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.     

Agronomic performance and combining ability estimates of yellow maize inbred lines under adequate and deficit moisture conditions

Journal of Crop Science and Biotechnology - Breeding for drought tolerance and increased grain yield is vital in mitigating the threat posed by recurrent drought stress on maize production, as well...     

基于产量及主要品质性状的玉米自交系类群划分

用产量及主要品质性状对目前玉米生产上常用的7份自交系和本课题组选育的7份新自交系进行主成分和聚类分析,结果表明：入选的5个主成分因子对总变异的贡献达83.191%,自交系698-3和109可以作为较好的品质育种亲本;而48-2和226则是较好的高产育种亲本.自交系间的遗传距离变异范围为0.342～21.910,根据遗传距离可将14份自交系分为7类,其分类结果与育种实践相吻合.     

Combining ability and GGE biplot analyses for resistance to northern leaf blight in tropical and subtropical elite maize inbred lines

The incidence and severity of northern leaf blight (NLB) disease has increased in Southern Africa in the past years with previously resistant cultivars being affected; implying more resistant sources have to be identified and inheritance of NLB resistance investigated. Therefore, 45 F₁ hybrids generated in a half diallel mating of ten elite maize inbred lines were evaluated in six environments for combining ability, genotype × environment interaction and effect of NLB disease on grain yield. General and specific combining ability (GCA and SCA) were highly significant (P < 0.001) for both NLB disease and grain yield. The GCA/SCA ratio was close to unity for both NLB (0.96) and grain yield (0.89), indicating predominance of additive over non-additive gene action for the traits in these inbred lines. Parent P2 and P7 had good GCA for both NLB disease resistance and high grain yield. The NLB disease ratings on the maize hybrids and inbreds ranged from 1.0 to 8.5 (approximately 0–75 % severity). Negative slope coefficients of the linear regression indicated maize yield decrease of 280–610 kg ha^?1 for NLB final disease severity of about 25–75 %, respectively, stressing the need for resistant cultivars to manage the disease. Genotype and (genotype × environment) (GGE) biplots indicated absence of crossover interaction and revealed positive associations among environments, signifying the suitability of all the environments for disease screening. Therefore, the significant additive effects for NLB disease and grain yield entail that breeding progress would be made through selection and a few disease ‘hot-spot’ sites, such as Cedara (South Africa) and Mpongwe (Zambia) can be used for disease screening.     

Genetic diversity of tropical maize inbred lines combining resistance to Striga hermonthica with drought tolerance using SNP markers

Striga hermonthica and drought are the major stresses limiting maize yields in sub‐Saharan Africa. The search for diverse maize lines’ tolerance to drought and resistance to S. hermonthica (DTSTHR) is very crucial for yield improvement in areas affected by the two stresses. Understanding the genetic diversity among the lines is important to develop cultivars resistant to S. hermonthica and tolerant to drought. The lines were developed from biparental crosses of drought‐tolerant and Striga‐resistant lines. A total of 128 DTSTHR maize lines were characterized using single‐nucleotide polymorphism (SNP) markers. Results of the cluster analysis based on 3297 SNP markers showed four distinct groups consistent with the pedigrees of the lines. Furthermore, model‐based analysis also formed the same groups of the DTSTHR lines. Integrating the pedigree information with combining ability and the SNP analyses may provide defined heterotic groups for maize improvement work in West and Central Africa. These results also help breeders to utilize DTSTHR lines present at IITA for developing biparental crosses without disrupting the heterotic groups they have established in their breeding programmes.     

玉米自交系KA105和91227的配合力分析

用陕A群自交系KA105、91227与甘肃省自育NSS群的14个自交系进行配合力测定,结果表明,KA105与各自交系单株产量的一般配合力(GCA)总体比较高,91227与各自交系单株产量的特殊配合力(SCA)总体比较高,单株产量总配合力(TCA)效应值较高的组合依次为KA105×1802、KA105×F5001、KA105×F0601和91227×1802。各性状的特殊配合力(SCA)的相关性分析表明,单株产量与秃尖长呈负相关,与其他性状均呈正相关,其中与穗位高、出籽率呈极显著正相关。在自交系选系中株高、穗长、出籽率、轴粗、雄穗分枝、穗行数、百粒重和穗粗可以早代进行选择,单株产量、穗位高和行粒数可在高代进行选择。     

