Analysis of Per Se and Genetic Diversity of Maize Synthetic Populations for Grain Quality: Implications for Breeding

Synthetic populations of maize (Zea mays L) are low-cost and stable varieties, obtained by cross pollination of a group of inbred lines, local population or hybrids. The main advantage of these populations is that the heterosis does not diminish significantly in F2. In order to complete the research on the combining ability of maize synthetic populations, the objective of this work was to study seven maize synthetic populations, determining their general combining ability (GCA) and specific combining ability (SCA) for kernel starch content, as well as their potential as source populations in breeding programmes.To achieve the proposed objectives, we studied top cross hybrids of the type “inbred line x synthetic population” resulted from the crossing between seven synthetic maize populations and four early inbred lines used as tester. For all experimental conditions, the differences between genotypes were statistically assured for kernel starch content. The experimental years and testing locations have provided conditions for differentiation of genotypes for starch content and interactions between the environment and genotypes were statistically significant, indicating dependence of starch content on environmental conditions. The additive effects for starch content provided by GCA were high for Tu SRR 5DR(6I)(5) and Tu SRR 5D (2I)(2). Non additive effects, corresponding to SCA were high for the following hybrid combinations: TC 233 x TuSyn 1 (3), CO 255 x Tu SRR 5D (2I)(2) and TC 209 x Tu SRR 5DR(6I)(5). In the case of synthetic maize populations, the determinism of starch is influenced equally by GCA and SCA.

Diallel analyses provide estimates of general combining ability (GCA) and specific combining ability (SCA) effects to facilitate efficient utilization of maize (Zea mays L.) inbred lines in breeding programs. Multi-environment trials are commonly conducted to evaluate GCA, SCA, and the stability of grain yield (GY) for single-crosses across environments (E). In these studies the significant GCA × E and SCA × E interactions are usually not examined, yet they indicate that the rankings of the parental inbred lines for GCA and SCA change across environments. The major objective of this study was to quantify stability of GCA and SCA effects of nine maize inbred lines developed in Iran using a 9 × 9 diallel mating design. The 36 single- cross hybrids were evaluated for GY, kernel rows per ear (KR), and kernels per row (KN) at three locations across two years (six environments), using a randomized complete-block design with four replicates. Rank sum and rank variance were used to measure the stability of GCA and SCA for GY across environments, and the Quade's test was used to separate the rank sums. The main effect of E, hybrid, and hybrid × E was significant. Significant GCA and SCA effects were found for the traits, with GCA being more important than SCA for KR, but vice versa for GY and KN. Significant GCA × E and SCA × E were observed for the traits, indicating changes in ranking of GCA and SCA across environments. Inbred lines KE75039 and K1263/2-1 had significant positive GCA for GY. The highest SCA for GY resulted from KE75039 × K2331 cross (15.07 Mg ha−1). Ranking of GCA and SCA for GY across environments exhibited different patterns for the parental inbred lines. Inbreds KE75039 and K1263/2-1 exhibited high stability for GCA across environments for GY, and they contributed only 9% and 7% to GCA × E interaction, respectively. Cross combination KE75039 × K2331 had the highest stability for SCA across the environments, followed by K2331 × K1263/2-1 and K1263/1 × OH43/1-43 crosses. The three other notable cross combinations with relatively stable SCA each had inbred line K1263/1 in common. Combining ability and stability analyses suggest that maize breeding programs in Iran could improve GY by using inbred lines KE75039, K1263/1, and K1263/2-1. It is suggested that new adapted germplasm be introduced to broaden the genetic base of maize germplasm available in Iran.

