Ear Aspect Research Articles

Genetic diversity assessment of extra-early maturing yellow maize inbreds and hybrid performance inStriga-infested andStriga-free environments

SUMMARYMaize (Zea maysL.), a major staple food crop in West and Central Africa (WCA), is adapted to all agro-ecologies in the sub-region. Its production in the sub-region is greatly constrained by infestation ofStriga hermonthica(Del.) Benth. The performance and stability of the extra-early maturing hybrids, which are particularly adapted to areas with short growing seasons, were assessed underStriga-infested andStriga-free conditions. A total of 120 extra-early hybrids and an open-pollinated variety (OPV) 2008 Syn EE-Y DT STR used as a control were evaluated at two locations each underStriga-infested (Mokwa and Abuja) andStriga-free (Ikenne and Mokwa) conditions in 2010/11. TheStriga-resistant hybrids were characterized by higher grain yield, shorter anthesis–silking interval (ASI), better ear aspect, higher numbers of ears per plant (EPP), lowerStrigadamage rating, and lower number of emergedStrigaplants at 8 and 10 weeks after planting (WAP) compared with the susceptible inbreds. UnderStrigainfestation, mean grain yield ranged from 0·71 to 3·18 t/ha and 1·19 to 3·94 t/ha underStriga-free conditions. The highest yielding hybrid, TZEEI 83×TZEEI 79, out-yielded the OPV control by 157% underStrigainfestation. The hybrids TZEEI 83×TZEEI 79 and TZEEI 67×TZEEI 63 were the highest yielding under bothStriga-infested andStriga-free conditions. The genotype main effect plus genotype×environment interaction (GGE) biplot analysis identified TZEEI 88×TZEEI 79 and TZEEI 81×TZEEI 95 as the ideal hybrids across research environments. Twenty-three pairs of simple sequence repeat (SSR) markers were used to assess the genetic diversity among the inbred lines. The correlations between the SSR-based genetic distance (GD) estimates of parental lines and the means observed in F1hybrid underStrigainfestation and optimum growing conditions were not significant for grain yield and other traits except ASI under optimum conditions. Grain yield of inbreds was not significantly correlated with that of F1hybrids. However, a significant correlation existed between F1hybrid grain yield and heterosis underStrigainfestation (r=0·72,P<0·01). These hybrids have the potential for increasing maize production inStrigaendemic areas in WCA.

Relative changes in genetic variability and correlations in an early-maturing maize population during recurrent selection

Four cycles of S(1) family recurrent selection to improve grain yield and resistance to Striga hermonthica have been completed in TZE-Y Pop STR C(0.) In order to determine whether or not to continue with the recurrent scheme, it was desirable to evaluate the amount of residual genetic variance and associated parameters in the population. The objective of this study was to characterize the relative changes in the levels of the genetic variances, heritability estimates and genetic correlation coefficients, and to predict future gains from selection for grain yield, Striga resistance and other agronomic traits. Fifty S(1) families, derived from each cycle, were evaluated under Striga-infested and Striga-free conditions at Mokwa, Ikenne and Abuja, Nigeria, in 2005 and 2007. Under Striga infestation, genetic variances for grain yield, days to anthesis, plant height and Striga damage generally increased in the advanced cycles of selection. In contrast, the genetic variances for days to silk, anthesis-silking interval, ears per plant, ear aspect and number of emerged Striga plants decreased with selection. The advanced cycles of selection significantly out-yielded the original cycle in both research environments. Heritabilities for grain yield, Striga damage and number of emerged Striga plants were significantly greater than zero. The realized gains from selection for grain yield under Striga infestation (52kgha(-1)cycle(-1)) and Striga-free conditions (130kgha(-1)cycle(-1)) were remarkably lower than the predicted gains (350 and 250kgha(-1)cycle(-1), respectively). Adequate genetic variability exists in cycle 4 of the scheme to ensure future gains from selection.

