Inheritance of Karnal bunt-free trait in bread wheat

A Karnal bunt (KB)‐free wheat stock (‘KBRL22’) obtained from a cross of two resistant lines (‘HD29’ and ‘W485’) was used as a donor to introgress the KB‐free trait into ‘PBW343’(an ‘Attila’ sib), the most widely grown wheat cultivar in India. The number of KB‐free and KB‐affected plants in BC ₁, BC₂, BC₃ and BC₄ as well the F₂ was recorded after artificial inoculations. The segregation pattern in these generations clearly indicated two independently segregating, dominant genes which jointly confer the KB‐free attribute. The importance of the KB‐free line generated in this experiment is discussed.     

Inheritance of the four-seeded-pod trait in a soybean mutant and marker-assisted selection for this trait

A high seeds‐per‐pod value is a crucial component of soybean seed yield, but reliable information is lacking on the inheritance and early selection for the four‐seeded pod (4SP) trait. The inheritance of 4SP was followed in crosses originating from an EMS‐derived mutant line (E182, 15% 4SP) with its parental cultivar, ‘Ludou No. 4’ (no 4SP), and the efficiencies of both a molecular and morphological marker selection were determined. The plants of two F₂ populations (with E182 as one of the parents) showed a segregation ratio of 3 : 1 (low to high SP values), indicating a single recessive locus; this mode of inheritance was confirmed by subsequent analysis of the F_{2 : 3} families. Among four microsatellite markers linked with the 4SP trait, Sat_107 was the closest to the 4SP locus (3.2 ± 1.11 cM). Both the molecular marker Sat_107 and the morphological marker, narrow leaflet (NL) associated with the 4SP locus were effective in selecting the 4SP trait, although with different efficiencies. The molecular marker was efficient in selecting soybean progenies from the cross in which one parent was the E182 mutant line because it was tightly linked to the mutated 4SP locus. In the other cross, with 4SP not derived from E182, the efficiency was reduced in comparison with the morphological marker.     

Inheritance of tillering and flowering-time in early maturing maize

Summary A diallel cross and F₂ populations derived from eight early maturing maize inbreds were used to investigate the inheritance of tillering and flowering-time (anthesis), and the possible relationship between tillering and flowering-time. Incomplete dominance for increased tillering was observed; potence ratios, representing the overall degree of dominance, ranged from 0.26 to 0.52. Dominance for early flowering ranged from incomplete with a potence ratio of 0.55 to overdominance with a potence ratio of 1.40. Broad-sense heritabilities were low for both characters. The genetic component of variation for tillering was due to general combining ability effects; specific combining ability effects were not significant. A significant negative linear relationship between tillering and flowering-time was found. Lack of independent assortment of tillering and flowering-time in F₂ populations indicated that the two characters are genetically related.     

QTL mapping of maize (Zea mays) stay-green traits and their relationship to yield

A maize genetic linkage map derived from 115 simple sequence repeat (SSR) markers was constructed from an F₂ population. The F₂ was generated from a cross between a stay-green inbred line (Q319) and a normal inbred line (Mo17). The map resolved 10 linkage groups and spanned 1431.0 cM in length with an average genetic distance of 12.44 cM between two neighbouring loci. A total of 14 quantitative trait loci (QTL) were detected for stay-green traits at different postflowering time intervals and identified by composite interval mapping. The respective QTL contribution to phenotypic variance ranged from 5.40% to 11.49%, with trait synergistic action from Q319. Moreover, maize stay-green traits were closely correlated to grain yield. Additional QTL analyses indicated that multiple intervals of stay-green QTL overlapped with yield QTL.     