Knowledge of combining ability and genetic diversity are important prerequisites for the development of outstanding hybrids that are tolerant to high plant density. This work was carried out to assess general combining ability (GCA) and specific combining ability (SCA), identify promising hybrids, estimate genetic diversity among the inbred lines and correlate genetic distance to hybrid performance and SCA across different plant densities. A total of 28 F1 hybrids obtained by crossing eight adverse inbred lines (four local and four exotic) were evaluated under three plant densities 59,500 (D1), 71,400 (D2) and 83,300 (D3) plants ha−1 using spilt plot design with three replications at two locations during 2018 season. Increasing plant density from D1 to D3 significantly decreased leaf angle (LANG), chlorophyll content (CHLC), all ear characteristics and grain yield per plant (GYPP). Contrarily, days to silking (DTS), anthesis–silking interval (ASI), plant height (PLHT), ear height (EHT), and grain yield per hectare (GYPH) were significantly increased. Both additive and non-additive gene actions were involved in the inheritance of all the evaluated traits, but additive gene action was predominant for most traits. Inbred lines L1, L2, and L5 were the best general combiners for increasing grain yield and other desirable traits across research environments. Two hybrids L2 × L5 and L2 × L8 were found to be good specific combiners for ASI, LANG, GYPP and GYPH. Furthermore, these hybrids are ideal for further testing and promotion for commercialization under high plant density. Genetic distance (GD) among pairs of inbred lines ranged from 0.31 to 0.78, with an average of 0.61. Clustering based on molecular GD has effectively grouped the inbred lines according to their origin. No significant correlation was found between GD and both hybrid performance and SCA for grain yield and other traits and proved to be of no predictive value. Nevertheless, SCA could be used to predict the hybrid performance across all plant densities. Overall, this work presents useful information regarding the inheritance of maize grain yield and other important traits under high plant density.

General combining ability (GCA) and specific combining ability (SCA) have been applied in breeding maize and other crops for decades. Sugarcane breeding has seen low genetic gains, which may be attributed to limited exploitation of GCA and SCA effects. The objectives of this study were to determine GCA and SCA effects for cane yield in unselected South African breeding populations, calculate the ratio of SCA to GCA effects, and evaluate the implications for sugarcane breeding. Data from 35 Stage 1 unselected populations was analysed to determine SCA and GCA variance. There was highly significant SCA variance compared to GCA variance across all populations suggesting that SCA effects were more important in sugarcane breeding than GCA effects. The SCA effects were larger than GCA effects suggesting that utilising SCA effects in sugarcane breeding will increase cane yield more than utilizing GCA effects. Between the GCA effects, female variance was greater and more significant than male variance, which was largely non-significant, suggesting potential confounding from the use of polycrosses at crossing where the true identity of the male parent is unknown. The SCA effects can be utilised in sugarcane breeding through the development of heterotic groups and reciprocal recurrent breeding and selection, a strategy routinely followed in maize breeding.

SummaryCombining ability is a measure for selecting elite parents and predicting hybrid performance in plant breeding. However, the genetic basis of combining ability remains unclear and a global view of combining ability from diverse mating designs is lacking. We developed a North Carolina II (NCII) population of 96 Oryza sativa and four male sterile lines to identify parents of greatest value for hybrid rice production. Statistical analyses indicated that general combining ability (GCA) and specific combining ability (SCA) contributed variously to different agronomic traits. In a genome‐wide association study (GWAS) of agronomic traits, GCA and SCA, we identified 34 significant associations (P < 2.39 × 10−7). The superior alleles of GCA loci (Ghd8, GS3 and qSSR4) accumulated in parental lines with high GCA and explained 30.03% of GCA variance in grain yield, indicating that molecular breeding of high GCA parental lines is feasible. The distinct distributions of these QTLs contributed to the differentiation of parental GCA in subpopulations. GWAS of SCA identified 12 more loci that showed dominance on corresponding agronomic traits. We conclude that the accumulation of superior GCA and SCA alleles is an important contributor to heterosis and QTLs that greatly contributed to combining ability in our study would accelerate the identification of elite inbred lines and breeding of super hybrids.

For tropical areas like Brazil, genotype x environment interaction is an important source of variation. Our objectives were to examine the combining abilities and their interaction with environments in ten selected maize (Zea mays L.) inbred lines in diallel crosses and to identify candidates for promising hybrid combinations. Crosses and checks were evaluated through a 7 x 7 triple lattice design at three locations during the 1984/85 season. Several agronomic traits were evaluated, but here only data on ear yield are discussed. Yield data were adjusted for stand variation (correction to 50 plants per plot) and grain moisture (15.5%). Data for ear yield were analysed using an adaptation of Griffing’s method IV for complete diallel crosses, and experiments were repeated in several environments. The means of the crosses over all environments ranged from 6.6 t/ha to 10.3 t/ha. The combining ability analysis of diallel data across environments showed highly significant (P&lt;0.01) effects for environment, general combining ability (GCA), specific combining ability (SCA), and GCA x environment interaction. The SCA x environment interaction was not significant. Results showed that both GCA and SCA were important for this diallel cross. Considering the 13 hybrids that showed higher yields than the commercial hybrid controls, contributions by GCA and SCA effects were 56% and 44%, respectively. On the other hand, selecting only the best five hybrids, SCA effects were always more important than GCA effects for each environment and over all environments.

