Potential for soybean rust tolerance among elite soybean lines in Uganda

Soybean rust, (Phakopsora pachyrhizi), currently the most devastating disease of soybeans worldwide, is known to challenge single resistance genes deployed against it and therefore, disease tolerance is indisputably the most viable measure in controlling the pathogen. Studies were conducted at Namulonge in Central Uganda to assess the level of tolerance to soybean rust among selected elite soybean lines. Seven elite lines together with three local checks were tested in a split-plot design where some plots were protected with fungicide to estimate the level of tolerance to soybean rust. The experiment was conducted for three cropping seasons beginning second rains of 2005. A rust tolerance index (RTI) was computed for each test line as the ratio of yield from unprotected plots to yield from protected plots. The study showed that high levels of tolerance to soybean rust were present in the test lines. The soybean lines that showed high levels of tolerance included MNG 10.3 and MNG 3.26 all showing RTIs higher than 0.93. These lines also out-yielded the local checks by about 400 kg ha⁻¹ and are recommended for multi-location testing.     

Saccharin-induced systemic acquired resistance against rust (Phakopsora pachyrhizi) infection in soybean: Effects on growth and development

We examined the effect of saccharin on the systemic acquired resistance (SAR) response of soybean to the fungus Phakopsora pachyrhizi, the causal agent of soybean rust. Plants were grown hydroponically in half-strength Hoagland’s solution and were challenged with the pathogen 1, 5, 10 and 15 d after treatment with 3 mM saccharin applied either as a foliar spray or a root drench at the 2nd trifoliate (V3) and early reproductive (R1) stages. Plants were destructively harvested and assessed for visible rust symptoms 2 wk after inoculation. Mode of saccharin application was a significant factor influencing the severity of rust infection. Saccharin applied as a root drench was more effective than the foliar spray treatment at inducing SAR, with increased resistance observed 1 d after application. Systemic protection against rust infection was still apparent 15 d after application of saccharin as a root drench. In contrast, foliar treatment with saccharin did not increase systemic protection until 15 d after treatment. When systemic protection was induced by the application of saccharin in either manner, there was no significant reduction of plant growth, except when plants were inoculated 15 d after the saccharin application as a root drench at the R1 stage of development.     

Assessing tolerance to soybean rust in selected genotypes

Breeding for tolerance to soybean rust is potentially one of the solutions to combating soybean rust; however, very little progress in tolerance breeding has been documented. Fourteen pre-selected genotypes were evaluated in a sprayed versus unsprayed split-plot trial conducted over three seasons for their tolerance to soybean rust. Different assessments of tolerance were compared for their effectiveness in discriminating between genotypes. Conventional methodology using a yield loss % index for assessing tolerance produced results which were poorly correlated with each other over seasons, which likely accounts for the historic lack of breeding success. This study has used the superiority measure (P_i) of Lin and Binns and the ecovalence statistic (W_i) of Wricke in a biplot to identify the most tolerant genotypes. A novel statistic (W_iP_i) has been generated from this biplot which facilitates the simultaneous selection for general performance and yield stability of genotypes under a range of rust stress conditions.     

大豆资源抗疫霉根腐病基因分析

采取下胚轴创伤接种法鉴定156份大豆资源对13个不同毒力基因型大豆疫霉菌株的抗性。结果表明,125份资源分别抗1-13个菌株,占鉴定资源总数的80.13%。125份抗性大豆资源对13个大豆疫霉菌株共产生90种反应型。通过与13个鉴别寄主的反应型比较发现,有9份大豆资源产生的5种反应型与含有已知抗病基因的大豆资源的反应型相同;12份大豆资源产生的5种反应型与已知2个抗病基因组合的反应型一致,另外,还有至少抗1个菌株的104份大豆资源产生的80种反应型,既不同于已知单个抗病基因的反应型,也不同于2个已知抗病基因组合的反应型,推测可能含有新的抗病基因或基因组合。     

