Rind puncture resistance in maize: inheritance and relationship with resistance to pink stem borer attack

The main pest of maize in north‐western Spain is the pink stem borer, Sesamia nonagrioides, and stem lodging is one of the consequences of attack. Since rind puncture resistance is related to stem lodging resistance, the objectives of this work were to estimate the genetic effects involved in the inheritance of rind puncture resistance and to determine the phenotypic correlation coefficients between rind puncture resistance and pink stem borer damage. Six generations from the crosses ‘CM109’בEP31’ and ‘CM109’בEP42’ and a 10‐inbred line diallel were evaluated in Pontevedra, Spain, in 1995 and 1996. The inheritance of rind puncture resistance had two significant components, one additive and one dominant. Non‐allelic and genotype × environment interactions were not significant. Improvement for internode rind puncture resistance to increase stem strength and stalk lodging resistance could have some positive influence on resistance to pink stem borer. However, its use as an estimator of pink stem borer resistance cannot be generalized and so must be restricted to programmes that involve materials exhibiting physical resistance to pink stem borer attack.     

Diallel inheritance of relevant traits in cassava (Manihot esculenta Crantz) adapted to acid-soil savannas

There is a limited knowledge on the inheritance of traits with agronomic relevance in cassava. A diallel study among 10 parental clones was conducted in the acid-soils environment in the eastern savannas of Colombia. Thirty clones were obtained for each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore, the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant effects for five of the six variables analyzed (harvest index, dry matter content, height of first branching, reaction to super elongation disease, and plant type scores). Fresh root yield showed strong genotype × environment interaction and differences between crosses reached statistical significance in only one of the two environments analyzed. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays an important role particularly in the cases of fresh root yield and harvest index.     

Genetic analysis of quantitative traits across environments in linseed (Linum usitatissimum L.)

Summary Fourteen lines of linseed (Linum usitatissimum L.) were evaluated for general and specific combining ability through line × tester cross analysis using five diverse testers in two different environments. Seventy F₁'s and nineteen parental genotypes were raised in completely randomized block design with two replications with respect to yield and yield related traits. Considerable genetic variation was observed for all the traits studied. The additive as well as non-additive gene effects played significant role in the inheritance of yield and related traits with preponderance of non-additive gene effects for all the traits studied. Higher proportion of general combining ability × environment interaction variance as compared to specific combining ability × environment estimates was recorded. Additive genetic variances were more sensitive than non-additive genetic variances to the changing environment. Low estimates of heritability (narrow sense) for primary branches per plant, capsules per plant, seeds per capsule, seed yield per plant, harvest index and oil content and medium heritability for days to 50% flowering, days to maturity, plant height and 1000-seed weight was observed. Among the female parents LCK-9816, Parvati, Himalini, KL-168 were good general combiners for yield and related traits along with oil content, whereas among male parents, Surbhi and KL-224 were good general combiners for yield related traits and oil content but KL-221 was good general combiner for seed yield and related traits.     

Genetic analysis and breeding use of blast resistance in a japonica rice mutant R917

R917, a japonica rice mutant with broad-spectrum of resistance to blast, was selected after treatment of the F₁ seeds from the cross between Chengte 232 and Xiushui 37 with 10 krad of ⁶⁰Co γ-ray. R917 was evaluated for blast resistance in multiple years and locations. It was resistant to 136 of 138 strains of Magnaporthe grisea collected from different regions in China with a resistance frequency of 98.55%, much higher than 86.13% and 10.15% of Chengte 232 and Xiushui 37. To analyze its inheritance of resistance to blast, R917 was crossed with the susceptible cultivar, Nonghu 6, and its two parents. It had a single dominant resistance gene to Chinese races ZB13, ZC15 and ZE3, nonallelic to those of Chengte 232 and Xiushui 37. When inoculated with 7 Japanese differential strains, R917 showed the same reaction pattern as Toride 1 and differed from the other differential varieties. But R917 was different from Toride 1 in its reaction to 7 Chinese strains. Allelism test indicated that the resistance genes between R917 and Toride 1 were nonallelic to Chinese races ZC15 and ZE3. R917 was a semi dwarf with strong stem, narrow and erect leaf, tight plant type and monogenic broad-spectrum resistance to blast. Several lines with desirable agronomic traits newly bred using R917 as a donor of blast resistance had the same broad-spectrum of resistance to blast as R917, indicating there was no linkage drag between the resistance gene and other important agronomic genes in R917. R917 has been used as a donor in rice breeding programs in China. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于通路分析剖析水稻农艺性状配合力和杂种优势

