Construction of high-density linkage map and identification of QTLs associated with resistance to black rot in radish (Raphanus sativus) by RAD sequencing

High-density marker-based QTL mapping can serve as an effective strategy to identify novel genomic information to facilitate crop improvement. In this study, we genotyped an F₂ population (KB12-1 × PP12-1) using a RAD-seq approach and constructed a high-density linkage map for radish. After a series of filtering procedures were performed, 17,124 SNPs and 3,336 indels with aa × bb genotyping were retained to obtain bin markers. Then, a linkage map comprising a total of 1,221 bin markers in nine linkage groups spanning 1,467.3 cM with an average marker interval of 1.2 cM was constructed. We evaluated the resistance of the F₂ mapping population to black rot using F₃ progeny, and two major QTLs related to black rot resistance were identified based on this map. Among these QTLs, qBRR2 on Chr.2 explained 26.97% of the phenotypic variation with a LOD score of 11.93, and qBRR7 on Chr.7 accounted for 27.06% of the phenotypic variation with a LOD score of 11.83. The additive effect of qBRR2 was positive (14.97); however, qBRR7 had the opposite effect (−11.99). The high-density linkage map and the major QTLs qBRR2 and qBRR7 provide new important information for disease resistance gene discovery and utilization in genetic improvement.     

Phellinus torulosus on Cupressus sempervirens in Italy

Phellinus torulosus was reported for the first time on Cupressus sempervirens in Tuscany, Italy. This fungus causes white rot in roots and stems and may also invade and kill the cortical tissue. The invasion of trees by the fungus and its subsequent spread is probably facilitated by fire scars.     

Accumulation of soluble phenolic compounds in sunflower capitula correlates with resistance to Sclerotinia sclerotiorum

Disease symptoms and total soluble phenolics content have been analysed in four sunflower (Helianthus annuus L.)lines with different resistance levels(from highly susceptible to resistant) to head rot caused by Sclerotinia sclerotiorum (Lib.) de Bary. At the beginning of the flowering stage, capitula were inoculated by spraying with a water suspension of ascospores, and disease symptoms were evaluated from day 6 to day14 after inoculation. The most susceptible genotypes showed all their ovaries to be necrosed and abundant lesions in corollas, bracts and receptacle. In the resistant line, the ovary and corolla were only partially necrosed with no symptoms in the bracts or the receptacle. Total soluble phenolics were extracted and quantified from different parts of the capitulum in both inoculated and non-inoculated plants. The amount of phenolic compounds depended on the sunflower line, the time after inoculation, and the tissue. Higher constitutive and induced phenolic content as well as phenylalanine ammonia-lyase activity were present in the most resistant line, these differences correlated with the absence/presence of disease symptoms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding wheat and rye for resistance to Fusarium diseases

Fusarium culmorum and F. graminearum Groups 1 and 2 cause seedling blight, crown rot, foot rot and head blight in wheat and rye that may affect grain yield and quality for baking and feeding. This review starts with an analysis of Fusarium populations with regard to their genetic variation for aggressiveness, mycotoxin production, and isolate-by-host genotype interaction. To assess resistance in the different host growth stages, quantitative inoculation and disease assessment techniques are necessary. Based on estimated population parameters, breeding strategies are reviewed to improve Fusarium resistance in wheat and rye. Epidemiological and toxicological aspects of Fusarium resistance that are important for resistance breeding are discussed. F. culmorum and F. graminearum display large genetic variation for aggressiveness in isolate collections and in naturally occurring populations. The production of mycotoxins, especially deoxynivalenol and its derivatives, is a common trait in these populations. Significant isolate-by-host genotype interactions were not found across environments in wheat and rye. Artificial infections in the field are indispensable for improving Fusarium crown rot, foot rot and head blight resistance in wheat and rye. For a reliable disease assessment of large populations, disease severity ratings were found to be the most convenient. The differentiation of host resistance is greatly influenced by an array of nongenetic factors (macro-environment, microclimate, host growth stage, host organ) that show significant interactions with host genotype. Selection for environmentally stable resistance has to be performed in several environments under a maximum array of different infection levels. Selection in early growth stages or on one plant organ does not in most cases allow prediction of resistance in adult-plant stages or another plant organ. Significant genetic variation for resistance exists for all Fusarium-incited diseases in breeding populations of wheat and rye. The patho-systems studied displayed a prevalence of additive gene action with no consistent specific combining ability effects and thus rapid progress can be expected from recurrent selection. In wheat, intensive testing of parental genotypes allows good prediction of the mean head blight resistance after crossing. Subsequent selection during selfing generations enables the use of transgression towards resistance. In hybrid breeding of winter rye, the close correlation between foot rot resistance of inbred lines and their GCA effects implies that selection based on the lines per se should be highly effective. This is not valid for F. culmorum head blight of winter rye caused by a greater susceptibility of the inbred lines compared to their crosses. For both foot rot and head blight resistance, a high correlation between the resistance to F. graminearum and F. culmorum was found in wheat and rye. Mycotoxin accumulation occurs to a great extent in naturally and artificially infected plant stands. The correlation between resistance traits and mycotoxin contents are medium and highly dependent on the environment. Further experiments are needed to clarify whether greater resistance will lead to a correlated reduction of the mycotoxin content of the grains under natural infection.     