Combining ability analysis was studied in an 8 × 8 diallel set of black gram genotypes. Variance due to general combining ability (GCA) among the parents for all the traits, and due to specific combining ability (SCA) among the crosses was deduced. Combining ability analysis is an important tool to find out gene actions and it is frequently used by plant breeder to choose parents with high GCA and hybrids with high SCA effects. GCA is associated with additive genetic effects, whereas SCA is taken as the measure of non-additive type of gene actions, arising largely from dominance and epistatic deviations with respect to certain traits. GCA is attributed to additive and additive gene effects epistasis and is theoretically fixable on the other hand; SCA attributed to non-additive gene action due to dominance or epistasis or both and is non-fixable. The presence of non-additive genetic variance is the primary reason for initiating the hybrid programme. GCA variance (σ 2 gca ) was invariably lower than SCA variance (σ 2 sca ) for almost all characters indicating preponderance of non-additive gene action. The percentage of heritability in broad sense was highest with days to maturity (94.78%) followed by days to 50% flowering (94.67%). The gca effect ranged from -0.16 to 0.25. OBG-31 (0.25) had maximum significant positive gca effect followed by Keonjhar Local (0.24). OBG-17 (-0.16) and TU-94-2 (-0.16) witnessed the maximum negative gca effect for yield/plant followed by B-3-8-8 (-0.14). For yield the range of sca varied from -0.64 to 1.02. Among the 28 F 1 hybrids B-3-8-8 × PU-30 (1.02) had the highest sca effect followed by PU-35 × LBG-17 (0.71) and PU-30 × OBG-31 (0.48) for yield/plant. The mean yield per plant was recorded highest in PU-35 × LBG-17 (6.19) followed by OBG-31 × Keonjhar Local (6.16), LBG-17 × OBG-31 (6.15) and B-3-8-8 × PU-30 (6.14). Among 28 cross combinations 11 crosses exhibited positive sca effect (9 were significant) for this character whereas 17 crosses exhibited negative sca effect (13 were significant).

ABSTRACTEarly-maturing maize (Zea Mays L.) germplasm developed from diverse sources has the potential for use in developing maize hybrids suitable for increasing maize production in the dry ecologies of eastern Africa. A diallel study was conducted to estimate general combining ability (GCA) of 12 early-maturing maize inbred lines, identify potential single-cross hybrids for use as parents, assess genetic diversity among the inbred lines, and relate genetic distance to specific combining ability (SCA) and hybrid performance. Sixty-six F1 diallel hybrids were evaluated under optimal and drought stress conditions at four locations in Kenya and Uganda. The parental inbred lines were genotyped using 94 single nucleotide polymorphism (SNP) markers. Additive gene action was more important than nonadditive gene action for inheritance of grain yield (GY) under optimal conditions. However, nonadditive gene effects were more important in the inheritance of GY under drought and across all environments. Inbred lines CKL0722, VL058014, and CZL0724 were among the best with positive GCA effects for GY across both optimal and drought stress conditions. The correlation between SCA and both genetic distance and F1 GY was significant under both drought stress and across all environments. Inbred lines with desirable GCA effects for GY and other agronomic traits and hybrids with good performance under both optimal and drought stress conditions are potential parents for development of various types of high-yielding, stress-tolerant, and early-maturing hybrids.

Ascertaining the relationship of genetic diversity and combining ability would aid the design of a breeding strategy for maize hybrids. Twelve tropical maize inbreds were crossed in a half-diallel to study gene action for yield and other traits and also to determine the relationship between heterosis, combining ability for grain yield and molecular genetic distance in the set of lines. Sixty-six crosses and their 12 parental lines were evaluated in five Kenyan locations in 2011 and 2012. Genetic distances between lines was quantified using 28 SSR markers. General combining ability (GCA) and specific combining ability (SCA) mean squares were both important for grain yield and other traits. However, SCA was more important than GCA for grain yield. Line C92 had the best GCA effects (0.63; p < 0.001), whereas MUL71 × OSU23i (1.11; p < 0.01) had the highest SCA. The correlation coefficient between genetic distance (GD) and SCA was high, positive and significant (0.62; p < 0.001), as was that between GD and heterosis (0.68; p < 0.001), suggesting some predictive value. Cluster analysis based on simple sequence repeat (SSR) markers revealed three groups that were in conformity with SCA and heterosis clusters. This study supports the use of the selected SSR markers for further exploration as a complementary tool to field evaluations for heterotic grouping.

