the most allelopathic, “Hashikolmi” as weakly allelopathic and “Holoi” as nonallelopathic – were raised following a nonweed control method. The infestation levels of weed species were calculated using Simpson's Diversity Index (SDI), which ranged from 0.2 to 0.56. However, a significant correlation coefficient (0.87, P < 0.001) was obtained from these field data compared with the root inhibition percentage from the laboratory bioassay, and the “Boterswar” variety was the most allelopathic. The interactions between the allelopathic variety “Boterswar,” weakly allelopathic variety “Hashikolmi” and Echinochloa oryzicola via a target (rice)‐adjacent (E. oryzicola) cogrowth culture were determined in a hydroponic arrangement. The relative competitive intensity (RCI) and the relative neighbor effect (RNE) values showed that the crop–weed interaction was facilitation for “Boterswar” and competition for “Hashikolmi” and E. oryzicola in rice/E. oryzicola cogrowth cultures. The allelopathic effects of “Boterswar” were much higher than the resource competition in rice/E. oryzicola cogrowth cultures. The converse was observed for “Hashikolmi.” Moreover, the mineral content of E. oryzicola was severely affected by “Boterswar”/E. oryzicola cogrowth cultures’ exudate solution. Therefore, the allelopathic potential of “Boterswar” variety might be useful for developing the weed‐suppressing capacity of rice, which will likely have a significant influence on paddy weed control.     

Use of phytotoxic rice crop residues for weed management

There is a general perception among Cambodian rice (Oryza sativa) farmers that, after harvesting, rice crop residues that are incorporated into the field benefit the growth of the subsequent rice crop. However, the effect of this action upon weed establishment and growth has not yet been considered. A series of pot and field trials were conducted to determine whether such action could inhibit weed establishment and/or growth. The pot studies first evaluated the response of the test plant (rice line ST‐3) and three weed species, barnyardgrass (Echinochloa crus‐galli), small umbrella sedge (Cyperus difformis), and water primrose (Ludwigia octovalves), to the residue of 16 rice lines and the field trials were later conducted to evaluate the response of the same test plants to the residue of seven putatively allelopathic rice lines and one non‐allelopathic rice line. The residue of all the studied rice lines, depending on how long they had been incorporated into the soil, reduced the establishment and growth of all three weed species, as well as the rice crop. However, if the residue's incorporation was delayed by 2 weeks or only a proportion of the residue was incorporated, the rice crop could withstand the growth‐inhibiting effect, while the inhibition of the establishment and growth of the three weed species was retained. These responses of rice and the weeds to rice crop residues might provide a basis for a weed management strategy, particularly in the resource‐poor rice‐production systems of Cambodia.     

The allelopathic effect of three Amaranthus spp. (pigweeds) on wheat (Triticum durum)

The allelopathic effect of Amaranthus retroflexus L., Amaranthus blitoides S. Wats, and Amaranthus gracilis Desf. on wheat Triticum durum L. was investigated under laboratory, glasshouse and field conditions. Laboratory experiments showed that fresh shoot or root extract of the three weed species reduced germination, coleoptile length, root length and root dry weight of wheat seedlings. The inhibitory effects were rate dependent, with low concentrations of shoot extract promoting shoot growth of wheat. Fresh plant extracts were more phytotoxic than dried plant extracts and shoot extracts had higher detrimental effects than root extracts. In pot experiments, dried shoot extract of A. gracilis increased shoot and root dry weights of wheat seedlings. For A retroflexus and A. blitoides the extracts of these and dried shoots (8 g kg^?1), which had been added to soil mixtures significantly reduced ger-mination and growth of wheat seedlings. Addition of up to 16 g kg^?1 of A. gracilis residues promoted shoot growth of wheat and had no significant harmful effect on root growth. Roots appeared more sensitive to allelopathic effect than shoots. Under field conditions, incorporation of A. retroflexus or A. blitoides residues in the soil reduced height, grain and straw yield of wheat, whereas A. gracilis residues stimulated plant height and increased yield.     

Etude du stock en semences d'Echinochloa crus-galli (L.) Beauv. dans le sol des rizières du Gharb (Maroc)

Study of the seed stock of Echinochloa crus-galli (L.) Beauv. in the soil of rice-fields in Gharb (Morocco) Estimates of the numbers of viable caryopses of Echinochloa crus-galli were made on soil samples taken from twenty-six rice-fields in Gharb (Morocco). Fields were chosen according to three factors: soil type, rotation and number of years in rice. The mean value of the stock of E. crus-galli caryopses is 1285 m^?2 to 60 cm depth. Its mean contribution to the total seed stock is 7.2%. The sampling plan permitted analysis of soil effects on the rotation three rice: three alternative crops and of rotation on merja soil (this soil is characterized by the smallest stocks in rotations — three rice: three other crops and three rice crops: one other). The mean distribution of caryopses in the soil profile was 85%, 12.5% and 2.5% respectively in the 0–20, 20–40 and 40–60 cm horizons. Field emergence of seedlings of E. crus-galli. from harvest to the sowing of the following crop, represented 0.65% of the stock in the soil.     

Isolation and purification of growth‐inhibitors from Vietnamese rice cultivars

Bioactive compounds that are produced by select rice cultivars have the potential to control barnyardgrass, a major rice yield‐limiting factor. In this study, the Vietnamese rice cultivars, OM 3536, OM 4498 and OM 5930, were selected and their inhibitory activity on cress, lettuce, canola and barnyardgrass was evaluated by using donor–receiver bioassays. These bioassays revealed that OM 3536 and OM 5930 exerted the greatest inhibitory activity, with an average growth inhibition of 57.2% on the roots and shoots of barnyardgrass. A bioassay‐guided approach was used to identify the allelopathic fractions from OM 5930 and was coupled with reverse‐phase chromatography in order to isolate several growth‐inhibitory fractions. The effective dose of the aqueous methanol extract of the rice plants that was required for 50% inhibition (ID₅₀) of the shoot and root growth of the four test plant species, as determined by a logistic regression analysis, averaged 0.091 and 0.062 g mL^?1 for OM 5930 and 0.112 and 0.072 g mL^?1 for OM 3536, respectively. The ID₅₀ of the barnyardgrass roots and shoots in the assays, as determined by a logistic regression analysis, was 0.044 and 0.149 g mL^?1 for OM 3536 and 0.052 and 0.114 g mL^?1 for OM 5930, respectively. A growth‐inhibitory fraction in the aqueous methanol extract of OM 5930 was isolated and the inhibitory activity on lettuce seedlings was determined. At a concentration of 100 p.p.m., this growth‐inhibitor inhibited lettuce root growth by up to 80.2%, compared to the control plants. These findings demonstrate that the dried plant tissues of Vietnamese rice cultivars could contain bioactive compounds that strongly inhibit plant growth.