按照NCII遗传交配设计构建测交群体,考察包括产量性状在内的9个农艺性状,对水稻农艺性状表型、配合力和杂种优势进行通路分析,以期为水稻品种的培育和改良提供理论基础。结果表明,主穗实粒数与生物调控、千粒重与半胱氨酸和蛋氨酸代谢、主穗长与SNARE相关囊泡运动、主穗一/二次枝梗与依赖DNA的转录、株高与大分子代谢过程、主穗颖花数与花粉识别、有效穗数与水解酶活性、单株实粒重与嘌呤核苷结合等通路相关。为获得优良性状,高配合力,杂种优势可以从某一性状的相关通路进行研究,找到调控该通路的相关基因,以期为改良水稻一般配合力和获得杂种优势提供一定帮助。     

The genetics of resistance in sunflower capitula to Sclerotinia sclerotiorum measured by mycelium infections combined with ascospore tests

To enhance efficiency of breeding programmes for Sclerotinia sclerotiorum resistance in sunflower capitula, two separate resistance tests have been recommended. However, the time necessary to develop genotypes with two types of resistance makes this impractical. A strategy to combine the two tests was consequently proposed to reduce the number of seasons per selection cycle, but genetic studies were necessary to determine if it could be applied in breeding programmes. This was the objective of this work. Data from two genetically different sunflower inbred lines and their F1, F2 and backcross generations were analysed in two years to determine the genetics of resistance to S. sclerotiorum in capitula measured by application on the same plants of a mycelium test combined with an ascospore test. Effects of maternal origin were detected when the reciprocal generations were evaluated for the mycelium test. This suggests the importance of choice of the inbred line used as female in population formation by hybridisation. Progeny subjected to the mycelium test did not show any change in relative reactions to two S. sclerotiorum isolates suggesting that ranking genotypes according to the results of combined S. sclerotiorum tests is repeatable across Sclerotinia isolates and experimental seasons. Moderate narrow sense heritability indicated that selection of the best F2 plants should be effective. Genetic gain from selection is possible because a reduction of lesion areas produced by the mycelium test can be expected. Additive gene effects contribute significantly to reduction in lesion area. Consequences of results in population improvement for S. sclerotiorum resistance in capitula are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mapping and validation of QTLs for rice sheath blight resistance

Sheath blight, caused by Rhizoctonia solani, is one of the most serious diseases of rice. Among 33 rice accessions, mainly from National Institute of Agrobiological Sciences (NIAS) Core Collection, we found three landraces from the Himalayas—Jarjan, Nepal 555 and Nepal 8—with resistance to sheath blight in 3 years’ field testing. Backcrossed inbred lines (BILs) derived from a cross between Jarjan and the leading Japanese cultivar Koshihikari were used in QTL analyses. Since later-heading lines show fewer lesions, we used only earlier-heading BILs to avoid association with heading date. We detected eight QTLs; the Jarjan allele of three of these increased resistance. Only one QTL, on chromosome 9 (between markers Nag08KK18184 and Nag08KK18871), was detected in all 3 years. Chromosome segment substitution lines (CSSLs) carrying it showed resistance in field tests. Thirty F₂ lines derived from a cross between Koshihikari and one CSSL supported the QTL.     