甘兰型油菜品质性状的变化与抗(耐)菌核病的关系

经1987～1992年时甘兰型油菜品质资源田间自然抗病性的连续观察鉴定(包括同一品种不同品质的单株)和同一品种不同发病级别单株种子内芥酸、硫甙、油份等品质的测试分析。结果是油菜菌核病的发病程度与这些品质性状的关系密切。即抗病性的强弱与芥酸、硫甙的含量成正相关,与油份的含量成反相关,不同发病级别的单株种子与产油量成反相关。根据分析结果笔者认为,在进行双低油菜育种过程中,应将低代材料置于易于发生菌核病的环境中选择,在发病极度严重时还要注重保留那些耐病的单株,这是集优质、丰产、耐病为一体的有效途径。同时在优质油菜生产中要作好防病工作。     

Chromosomal location of Fusarium head blight resistance genes and analysis of the relationship between resistance to head blight and brown foot rot

In order to identify chromosomes involved in resistance to Fusarium head blight, a set of 21 substitution lines of Triticum macha (resistant) chromosomes into ‘Hobbit’'sib’(susceptible) were evaluated in trials over 2 years. For the first year's trial, all plants were inoculated on the same day with a conidial suspension of F. culmorum. For the second trial, individual plants were inoculated precisely at mid anthesis of each plant over a period of 2 weeks. The disease level was assessed by visual scoring, relative ear weight and F. culmorumn‐specfic quantitative polymerase chain reaction. The results showed that T. macha chromosomes 1B, 4A and 7A conferred good overall resistance, suggesting that they carry important genes for resistance. In two additional trials, T. macha and ‘Hobbit’'sib’ were evaluated for resistance to brown foot rot. The results showed that T. macha was more susceptible than ‘Hobbit’‘sib’, indicating that stem base disease response is not correlated with head blight resistance in these cultivars.     

Sclerotinia resistance in sunflower: I. Genotypic variations of hybrids in three environments of Argentina

Sclerotinia sclerotiorum infections on sunflower capitula produce white rot, one of the most dangerous diseases sunflower bears in all humid areas. Therefore, disease quantification on developed genetic materials is a very important action in sunflower breeding. Given the horizontal type of resistance these evaluations should be made in different environments. Several hybrids obtained after crossing seven female × seven male sunflower inbred lines in a factorial mating design were evaluated for resistance to white rot in two locations in the southeast of the province of Buenos Aires, Argentina. Disease incidence and the symptom appearance index indicated significant genotypic effects and genotype × environment (G × E) interactions. Genotypic effects were a greater source of variance than the G × E interaction effects. The G × E interactions only represented changes in magnitude. These results were used to identify the best genotypes for both resistance factors. Four hybrids showed low disease incidence values under both artificial and natural infections, of which only two had high values of the symptom appearance index at both locations. These hybrids are considered to have adequate resistance attributes for the ascosporic penetration and the mycelium extension in the capitulum tissue and could therefore be sown in the province of Buenos Aires without increasing risks of S. sclerotiorum attacks.     

大叶伞干腐病病原菌的鉴定及杀菌剂毒力测定

为明确大叶伞干腐病的病原菌种类,筛选有效药剂,为病害防治提供理论依据,对该病病原菌进行了鉴定,并进行了杀菌剂毒力测定。在形态学基础上,结合rDNA-ITS序列分析,对大叶伞(Schefflera actinophylla)干腐病病原菌进行鉴定,结果为可可毛色二孢菌(Lasiodiplodia theobromae)。采用菌丝生长速率法,测定了8种杀菌剂对大叶伞干腐病菌的抑制作用,结果表明：50%多菌灵可湿性粉剂抑菌效果最好,EC50为0.02 μg/mL,其次为45%咪酰胺水乳剂、43%戊唑醇悬浮剂和10%苯醚甲环唑水分散性粒剂和25%丙环唑乳油,EC50值均小于1 μg/mL。     

14种悬浮种衣剂防治玉米地下害虫、蚜虫和茎基腐病的防效评价

摘 要：为有效控制玉米地下害虫、蚜虫和茎基腐病的常年危害,筛选具有较好控制作用的种衣剂,笔者开展了14种悬浮种衣剂田间药效试验。试验表明：14种种衣剂对供试玉米品种出苗安全;氟虫腈?噻虫嗪（30%悬浮种衣剂）(1:1000)处理的出苗率96.7%为最高值。氟虫腈?噻虫嗪（30%悬浮种衣剂）(1:1000)对玉米地下害虫、玉米蚜虫的防治效果分别达84.8%、80.0%。精甲?咯?嘧菌（11%悬浮种衣剂）(1:2000)对玉米茎基腐病的防治效果达73.7%。说明以噻虫嗪、氟虫腈和甲霜灵为主的复配防治玉米地下害虫、蚜虫、茎基腐病,能够取得较好的防治效果。建议针对不同的生态类型区域,结合品种、施肥、管理等措施选用不同的配方,以取得最佳的防治效果。     

Antifungal activity of sulfur-containing salts against the development of carrot cavity spot and potato dry rot

In the search for alternatives to synthetic fungicides to control postharvest disease, sulfur-containing salts were evaluated for their effects on the mycelial growth of various fungal or fungus-like pathogens and their ability to control carrot cavity spot (Pythium sulcatum) and potato dry rot (Fusarium sambucinum). Results showed that metabisulfite-containing salts provided strong inhibition of all the tested fungi. Furthermore, some sulfate-containing salts were also directly inhibitory to P. sulcatum (calcium sulfate and ammonium sulfate) and to F. sambucinum (sodium sulfate). The metabisulfite salts also provided 100% inhibition of cavity spot and dry rot at concentrations of 50 and 200 mM, respectively. Calcium sulfate and sodium sulfate also significantly reduced carrot cavity spot lesions at 50 mM and ammonium sulfate, magnesium sulfate, potassium sulfate and sodium sulfate reduced potato dry rot lesions at 200 mM. These results indicate that various sulfate and metabisulfite salts could be used to control these postharvest microorganisms.