Breeding Elite Lines of Apple Carrying Pyramided Homozygous Resistance Genes Against Apple Scab and Resistance Against Powdery Mildew and Fire Blight

Plant Molecular Biology Reporter - The development of high-quality cultivars, with durable disease resistance, is a major objective of apple breeding. The selection procedures of modern breeding...     

梨种质对梨火疫病的抗性研究

针对未来梨火疫病侵入我国的风险,采用幼果人工接种鉴定技术,对保存的54份梨种质资源进行梨火疫病抗性评价。通过接种后的症状鉴别、再分离细菌的分子检测,证明有16份种质对梨火疫病表现感病,其中9份为中国种质,7份为引进种质。中国的37份（80．4％）梨种质表现抗梨火疫病,而引进种质中表现抗病的仅有1份（12．5％）。结果初步表明,在中国梨种质中可能存在较丰富的抗梨火疫病资源;东方梨的抗性较西方梨更强;而在梨的地方品种中蕴藏着良好的抗病性。     

First Report of Erwinia amylovora Fire Blight in Belarus

Erwinia amylovora is a phytopathogenic bacterium that causes fire blight, an economically important disease of Rosaceae . Several isolates from pears and apples with fire blight symptoms from Belarus were identified as E. amylovora . All tested isolates were yellow and mucoid on MM2Cu medium, positive in levan production and showed pathogenicity in immature pear fruits. These isolates have identical total protein patterns with E. amylovora 1/79. The PCR with specific primers for E. amylovora harpin gene also gave positive results.     

Microbial Community Dysbiosis and Functional Gene Content Changes in Apple Flowers due to Fire Blight

Despite the plant microbiota plays an important role in plant health, little is known about the potential interactions of the flower microbiota with pathogens. In this study, we investigated the microbial community of apple blossoms when infected with Erwinia amylovora. The long-read sequencing technology, which significantly increased the genome sequence resolution, thus enabling the characterization of fire blight-induced changes in the flower microbial community. Each sample showed a unique microbial community at the species level. Pantoea agglomerans and P. allii were the most predominant bacteria in healthy flowers, whereas E. amylovora comprised more than 90% of the microbial population in diseased flowers. Furthermore, gene function analysis revealed that glucose and xylose metabolism were enriched in diseased flowers. Overall, our results showed that the microbiome of apple blossoms is rich in specific bacteria, and the nutritional composition of flowers is important for the incidence and spread of bacterial disease.     

Identification of Novel Strain-Specific and Environment-Dependent Minor QTLs Linked to Fire Blight Resistance in Apples

Since its first report almost 200 years ago, fire blight, caused by the gram-negative bacterium Erwinia amylovora, has threatened apple and pear production globally. Identifying novel genes and their functional alleles is a prerequisite to developing apple cultivars with enhanced fire blight resistance. Here, we report 13 strain-specific and environment-dependent minor QTLs linked to fire blight resistance from a segregating Malus sieversii × Malus × domestica mapping population. Interval mapping at 95% confidence and Kruskal–Wallis analysis at P value =?0.005 were used to identify QTLs for three strains of E. amylovora differing in virulence and pathogenicity. The QTLs identified explain a small to moderate part of resistance variability, and a majority was not common between years or E. amylovora strains. These QTLs are distributed in eight linkage groups of apples and comparison of their map position to previously identified fire blight resistance QTLs indicates that most are novel loci. Interaction between experimental conditions in the greenhouse and field, and between years, and differences in virulence levels of strains might be responsible for strain- and year-specific QTLs. The QTLs identified on LG10 for strain Ea273 in 2011 and strain LP101 in 2011, and on LG15 for strain LP101 could be the same QTLs identified previously with strain CFBP1430 in cultivar “Florina” and “Co-op16 × Co-op17” mapping population, respectively. We discuss the potential impact of newly identified minor fire blight QTLs and major gene-based resistance on the rate of mutation in pathogen populations to overcome resistance and durability of resistance.     