Combining ability, genetic diversity and heterosis in relation to F1 performance of tropically adapted shrunken (sh2) sweet corn lines

With 6 tablesAbstractThe objectives of this study were to evaluate the importance of heterosis for agronomic and quality traits in shrunken (sh2) sweet corn, assess the usefulness of combining ability to predict the value of parents and their crosses for further genetic improvement and examine whether genetic divergence can predict heterosis or F1 performance. Ten genetically diverse shrunken (sh2) sweet corn inbred lines were used to generate 45 F1s. F1s and parents were evaluated for agronomic and quality traits across environments. Heterosis was more important for yield‐related traits than it was for ear aspects and eating quality. Heterosis for most traits was mostly dependent on dominance genetic effects of parental lines. Parents and F1per se performance were highly correlated with general combining ability effects and mid‐parent values, respectively, for most traits. Hybrid performance for flavour and plant height was significantly but weakly related to simple sequence repeat (SSR)‐based genetic distance (GD). Phenotypic distance (PD), estimated from phenotypic traits was correlated with heterosis for total soluble solids, ear length and flavour.

Correlation and heritability estimates of maize agronomic traits for yield improvement and Striga asiatica (L.) Kuntze tolerance

A study was carried out to estimate percent heritability and correlation coefficients of desirable maize agronomic characters under artificial infestation with Striga lutea. Forty five F1 hybrid maize of varied striga tolerance and their ten parents inbred were evaluated along with two check entries. This was sited in three locations representing different agro ecologies of south western Nigeria in 1999 cropping season. The results showed high and moderate heritability estimates of 94.0 and 40.0 for striga emergence count and striga syndrome rating respectively, while low heritability estimates of 13.0, 11.32, 16.0, 5.70 and 16.22% were obtained for tolerance index, days to tasseling, days silking, kernel rows/cob and grain yield respectively. Genotypic correlation coefficients of striga emergence count with maize agronomic traits were positive and significant, while phenotypic correlation between striga count and other maize agronomic traits were also positively and significantly correlated, except striga count which was negatively correlated with striga syndrome rating. On the other hand, maize ear aspect alone contributed 19.4% to grain yield, while inherent yield loss of 23.0% was estimated if striga is left uncontrolled. Parameter estimates revealed that all striga and maize agronomic traits were positively associated with grain yield except plant and ear heights under striga infestation. Although, implications of these estimates have been discussed, this study affirmed that genotypic and phenotypic correlation coefficients as well as heritability estimates were found suitable as models for yield improvement and selection for S. lutea tolerant genotypes. Key words: Heritability estimates, correlation coefficient, striga tolerance rating, grain yield.

Relationships among Traits of Tropical Early Maize Cultivars in Contrasting Environments

Secondary traits can improve precision with which drought or low soil nitrogen (low‐N) tolerant maize (Zea mays L.) genotypes are identified, compared to measuring only grain yield under each stress. The objective of this study was to identify secondary traits for indirect selection for yield improvement under drought and/or low‐N. Two sets of experiments were conducted at four locations in Nigeria for 2 yr. In the first experiment, cultivars were evaluated under low (30 kg ha−1) and high (90 kg ha−1) N and drought and well‐watered environments in the second experiment. Most reliable traits for selection for yield under drought were ear aspect (EASP), plant aspect (PASP), anthesis‐silking interval (ASI), and number of ears per plant (EPP). Days to anthesis (DYA) and silking (DYS) were the most reliable under well‐watered environments. Under low‐N, most reliable traits were DYA, DYS, stay green characteristic (LDTH), ASI, plant height (PLHT), EPP, EASP, and PASP whereas PLHT, EPP, PASP, and EASP were most reliable traits under high‐N environments. The ASI, EPP, EASP, and PASP were identified as most reliable traits for simultaneous selection of drought and low‐N tolerant genotypes. Under drought, cultivars TZE‐Y DT STR C4, TZE‐W DT STR C4, and TZE Comp 3 DT C1F2 were outstanding and closest to the ideal cultivar. Seven cultivars were closest to the ideal under low‐N, two of which were among the three selected under drought stress. Faster progress in selecting for improved grain yield is possible using EPP, EASP, PASP, and ASI under either drought or low‐N.

