水稻化感生物测试方法的比较及应用

选用8个化感作用潜力各异的水稻品种(系)：PI312777、Lemont、Moroberekan、IAC25、IACA7、IAC120、Batatais、Iguape Cateto为供试材料,以田间伴生稗草为受体材料,比较分析了目前较为通用的3种生物测试方法：琼脂迟播共培法(RSA)、石英砂迟播共培法(RSS)和根系分泌物培养法(SRE)对水稻化感潜力的测试效果．结果表明,RSA法应用于测试水稻化感作用潜力的效果最好,RSS法和SRE法的测试结果虽较为一致,但两者都存在不足．据此,运用RSA法对57个水稻材料进行了化感抗草种质资源的初步筛选,从中获得5个强化感作用潜力的水稻材料：Iguape Cateto、PI312777、Azucena、Taichung Native 1和IAC25．     

Response and relation of allantoin production in different rice cultivars to competing barnyardgrass

The production of secondary metabolites and biomass of plants may be altered by coexistence and competition. Rice has coexisted with barnyardgrass in paddy systems for centuries and represents a model system for understanding plant–plant interactions. Despite increasing knowledge of allelochemicals produced and released by rice involved in coexistence of these two species, relatively little is known about the role and production of beneficial chemicals of rice in response to competing barnyardgrass. The purpose of this study was to quantify the growth-stimulating allantoin (5-ureidohydantoin) and its effect on barnyardgrass growth in a rice–barnyardgrass system. In this system, rice produced and released allantoin but barnyardgrass did not. The production of allantoin by rice responded to competition from barnyardgrass, and its concentration varied among rice cultivars tested. At 1:1 barnyardgrass and rice mixture proportion, allantoin concentration in allelopathic cultivars was obviously lowered by competing barnyardgrass, while no significant variation of allantoin concentration was observed in non-allelopathic cultivars. Barnyardgrass biomass was reduced in mixed-culture with rice cultivars, in particular, allelopathic cultivars. There was a positive relationship between allantoin concentration in rice cultivars and barnyardgrass biomass. Furthermore, allantoin stimulated the growth of barnyardgrass once released from rice or added to soil. The results suggest that rice plants of allelopathic cultivars appear to be able to detect the presence of competing barnyardgrass and respond by decreasing production of growth-stimulating allantoin, regulating the growth of barnyardgrass. In this manner, given rice cultivars may alleviate the competition of barnyardgrass and provide greater benefit to their own growth.     

不同水层和密度条件下化感作用水稻对无芒稗的干扰控制作用

不同水层下水稻对无芒稗的干扰控制作用研究表明,水稻化感作用品种吓一跳、谷梅2号和中156对无芒稗的株高抑制作用比无化感作用品种秀水63和春江11呈显著性差异．随盆栽水稻密度增加,水稻对无芒稗的干扰控制作用加大．在每盆4株栽植密度下,水稻化感作用品种鸡早籼、谷梅2号显著抑制无芒稗植株株高;在每盆32株密度时,水稻化感作用品种吓一跳、PI312777、TN1等对受控无芒稗的干扰控制与无化感作用品种春江11相比,呈显著性水平．     

水稻品种化感潜力的双重评价与筛选

以初筛获得的7份水稻品种为材料,用特征次生物质标记法在HPLC上测定化感指数AI值并结合田间小区试验进行双重评价与筛选,得到3份既具高化感指数又具较高田间抗草活性的水稻化感品种(系),它们是:我国台湾品种I-Kung-Pao、Parahainakoru和大陆品种HB-1。它们对无芒稗根长抑制率分别达57%、64%、55%,均超过50%;其化感指数分别是0.61、0.56、0.59,均与美国化感潜力品种PI312777的化感指数0.59相近;结果表明,水稻品种I-Kung-Pao、Parahainakoru和HB-1是我国宝贵的化感品种资源。     

Genomic analysis of allelopathic response to low nitrogen and barnyardgrass competition in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