Genetic components of pod shattering in soybean

Half diallel crosses among ten pure breeding lines of soybean were made in 1997 and 1998 to study the inheritance of pod shattering in soybean. Evaluation for pod shattering among F₂ segregating populations was carried out in an oven set at 80 ^°C for 12 hours. Diallel analysis was carried out to estimate genetic parameters and detect presence of non allelic interaction of genes affecting pod shattering. Hayman's diallel analysis indicated significant variation of Wr + Vr and Wr – Vr over arrays, suggesting epistatic gene action. Similarly results from a joint regression coefficient over replications were significantly (p < 0.05) different from unity and zero, suggesting presence of non allelic interaction of genes. The intercept was positive, suggesting partial dominance for the shattering trait. Both general combining ability (GCA) and specific combining ability (SCA) effects were significant (p < 0.05). This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of resistance/susceptibility in individual F3 families of rice against strains of Magnaporthe grisea containing different genes for avirulence

A cross was made between rice cultivars Katy and Lemont. F3 families were produced from individual F2 plants. Approximately 25 plants of each F3 family were inoculated with each of 8 different strains of Magnaporthe grisea. Each strain of the pathogen was known to have different genes for avirulence on Katy or Lemont. Each F3 family was recorded as having all plants resistant, segregating for resistance, or all plants being susceptible. The results suggest that the ‘single’ gene for resistance in Katy is a tightly linked cluster of at least seven genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of resistance to kernel infection by Aspergillus flavus in maize *

Although kernel infection by Aspergillus flavus Link ex Fries and subsequent pre-harvest aflatoxin contamination of maize (Zea mays L.) grain are major production problems in the south-eastern United States and elsewhere in the world, limited progress has been made in developing and identifying sources for resistance. Genetics of kernel infection by A. flavus remains poorly understood. A 10-parent diallel experiment was conducted in 1992 and 1994 to study the genetic nature of percentage kernel infection (PKI) by A. flavus. General combining ability (GCA), specific combining ability (SCA), and reciprocal mean squares for PKI were significant. The GCA and SCA sums of squares were about equal. The GCA, SCA, and reciprocal effects varied across years, which implied that percentage kernel infection was greatly influenced by environments. The percentage kernel infection was always greater when Mo 17 was the male parent in a cross than when it was the female parent. The percentage kernel infection mean for female Mo 17 was 38.5% lower than that for male Mol7. Similarly, percentage kernel infection mean for female L668 was 23.7% lower than that for male L668. The use of inbred lines L729 and B73 as female parents should be avoided, as they showed significant, positive maternal reciprocal effects.     

Estimates of additive and dominance effects for Fusarium head blight resistance of winter triticale

The most effective strategy to control Fusarium head blight (FHB), a devastating disease of small‐grain cereals, is breeding resistant cultivars. This resistance study of F₁ crosses, F₂ and backcross generations of triticale estimates heterosis, general and specific combining ability (GCA, SCA), additive and dominance effects and compares parents with segregating generations. The genetic material consisted of 10 parents with their 45 F₁ crosses and of six parents with their 15 F₂ progeny and backcrosses to each parent. Genotypes were grown in various environments and artificially inoculated with an aggressive isolate of F. culmorum. FHB was assessed, by visual rating, as the mean of four to five individual ratings of disease development. Heterosis for FHB was of little importance. The correlation between the FHB rating of F₁ crosses and their mid‐parent performance was close. GCA was the predominant source of variation, although the significance of the SCA variance also implied non‐additive allelic interaction. The preponderance of additive gene effects is encouraging for increasing resistance by a recurrent selection programme. The relationship between the GCA effect of a parent and its per se performance was close, which gives the possibility of predicting FHB resistance in F₁ crosses. Additive effects were predominant in the F₂ progeny and also in the backcrosses. Transgressive segregants could not be detected. Searching for them should be postponed to the F₃ or later generations.     