Cultivar evaluation and trait analysis of tropical early maturing maize under Striga-infested and Striga-free environments

Striga hermonthica is a major constraint to maize ( Zea mays L.) production in sub-Saharan Africa. The use of secondary traits that have high heritability and genetic correlation with grain yield can improve the precision with which Striga resistant genotypes are identified. Fifteen early cultivars were evaluated under Striga-infested and Striga-free conditions for 2 years at Mokwa and Abuja, Nigeria. The objective was to examine their performance based on multiple traits under stress and non-stress conditions and analyze the interrelationship among traits using genotype-by-trait (GT) biplot so as to assess the value of traits used in the base index for selection for Striga resistance and improved grain yield (YLD). TZE-W DT STR C 4 had the best performance based on multiple traits while TZE-W DT STR C 4, TZE-Y DT STR C 4, Multicob Early DT, and TZE-W DT STR QPM C 0 were the closest to the ideal cultivar when Striga infested. Ears per plant, Striga damage at 8 and 10 weeks after planting, and ear aspect (EASP) were the most reliable traits for selecting for resistant genotypes. Striga emergence count at 8 and 10 weeks after planting were not among the reliable traits identified for selection for improved grain yield and their inclusion in the base index needs to be further verified. EASP had high correlation with grain yield and was one of the most reliable traits for selection for increased grain yield under Striga infestation and should be included in the index.

Participatory selection and characterization of quality protein maize (QPM) varieties in Savanna agro- ecological region of DR-Congo

Maize (Zea mays L.) is a major cereal crop for human nutrition in the Democratic Republic of Congo (DR- Congo). Prevailing normal maize is deficient in two essential amino acids, lysine and tryptophan. Participatory variety selection was applied to select diversified quality protein maize (QPM) varieties that possess farmers’ preferred plant and grain traits. The varieties were planted with and without chemical fertilization. Selection was based primarily on agronomic traits such as time to maturity, plant and ear aspect, disease and insect resistance, yield and yield components as well as flour quality. There were significant differences among QPM varieties for several agronomic traits. The use of participatory approach in agricultural research allowed selection of one QPM, (QPMSRSYNTH), and one normal improved maize (AK9331-DMR-ESR-Y) for their yield advantage over currently released normal maize varieties in more than one criterion. The adoption of these newly introduced varieties is expected to be high since they were selected based on farmer’s preference. Key words: Quality protein maize, participatory varietal selection, DR-Congo.

Effects of Recurrent Selection for Grain Yield and Striga Resistance in an Extra‐Early Maize Population

ABSTRACTStriga hermonthica (Del.) Benth threatens maize (Zea mays L.) production in sub‐Saharan Africa. In an extra‐early population, S1 families derived from four cycles of recurrent selection for grain yield and Striga resistance were evaluated with and without Striga infestation at three locations in Nigeria for 2 yr to determine relative changes in genetic variances, heritabilities, and genetic correlations for yield and other traits. Under infestation, yield was not correlated with other traits at C0 but was significantly correlated with ears per plant (EPP), Striga damage, and emerged Striga plants in advanced cycles. Genetic correlations between yield and most traits were significant in C0 when Striga‐free but was reduced in advanced cycles. Genetic variances and heritabilities for yield and ear aspect increased in advanced cycles. Genetic variances decreased with selection for emerged Striga counts and EPP under infestation. A response to selection for improved yield, Striga emergence and EPP is expected in subsequent cycles. Low genetic variances and heritabilities for Striga damage and low predicted gain cycle−1 for all traits except numbers of emerged Striga plants suggest a need to introgress novel resistance genes into the population for faster progress from selection for increased yield.

Combining ability of early-maturing quality protein maize inbred lines adapted to Eastern Africa