To explore the molecular mechanism of allelopathic rice in response to low nitrogen (N) supply or accompanying weed stress, allelopathic rice PI 312777 and its counterpart Lemont were grown under low N supply or co-cultured with barnyardgrass [Echinochloa crus-galli (L.) Beauv.] in hydroponics. The suppression subtractive hybridization (SSH) technique was employed to isolate the up-regulated genes in the treated rice accession. The results indicated that the expression of the genes associated with N utilization was significantly up-regulated in allelopathic rice PI 312777, and the higher efficiency of N uptake and its utilization were also detected in PI 312777 than that in Lemont when the two rice accessions were exposed to low N supply. This result suggested that the allelopathic rice had higher ability to adapt to low N stress than its non-allelopathic counterpart. However, a different response was observed when the allelopathic rice was exposed to accompanying weed (barnyardgrass) co-cultured in full Hoagland solution (normal N supply). It showed that the expression of the genes associated with allelochemical synthesis and its detoxification were all up-regulated in the allelopathic rice when co-cultured with the target weed under normal N supply. The results suggested that the allelopathic rice should be a better competitor in the rice-weed co-culture system, which could be attributed to increasing de novo biosynthesis and detoxification of allelochemicals in rice, consequently resulting in enhanced allelopathic effect on the target and preventing the autotoxicity in this process. These findings suggested that the accompanying weed, barnyardgrass is not only the stressful factor, but also one of the triggers in activating allelopathy in rice. This implies that the allelopathic rice is sensible of the existing target in chemical communication.     

水稻抗草品种选育研究初报

利用PI312777抗草稻种材料,与本单位优质稻核心种质及其衍生系统材料广泛杂交配组,创建一批以PI312777衍生系统为主的新型育种材料。建立水稻抗草育种圃,重点针对抗草特性和综合农艺性状,通过田间抑草效应筛选,培育水稻抗草苗头株系,在稳定世代(F4代以上)应用以水稻特征次生物质为标记评价水稻品种(系)化感潜力的方法,辅助选育水稻抗草新品种(系)。初步提出适合华南稻区的以田间筛选和评价为主,以特征次生物质标记评价水稻品种(系)化感潜力的方法为辅,田间与实验室相结合,操作性强、简便有效的水稻抗草育种方法。     

Identification and comparative analysis of microRNAs in barnyardgrass (Echinochloa crus‐galli) in response to rice allelopathy

Rice allelopathy is a hot topic in the field of allelopathy, and behaviour of donor allelopathic rice has been well documented. However, few study addresses response of receiver barnyardgrass (BYG). We found that expression of miRNAs relevant to plant hormone signal transduction, nucleotide excision repair and the peroxisome proliferator‐activated receptor and p53 signalling pathways was enhanced in BYG co‐cultured with the allelopathic rice cultivar PI312777, the expression levels of these miRNAs in BYG plants were positively correlated with allelopathic potential of the co‐cultured rice varieties. Treatment of BYG plants with rice‐produced phenolic acids also increased miRNA expression in BYG, while treatment with rice‐produced terpenoids had no obvious effect on miRNA expression. In the hydroponic system, the largest number of Myxococcus sp. was found in the growth medium containing rice with the highest allelopathic potential. The addition of phenolic acids in the hydroponic medium also increased the number of Myxococcus sp. More interestingly, inoculation with Myxococcus xanthus significantly increased miRNA expression in the treated BYG. Jointed treatments of ferulic acid and M. xanthus led to strongest growth inhibition of BYG. The results suggest that there exist involvement of Myxococcus sp. and mediation of miRNA expression in rice allelopathy against BYG.     

