Genetic diversity of rice sheath blight isolates (Rhizoctonia solani AG-1 IA) from different rice cultivars

Rhizoctonia solani AG 1 IA, the non specific, soil borne, and plant casual agent of rice sheath blight, occurring world widely in rice fields, has become a major disease to rice. In this study,relationships among R. solani AG 1 IA isolates, collected from different rice cultivars were reported.     

玉米纹枯病的发生规律与综合防治对策

近年来,江华县积极推进农业结构战略性调整,在粮食作物生产上适当调减水稻尤其是早稻面积,大力发展玉米、红薯、大豆等旱粮作物,其中全县玉米种植面积和产量分别由1995年的2200hm2,2760kg/hm2发展到2002年的7000hm2,5250kg/hm2。随着玉米种植面积的扩大和栽培水平的提高,玉米纹枯病的发生和危害越来越普遍和严重,日益成为玉米高产稳产的一个重要障碍。1　玉米纹枯病的发生特点1.1　病原玉米纹枯病与水稻纹枯病同属担子菌亚门真菌,病菌菌丝初期无色,倒棍棒形,顶端生有4个担孢子,担孢子无色、卵圆形。菌丝生长最适温度为30℃左右,在10℃以…     

辽河三角洲水稻纹枯病菌丝融合群测定

辽河三角洲是辽宁省水稻主产区,水稻纹枯病近年来持续严重发生,本研究对辽河三角洲稻区的不同水稻品种上分离获得的纹枯病菌菌株进行融合测试,以便探明水稻品种来源各异的病菌菌群类别及其分布的关系,研究探讨辽河三角洲水稻纹枯病菌菌丝融合群构成,为生产上病害流行、预测以及针对性进行水稻品种选育和推广应用,提供理论基础。     

关于噬菌体在防治水稻白叶枯病上的研究

培育抗白叶枯病菌的水稻品种,是公认的防治水稻白叶病的一条有效途径。但由于水稻抗性基因单一,容易导致对该病抗性的脆弱;化学防治方法的效果不理想。且易造成环境污染。因此。急需探索一条有效、安全、廉价的新途径。本研究从生物防治的角度出发,建立了一套新的技术体系。利用噬菌体来防治水稻白叶枯病。结果显示。特殊的病原噬菌体能够显著地降低水稻白叶枯病的发病率。     

唐山地区水稻条纹叶枯病迅速上升原因及防治对策

针对唐山地区水稻条纹叶枯病害逐年加重的实际情况,调查总结了该病发生特点,分析了发病原因,主要是由灰背稻飞虱带毒传播引起的。同时提出了防治对策,重点抓好“三统一”防治稻飞虱。     

Biological control of wheat stripe rust by an endophytic Bacillus subtilis strain E1R-j in greenhouse and field trials

Endophytic Bacillus subtilis strain E1R-j, isolated from wheat roots, inhibits a wide range of microorganisms. In this study, we determined its inhibitory effect on urediniospore germination of Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust and biocontrol effect on the rust development using bacterial cell suspension (BCS) and fermentation liquid with and without bacterial cells (FLBC and FL). Urediniospore germination was significantly inhibited by all three formulations in vitro. The maximum inhibition rate was 84.1% treated with the 10-fold dilution of original formulation of FLBC. Microscopic observation revealed that the bacterial treatments caused urediniospores and germ tubes ruptured, which resulted in protoplasm release and dysfunction of fungal structures. Urediniospore germination was also significantly inhibited by spraying E1R-j on leaf surface before inoculation. Formulations FLBC and FL were both better than formulation BCS. In a condition-controlled greenhouse, application of FLBC and FL 24 and 0 h before Pst inoculation displayed a protective mode in reducing disease severity, and the control efficacy was between 54.0% and 87.7%. For formulation BCS, only the application of 24 h before Pst inoculation significantly reduced rust severity with control efficacy 51.8%. The incidence of diseased leaves in the treatments of FLBC and FL were significantly reduced compared to the non-treated plots in the field experiments conducted in the season 2007–2008. The control efficacy was 51% and 43% for the two treatments, respectively. This study is helpful for further developing a biocontrol approach for managing stripe rust.     

Improvement of bacterial blight resistance of hybrid rice in China using the Xa23 gene derived from wild rice (Oryza rufipogon)

A novel bacterial blight (BB) resistance gene, Xa23, identified from Oryza rufipogon was introgressed into three popular restorer lines (Minghui63, YR293 and Y1671) for wild abortive cytoplasmic male sterility by marker-assisted backcross breeding approach in combination with artificial inoculation and stringent phenotypic selections. The three derived BB resistant restorer lines (Minghui63-Xa23, YR293-Xa23 and Y1671-Xa23) and their hybrid combinations with Zhenshan97A (Shanyou63-Xa23), NongfengA (Fengyou293-Xa23) and Zhong9A (Zhongyou1671-Xa23) demonstrated similar BB resistance spectrum as the donor parent, CBB23 (B). The newly developed BB resistant restorers and their derived hybrids were identical to their respective original versions for agronomic traits especially under disease free condition. However, under severe disease condition, the three BB resistant restorer lines exhibited significantly higher grain weight and spikelet fertility as compared to the respective original restorer lines thus further resulting in BB resistant hybrids with significantly higher grain yields than their respective popular original hybrids. The results indicated that the Xa23 gene could completely express its dominant broad spectrum resistance in different backgrounds of both restorer and male sterile lines across different growth stages, suggesting its immense breeding value in BB resistance improvement for hybrid rice. Moreover, a reasonable utilization and deployment of Xa23 gene for efficient control of BB disease in hybrid rice production was recommended.     

