Genetic analyses of resistance of the wheat differential cultivars Carstens V and Spaldings Prolific to two races of Puccinia striiformis

Genetic analysis of resistance of wheat seedlings to two races of Puccinia striiformis was conducted on F₁, F₂ and F₃ generations from crosses Carstens V (CV) × Lee, Spaldings Prolific (SPA) × Lee and CV × SPA. F₂ generations from crosses of CV and SPA with Strubes Dickkopf (SD) were also studied. The plants were classified into six resistance classes and analysed by factorial correspondence analysis and nonhierarchical classification. The two P. striiformis isolates tested were a French isolate of race 43E138 and a Lebanese isolate of race 2E16, selected for the differences in their virulence spectra for the common differential cultivars Strubes Dickkopf and Nord Desprez. Resistance of CV and SPA was recessive and dominant to races 43E138 and 2E16, respectively. CV possessed three or four resistance genes, one of them being expressed with both races. Two genes of CV had a cumulative effect for resistance to 43E138 and two or three gave dominant resistance to 2E16. SPA had three resistance genes, all of which gave resistance to 2E16 and two of which also gave resistance to 43E138. SPA had one gene in common with CV for resistance to both races. Furthermore, the gene for resistance to race 2E16 in CV and SPA was allelic with a gene in SD, and was probably Yr25 .     

水稻不同品种或组合对甲磺隆耐药性差异的机制研究

以水稻乙酰乳酸合成酶(ALS)比活力为研究对象,通过在离体和活体条件下比较其对甲磺隆的敏感性水平,探讨了水稻不同品种或组合的耐药性差异机制。结果表明,离体条件下不同水稻品种或组合ALS对甲磺隆均较敏感,当甲磺隆浓度为100 μg/L时,对ALS比活力抑制率达60%以上,且活力百分比与甲磺隆浓度对数成直线负相关关系,相关程度显著或极显著;活体条件下ALS活力均受到甲磺隆不同程度的抑制,但同一品种ALS活力不随甲磺隆浓度的变化而呈现规律性变化。在甲磺隆浓度相同时,活体条件下所有供试水稻品种ALS活力均显著高于离体条件下的ALS活力,影响程度与植株耐药性差异基本一致,说明甲磺隆在水稻体内存在较强代谢失活作用,代谢失活差异是水稻不同品种或组合对甲磺隆的耐药性差异机制。     

甘薯根腐病抗性在不同环境条件下的表现及遗传趋势

结果表明,甘薯根腐病发病轻重与环境条件有很大关系,表现为干旱少雨的年份发病较重,降雨量较多的年份发病较轻;土壤瘠薄的发病较重,肥力条件较好的则发病较轻;通常情况下,年份间品种的抗性表现较为一致,但遇特殊气候则年份间品种的抗性有一定的差异。对1150份甘薯品种资源及育种材料的根腐病抗性鉴定结果表明,高抗型材料占14.6％,抗病型占15.7％,感病型占26.0％,高感型占43.7％。对754份材料及亲本的抗性分析表明,不同的抗性组合后代中均可分离出高抗至高感类型的材料,杂交后代的抗性强弱随双亲抗性水平的提高而提高。中国自1970年以来采用品种间杂交和种间杂交育种技术,先后育成了一批高产、优质的高抗型优良品种。     

Identification of ALS inhibitor‐resistant Amaranthus biotypes using polymerase chain reaction amplification of specific alleles

Summary Polymerase chain reaction (PCR) amplification of specific alleles (PASA) was adapted as a molecular marker‐based method for the rapid detection of point mutations in Amaranthus retroflexus and Amaranthus rudis leading to ALS inhibitor resistance. Two pairs of primers were designed for the specific amplification of alleles of the ALS gene of susceptible and resistant biotypes. The allele‐specific primer matched the desired allele, but mismatched the different allele at its 3′ end. Differentiation was carried out by comparison of the amplified DNA fragments in gel electrophoresis after PASA‐PCR. In A. rudis, differentiation was possible with one PCR and genomic DNA as probe. A ‘nested’ PCR was necessary for the differentiation of sensitive and resistant A. retroflexus. PASA is useful for the identification of resistant weed biotypes and also as a monitoring tool to map resistance occurrence and distribution. Advantages include the fast and clear separation of those plants with and without mutations at an early stage of development, its easy and consistent performance and quick results compared with existing resistance detection tests. These advantages, when combined with management strategies, enable further activities to reduce herbicide resistance.     