Reaction of incompatible isolate of Pyricularia grisea on rice leaves stripped of epicuticular wax reflects blast conduciveness of soils

Upland rice cultivars were evaluated in the greenhouse for susceptibility to the rice blast disease caused by Pyricularia grisea Sacc., on two upland soils from the Philippines previously considered to be “blast conducive” and “blast non-conducive”. Under monocyclic inoculation tests plants grown in conducive soil showed significantly greater lesion development than plants of the same cultivar grown in non-conducive soil: cultivars considered to be susceptible to the isolates used showed increased number of susceptible-type lesions; resistant cultivars showed increased number of hypersensitive resistant-type lesions. A similar effect was observed under polycyclic tests where several generations of the pathogen were allowed to develop on the test plants. Dilution of conducive soil with non-conducive soil resulted in a corresponding reduction of disease severity, although this was most pronounced on resistant cultivars. Removal of leaf epicuticular waxes (LEW) using organic solvents increased the number of resistant-type lesions on resistant cultivars grown in both soils following inoculation. Susceptible plants were not suitable for quantifying the relative blast conduciveness of a soil because of the extreme environmental sensitivity of the bioassay and the tendency of lesions to coalesce. Comparing numbers of resistant-type lesions on leaves of plants stripped of LEW and inoculated with an incompatible P. grisea isolate among plants grown in different soils proved to be a satisfactory means of distinguishing the relative blast conduciveness of soils under controlled conditions. This method was field tested in eastern India and results corroborated farmer assessment of which soils were blast conducive. Using incompatible isolate-cultivar combinations and LEW-free leaves is proposed as a simple bioassay for assessing blast conduciveness of soils and should prove useful in regional characterization of rice blast risk.     

Canola cultivar performance in weed-infested field plots confirms allelopathy ranking from in vitro testing

Crop competition and allelopathy are two cultural control options for possible inclusion in cropping systems. This research aimed to identify superior allelopathic canola genotypes through a two-year field study. First year screening results of 312 diverse Brassica genotypes showed genotypes differed significantly in their ability to suppress weed infestations. Crop plant height was correlated with the competitive ability of several genotypes, while other genotypes showed good weed-suppressive ability despite being short. Thirty-six of the genotypes grown in the field had been previously assessed for their allelopathic ability to inhibit the growth of annual ryegrass (Lolium rigidum) seedlings using an in vitro technique. The highly allelopathic genotypes: Av-opal, Sardi603, Rivette and Atr-beacon performed well against annual ryegrass in the laboratory and also against other species, including Capsella bursa-pastoris, Sisymbrium orientale and Hordeum leporinum in the field. The weakly allelopathic Barossa and X-06-6-3725 genotypes performed poorly both in the laboratory studies and in the field. The following year, field testing of selected genotypes at two sowing dates further suggested that the most allelopathic genotypes in the laboratory bioassay were generally those that suppressed weed numbers and their biomass in the field. The late sowing time increased the natural weed pressure leading to a decrease in both canola grain yield and quality. Many of the highly allelopathic canola genotypes, which caused low weed populations in the field, had relatively low grain yield. This suggests that the allelopathic trait is independent of local adaptation and yields potential under weed-free conditions. Ideally, cultivars with both high allelopathy and high competitive ability would be most useful to help farmers maximise yield and control weeds. Selection for allelopathy in canola shows potential as a future non-chemical weed control option and requires further investigation.     

The relation between growth inhibition and secretion level of momilactone B from rice root

Abstract

The growth inhibitory activity of seven rice (Oryza sativa L.) cultivars and the secretion level of momilactone B from these rice cultivars were determined to understand chemical basis of the interaction of rice with other plant species. All rice cultivars inhibited the growth of hypocotyls and roots of lettuce (Lactuca sativa L.) seedlings when the lettuce was grown together with the rice, and showed different range of the inhibitory activity. These results suggest that all rice cultivars may possess allelopathic activity and the activity may be cultivar dependent. Momilactone B, which is a potent growth inhibitor, was found in root exudates of all rice cultivars, and the momilactone B concentration was also cultivar-dependent. The allelopathic activity of each rice cultivar was closely correlated with momilactone B concentration in the root exudates. The present results suggest that rice cultivars possess various allelopathic activities and their allelopathic activity may depend on the secretion level of momilactone B. Therefore, momilactone B may play an important role in rice allelopathy and in the chemical interactions of rice with other plant species.     