Metabolite profiling of sheath blight disease resistance in rice: in the case of positive ion mode analysis by CE/TOF-MS

Rice sheath blight is an important disease caused by Rhizoctonia solani. The resistant and susceptible rice lines (32R and 29S, respectively) showed different responses to R. solani infection in metabolite levels. The aim of this study was to characterize the metabolite levels in rice lines during R. solani infection using capillary electrophoresis equipped with time of flight mass spectrophotometry (CE/TOF-MS) in positive ion mode. Hundred metabolites were identified and classified into six clusters by hierarchical cluster using Mass Profiler Professional software. Changes in metabolite level at inoculated 32R and 29S were mapped on branches of tricarboxylic acid and glycolysis pathway. Volcano plot successfully filtered the metabolites based on fold change and p-value. The volcano plot result showed that 10 metabolites were up and down regulated in inoculated 32R relative to 29S. One metabolite, chlorogenic acid, showed a positive response in 32R. Meanwhile, pipecolic acid showed as the highest magnitude of fold change and p-value significance level in 29S. In addition, eight amino acids; glutamate, γ-aminobutyric acid, glycine, histidine, phenylalanine, serine, tryptophan, and tyrosine showed increase in 29S after R. solani inoculation.     

Evaluation of Bt (Bacillus thuringiensis) rice varieties against stem borer (Chilo suppressalis)

Three transgenic rice varieties namely Khazar, Neda and Nemat, all containing a cry1Ab gene, were evaluated through PCR analysis and field examinations for their resistance at natural infestation of insect pests during 2007. The results showed that all transgenic varieties produced 1.2 kb PCR product derived from application of cry1Ab gene. In field conditions, transgenic varieties exhibited high levels of resistance against natural infestation of stem borer and the damaged plants based on dead heart or white heat for them were less than 1%. Moreover, in stem-cut bioassay 100% of released larvae died within four days after infestation. These results demonstrate that expression of cry1Ab gene in the genome of transgenic varieties provided season-long protection from the natural infestation of lepidopteran insects.     

锐星防治水稻二化螟田间药效试验

小区试验表明，锐星可湿性粉剂对水稻二化螟具有较好的保苗杀虫效果，每667m^2使用70g的防效分别是82．74％、77．89％，优于90％杀虫单原粉50g，作为无公害生物杀虫剂其应用前景颇为广阔。     

The critical period for control of early blight (Alternaria solani) of potato

The purpose of this study was to identify when the critical period for control of early blight occurs and thus the need to initiate a spray schedule of protectant fungicides. The initiation of weekly fungicide spray schedules was staggered to identify the critical period. The accumulation of 400 P-Days, environmental conditions favorable for sporulation, spore dissemination and plant infection and airborne spores ofA. solani were detected prior to the critical period each year. Since early blight is a disease of old plants, host susceptibility appeared to be involved in the timing of the critical period in addition to favorable weather and the presence of the pathogen. A measure of potato plant development, and therefore susceptibility toA. solani, is needed to adequately predict the critical period. The accumulation of 400 P-Days may aid in the prediction of the critical period by estimating the time of plant susceptibility and therefore the timing of the first necessary fungicide spray.     

Biological weed control in rice with a strain of Colletotrichum gloeosporioides (Penz.) Sacc. used as a mycoherbicide

An indigenous fungal pathogen of the native leguminous weed, northern jointvetch (Aeschynomene virginica [L.] B.S.P.) was found to cause an anthracnose disease at endemic levels annually on its host in Arkansas rice and soybean fields without apparent impact on competitive ability or dispersal of the weed. The pathogen was isolated in pure culture and identified as a host-specific strain of Colletotrichum gloeosporioides, an intensively studied ‘group species’ which causes many anthracnose diseases and consists of species and strains representing wide latitudes of hosts specificity and virulence on both economic crops and wild plants in the tropical and temperate regions of the world. An understanding of anthracnose disease aetiology gained from the literature and confirmed by empirical studies with the weed and fungus revealed that the pathogen was specific and potentially devastating to its weed host, but was constrained in natural situations by poor capacity for dissemination of inoculum. Its spores, although produced in abundance, develop late, are sticky and dispersed mainly by splashing rain or insects, mechanisms that are suppressed on annual weed plants interspersed with annual crop plants. For the fungus to be effective as a biological control agent (i.e. as a mycoherbicide), complete coverage of a field with inoculum at appropriate times and levels to compensate for the pathogen's poor capacity for dissemination would be required. A multidisciplinary team of plant pathologists, weed scientists, veterinary scientists and fermentation scientists investigated the practical potential of the mycoherbicide concept with this host-pathogen combination and found it to be biologically feasible, registerable and commercially practical. The fungus is marketed as living dry spores for use on a comparatively small area weed problem and in a crop-management programme that relies heavily on chemical pesticides. Extension of this concept to control other weeds or other pests seems possible and practical.     