基于叶片面积玉米叶片保绿度开花后衰减特性初步研究

摘要：采用Excel工作表及Origin7.0统计分析软件对基于绿叶面积玉米叶片保绿度开花后衰减特性进行了初步研究,结果表明：玉米开花后叶片保绿度衰减符合方程y=aeb-cx/(1+eb-cx);不同基因型玉米叶片保绿度衰减启动时间、最大衰减速率和最大衰减速率出现时间等衰减特性差异较大;即使相同基因型在不同环境条件下叶片衰减特性也不尽相同。采用y=aeb-cx/(1+eb-cx)模拟方程能比较全面揭示叶片保绿度的动态变化过程。     

玉米叶片保绿度开花后衰减特性与产量性状相关性初步研究

摘要：采用Excel工作表及Origin7.0、DPS统计分析软件对不同基因型玉米开花后叶片保绿度衰减特性与产量性状相关性进行了初步研究,结果表明：叶片保绿度最大衰减速率出现时间、最大衰减速率对产量性状影响大于叶片保绿度衰减启动时间对产量性状影响,最大衰减速率出现时间越晚、最大衰减速率越低,越有利于获得较高的单穗粒重、百粒重、穗粒数、容重、出籽率。     

玉米种质苗期耐冷性状的遗传分析

摘要：早春低温冷害是黑龙江省主要的自然灾害之一,已成为影响本区域玉米产量水平提高的重要因素。本研究选择不同耐冷玉米种质8份,按Griffing Ⅱ的设计组配,分析低温逆境下玉米出苗及幼苗期性状的遗传规律。相关分析表明,相对出苗指数、相对出苗率、相对苗干重、相对根干重两两相关,相对出苗率与相对根总长相关,上述性状适合作为玉米幼苗耐冷性鉴定的指标。不同亲本的GCA方差、不同组合的SCA方差在相对出苗率、相对发芽指数、相对苗干重、相对根干重、相对根总长等性状上的差异显著。非加性基因效应在相对出苗率、相对发芽指数、相对苗干重、相对根干重、相对根总长中起到重要作用,且狭义遗传力普遍较低,各性状均低于50%,高低次序为相对发芽指数>相对出苗率>相对根干重>相对苗干重>相对根总长,上述性状选择适宜在中晚代进行选择。     

Inheritance of the responses to a defoliation treatment affecting cold tolerance in maize

Previous studies revealed that defoliation can bring about differential responses in maize (Zea mays L.) genotypes for cold tolerance. This research was conducted to study the inheritance of the responses to defoliation for germination at low temperature and for seedling traits in early-sown field trials. Six inbred lines were crossed according to the complete diallel scheme, thus producing 36 genotypes. At milk ripening stage, half of the plants of each genotype were completely defoliated (D) whereas the other half were not (ND). Two experiments were conducted for two years, one in the germinator and one in the field. The response to defoliation was evaluated as (D–ND). Across the two years, the D treatment caused an average kernel weight decrease of ?56 mg (?23.1 % as referred to ND), an increase of 2.3 % for germination at 9 °C (G9) and a reduction of ?0.3 d for the average time of germination (ATG); in contrast, the defoliation effect was negligible for germination at 25 °C. In the field, the defoliation effects were more notable in the first (colder) year and led to an increase of 2.0 % for field emergence (FE) and to a decrease of ?2.7 g for seedling fresh weight (SFW). The genotypic variation for the (D–ND) response was significant for additive, dominance and reciprocal effects for G9, ATG, FE and SFW. There was consistency among lines across traits for additive effects, with Lo1016 and Os420 showing the best and the worst effect, respectively.     

Adaptation of tropical maize germplasm to temperate environments

Maize (Zea mays L.) is one of few crops that can offer significant genetic gains with the utilization of genetic diversity. Genetically broad-based germplasm has the potential to contribute useful and unique alleles to U.S. Corn Belt breeding programs not present in current U.S. genome sequences (e.g. B73, NAM, etc.). Our objectives were to determine if unique tropical genetic materials have been effectively adapted to temperate environments and how their agronomic performance was relative to adapted populations. An important long-term objective of the Iowa and North Dakota maize breeding programs has been, in addition to the typical elite by elite line pedigree selection cultivar development process, to adapt exotic and unique germplasm, maximize their genetic improvement, and develop unique products for breeding and commercial uses. Stratified mass selection methodology for earliness has been utilized for the adaptation of tropical and temperate populations to Iowa and North Dakota environments. This method has allowed screening of up to 25,000 genotypes per population cycle at a rate of one cycle per year. In addition, the estimated cost per year our programs had for the adaptation of each population was less than $2,000 which could successfully be applied in any breeding program across the globe. This cost has been less than 1 % of the total cost for finding minor genes on the same trait. Our results showed the successful adaptation of exotic populations was independent from genetic background. We can speculate there are a few major genes responsible for most of flowering date expression. We encourage the use of technology to target traits according to their genetic complexity. Stratified mass selection at the phenotypic level has been successful. Each of the populations with either 25 of 100 % tropical germplasm are available for anyone who may desire to expand the germplasm base of their breeding programs with tropical germplasm adapted to temperate mid- and short-season U.S. Corn Belt environments.     