Combining ability of maize inbred lines containing genes from Zea diploperennis for resistance to Striga hermonthica (Del.) Benth

Maize ( Zea mays ) is a staple food crop in sub-Saharan Africa, but its production is threatened by Striga hermonthica (Del.) Benth. Transfer of resistance genes from wild relatives may increase resistance to S. hermonthica in tropical maize. The objective of this study was to determine the combining ability of resistance to S. hermonthica among lines containing Zea diploperennis and tropical germplasm. Forty-five diallel crosses of 10 inbred lines were evaluated in an alpha-lattice design with and without artificial Striga infestation at two locations each in the Republic of Benin and Nigeria for 3 years. Results of analyses showed that only general combining ability (GCA) mean square was significant (P = 0.01) for number of emerged Striga plants (NESPP), while both GCA and specific combining ability (SCA) mean squares were significant for host damage score (HDS) and grain yield under Striga infestation. The ratio of GCA to SCA mean squares for the three traits varied from 3.5 to 57.5. Although GCA × environment interaction was significant for the three traits, two inbred lines containing Z. diploperennis (ZD 551) and tropical (TZL TC 87) germplasm had negative and significant GCA effects for NESPP and HDS and positive GCA effects for grain yield under Striga infestation in the two countries. Correlation between NESPP and HDS was strong and significant ( r  = 0.87, P = 0.01). Our results highlight the importance of harnessing useful genes from wild relatives to improve resistance to S. hermonthica in adapted maize germplasm.     

外来玉米种质的抗病、抗逆性选育

摘要：针对我国玉米种质遗传基础狭窄,缺少优良抗性种质资源的问题,利用外引温热带玉米种质改良国内种质的方法,即鉴定并发掘外引玉米种质的优良抗病、抗逆基因,通过与国内骨干系杂交或组建抗病、抗逆群体后,鉴别筛选出含抗病、抗逆基因的材料回交纯合,最终选育出新的自交系用于我国杂交种的培育,从而提高国内玉米的抗病性和抗逆性,并利用外来种质的优良抗逆基因选育出特早熟玉米新品种植9831。     

Heterotic orientation of tropical maize inbred lines towards populations ZM523 and Suwan-1 under downy mildew infestation

Development of top cross varieties with downy mildew (DM) resistance is one approach to enhance maize productivity in tropical lowland environments. The objective of this study was to determine heterotic orientation of 18 advanced maize inbred lines towards popular open pollinated synthetic populations ZM523 and Suwan-1 under the prevalence of DM. The 36 top crosses, four hybrid check varieties and two testers, ZM523 (Z) and Suwan-1 (S) were evaluated in a 6 × 7 α-lattice design with two replications across three environments. General combining ability effects were significant (P ≤ 0.05) for DM resistance and grain yield, suggesting that genes with additive effects were important in controlling the traits. Specific combining ability (SCA) effects were not significant for DM suggesting small influence of DM resistance by the genes with non-additive effects; but SCA effects were significant for grain yield, indicating that non-additive gene effects played a significant role in governing the grain yield. Based on the SCA data, ten lines were grouped with Suwan-1 and eight lines with ZM523. Using the heterosis data, the lines were fitted into three groups that were designated as S, Z and SZ orientation. The lines ML2, ML30 and ML42, which displayed positive heterosis with both testers for grain yield, were allocated to the SZ-group. The lines ML8, ML10, ML25, ML45, and ML48 exhibited positive heterosis with Suwan-1 and were therefore, classified in the Z-group, and line ML19 that showed positive heterosis with ZM523 was fitted in the S-group. The remaining eight lines did not show any significant and positive heterosis with both testers hence they could not be classified based on heterosis data, suggesting that hybrid breeding efficiency could be improved by expanding the number of testers. Line ML42 displayed the highest level of heterosis with both Suwan-1 (32 %) and ZM523 (29 %) and outperformed all the standard check varieties qualifying it as a potential candidate for further testing. Generally, there was consistency of heterotic grouping of the lines using SCA and heterosis data.     