β- 氨基丁酸诱导甜( 辣) 椒抗疫病作用的研究

 报道了用β- 氨基丁酸( DL-β-aminon-butyric acid, BABA) 喷雾处理辣椒叶片和茎后的诱导抗疫病作用。研究证明: 高浓度BABA ( 1 000 g/mL) 对离体辣椒疫霉病菌无抗菌活性, 用其喷雾处理辣椒的茎叶所诱导的抗疫病作用可完全控制其危害; 用BABA 诱导处理后3 d 接种辣椒疫霉病菌, 辣椒植株开始表达出较高的诱导抗性, 这种抗病作用可持续20 d 以上, 并表现出与数量抗病性相似的特性。     

Role of polymerase β in DNA metabolism and genomic instability

The major role of DNA polymerase β was thought to be limited in its involvement in short patch base excision repair by removing 5’-deoxyribose phosphate and base insertion. However, the recent researches indicate that polymerase β might take part in a wide spectrum of DNA metabolism reactions, including long patch base excision repair, DNA replication, recombination, meiosis and transleisional DNA synthesis. Because of its wide and important cellular function, an inappropriate intracellular polymerase β level might be associated with genomic instability. Down-regulation or mutation of polymerase β is mutagenic due to deficient in DNA repair, while overexpression of this error-prone β polymerase might perturb the normal function of other accurate polymerases and cause genomic instability as well.     

Identification of a major gene (Mex-1) from Coffea canephora conferring resistance to Meloidogyne exigua in Coffea arabica

Among the most damaging root-knot nematode species, Meloidogyne exigua is especially common in Latin America and constitutes a major agronomic constraint in all major coffee-growing ( Coffea arabica ) areas. Growing nematode-resistant coffee represents the most promising option for control of the pest. The present study aimed to determine the mode of inheritance of the M. exigua resistance transferred into C. arabica from a related species, Coffea canephora , and to identify associated molecular markers. Segregation data analysis of F ₂ progeny derived from a cross between the resistant introgression line T5296 and the susceptible accession Et6 showed that the resistance to M. exigua is controlled by a simply inherited major gene (designated the Mex -1 locus). The gall index distribution exhibited by the F ₂ individuals suggested incomplete dominant expression. Fourteen AFLP markers were found associated with the resistance to M. exigua and a localized genetic map of the chromosome segment carrying Mex -1 was constructed. Furthermore, the association of the identified AFLP markers with Mex -1 was confirmed by analysis of a set of genotypes involving 28 introgression Arabica lines either resistant or susceptible to M. exigua in field conditions. These results represent an important starting point to enhance backcross breeding programmes and to perform an early selection of resistant seedlings.     

Further Contributions to the Development of a Differential Set of Pea Cultivars (Pisum sativum) to Investigate the Virulence of Isolates of Aphanomyces euteiches

Common root rot (Aphanomyces euteiches Drechs.) has become a very destructive disease in the French pea crops since 1993. For an accurate investigation of the virulence variability among French A. euteiches populations and between French and foreign populations, a new set of differential pea genotypes was developed. Thirty-three American and European pea lines, displaying different levels of resistance, were screened in a growth chamber against two French isolates. Symptoms (disease severity from 0 to 5, evaluating symptom surface on roots and epicotyl) and percentage of top fresh weight (inoculated/uninoculated top fresh weight ratio) were measured. From this screening 12 relatively resistant lines, from various genetic backgrounds, were identified along with a highly susceptible control. This set of 13 genotypes was inoculated under controlled conditions with 14 isolates from France, Sweden, USA, Canada and New Zealand, to investigate genotype–isolate interactions. Root symptoms were rated (disease severity), and a susceptibility/resistance threshold was established at disease severity = 1. Significant quantitative interactions were observed, and five 'resistance patterns' were identified, leading to a set of six pea genotypes: Baccara (susceptible), Capella, MN313, 902131, 552 and PI180693. Fields trials of this set in 1999 and 2000 gave the same resistance rankings than in growth chamber conditions. This set will allow more accurate assessments of the variability in virulence/aggressiveness of A. euteiches isolates from France and foreign countries, and further investigations of the epidemiological and genetic basis of pea–A. euteiches interactions.     