甘蓝型油菜紫红叶标记性状的遗传及利用探讨

通过遗传分析得出：紫红叶色甘蓝型油菜的紫红叶性状受1对显性基因控制，紫红叶色对绿色呈显性。利用紫红叶色标记性状材料作父本，绿叶核不育系作母本进行隔离制种试验，结果表明：制种中必须拔除不育系中的可育株。同时进行了紫红叶标记材料利用方法探讨。     

Identifying quantitative trait loci for the general combining ability of yield-relevant traits in maize

Maize is the most important staple crop worldwide. Many of its agronomic traits present with a high level of heterosis. Combining ability was proposed to exploit the rule of heterosis, and general combining ability (GCA) is a crucial measure of parental performance. In this study, a recombinant inbred line population was used to construct testcross populations by crossing with four testers based on North Carolina design II. Six yield-relevant traits were investigated as phenotypic data. GCA effects were estimated for three scenarios based on the heterotic group and the number of tester lines. These estimates were then used to identify quantitative trait loci (QTL) and dissect genetic basis of GCA. A higher heritability of GCA was obtained for each trait. Thus, testing in early generation of breeding may effectively select candidate lines with relatively superior GCA performance. The GCA QTL detected in each scenario was slightly different according to the linkage mapping. Most of the GCA-relevant loci were simultaneously detected in all three datasets. Therefore, the genetic basis of GCA was nearly constant although discrepant inbred lines were appointed as testers. In addition, favorable alleles corresponding to GCA could be pyramided via marker-assisted selection and made available for maize hybrid breeding.     

Inheritance of yield and yield-related traits in highland maize hybrids of Uganda

Although many studies have been conducted on gene action of grain yield and yield related traits in maize, none of them focused on highland maize in Uganda. This study was conducted to establish the gene action controlling inheritance of yield and its related traits in highland maize hybrids. Thirty-six F₁ hybrids generated from a 9 x 9 half diallel mating design, were planted with two local checks in three highland locations; Kalengyere, Kachwekano, and Buginyanya with two replications using a 2 x 19 alpha (0, 1) lattice design. Results showed that inheritance of ear length and anthesis-silking interval was controlled by both additive and non-additive gene action while the inheritance of days to anthesis, days to silking was mainly controlled by additive gene action. The inheritance of grain yield and other yield related traits was greatly influenced by environment and genotype x environment interaction. Considering the great influence of the environment and genotype x environment interaction on most of the traits including grain yield, further testing in additional locations over more seasons and broadening the genetic base of the parents is encouraged.     

Genetic analysis of tropical maize inbred lines for resistance to maize lethal necrosis disease