我国大豆核心种质南方材料对SMV流行株系的抗性评价

用人工接种方法,研究我国南方大豆核心种质93份野生大豆和99份栽培品种对黄淮与南方大豆产区SMV流行株系（SC-3、SC-7）和北方大豆产区流行株系(SC-11、SC-13）的抗性。结果显示,栽培大豆樟潭大青豆对4个株系表现无症状,ZYD03715、ZYD04257、上饶青皮豆3份材料对除SC-7外的3个株系表现无症状,5份材料（ZYD04203、ZYD04856、82-16、82-24和渠县八月黄）对SC-3和SC-7两个株系表现无症状,另有8、2、4份材料分别对SC-3、SC-7、SC-13表现无症状。参试材料中,免疫、高抗和高感材料较少,中度抗性的材料所占比例较高;来自四川的17份材料抗性较好。     

大豆食心虫抗性品种鉴定及抗性性状分析

38份大豆品种（系）大豆食心虫抗性鉴定结果表明，供试品种间在着显著差异。筛选出高抗大豆食心虫品种1份和抗性品种17份。抗虫性状分析表明，虫食粒率与百粒重，荚皮内糖分含量呈极显著正相关，而与荚皮内纤维素含量，荚皮硬度，荚皮颜色呈极显著负相关。     

一个大豆锈病新抗源的筛选与鉴定

采用离体叶片接种方法对2007-2010年收集的1 000份大豆种质资源进行抗性筛选,得到1份高抗材料SX6907。SX6907在接种后20d不产生侵染病斑;在高浓度锈菌接种时,产生少数红褐色RB（Red-brown）病斑,但无孢子堆破裂现象,无孢子产生;SX6907的接种表现与已知抗病品种主要表现为黄褐色TAN型感病病斑明显不同。组织学观察表明, SX6907在接种部位造成细胞坏死,侵染点无孢子形成,其抗性表现为抗锈菌侵染。SX6907是一个优异的抗锈病资源,可做亲本在抗锈病育种中应用。     

大豆锈病研究进展

1899年在中国的吉林首次报道了由豆薯层锈菌(Phakopsora pachyrhizi Syd)引起的大豆锈病。20世纪60年代大豆锈病成为热带、亚热带地区大豆生产中最严重的病害，进入本世纪后，大豆锈病成为世界性病害。对大豆锈病较为系统的研究始于20世纪70年代，目前对大豆锈病的病原菌分类、分布及其寄主、病原夏孢子生物学特性、病害流行、抗锈资源鉴定、抗锈遗传都有较为详细的研究，但对冬孢子的作用、生理小种的分化和鉴定、锈菌的交替寄主、锈病的初侵染源都还缺乏深入的研究，至今尚未发现对锈菌免疫的抗源，限制了锈病的防治和抗锈遗传育种的开展。     

大豆锈菌冬孢子在侵染循环中的作用

在自然条件下形成的大豆锈菌（Phakopsora pachyrhizi Sydow)冬孢子不能萌发直接浸染大豆，落入土中的病菌残体也不能引起大豆植株发病，说明在我国锈菌虽然能在自然条件下形成冬孢子，但不能成为大豆锈病初次侵染源。     

中国大豆种质资源抗大豆锈病鉴定

１９９６～１９９９年对我国１０１８份大豆种质资源进行抗大豆锈病鉴定,其结果未见免疫和高抗资源,仅有嘟噜豆－２等９份中抗资源,占鉴定总数的０．８８％,感病资源１００９份,占鉴定总数的９９．１２％。     

大豆抗大豆花叶病毒研究进展

由大豆花叶病毒(soybean mosaic virus,SMV)引起的大豆花叶病毒病是一种世界性大豆病害,严重地影响了大豆的产量和品质.本文介绍了国内外大豆抗SMV的最新研究进展,主要包括:抗源筛选、抗性遗传、抗性基因的精细定位和分子标记辅助选择以及大豆对SMV候选抗性基因的研究等,并对该领域的研究进行了初步展望,以期为大豆抗SMV分子育种和抗性候选基因的功能研究提供参考.     