不同类型稻种资源对稗草化感潜力差异评价

以120份不同类型稻种资源为研究对象,将田间鉴定和室内叶浸提液处理鉴定方法相结合,对其化感作用差异进行了鉴定评价.结果表明,在田间不同类型稻种资源对稗草生长的抑制效果大小趋势为地方品种＞选育品种(系)＞引进品种(系)＞杂交水稻(恢复系和不育系),对稗草苗鲜重和苗干重的抑制效果大于对苗高的抑制效果.室内叶浸提液处理鉴定结果,不同类型稻种资源间化感作用差异相对较小,但仍以地方品种较强,并对稗草根长的抑制效果大于对稗草苗高的抑制效果.地方品种中具有较强化感作用的种质资源频率高于其他类型品种,今后要加强对地方品种资源的化感潜力鉴定和评价.     

不同供氮条件下水稻的化感抑草作用与资源竞争分析

为探讨化感水稻在不同氮素水平下的生物干扰现象,提出了一种新的测试方法———化感竞争分离法(allelopathyandcompetitionseparation basedbioassay,ACS),成功地区分了在稻/稗共生系统中水稻化感作用与资源竞争及其在不同N条件下的反应特性.结果表明,水稻PI312777具有较强的生物干扰能力.在不同N水平下,其资源竞争能力较强且表现稳定,但化感作用潜力则随供N水平的下降而明显增强.水稻Lemont不具化感作用潜力,在供N水平正常或充足条件下,其资源竞争能力减弱,但在N胁迫下却明显增强.这是在环境资源贫乏时,稻/稗共生系统中生态位竞争加剧的结果.     

Salt tolerance of rice cultivars

Summary The dry matter production and the concentration of nutrients in rice (Oryza sativa L.) cultivars from soil adjusted to different levels of salinity were evaluated under a greenhouse conditions. Soil salinity levels were produced by applying 0.34 mol l^–1 solution of NaCl which resulted in the following levels, control (0.29), 5, 10 and 15 dS m^–1 conductivity of saturation extract. The effect of salinity on dry matter production varied from cultivar to cultivar.The concentrations of P and K in the tops of rice cultivars decreased with increasing soil salinity. But the concentrations of Na, Zn, Cu and Mn increased.Significant varietal differences were found in relation to salinity tolerance. Based on dry matter yield reduction, rice cultivars were classified as tolerant, moderately tolerant, moderately susceptible or susceptible.     

Potential biological control of weeds in rice fields by allelopathy of dwarf lilyturf plants

Dwarf lilyturf (Ophiopogonjaponicus Ker-Gawl), a medicinal plant, hasbeen used for sore throat therapy andinhibition of physiological thirst sinceancient times. Experimental studies wereconducted to determine the allelopathic effectsof dwarf lilyturf plants on germination andgrowth of three main weed species, viz.,barnyardgrass (Echinochloa crusgalli L.),monchoria (Monocharia vaginalis P.) andsmallflower umbrella (Cyperus difformisL.), in rice production and on emergence andgrowth of weeds in rice fields in Japan. Theseresults showed that all aqueous extracts (1, 2,4, 8%, w/v) from the dried powders ofunderground parts of dwarf lilyturf containedwater-soluble substances that significantlyinhibited seed germination and seedling growthfor monchoria and smallflower umbrella. Withrespect to barnyardgrass, all aqueous extractshad less effect on germination, but lowconcentrations (<2%, w/v) had stimulatoryeffects on growth. However, higherconcentrations (>4%, w/v) had significantinhibitory effects. In a glasshouse experiment,all treatments (50, 100, 150 g m^–2) of thedried powders significantly inhibited theemergence and dry weights of weeds in ricepaddy fields and the inhibition became strongeras the concentration increased, except that50 g m^–2 concentration had slightstimulatory effects on the emergence ofbarnyardgrass. The 150 g m^–2 concentrationmarkedly inhibited emergence (77.6%) and dryweight (91.1%) of rice field weeds. Inaddition, all treatments had no inhibition oninitial rice plant growth. Dwarf lilyturfplants may have inhibitory potential on weedsas a natural rice field herbicide.     