Maize lethal necrosis (MLN) disease is a recent outbreak in eastern Africa and has emerged as a significant threat to maize production in the region. The disease is caused by the co-infection of Maize chlorotic mottle virus and any member of potyviridae family. A total of 28 maize inbred lines with varying levels of tolerance to MLN were crossed in a half-diallel mating design, and the resulting 340 F₁ crosses and four commercial checks were evaluated under MLN artificial inoculation at Naivasha, Kenya in 2015 and 2016 using an alpha lattice design with two replications. The objectives of the study were to (i) investigate the magnitude of general combining ability variance (σ _GCA ² ) and specific combining ability variance (σ _SCA ² ) and their interaction with years; (ii) evaluate the efficiencies of GCA based prediction and hybrid performance by means of a cross-validation procedure; (iii) estimate trait correlations in the hybrids; and (iv) identify the MLN tolerant single cross hybrids to be used as female parents for three-way cross hybrids. Results of the combined analysis of variance revealed that both GCA and SCA effects were significant (P < 0.05) for all traits except for ear rot. For MLN scores at early and late stages, GCA effects were 2.5–3.5 times higher than SCA effects indicating that additive gene action is more important than non-additive gene action. The GCA based prediction efficiency for MLN resistance and grain yield accounted for 67–90% of the variations in the hybrid performance suggesting that GCA-based prediction can be proposed to predict MLN resistance and grain yield prior to field evaluation. Three parents, CKDHL120918, CML550, and CKLTI0227 with significant GCA effects for GY (0.61–1.21; P < 0.05) were the most resistant to MLN. Hybrids “CKLTI0227 × CML550”, “CKDHL120918 × CKLTI0138”, and “CKDHL120918 × CKLTI0136” ranked among the best performing hybrids with grain yield of 6.0–6.6 t/ha compared with mean yield of commercial check hybrids (0.6 t/ha). The MLN tolerant inbred lines and single cross hybrids identified in this study could be used to improve MLN tolerance in both public and private sector maize breeding programs in eastern Africa.     

Development of in vivo haploid inducers for tropical maize breeding programs

Lack of adapted haploid inducers currently impedes adoption of the doubled haploid technology in tropical maize breeding programs. Our objective was to generate inducers with improved adaptation to tropical conditions. We developed segregating generations from crosses between temperate inducers having haploid induction rates (HIR) of 8–10 % and tropical CIMMYT maize lines (CML; HIR = 0 %) and evaluated these for HIR and agronomic performance under tropical lowland field conditions. The applied pedigree breeding scheme comprising mass selection on individual F₂ plants for highly heritable and visually scorable traits, followed by family-based selection for HIR and other agronomic characteristics in advanced selfing and backcross (BC) generations seems highly suitable for breeding improved haploid inducers with adaptation to different agroecologies. The most advanced tropical inducer candidates (TIC) combine HIR of up to 10 % with improved pollen production, disease resistance, and plant vigor compared to temperate inducers under tropical conditions. Agronomic characteristics were significantly improved in the BC to CML compared to BC to inducers, while mean HIR of both populations were similar, indicating that backcrossing to the adapted parent was suitable to improve adaptation of new inducers without sacrificing high HIR. When screening random open-pollinated maize accessions, HIR of up to 3 % were observed, suggesting that novel genetic variation may be present in maize accessions that could be exploited to improve HIR in maize. In conclusion, tropical inducer development proceeds well, but evaluation of TIC in multi-environment trials needs to be completed before large-scale dissemination can commence.     

Identification of maize brace-root quantitative trait loci in a recombinant inbred line population

Brace roots are vital constituents of the root system in maize. Their contribution to plant development is affected by brace-root traits (BRTs) including tier number (TN), root number (RN) and radius of the brace root (RBR). However, the genetic control of BRTs still remains elusive. Here, we have identified quantitative trait loci (QTLs) from 207 recombinant inbred lines of BY815/K22 grown in three environments to dissect the genetic architecture of BRTs in maize. All three of BRTs were highly heritable and were affected by genotype, environment and the interaction between them. RBR was positively correlated with both RN and TN. Eight QTLs were identified, 3 for TN, 3 for RN and 2 for RBR, and located on chromosome 1, 2, 9 and 10. They together explained 26.4% (TN), 21.5% (RN) and 13.4% (RBR) of phenotypic variation. Sixty of annotated genes were identified from the narrower QTLs by the bin-map method, including genes for signal transduction, gene expression regulation, and metabolism and related processes. The results also show that the interaction may occur between QTLs for BRTs. Our results can help to further study the genetic basis of BRTs and improve the approaches to control maize brace-root system through SNP marker-assisted selection.     