水稻籼粳交恢复系茎秆抗倒性的配合力分析

本研究以通过不断聚合和累加不同籼粳亚种有利基因的方法,自育成的不同籼粳分化类型的12个恢复系,与8个两系和三系不育系为材料,采用植物数量性状配合力（NCⅡ设计）分析方法,研究了6个茎秆抗倒性状的配合力和群体遗传参数。结果表明：所考察的6个茎秆抗倒性状的遗传受亲本基因加性效应和非加性效应的影响。倒伏指数、抗折力以非加性效应为主;株高、弯曲力矩、茎椭圆截面积以基因加性效应为主;亲本基因加性效应和非加性效应对后代茎壁截面积的作用相似。恢复系的遗传效应对杂交组合茎秆抗倒性起主要作用。抗折力和弯曲力矩性状除了受亲本特殊配合力的影响外,恢复系的一般配合力也起重要作用。K17A、广抗13A和II-32A三个不育系表现降低籼粳杂种株高超亲和提高抗倒性的遗传效应;明恢509、明恢512、明恢502和明恢398四个恢复系在降低倒伏指数方面较其他恢复系具有明显优势,且株高一般配合力为负效应,在提高茎秆抗倒性为目标的育种实践中有重要利用价值。     

Genetic analysis of salt tolerance at seedling and reproductive stages in rice (Oryza sativa)

Salinity is a major abiotic stress that limits rice production across rice areas as high‐yielding modern rice varieties are generally sensitive to salt stress. The study was conducted to deduce heritability and combining ability estimates of rice for various morphological and physiological traits using a 7 × 7 full‐diallel‐cross analysis at seedling and reproductive stages. The salinity stress treatment was 12 dS m^?1 at the seedling stage and 8 dS m^?1 at the reproductive stage. Diallel analysis revealed high for salinity tolerance scores and shoot height, moderate for shoot dry weight and root dry weight and low for Na⁺ and K⁺ concentrations and K⁺/Na⁺ ratio. The low‐to‐moderate narrow‐sense heritability for number of panicles, number of fertile spikelets, grain weight, spikelet fertility and K⁺/Na⁺ ratio suggests a large breeding population and delayed selection for tolerance until later generations. Significant maternal effects indicate that selection of the female parent is very important for desired trait development. The results of this study confirmed that salinity tolerance at the seedling and reproductive stages is regulated by a different set of genes that could be pyramided using different donors to enhance the level of tolerance.     

Analysis of diallel crosses between wheat genotypes with genetically different resistance to Pseudocercosporella herpotrichoides (Fron) Deighton

Two diallels were analysed for general combining ability (GCA) and specific combining ability (SCA) to study the resistance of crosses‐between wheat genotypes, advanced to the F₅ generation, to Pseudocer‐cosporella herpotrichoides. The parents either carried the resistance‐gene Pch‐1 or had different levels of quantitative resistance, one genotype was susceptible. At medium milk‐ripening, significant effects were‐found for GCA and SCA. GCA effects were the more important. Diallel crosses between genotypes, all carrying Pch‐1, revealed interactions‐of the gene with the genotypic background. Some combinations had a‐higher level of resistance than the best parent. In these populations'CH‐75417’ was involved as a parent. Both ‘CH‐75417’ and ‘F–210.13.4.42’ had significant GCA effects. Crosses between quantitatively resistant parents yielded populations that transgressed both parents. The increased resistance level was associated with ‘Cappelle‐Desprez’, distinguished by its high GCA. In some crosses SCA contributed significantly to an increase in resistance level. Selection for resistance within the best advanced populations is recommended since it‐takes advantage of additive gene action and the high heritability estimates based on ELISA values in plant progenies.     

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.     