Development of Poliovirus Having Increased Resistance to Chlorine Inactivation

A laboratory strain of poliovirus (LSc) became progressively more resistant to chlorine inactivation during a series of repeated sublethal exposures to the halogen.     

Copper-Based Compounds against Erwinia amylovora: Response Parameter Analysis and Suppression of Fire Blight in Apple

Fire blight, caused by Erwinia amylovora, is one of the major bacterial disease of apple and pear, causing enormous economic losses worldwide. Several control measures against E. amylovora have been reported till date, however, none of them have proved to be effective significantly against the pathogen. In this study, mechanisms of the copper-based control agents (CBCAs): copper oxychloride (COCHL), copper oxide (COX), copper hydroxide (CHY), copper sulfate basic (CSB), and tribasic copper sulfate (TCS) and their disease severity reduction efficacy against E. amylovora were analyzed. Bis-1,3-dibutylbarbituric acid trimethine oxonol, carboxyl fluorescein diacetate succinimidyl ester, and 5-cyano-2,3-ditolyl tetrazolium chloride staining were used to check the damage of membrane potential, cytoplasmic pH_in, and respiration of CBCAs-treated E. amylovora, respectively. High disturbance in the membrane potential of E. amylovora was found under COX and COCHL treatments. Similarly, higher significant changes in the inner cytoplasmic pH_in were observed under COX, COCHL, and TCS treatment. CHY and COCHL-treated E. amylovora showed a significant reduction in respiration. In vitro bioassay results revealed that CHY, CSB, and TCS at 2,000 ppm reduced the severity of fire blight both in pre- and post-treatment of CBCAs in immature apple fruits and seedlings. Overall, the most effective CBCAs against E. amylovora could be CHY at 2,000 ppm as its showed inhibition mechanisms and disease severity reduction.     

Breeding for the Digenic Apple Resistance to Scab

The results of the apple breeding for digenic resistance to scab (1979–2000), which is more long-term than the monogenic breeding, have been reviewed. The hybrid seeds obtained from the reciprocal crossing between the V _f and V _m resistance gene donors served as the original material. The seed progeny yielded by backcrosses between these hybrids and the susceptible cultivars were examined (age—first true leaves) using inoculation in a greenhouse. The following criteria were proposed for breeding parental forms and the cultivars of the V _f v _f V _m v _m genotype: (1) phenotype segregation in the progeny of three resistant: one susceptible seedling and (2) the presence in the progeny of two types of resistant seedlings: those with the class 1 resistance (points and spots—hypersensitivity) typical of the V _m gene and those with the class 2–3 resistance (chlorotic and necrotic spots) typical of the V _f gene.     

Rice Resistance to Sheath Blight Mediated by Potassium

This study investigated the effect of potassium (K) on sheath blight (Rhizoctonia solani) development on rice plants from cultivars BR‐IRGA 409 and Labelle grown in nutrient solution containing 0, 50 and 100 mm of K. Sheath blight progress on inoculated sheaths was evaluated by measuring the relative lesion length at 48, 72, 96 and 120 h after inoculation (hai). Data were used to calculate the area under relative lesion length progress curve (AURLLPC). The foliar K concentration on leaf sheaths tissue increased by 61.48 and 116.05% to cultivars BR‐IRGA 409 and Labelle, respectively, as the K rates increased from 0 to 100 mm . A linear model best described the relationship between the AURLLPC and the K rates. The AURLLPC decreased by 29.2 and 21.3% for cultivars BR‐IRGA 409 and Labelle, respectively, as the K rates in the nutrient solution increased. It can be concluded that high K concentration on leaf sheaths tissue was important to decrease sheath blight symptoms on rice leaf sheaths.     