Assessing the suitability of stress tolerant early-maturing maize (Zea mays) inbred lines for hybrid development using combining ability effects and DArTseq markers

Identification of hybrids for commercialization is crucial for sustainable maize production in sub-Saharan Africa (SSA). One hundred and ninety test crosses, 10 tester × tester crosses + 10 hybrid checks were evaluated across 11 environments, 2017 to 2019. Inheritance of grain yield under Striga infestation, optimal and across environments was influenced by additive genetic action, but there was greater influence of nonadditive gene action under drought stress conditions. Nine, seven and two inbreds had significant and positive general combining ability (GCA) effects for grain yield under Striga-infested, optimal and drought stress environments, respectively, and would contribute high grain yield to their progenies. Heterotic grouping methods based on specific and GCA, GCA effects of multiple traits and DArTseq markers classified the inbreds into five, three and two heterotic groups, respectively, across research conditions. The DArTseq markers method that classified the inbred lines into two major heterotic groups and was one of the most efficient methods should be adopted for practical purposes in maize breeding programmes in SSA. Hybrids TZEI 7 × TZdEI 352, TZEI 1238 × TZEI 7 and TZEI 1252 × TZEI 7 had outstanding grain yield under contrasting environments and should be tested on-farm for commercialization in SSA.     

Stability analysis of yield and aflatoxin accumulation resistance in maize using GGE biplot

Journal of Crop Science and Biotechnology - Maize (Zea mays L.) is the most important cereal crop in sub-Saharan Africa. However, its production is constrained by many factors including low yields...     

Mid-parent heterosis and combining ability of European corn borer resistance in maize

Success in breeding maize resistant to the European corn borer has been limited, with the exception of leaf feeding resistance. The inheritance of resistance to leaf, sheath-collar and ear damage in four maize germplasms and their six F₁ crosses was evaluated by diallel analysis. Plants in a completely randomized design were artificially infested at the whorl, anthesis or full silk stage of plant development and were evaluated in the field for insect damage. A damage index based on size, number and location of lesions was calculated for each stage. Stowell's Evergreen (susceptible) had a mean damage index three to six times that of Maiz Amargo (resistant) at the whorl stage and the progeny plants were more resistant than the susceptible parent. Maiz Amargo and its crosses had significantly lower mean indices than Stowell's Evergreen for sheath-collar damage in Year 1 but not Year 2. Zapalote Chico, Maiz Amargo and their cross were significantly less damaged than other genotypes at the full silk stage. Heterosis values indicated an increase in resistance of crosses over the midparent average at all three stages of development. General combining ability (GCA) was highly significant for all types of damage, but specific combining ability was significant only for leaf damage. Based on estimates of GCA, Maiz Amargo was the best source of resistance to leaf and sheath-collar damage and both Zapalote Chico and Maiz Amargo would be good parents for ear damage resistance. Results suggest that resistance at different plant development stages can be combined.     

玉米改良Reid群不同种质自交中代配合力分析

以改良Reid群内7个自交系（8112、478、5003、掖107、7922、97039、B73）组配测交种的自交后代为试验材料，获得68个测交组合，进行配合力测定，结果表明：玉米自交中代各性状的狭义遗传力都较低．其中狭义遗传力相对较高的性状有株高、穗住、穗粗、穗行数、穗重和穗粒重；根据测配结果，选出综合性状优良的自交中代有Al—3—2、B3—10—3、B3—9—1，从而淘汰中代姊妹系间分离出的低配合力自交系，使高配合力个体在下代出现的机率增大，有利于集中选择，减少工作量，选择效果更强。     

Heterotic groups based on yield-specific combining ability data and phylogenetic relationship determined by RAPD markers for 28 tropical maize open pollinated varieties

Twenty eight maize open pollinated varieties (OPVs) were crossed in a diallel scheme and the 378 F₁'s were evaluated in 10 environments in Brazil. Based on yield-specific combining ability data (SCA), these varieties were classified in four heterotic groups. The consistence of the proposed heterotic groups was confirmed comparing intra- and inter-group F₁ values and midparent heterosis. Superior OPVs combinations for use as a source of inbreds in hybrid breeding programs were determined. RAPD markers were used to genotype these varieties. A UPGMA dendogram, based on marker data from 50 primers and 178 polymorphic bands, was obtained. Phylogeny obtained with RAPD markers agreed with known pedigree data. Dent germplasm tended to group separately from flint germplasm. Multidimensional Scaling Analysis on marker data and morphological data showed a higher degree of genetic divergence among the dent germplasm than among the flint germplasm used in this study. Correlation between RAPD marker estimated genetic distance and SCA for yield was low and positive (r = 0.16^**). This revised version was published online in August 2006 with corrections to the Cover Date.