Field experiments were conducted at National Horticultural Research Institute, Bagauda (11°33´N; 8°23´E) in the Sudan Savannah and Institute for Agricultural Research, Samaru (11011´N; 07038’E) in the Northern Guinea Savanna ecological zones of Nigeria. The experiments were conducted between July-October, 2014 rainy season to estimates mean squares for general combining ability (GCA), specific combining ability( SCA) and interaction between general combining ability and location (GCA x location) and specific combining ability and location Interactions ( SCA x location) for agronomic traits and kernel quality traits. The study comprised of 15 hybrid lines, 6 parental lines along with 4 checks which were laid out in partially balanced lattice design with three replications. Analysis of variance revealed significant (P≤ 0.01) GCA for days to maturity (27.74), ear length (8.85cm) , ear diameter (22.25cm), plant height (1501.60cm), field weight (1.70kg), moisture content at harvest (16.48%) and yield (10947553.16 kgha-1) indicating the additive gene action contributing the expression of these traits. The mean squares due to SCA were highly significant (P≤ 0.01) for days to maturity (7.49), ear length (10.06cm), ear diameter (26.96cm) and moisture content at harvest (6.78%) indicating the preponderance of non-additive gene action in the expression of these traits. The mean squares for GCA× location and SCA× location were not significant for all traits except percent whole kernel which shows highly significant GCA × location interaction (2077.97%) and this indicated that, different parental genotypes behaved differently with respect to this trait under different location.Keywords: Agronomic traits, Genetic, General Combining Ability, Inbred lines, Kernel Quality and Specific Combining Ability

Summary General combining ability (G.C.A.) and specific combining ability (S.C.A.) were determined for several characters in diallel crosses of seven non-inbred plants of a late-flowering variety of red clover. Significant differences in G.C.A. and S.C.A. between the seven parents were found for yield in spring, summer and autumn. Significant differences in G.C.A. and S.C.A. for habit, persistence and flowering were also found. Estimates of the variances of G.C.A. and S.C.A. for the seven parents showed that S.C.A. variances were generally higher than G.C.A. variances for visual estimates of yield for these seasons, but for the other characters studied estimates of G.C.A. variances were generally greater than S.C.A. variances. There was also some indication that both G.C.A. and S.C.A. interacted with seasons.

The parasitic weed Striga affects maize on an estimated 20 million ha in Africa, making it a major cause of maize yield reduction from near world average of 4.2 t/ha few decades ago to the present 1.5 t/ha. The objectives of this study were to examine the combining ability of 20 inbred lines and identify single crosses which can be used to develop other hybrids resistant to Striga hermonthica (Del.) Benth. Fourteen female lines were mated using North Carolina Design II with all six males. The resulting 84 F1s along with six commercial checks were evaluated in four separate trials for two rainy seasons during 2010. The trials were conducted on station under both artificial Striga infestation and Striga free environments using standard procedures at the Kibos and Alupe sites, both in the Kenya’s Lake Victoria Basin. Data were recorded on Striga counts, Striga damage rating (SDR), grain yield and other agronomic traits. General combining ability (GCA) and specific combining ability (SCA) effects were computed using SAS. The new F1 hybrids outperformed the commercial checks in grain yield and reaction to Striga. Single crosses JI-30-3/TESTR 151, JI-30-18/TESTR 151, CML206//56/44-6-3-7-1/TESTR 149 and JI-30-18/TESTR 156 gave the highest yield while single cross JI10-28-#/TESTR 136 gave the lowest yield. The ratio of GCA: SCA mean squares exhibited a predominance of additive gene effects in the inheritance of Striga resistance traits as opposed to dominance gene effects. Inbred lines with good GCA for yield and Striga resistance traits were identified as TESTR 151, TESTR 156 and OSU231//56/44-6-4-17-3. The high GCA inbred lines and the superior single crosses will provide a basis for future use perse and also development of three-way and double cross hybrids to be grown in Striga prone areas of the Lake Victoria Basin in eastern Africa. Key words: Maize, Striga hermonthica, general combining ability (GCA), specific combining ability (SCA), host plant resistance, sub-Saharan Africa.