Both incidence and severity of white rust disease reflect host resistance in Brassica juncea germplasm from Australia,China and India

White rust (Albugo candida) is a highly destructive disease of oilseed Brassicas such as Brassica juncea and B. rapa, and has caused serious yield losses in Australia, China and India on both species. The first commercial B. juncea varieties are now being deployed in Australia, but their response to Australian strains of A. candida is yet to be defined under Australian field conditions. To identify useful sources of host resistance for Australia, China and India, in B. juncea, three field trials were undertaken in Western Australia. Forty-four B. juncea genotypes, viz. 22 from India, 12 from Australia and 10 from China, were tested. Varying levels of host resistance to Australian strains of A. candida (race 2) were identified among the genotypes from the three countries. Genotypes CBJ-001, CBJ-003 and CBJ-004 from China consistently showed high levels of resistance to A. candida on leaves across the three trials. Overall, the genotypes from China showed the best resistance, followed by the genotypes from Australia, with those from India being the most susceptible. The most susceptible genotypes were RL1359, RH30 and Seetha from India. It is noteworthy that both the incidence and severity of disease reflected varying levels of host resistance in the germplasm from the three countries, irrespective of whether screening was undertaken in the field using natural or artificial inoculation. Differentiation of resistance among these genotypes was similar to that we reported previously for artificially-inoculated seedlings or adult plants under glasshouse conditions, indicating that a choice of options is available to plant breeders to reliably differentiate host resistance among genotypes to white rust in B. juncea.     

部分国家和省（市）区试品种对大豆花叶病毒的抗性分析

对2003—2005年参加国家及江苏、北京、山东等省市大豆区域试验的162个品种,在分别接种我国大豆主产区6个大豆花叶病毒流行株系SC-3、SC-8、SC-11、SC-12、SC-13和SC-17情况下,对其抗性进行了分析。结果表明,冀B04-3、潍豆6号、BN101、恒盛一号、滨豆95-20、中品02-046、东大2号和东大4号8个品种对6个株系表现抗侵染,占参试品种总数的4.94%;油春01-32、贡豆114-1、中豆32、冀G04-85、中作00-683、科02-17和中品661对5个株系表现抗侵染,占参试品种总数的4.32%;另外,分别有6个和8个品种对4个株系和3个株系表现抗侵染。中作01-03、蒙89-52、山宁11号、京黄03-5、承豆7号和南豆99对6个株系表现抗扩展。以上品种不仅可直接用于生产,也可用作抗SMV育种的抗源。研究还显示,参试材料中无症状和高抗品种约占37%,高感类型占23.5%,其余为中间型。来自于黄淮海大豆产区的品种一般抗性较好。     

Multiple-disease resistance in Vicia faba: Multi-environment field testing for identification of combined resistance to rust and chocolate spot

The aim of this work was to identify Vicia faba germplasm resistant both to rust and chocolate spot. A collection of 43 accessions of V. faba previously identified as chocolate-spot resistant was evaluated for rust and chocolate spot resistance in Egypt and in Spain. The genotype and genotype × environment (GGE) biplot analyses allowed the selection of 11 accessions resistant to both diseases in those locations. These 11 accessions were evaluated for rust in an additional field trial in Spain, all performing better than the susceptible check. The joint analysis of the 11 accessions in the four field trials where they had been evaluated revealed no significant effects either for genotype, environment or the genotype × environment interaction. They are hence promising sources of resistance, both for their low severities and their stable responses across the studied environments. This collection was also tested under controlled conditions against the Egyptian and the Spanish isolates of rust present in the field trials further underlining the stable performance of these genotypes. Finally, the effect of previous infection with chocolate spot on rust resistance was assessed under controlled conditions and no influence of it was found.     