Components of Resistance to Bacterial Blight Disease of Rice

Studies on the genetic variation, correlation, correlated response and path analysis were conducted on 8 rice cultivars to bring out the association and channelling of the pathway of different components of resistance to Xanthomonas campestris pv. oryzae. High genotypic coefficient of variation coupled with high heritability and genetic gain was observed for lesion size (LS) and the area under disease progress curve (AUDPC) indicating the predominance of additive gene effects. There was a strong association among all the components both at genotypic and phenotypic levels. Genotypic correlations were higher than the corresponding phenotypic correlations indicating the modifying effect of environment on association of components at genotypic level. Maximum correlated response and relative selection efficiency on AUDPC was observed through indirect selection for LS followed by the number of bacteria per unit leaf area (NB). Path analysis revealed highest direct effect of LS on AUDPCboth at genotypic and phenotypic levels. Indirect effects of fairly high magnitude were also exerted by incubation period (ICP) and NB towards AUDPC.     

Phenotyping of Partial Physiological Resistance to Rice Sheath Blight

Sheath blight, caused by Rhizoctonia solani, is one of the most important rice diseases worldwide especially under irrigated agro‐ecosystems. To date, no rice accession with complete resistance to sheath blight has been reported. However, a number of genotypes with varying levels of resistance have been reported. Twelve genotypes (including mega varieties) viz. Tetep, Jasmine 85, Te‐Qing, Duduruchi, Betichikon, Khatochalani, D‐6766, D‐256, Swarna, Sarju‐52, MTU‐1010 and Samba Mashuri were evaluated for quantitative measurement of partial physiological resistance to sheath blight under controlled conditions using detached tiller method. Three independent experiments, each involving three replications, were conducted. Seven days after inoculation, the following disease variables were measured: number of lesions, lesion length, vertical sheath colonization (VSC) on the tiller, disease severity, relative vertical sheath colonization (RVSC) and survival of the leaf blade. Variation between rice genotypes was observed for all the disease variables. Disease severity and VSC were the two most correlated variables, whereas the number of lesions and mean lesion length were the least correlated variables. The ranking of varieties often differed depending on the disease variable considered. Amongst the genotypes tested, D‐256, Tetep and Jasmin‐85 had the lowest number of lesions and disease severity. Similarly, Tetep and D‐256 showed the lowest levels of RVSC, whilst Jasmine‐85 was found to be intermediate. D‐6766, Samba Mashuri and Betichikon showed the highest levels of disease variables. The fraction of dead leaves ranged from 0.00 to 0.38. No dead leaves were observed in Te‐Qing, Swarna and MTU‐1010. The highest fraction of dead leaves was observed for Betichikon (0.38) followed by Duduruchi and D‐6766 (0.33). Our results suggest that this method in combination with other phenotyping methods could be used to quantify partial resistance to rice sheath blight.     

抗疫病加工型辣椒细胞质雄性不育恢复系的创制

为加快抗疫病加工型辣椒细胞质雄性不育(cytoplasmic male sterility,CMS)恢复系的创制,该试验以单生、长果自交系481 4 10为母本,以抗疫病的恢复系939 1和1021(1) 1为父本配制杂交组合,采用花药培养技术将抗疫病恢复系的Rf基因和抗疫病基因导入单生、长果自交系中,并利用分子标记辅助选择(molecular marker assisted selection, MAS)技术鉴定DH系(Double Haploid line)的Rf基因以及抗病性,进一步用室内苗期抗性鉴定的方法验证MAS筛选的含Rf DH系对疫病的抗性。结果表明：(1)花药培养的供体亲本(481 4 10×939 1)F₁诱导出22个胚状体,成苗后经倍性鉴定获得11个花培DH系;而由供体亲本［481 4 10×1021(1) 1］F₁获得 9个DH系。(2)分子标记CRF SCAR对花培DH系进行分子标记辅助选择验证结果表明,来自供体(481 4 10×939 1)F₁的DH系中有7个可扩增出870 bp的特异条带,占63.6%;而供体［481 4 10×1021(1) 1］F₁获得的DH系中则有8个能扩增出870 bp的特异条带,占88.9%。(3)分子标记FQ01/RQ01对DH系进行分子标记辅助选择筛选结果发现,来自供体(481 4 10×939 1)F₁的DH系有5个能扩增出717 bp的特异条带,占45.5%;而来自供体［481 4 10×1021(1) 1］F₁的DH系有4个可扩增出717 bp的特异条带,占44.4%。(4)MAS技术初步筛选到7个携带Rf的抗疫病DH系,分别命名为‘渝辣选3 2/3 3/3 5/7 1/7 5/7 6/7 9’;苗期抗性鉴定结果显示,7个DH系中5个DH系抗疫病,2个中抗疫病;农艺性状调查和测交实验表明,‘渝辣选3 2’和‘渝辣选7 1’是单生朝天椒、果实较长,味辣,均为CMS恢复系。该研究创制的2个DH系为利用辣椒CMS三系配套选育抗病新品种奠定了基础。     