Ear rot, aflatoxin accumulation, and fungal biomass in maize after inoculation with Aspergillus flavus

The present study was aimed at evaluating recombinational variability for combining ability in F4 generation. To assess variability for combining ability, twenty eight F4 (Gossypium barbadense L.) lines were crossed with four common diverse testers (Gossypium hirsutum L.) viz., DH 98-27 (T1), ZCH8 (T2), 178-24 (T3) and DH 18-31 (T4) for use in assessing the variability for combining ability. The entire experimental material was planted on a medium black soil at College of Agriculture, Dharwad under irrigated condition. All the 53 F5 (included Suvin variety as check) barbadense lines, four hirsutum testers and derived F1 crosses along with the straight crosses (Bench Mark Crosses (BMC)) and ruling commercial checks (MRC 6918 Bt check and DCH 32 non Bt check) were sown during kharif 2011 in a Randomized Block Design with two replications and a spacing of 90 cm between rows and 60 cm between the plants within a row. Among the barbadense lines (males), the mean sum of squares (MSS) were not significant for all the characters except mean boll weight, reproductive points on sympodia and seed cotton yield which showed highly significant differences, while number of bolls per plant and ginning outturn exhibited significant differences. Among the hirsutum testers (females) exhibited not significant difference for all the characters except number of bolls per plant and seed cotton yield which recorded highly significant differences, while mean boll weight and transpiration rate showed significant differences. Line x Tester interaction were highly significant differences for number of monopodia per plant, number of bolls per plant, mean boll weight, reproductive points on sympodia, seed index, lint index, photosynthetic rate, stomatal conductance and transpiration rate, while seed cotton yield had significant differences. The estimates of variance due to general combining ability (GCA), variance due to specific combining ability (SCA), the magnitude of SCA variances were greater than GCA variance for all 14 characters and the variance ratio was less than half in these traits, indicating that dominance variance was more than additive variance for these characters. For seed cotton yield, eight lines recorded significant gca effects, of which five lines exhibited positive significant gca effects. The highest gca effect was found by the line DB 533 x DB 534 F4 IPS 8 (363.15). Among the testers, the tester DH 98-27 had positive significant gca effect (94.65) and the tester DH 18-31 showed positive gca effect (35.44), while 178-24 (-77.43) recorded negative significant gca effect. Two crosses manifested positive significant sca effects, of which the cross DH 98-27 X (DB 534 x DB 533 F4 IPS 22) (680.34) recorded the highest positive sca effect. Based on weighted gca method ,the most potential combiners were found to be the lines DB 533 x DB 534 F4 IPS 26, DB 533 x DB 534 F4 IPS 17, DB 533 x DB 534 F4 IPS 8 and DB 533 x DB 534 F4 IPS 32 . Among the testers, the tester DH 18-31 based on weighted gca method is the most potential parent Key word: Recombinational variability, F4 barbadense lines, hirsutum testers, gca, sca

The concentrations of minerals in forages are important in satisfying animal requirements, but little attention has been given to determining these concentrations in forage sorghum [Sorghum bicolor (L.) Moench.] breeding programs. In this 2‐yr study, the objectives were to determine the contents, genetic variability, combining ability effects, and correlations for 12 mineral elements in 49 experimental hybrids of forage sorghum. Mineral elements studied were N, Mg, Si, P, S, Cl, K, Ca, Mn, Fe, Cu, and Zn. General combining ability (GCA) effects exceeded specific combining ability (SCA) effects for all elements except P, Cl, and Fe in females, and S and Cl in males. The GCA and SCA effects in females were low for both Fe and Cu. Genetic ratios, resembling heritability, were higher for GCA than SCA except for Cl and Fe in females, and S and Cl in males. Thirty phenotypic correlations among the 12 elements were statistically significant. Some of the highest values were from the relationships of N with P, S, Cu, and Zn; Mg with Si and Cu; Si with Ca; P with Cu and Zn; S with K; and Cu with Zn. Some of the highest phenotypic correlations calculated among the mineral elements and 12 agronomic and quality traits were the positive association of protein with P, and the negative relationship of height with N and P, Brix of stem juice with K, and neutral detergent fiber with P. Data obtained in these studies show the feasibility of altering the mineral content of forage sorghum by breeding.