Adapted early-maturing quality protein maize (QPM) hybrids with high grain yield potential in Eastern Africa would benefit maize farmers through increased grain production and subsequently higher income but they are not widely available. Fourteen early-maturing QPM inbred lines developed from POOL15QPM-SR, were crossed using the diallel mating design. The resulting single-cross hybrids were evaluated under six well-watered, drought stress and low nitrogen conditions at six locations in Eastern Africa. The objectives were to assess the grain yield potential of early-maturing F 1 QPM hybrids, estimate the general combining ability (GCA) and specific combining ability (SCA) for grain yield and other agronomic traits and determine the relationship between grain yield and other agronomic traits of the QPM hybrids. Days to anthesis, days to silking, anthesis–silking interval, ears per plant, root and stalk lodging, ear aspect, and grain yield were measured. Variation among hybrids was significant for all traits except root lodging. The best single-cross hybrid across environments was POOL15QPMFS538-B-3-B-B × POOL15QPMFS462-B-4-B-B (5.30 t ha −1). Mean squares due to GCA were significant, whereas mean squares due to SCA were not for measured traits indicating that additive genetic effects were much more important in this set of genotypes. Inbred line POOL15QPMFS538-B-3-B-B exhibited very good GCA effects for grain yield in well-watered environments and across environments for grain yield (0.74 t ha −1). Inbred line Pool15QPMFS478-B-3-B-B had the best GCA effect for grain yield under managed drought stress (0.26 t ha −1), while inbred line POOL15QPMFS319-B-2-B-B had the best GCA effect (−1.11 days) for reduced days to anthesis across environments. The new QPM inbred lines with desirable traits could be used to improve grain yield and protein quality of maize breeding programs in Eastern Africa.

Performance stability of maize genotypes across diverse hill environments in Nepal

The national maize improvement program in Nepal regularly receives elite maize (Zea mays L.) genotypes from CIMMYT and other countries and tests them for their performance stability in highly diverse environments. Studies were conducted on research stations and farmers’ fields at five sites in three years to determine performance stability of exotic maize genotypes. Replicated on-station and on-farm studies were conducted using 25 and 10 genotypes, respectively, including a local check and an improved check (Manakamana-3), in 2004–2006. We analyzed grain yield, days to flowering, plant and ear height, plant population, husk cover, and plant and ear aspect. Stability and genotype superiority for grain yield was determined using genotype and genotype × environment (GGE) biplot analysis that compares among a set of genotypes with a reference ‘ideal’ genotype, which has the highest average value of all genotypes and is absolutely stable. Several genotypes produced significantly higher grain yield than the local check. Four genotypes (‘Across9942 × Across9944’, ‘Open Ended White Hill Population’, ‘Population 44C10’ and ‘ZM621’), that produced significantly higher grain yield than the improved check, also had other agronomic traits (days to flowering, plant and ear height, number of ears, resistance to leaf blight, plant and ear aspect and husk cover tightness) equal to or better than the improved check. GGE-biplot analysis showed that Across9942 × Across9944 and ZM621 were the most superior genotypes in the on-station and on-farm trials, respectively. The findings from this study provide new information on the stability of the maize genotypes that are also adapted to other regions of the world. Such information could be useful for maize improvement program for the highlands in Nepal and other similar environments.

Gene action controlling grain yield and secondary traits in southern African maize hybrids under drought and non-drought environments

Breeding maize hybrids for drought tolerance would significantly reduce yield loss due to drought in southern Africa. Mode of gene action controlling yield and secondary traits was investigated by mating 27 inbred lines, in sets according to a North Carolina design II scheme. The resultant 72 experimental and eight commercial hybrids were evaluated in 8 × 10 α-lattice design with two replications, in four drought and two non-drought environments. Under drought conditions, only general combining ability (GCA) variance was significant for yield, indicating predominance of additive effects. In non-drought environments, both GCA and specific combining ability variances were significant for yield, indicating importance of additive and non-additive effects, respectively. Contributions of male (GCAm) and female GCA (GCAf) effects to hybrids varied depending on the trait and conditions. Superior GCAf to GCAm effects for yield under drought conditions, and for ASI, prolificacy and ear aspect under both drought and non-drought conditions, suggested that maternal effects might have modified these traits. Larger GCAm than GCAf for ASI and silking dates under normal conditions indicated that paternal genotypes played a greater role in determining these traits. Similar GCAm and GCAf for yield under normal conditions, silking and anthesis dates under drought indicated that both parents made similar contribution to hybrids. Possibly, complications due to modification of traits by cytoplasmic effects and cross-over G × E for yield might partly explain why only a few drought tolerant hybrids have been developed. Practical implications of these findings in breeding drought tolerance in maize are discussed.