Biological control of Macrophomina phaseolina (Tassi) Goid by Trichoderma harzianum

Four isolates of Trichoderma harzianum Rifai inhibited linear growth and microsclerotia production in Macrophomina phaseolina in vitro. The antagonist proliferated in dual liquid culture with M. phaseolina and significantly decreased the number of its viable propagules. Peat bran preparation of T. harzianum reduced disease incidence, in greenhouse-planted beans, by 37–74%. Coating melon seeds with T. harzianum conidia reduced disease incidence by 37·5–46·3%. In vitro growth of T. harzianum was affected less than that of the pathogen by applications of pentachloronitrobenzene or dazomet. The biocontrol agent was as effective as the chemicals, and combining the two under greenhouse conditions slightly enhanced disease control. In the field, charcoal root rot of melons and corn was reduced by 22% and 28%, respectively. Moreover, T. harzianum treatments in melons resulted in an earlier development of fruit.     

Rice varietal difference in sheath blight development and its association with yield loss at different levels of N fertilization

Variety and nitrogen (N) fertilizer input are the two main factors that influence the development of sheath blight (ShB) caused by Rhizoctonia solani in intensive and high-input rice (Oryza sativa L.) production systems. This study was conducted to determine the varietal difference in ShB development and its association with yield loss across N rates. Two indica inbred and two indica/indica F₁ hybrid varieties were grown under 0 and 90 kg N ha⁻¹ in 2003 wet season (WS) and under 0, 75, 145, and 215 kg N ha⁻¹ in 2004 dry season (DS). Inoculation was done in 3.2 m² in each experiment unit to achieve uniform disease development. Disease intensity was quantified by measuring relative lesion height (RLH) and ShB index (ShBI) of inoculated 10 hills at flowering and 14 days after flowering. Plant traits, grain yield, temperature, and relative humidity inside the canopy were also measured. Consistent and significant varietal differences in ShB intensity were observed across N rates in both WS and DS. Among the four varieties, IR72 and IR75217H had higher RLH and ShBI than PSBRc52 and IR68284H at all N rates. Sheath blight index at 14 days after flowering had the closest correlation with yield loss from ShB. Varieties with taller stature, fewer tillers, and lower leaf N concentration such as IR68284H generally had lower RLH and ShBI, and consequently lower yield loss from the disease. Disease intensity and yield loss from ShB increased with increasing N rates, but the magnitude of yield loss varied among varieties. This suggests that fertilizer N should be managed more precisely and differently for varieties with different plant type in order to reduce the disease development and maximize grain yield in the irrigated rice systems.     

Metabolite profile of whole grain ting (a Southern African fermented product) obtained using two strains of Lactobacillus fermentum

Ting is a traditional fermented sorghum product mostly eaten in Southern Africa, generally believed to be highly nutritious and rich in health beneficial properties. Although refined grains are mostly used for fermented foods, the use of whole grains (WGs) in fermented products is gradually gaining prominence due to their benefits. In this study, Lactobacillus fermentum strains were used singly and in combination for the fermentation of WG-ting from WG-sorghum and all possible metabolites profiled using gas chromatography-high resolution time of flight-mass spectrometry. 198 compounds were observed in the experimented samples, classified into different metabolic groups, with varying proportions: esters (23%), ketones (10%), fatty acids methyl esters (7%), and hydrocarbons (6%). Other important metabolites include vitamins, terpenes and terpenoids, phytosterols, phenols, and alcohols. Although similar lactic acid bacteria were used, differences were observed in levels of the metabolites and in some instances, the types of metabolites obtained differ. Much of the differences were attributed to varying fermentation behaviours of the strains, which could be related to their inherent genes. The correlation between metabolites from raw sorghum and the fermented product may assist in developing processing methods to retain the desired metabolites and enhance their functional potentials toward product improvement and for health benefits.     

Light use efficiencies of potato cultivars with late blight (Phytophthora infestans)

Summary Potato cultivars of different maturity classes and levels of resistance toPhytophthora infestans were grown under several disease intensities in three field trials. Seasonal courses of ground cover by green foliage and final tuber yields were determined. Light use efficiencies (LUE) were calculated from regression analyses of yield on cumulative light interception. Late blight reduced tuber yields by decreasing cumulative light interception without affecting LUE. No differences in LUE between cultivars or cultivar classes were detected. Therefore, the maintenance of green leaf area is important when breeding potatoes for optimal performance in the presence of late blight. The results support the hypothesis that the correlation between lateness and reported resistance of potato cultivars is due to the vigorous foliage growth of late cultivars.