Mapping of leaf and neck blast resistance genes with resistance gene analog, RAPD and RFLP in rice

An F₈ recombinant inbred population was constructed using a commercial indica rice variety Zhong 156 as the female parent and a semidwarf indica variety Gumei 2 with durable resistance to rice blast as the male parent. Zhong 156 is resistant to the fungus race ZC₁₅ at the seedling stage but susceptible to the same race at the flowering stage. Gumei 2 is resistant to ZC₁₅ at both stages. The blast resistance of 148 recombinant inbred lines was evaluated using the blast race ZC₁₅. Genetic analysis indicated that the resistance to leaf blast was controlled by three genes and the presence of resistant alleles at any loci would result in resistance. One of the three genes did not have effects at the flowering stage. Two genes, tentatively assigned as Pi24(t) and Pi25(t), were mapped onto chromosome 12 and 6,respectively, based on RGA (resistance gene analog), RFLP and RAPD markers. Pi24(t) conferred resistance to leaf blast only, and its resistance allele was from Zhong 156. Pi25(t) conferred resistance to both leaf and neck blast, and its resistance allele was from Gumei 2. In a natural infection test in a blast hot-spot, Pi25(t) exhibited high resistance to neck blast, while Pi24(t) showed little effect. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analysis of resistance to root-lesion nematode (Pratylenchus thornei) in wheat

The inheritance of resistance to root‐lesion nematode was investigated in five synthetic hexaploid wheat lines and two bread wheat lines using a half‐diallel design of F₁ and F₂ crosses. The combining ability of resistance genes in the synthetic hexaploid wheat lines was compared with the performance of the bread wheat line ‘GS50a’, the source of resistance to Pratylenchus thornei used in Australian wheat breeding programmes. Replicated glasshouse trials identified P. thornei resistance as polygenic and additive in gene action. General combining ability (GCA) of the parents was more important than specific combining ability (SCA) effects in the inheritance of P. thornei resistance in both F₁ and F₂ populations. The synthetic hexaploid wheat line ‘CPI133872’ was identified as the best general combiner, however, all five synthetic hexaploid wheat lines possessed better GCA than ‘GS50a’ The synthetic hexaploid wheat lines contain novel sources of P. thornei resistance that will provide alternative and more effective sources of resistance to be utilized in wheat breeding programmes.     

Screening immature bulbs of daffodil (Narcissus L.) crosses for resistance to basal rot disease caused by Fusarium oxysporum f. sp. narcissi

Summary Immature bulbs were used in two screening trials to identify daffodil genotypes resistant to basal rot disease caused by Fusarium oxysporum f. sp. narcissi. Progenies, having at least one parent with some resistance, were grown in compost infested with chlamydospores of the fungal pathogen, and survivors were recovered at final harvest. Survival rates were very low when one-year old bulbs were used; the greater survival of two-and three-year old bulbs indicates that resistance increased with bulb age. Selection pressure was influenced by inoculum concentration in the compost. Continuous variation of percentage bulb survival between progenies suggests a polygenic mode of inheritance; there was no evidence of maternal inheritance. Parental general combining ability (GCA) was highly significant and accounted for much of the difference in bulb survival between progenies, but non-additive parental effects were also apparent. GCA rankings in the two trials were similar and reflected the resistance of parental cultivars in the field. A three-dimensional graphing procedure was devised to depict goodness of fit of progeny data to the additive model.     

水稻协优9308重组自交系群体白叶枯病抗性的全基因组关联分析

白叶枯病是水稻生产最严重的细菌性病害,挖掘新的白叶枯病抗性基因资源并培育抗病品种是控制该病害的重要方法。本研究利用父母本抗性差异较大的协优9308衍生的139个重组自交系群体作为遗传材料,人工接种不同白叶枯菌后的病斑长度作为连续型表型,结合经DNA深度测序获得的476,505个单核苷酸多态性(single-nucleotide polymorphism,SNP)标记进行全基因组关联分析(genome-wide associated study,GWAS)。结果表明在P<1×10^–4下, 4个菌株处理后共鉴定到109个与白叶枯抗性显著关联的SNPs位点,解释表型变异率59.78%～63.29%。其中CR4接种发现了25个SNP位点其贡献率为61.00%,在这些SNP位点附近共筛选到19个基因,其中有2个为NBS-LRR抗病相关基因(LOC_Os11g43420和LOC_Os11g45930)。表达分析验证发现该2个基因在抗性亲本中恢9308的表达量分别为感病母本协青早B的4.42倍和8.86倍,表明其可能在正调控白叶枯病...