Response to Recurrent Selection for Resistance to Striga hermonthica (Del.) Benth in a Tropical Maize Population

ABSTRACTStriga hermonthica (Del.) Benth is an obligate root parasite infecting maize (Zea mays L.) and causing considerable yield losses in Africa. Few studies have been conducted to determine the effectiveness of recurrent selection for improving resistance to S. hermonthica in maize. The objective of this study was to evaluate genetic gain achieved in a composite subjected to six cycles of selection under S. hermonthica infestation. The selection cycles and checks were evaluated with and without S. hermonthica infestation at two locations in Nigeria for 2 yr. Selection for improved performance under S. hermonthica infestation significantly increased grain yield by 24% cycle‐1 and ears per plant by 9% cycle‐1. At the same time, the gain per cycle was −7% for relative yield loss, −5% for host damage rating, −9% for emerged S. hermonthica plants, −4% for anthesis–silking interval, and −5% for ear aspect. Selection under S. hermonthica infestation was accompanied by a concomitant increase in grain yield and improvement in plant aspect and ear aspect without S. hermonthica infestation. The observed progress in performance under S. hermonthica infestation demonstrates the effectiveness of recurrent selection for increasing polygenetic resistance against the parasite in tropical populations.

Genetic Analysis of Resistance to Gray Leaf Spot of Midaltitude Maize Inbred Lines

Gray leaf spot (GLS), caused by Cercospora zeae-maydis Tehon & E.Y. Daniels, poses a serious threat to maize (Zea mays L.) production in sub-Saharan Africa. The knowledge of inheritance of resistance to GLS in new inbred lines would be useful for efficient development of hybrids and synthetics. In this study, we determined (i) the mode of inheritance of resistance to GLS in midaltitude inbred lines, (ii) the effect of different doses of resistance to GLS in parents on the levels of resistance of their hybrids, and (iii) heterotic effects for GLS resistance. Ninety-six hybrids from 24 inbreds were produced using the Design II mating scheme. The parents and the hybrids were evaluated in separate trials in five environments in Nigeria. Both general (GCA) and specific (SCA) combining abilities were significant (P < 0.001), with GCA accounting for >70% of the variation for GLS scores, days to silking, plant height, ear height, ear aspect, and ear rot; 68% for grain yield; and 60% for plant aspect (visual phenotypic appeal) score. Predominantly, additive genetic effects influenced resistance to GLS and other traits in maize hybrids. Most of the crosses with one or more resistant parents produced resistant hybrids, whereas most crosses between susceptible lines generated susceptible hybrids. Prediction of GLS in hybrids using midparent values resulted in a R2 value of 0.53 for GLS disease score recorded 38 d after midsilking (GLS Score2). Negative heterosis observed in 75 hybrids for GLS Score2 suggested that resistance to GLS could be improved in midaltitude hybrids.

Book Review: Infections in Childhood. Ear, Nose and Throat Aspects

Book Review: Infections in Childhood. Ear, Nose and Throat Aspects

Field performance of Shrunken-2maize hybrids and its relationship with genetic distance of their inbred parents

Maize (Zea mays L.) is an important crop in West and Central Africa, where flint and dent types are the widely cultivated and used as food, feed and raw materials in industries. Sweet maize, the generic term used for maize types with elevated levels of sugar in their kernels, is increasingly popular in Nigeria and other countries of West Africa. This study evaluated the field performance of some super-sweet shrunken-2 (sh-2 ) maize hybrids and determined its relationship with SSR-based genetic distance of their inbred parents. A total of 21 shrunken-2 maize hybrids and seven shrunken-2 maize hybrid checks were evaluated. Analysis of variance was carried out on data collected and correlation analysis between the genetic distance of parental lines and agronomic traits of their hybrids. There were significant differences (P &lt; 0.01) among the hybrids for all agronomic traits studied. Field emergence ranged from 28.2 to 97.4%; while fresh cob weight and husk cover (1-9) ranged from 0.05 to 0.17 and 2.7 to 6.7 g plant-1, respectively. Among the hybrids, UI1 x UI75 was the most promising, combining high emergence with high fresh cob yield, good husk cover, resistance to endemic foliar diseases, good plant aspect and moderate ear aspect. Genetic distance between parental inbred lines was not useful for predicting hybrid performance among the sets of shrunken-2 inbred lines considered. The parental lines, however, have potential for use in shrunken-2 maize breeding programmes.