Separation of allelopathy from resource competition using rice/barnyardgrass mixed-cultures

Plant-plant interference is the combined effect of allelopathy, resource competition, and many other factors. Separating allelopathy from resource competition is almost impossible in natural systems but it is important to evaluate the relative contribution of each of the two mechanisms on plant interference. Research on allelopathy in natural and cultivated plant communities has been hindered in the absence of a reliable method that can separate allelopathic effect from resource competition. In this paper, the interactions between allelopathic rice accession PI312777, non-allelopathic rice accession Lemont and barnyardgrass were explored respectively by using a target (rice)-neighbor (barnyardgrass) mixed-culture in hydroponic system. The relative competitive intensity (RCI), the relative neighbor effect (RNE) and the competitive ratio (CR) were used to quantify the intensity of competition between each of the two different potentially allelopathic rice accessions and barnyardgrass. Use of hydroponic culture system enabled us to exclude any uncontrolled factors that might operate in the soil and we were able to separate allelopathy from resource competition between each rice accession and barnyardgrass. The RCI and RNE values showed that the plant-plant interaction was positive (facilitation) for PI312777 but that was negative (competition) for Lemont and barnyardgrass in rice/barnyardgrass mixed-cultures. The CR values showed that one PI312777 plant was more competitive than 2 barnyardgrass plants. The allelopathic effects of PI312777 were much more intense than the resource competition in rice/barnyardgrass mixed cultures. The reverse was true for Lemont. These results demonstrate that the allelopathic effect of PI312777 was predominant in rice/barnyardgrass mixed-cultures. The most significant result of our study is the discovery of an experimental design, target-neighbor mixed-culture in combination with competition indices, can successfully separate allelopathic effects from competition.     

Impact of allelopathic rice seedlings on rhizospheric microbial populations and their functional diversity

Field performance of rice allelopathic potential is indirectly regulated by the microflora in the rhizosphere. The present study aimed to investigate the dynamics of microbial populations and their functional diversities in the seedling rhizospheres of rice cultivars with varied allelopathic activities by employing agar plate bioassay, fumigation and BIOLOG analysis. Rice cultivars significantly affected the microbial carbon content in their associated rhizospheric soil. The microbial carbon contents were ranked in a decreasing order as Iguape Cateto (441.0 mg·kg^–1) > IAC47 (389.7 mg·kg^–1) > PI312777 (333.2 mg·kg^–1) > Lemont (283.8 mg·kg^–1) with the nil-rice control soil of 129.3 mg·kg^–1. Similarly, the respiration rate of the soils was 1.404, 1.019, 0.671 and 0.488 μgC·g^–1· h^–1 for PI312777, Iguape Cateto, IAC47 and Lemont, respectively. The respiration rate was only 0.304 μ gC·g^–1·h^–1 for the control soil. The microbial flora in the rhizospheric soil of different rice cultivars was dominated by bacteria (58.4%–65.6%), followed by actinomycete (32.2%–39.4%) and fungi (2.2%–2.8%). BIOLOG analysis showed that the value of Average Well Color Development (AWCD) differed significantly among rice cultivars. It was always the highest in the rhizospheric soil of the strongly allelopathic rice cv. PI312777, and the lowest in the rhizospheric soil of the poorly allelopathic rice cv. Lemont. The AWCD value reached the maximum in all the sampled soils after 144 hours of incubation. The AWCD values from the rhizospheric soils of PI312777, IAC47, Iguape Cateto and Lemont were 1.89, 1.79, 1.60 and 1.43 times higher than that of the control soil. Principal Component Analysis (PCA) identified 3 principal component factors (PCF) in relation to carbon sources, accounting for 70.1%, 11.3% and 7.0% of the variation, respectively. 19 categories of carbon sources were significantly positively correlated to the 3 principal components. Phenolic acids, carbohydrates, amino acids and amides were significantly correlated to the principal component 1, phenolic acids, carbohydrates and fatty acids to the principal component 2, and carbohydrates and hydroxylic acids to the principal component 3. Amino acids and amides were the two main carbon sources separating the 3 principal component factors. In addition, the total microbial population in the rhizospheric soil was significantly positively correlated with AWCD, microbial biomass carbon, microbial respiration and Shannon index. There was a significantly positive correlation between the total microbial population and the inhibition rate (IR) on the root length of lettuce owing to the different allelopathic activities of the rice cultivars. These results suggest that changes in microbial population, activity and functional diversity in the rhizospheres are highly cultivar-dependent. These changes might play an important role in governing the rice allelopathic activity in the field.     