Genetic analysis of field resistance to tan spot in spring wheat

Tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs., is an important constraint to wheat (Triticum aestivum L.) yield in many countries. Since the inheritance of field resistance to tan spot is poorly understood, this study was conducted to determine the genetic control of resistance in the field. Resistance was measured as disease severity caused by P. tritici-repentis race 1 in four crosses involving five wheat parents: parent 1 (P₁) = catbird; parent 2 (P₂) = Milan/Shanghai-7; parent 3 (P₃) = Alondra/Coc//Ures; parent 4 (P₄) = Bcb//Dundee/Gul/3/Gul); parent 5 (P₅) = ND/VG9144//Kal/BB/3/Yaco/4/Chil. P₁, P₂ and P₃ were resistant and P₄ was moderately resistant, whereas P₅ was susceptible to tan spot. The F₂-derived F₃ families and the parents were field evaluated at El Batán, Mexico, in 1996. When all the plants within a F₃ family expressed low levels of disease severity similar to that of the resistant parent it was classified resistant (R), otherwise the progeny was classified as susceptible (S). The progeny of the three crosses of the susceptible parent with the resistant and moderately resistant parents P₂, P₃, and P₄ segregated as 3R:13S whereas the progeny in the cross with P₁ showed a segregation ratio of 1R:15S. This suggests that each resistant parent possessed two genes conditioning resistance to tan spot severity caused by P. tritici-repentis race 1. Information on the inheritance of resistance measured as disease severity on adult plants under field conditions is of practical importance for wheat breeding programs seeking improvement in tan spot resistance.     

大豆抗锈种质的评价

对14个国内外大豆抗锈种质在福建地区的抗锈性及农艺性状进行了评价。结果表明:抗锈基因Rpp1、 Rpp2、Rpp3和Rpp4 (屏南豆)的抗性已被克服,抗锈种质樟子乌、九月黄和日向可能含有新的抗锈基因。来自国外 的抗锈种质在福建地区未能表现出对锈病的抗性,农艺性状较差,不适宜直接利用。     

Evaluation of the Ugandan sorghum accessions for grain mold and anthracnose resistance

Sorghum accessions from Uganda were evaluated for grain mold and anthracnose resistance during the 2005 and 2006 growing seasons at the Texas A&M University Research Farm, near College Station, TX. Accession PI534117 and SC719-11E exhibited the lowest grain mold severities of 2.4, whereas, accessions PI534117, PI534144, PI576337, PI297199, PI533833, and PI297210, with SC748-5 were highly resistant to anthracnose in both years. Accessions PI534117, PI297134, PI297156 exhibited low grain mold severities in 2006. Significant negative correlation was recorded between grain mold and percent germination and high temperature in both years. In 2006, daily precipitation recorded significant positive correlation with grain mold. The seed mycoflora was analyzed across sorghum lines and treatments. In 2005, Curvularia lunata and Fusarium thapsinum were the most frequently recovered fungal species with 31 and 21% incidence, respectively, followed by Alternaria spp. (19%) and F. semitectum (13%). In 2006, predominant colonizers were F. thapsinum (58%), followed by Alternaria and F. semitectum with 15 and 10, percent respectively, while C. lunata had a 6% incidence. In this study, PI534117 holds promise for multiple disease resistance, as it had the lowest disease severity of grain mold and was highly resistant to anthracnose in both years. It also has a high germination rate, a high seed weight, and its short stature is more advantageous for the new A-line conversion program.     

Evaluation of common bean lines for their reaction to tomato yellow leaf curl virus-Ir2