Comparison of Resistance to Tomato Leaf Curl Virus (India) and Tomato Yellow Leaf Curl Virus (Israel) among Lycopersicon Wild Species, Breeding Lines and Hybrids

The objective of this study was to screen wild and domesticated tomatoes for resistance to Tomato yellow leaf curl virus, Israel (TYLCV-Is) and Tomato leaf curl virus from Bangalore isolate 4, India (ToLCV-[Ban4]) to find sources of resistance to both viruses. A total of 34 tomato genotypes resistant/tolerant to TYLCV-Is were screened for resistance to ToLCV-[Ban4] under glasshouse and field conditions at the University of Agricultural Sciences, Bangalore, India. Resistance was assessed by criteria like disease incidence, symptom severity and squash-blot hybridization. All the tomato genotypes inoculated with ToLCV-[Ban4] by the whitefly vector Bemisia tabaci (Gennadius) produced disease symptoms. In some plants of the lines 902 and 910, however, the virus was not detected by hybridization. The tomato genotypes susceptible to ToLCV-[Ban4] by whitefly-mediated inoculation were also found susceptible to the virus under field conditions. However, there were substantial differences between genotypes in disease incidence, spread, symptom severity and crop yield. Despite early disease incidence, many genotypes produced substantially higher yields than the local hybrid, Avinash-2. Sixteen tomato genotypes from India resistant/tolerant to ToLCV-[Ban4] were also tested for TYLCV-Is resistance at the Hebrew University of Jerusalem, Rehovot, Israel. Accessions of wild species, Lycopersicon hirsutum LA 1777 and PI 390659 were the best sources of resistance to both viruses. Lines 902 and 910, which were, resistant to TYLCV-Is were only tolerant to ToLCV-[Ban4] and accession Lycopersicon peruvianum CMV Sel. INRA, resistant to ToLCV-[Ban4], was only tolerant to TYLCV-Is. Implications of using the resistant lines in breeding programme is discussed.     

Differential Responses to Pea Bacterial Blight in Stems, Leaves and Pods Under Glasshouse and Field Conditions

Resistance to pea bacterial blight (Pseudomonas syringae pv. pisi) in different plant parts was assessed in 19 Pisum sativum cultivars and landraces, carrying race-specific resistance genes (R-genes) and two Pisum abyssinicum accessions carrying race-nonspecific resistance. Stems, leaves and pods were inoculated with seven races of P. s. pv. pisi under glasshouse conditions. For both race-specific and nonspecific resistance, a resistant response in the stem was not always associated with resistance in leaf and pod. Race-specific genes conferred stem resistance consistently, however, there was variability in the responses of leaves and pods which depended on the matching R-gene and A-gene (avirulence gene in the pathogen) combination. R2 generally conferred resistance in all plant parts. R3 or R4 singly did not confer complete resistance in leaf and pod, however, R3 in combination with R2 or R4 enhanced leaf and pod resistance. Race-nonspecific resistance conferred stem resistance to all races, leaf and pod resistance to races 2, 5 and 7 and variable reactions in leaves and pods to races 1, 3, 4 and 6.Disease expression was also studied in the field under autumn/winter conditions. P. sativum cultivar, Kelvedon Wonder (with no R genes), and two P. abyssinicum accessions, were inoculated with the most frequent races in Europe under field conditions (2, 4 and 6). Kelvedon Wonder was very susceptible to all three races, whereas P. abyssinicum was much less affected. The combination of disease resistance with frost tolerance in P. abyssinicum enabled plants to survive through the winter. A breeding strategy combining race-nonspecific resistance derived from P. abyssinicum with race-specific R-genes should provide durable resistance under severe disease pressure.