Bipolaris eleusines,a potential mycoherbicide candidate for control of barnyardgrass (Echinochloa crus-galli)

An isolate of Bipolaris eleusines was investigated as a potential candidate for biocontrol of barnyardgrass and additional weeds in paddy rice fields and for safety to selected crop species under greenhouse conditions. Barnyardgrass appeared more susceptible at the three-leaf stage than older plants, and disease severity increased as the fungal inoculum increased from 1 × 10⁵ to 1 × 10⁷ conidia/ml when sprayed till run-off. The high application rate caused 73% mortality of barnyardgrass, relative to the non-treated control, but increasing application rate to >1 × 10⁷ conidia/ml did not enhance efficacy (P >.05). This B. eleusines isolate showed no pathogenicity to rice (Oryza sativa spp. indica, O. sativa spp. japonica and an O. sativa hybrid), corn, wheat or any dicot crop species tested while causing slight infection on sorghum and barley. We conclude that B. eleusines, with high efficacy against barnyardgrass and demonstrated safety to rice, is a promising mycoherbicide candidate worthy of further evaluation and development for control of barnyardgrass in paddy rice fields.     

Natural variation in the promoter of rice calcineurin B‐like protein10 (OsCBL10) affects flooding tolerance during seed germination among rice subspecies

Rice (Oryza sativa L.) has two ecotypes, upland and lowland rice, that have been observed to show different tolerance levels under flooding stress. In this study, two rice cultivars, upland (Up221, flooding‐intolerant) and lowland (Low88, flooding‐tolerant), were initially used to study their molecular mechanisms in response to flooding germination. We observed that variations in the OsCBL10 promoter sequences in these two cultivars might contribute to this divergence in flooding tolerance. Further analysis using another eight rice cultivars revealed that the OsCBL10 promoter could be classified as either a flooding‐tolerant type (T‐type) or a flooding‐intolerant type (I‐type). The OsCBL10 T‐type promoter only existed in japonica lowland cultivars, whereas the OsCBL10 I‐type promoter existed in japonica upland, indica upland and indica lowland cultivars. Flooding‐tolerant rice cultivars containing the OsCBL10 T‐type promoter have shown lower Ca²⁺ flow and higher α‐amylase activities in comparison to those in flooding‐intolerant cultivars. Furthermore, the OsCBL10 overexpression lines were sensitive to both flooding and hypoxic treatments during rice germination with enhanced Ca²⁺ flow in comparison to wild‐type. Subsequent findings also indicate that OsCBL10 may affect OsCIPK15 protein abundance and its downstream pathways. In summary, our results suggest that the adaptation to flooding stress during rice germination is associated with two different OsCBL10 promoters, which in turn affect OsCBL10 expression in different cultivars and negatively affect OsCIPK15 protein accumulation and its downstream cascade.     

Distribution of the genes causing F2 chlorosis in rice cultivars of the Indica and Japonica types

Summary Chlorotic plants were segregated in F₂ populations in varietal crosses of common rice. The genetic basis and distribution of the genes causing F₂ chlorosis in native cultivars were studied to examine the role of the F₂ chlorosis in varietal differentiation of rice. It was proven that this F₂ chlorosis was controlled by a set of duplicate genes, hca-1 and hca-2. The hca-2 gene was widely distributed in native cultivars of the Japonica type, while many Indica types carried its dominant allele hca-2 ⁺. Japanese cultivar J-147 carried hca-2. The hca-1 gene was frequently distributed in cultivars containing the Hwc-2 gene for F₁ weakness. We concluded that F₂ chlorosis does not cause or promote varietal differentiation in rice.