Tomato yellow leaf curl virus (TYLCV) can cause an economically relevant disease in the major tomato growing regions, and no resistance has been identified in commercial and wild tomato cultivars in Iran. In the present study, 34 common bean lines were screened for their reaction to TYLCV-Ir2 under greenhouse conditions. The experiment was conducted in a randomized complete block design with three replications. Bean plants were inoculated at the first trifoliate stage with viruliferous whiteflies (Bemisia tabaci biotype B) and were then sprayed with an insecticide and maintained in whitefly-proof greenhouse. The inoculated plants were monitored for the development of symptoms and the presence of viral DNA by polymerase chain reaction (PCR) four weeks after inoculation. Results revealed that out of the 34 lines, five were resistant. These lines exhibited either no symptoms or very mild symptoms and no viral DNA was detected in them by PCR. Two lines, which showed no typical disease symptoms but contained viral DNA, were identified as tolerant to TYLCV-Ir2. The vector feeding preference for common bean lines was assessed. Results indicated a significant difference in adult whitefly numbers among bean lines but there was no relationship between the number of whiteflies and disease symptom severity. The resistance to TYLCY-Ir2 expressed in common bean lines may be useful as source of resistance for the development of resistant commercial common bean cultivars.     

Potassium phosphite for control of downy mildew of soybean

Downy mildew of soybean, caused by Peronospora manshurica, is widely spread throughout Brazil. The objective of this study was to evaluate the use of potassium phosphite to control this disease. Field experiments were conducted during the growing season of 2006/2007 and 2007/2008 in the state of Parana in southern Brazil. The experimental design consisted of completely randomized blocks in a factorial arrangement (4 × 2) with four replications. Four rates of potassium phosphite (0, 375, 750 and 1500 g P₂O₅ + K₂O ha⁻¹) were applied at two growth stages, V6 (fifth trifoliolate leaf) and R2 (full flowering), followed by one or two applications of pyraclostrobin and epoxiconazole (66.5 + 25 g a.i. ha⁻¹) at R3 (pod development) or R2 and R5.1 (10% of pod filling), mainly for the control of Asian soybean rust (Phakopsora pachyrhizi) and powdery mildew (Microsphaera diffusa). Field experiments were conducted to quantify the severity of downy mildew on leaves, nutrient content in leaf tissue (N, P and K), leaf area index (LAI), yield and seed weight. The maximum severity of downy mildew was observed at a growth stage of R5.3 (50% of pods were ripe), with 14% and 46% of the leaf area affected in 2006/2007 and 2007/2008, respectively. Also it was detected some effect of phosphite on Asian rust control but it was mostly in the trial of 2007/08 when the epidemic was very low (9.7-21.8% of severity). There was a linear reduction in the severity of downy mildew and a significant improvement in the LAI with an increase in the rate of phosphite applied. During the 2006/2007 growing season, a significant yield improvement was observed due to the application of the highest rate of phosphite. Two fungicide applications following phosphite application significantly improved the control of Asian soybean rust and powdery mildew, yield and seed weight when compared to a single fungicide application.     

Feeding disruption tests for monitoring the frequency of larval lepidopteran resistance to Cry1Ac, Cry1F and Cry1Ab

An alternative to traditional larval lepidopteran resistance-monitoring bioassays was developed. Feeding disruption tests were developed for detecting insects resistant to three Bacillus thuringiensis (Bt) proteins: Cry1Ac, Cry1F and Cry1Ab. The assays rely on a diagnostic dose of Bt toxin in 100-μl hydratable meal pads of artificial diet containing blue indicator dye. The assay was formatted as a portable (palm-sized) plastic plate containing an array of 16 test wells, each containing a single hydratable meal pad with one insect added per well. The diagnostic dose was the concentration of Bt in meal pad rehydration solution that reduced 24 h dyed fecal production of Bt-susceptible neonates to ≤2 fecal pellets per larva. Bt-resistant neonates were able to consume the diagnostic dose of the insecticidal protein and produce >2 blue fecal pellets. The feces were distinctly visible on the white background of the feeding disruption test plate. Diagnostic doses were determined with lab-strain Bt-susceptible Heliothis virescens and Helicoverpa zea. For H. virescens, the diagnostic doses were 10, 20 and 15 μg/ml for Cry1Ac, Cry1F and Cry1Ab, respectively. For H. zea, the diagnostic doses were 40, 200 and 500 μg/ml, respectively. The assays were validated against a lab-strain of Bt-resistant H. virescens and with susceptible larval H. virescens collected as eggs from field-grown tobacco in North Carolina.