Laboratory Estimation of Field Resistance of Potato to Late Blight

Based on quantitative measurement of components of field resistance of potatoes to late blight, a multiple linear regression equation is derived for laboratory estimation of Area Under Disease Progress Curve. The equation accounts for 82% of variation in Area Under Disease Progress Curve. Transformation of data or inclusion of more terms do not improve the equation significantly. The method is suggested as a replacement or supplement to field testing.     

Sources of Resistance to Cowpea Bacterial Blight Disease in Nigeria

The development of resistant crop varieties depends on the reliability of the method of screening for resistance. One of the techniques widely used in evaluating field resistance is the field screening method. However, most cowpea varieties regarded as having field resistance are often found to be susceptible in farmers’ fields, where the inoculum density can be higher. This study rescreened 96 cowpea varieties, evaluated earlier in breeders’ fields as resistant to Xanthomonas campestris pv. vignicola, in field and greenhouse under high inoculum pressure. There were significant differences (P ≤ 0.05) in the reactions of cowpea varieties to bacterial blight in terms of disease incidence and severity. Results from the field screening showed that there were 69 susceptible, 25 moderately susceptible, and 2 resistant varieties. In artificial inoculation in the greenhouse IT81D‐1228‐14, IT82E‐16, IT93K‐2271‐2‐2, TVu 1235, and TVu 4630, which were moderately susceptible in the field showed a susceptible reaction. Tvu 12349 and Tvu 15549 gave consistent reactions in the field and in the greenhouse and are therefore good sources of stable resistance to bacterial blight pathogen. Stem canker incidence also varied significantly (P ≤ 0.05) among the cowpea varieties. Seventeen varieties did not manifest canker symptoms.     

云南“大粒水稻”对稻白叶枯病的抗性遗传

云南地方品种——云南大粒抗水稻白叶枯病菌“江陵691”,其抗性由2对具重叠作用的隐性抗性基因控制,与IR28、南粳15的显性抗病基因不等位;也与已命名的xa-5、xa-8、xa-9和xa-13 4个抗性基因也不等位。     

大麦赤霉病抗扩展性鉴定与评价

利用禾谷镰刀菌单花滴注接种研究了245份大麦品种对赤霉病抗扩展性。结果表明,大麦赤霉病抗性除了抗初侵染外还存在抗扩展类型。比较了接种后7d、14d和21d的病小穗数和病小穗率以覆由不同期病小穗率获得的病程曲线面积等7个指标性状,并对其进行遗传参数分析,发现21d病小穗率指标在品种间具帔大的变幅、遗传变异系数和遗传率,21d病小穗数和病程曲线面积与病小穗率呈极显著正相关。不同大麦品种抗扩展性表现不一,供试品种中以Suyin21、乌金一号、莆846193、盐97001、96AC20-30五个品种21d病小穗率最低,为高抗品种,占全部供试品种的2．04％。