Molecular mapping of quantitative trait loci for grain moisture at harvest in maize

In maize, high grain moisture (GM) at harvest causes problems in harvesting, threshing, artificial drying, storage, transportation and processing. Understanding the genetic basis of GM will be useful for breeding low‐GM varieties. A quantitative genetics approach was used to identify quantitative trait loci (QTL) related to GM at harvest in field‐grown maize. The GM of a double haploid population consisting of 240 lines derived from Xianyu335 was evaluated in three planting seasons and a high‐density genetic linkage map covering 1546.4 cM was constructed. The broad‐sense heritability of GM at harvest was 71.0%. Using composite interval mapping, six QTL for GM at harvest were identified on five chromosomes (Chr). Two QTL located on Chr1, qgm1‐1 and qgm1‐2, explained 5.0% and 10.8% of the phenotypic variation in GM at harvest, respectively. The QTL qgm2, qgm3, qgm4 and qgm5 accounted for 3.3%, 8.3%, 5.4% and 11.0% of the mean phenotypic variation, respectively. Because of their consistent detection over multiple planting seasons, the detected QTL appear to be robust and reliable for the breeding of low‐GM varieties.     

Association between AFLP-based genetic distance and hybrid performance in tropical maize

Identifying the best inbred combinations for the development of commercial hybrid maize varieties remains the main challenge to maize breeders. The aim of this work was to study associations between the genetic distance (GD) of 21 inbreds and the corresponding F₁ phenotypic data. Furthermore, the impact of grouping lines into genetically similar clusters was investigated. The 21 inbred lines were fingerprinted using amplified fragment length polymorphism markers. Parents and 210 F₁ progeny were evaluated in the field. Joint data analysis mostly revealed a tighter association between GD and the F₁ performance or mid parent heterosis in the intergroup than in the intragroup crosses. Despite these correlations, intergoup crosses should always be field‐tested before their release. Crosses showing low GD values should be discarded to avoid field‐testing costs. Better F₁ hybrid performance predictions can be achieved by integrating molecular and F₁ phenotypic data.     

Mapping QTLs for kernel oil content in a tropical maize population

Maize cultivars often have low kernel oil content. To increase the oil content, efficient maize breeding programs have to be developed, which require the knowledge of the inheritance of this trait. Thus, the objective of this research was to map quantitative trait locus (QTLs) and estimate their effects for kernel oil content in a tropical maize population. Two maize inbred lines, contrasting for kernel oil content, were used to develop an F₂ population. Four hundred and eight F₂ plants were self-pollinated, and their kernels (F_2:3 progenies) were used for kernel oil evaluation. A genetic map with 75 microsatellites was developed, and the QTLs were mapped using the composite interval map (CIM); also, estimates of genetic and phenotypic variances, and heritability coefficient were computed. The map presented 10 linkage groups, spanned 1,438.6 cM in length with an average interval of 19.18 cM between adjacent markers. The kernel oil content averaged 58.40 g kg^–1, and the broad-sense heritability was high (h²= 0.98). Thirteen QTLs were mapped, which were distributed into eight chromosomes, and explained 26.64% of the genetic variation. QTLs in chromosomes 1, 5, and 6 contributed the most for kernel oil content. Nine out of 13 QTLs with favorable alleles were from the parental inbred with the highest kernel oil content. The average level of dominance was partial, but gene action of the QTLs ranged from additive to overdominance. Eight out of 13 mapped QTLs were already reported for temperate maize populations.     

Using public databases for genomic prediction of tropical maize lines

In this paper, the aims were (a) to test the usefulness of using genomic and phenotypic information from public databases (open access) to predict genetic values for tropical maize inbred lines regarding plant and ear height; (b) to identify how the population structure, the use of optimized training sets (OTSs) and the amount of information originating from public databases affect the predictive ability. Thus, 29 training sets (TSs) were defined considering three diversity panels: the University of São Paulo (USP—validation set (VS)) and the ASSO and USDA North Central Regional Plant Introduction Station (NCRPIS) (external public panels—predictors), which were divided into four scenarios with different TS configurations. We showed that it is possible to use public datasets as a primary TS and that population structure can modify the predictive abilities of GS. In the four scenarios proposed, very large or very small sets did not provide predictive abilities over 0.53 for GS. However, OTSs composed of 250 individuals were sufficient to achieve predictive abilities over this limit.