Identification of superior parents and hybrids for improving canola production under optimum and late sowing conditions

Major advancement in canola breeding depends on heterotic hybrids that require high general combining ability (GCA) and specific combining ability (SCA) inbred lines. In order to estimate heritability, gene action type, GCA, SCA and heterosis and to identify superior hybrids with wider adaptation to cold, one hundred canola hybrids were produced by crossing 10 lines and 10 testers in a Line?×?Tester mating design. The F₁ and F₂ generations were sown in α-lattice design in 2012 and 2013 growing seasons under optimum (early October) and late sowing (early November) conditions to be evaluated for days to flowering, days to physiological maturity, number of pods per plant, number of seeds per pod, thousand seed weight, seed yield and leaf electrical conductivity. The combined analysis indicated sufficient genetic diversity in the population and significant difference between two sowing date. The Line?×?Tester analysis presented significant GCA and SCA effects for all studied traits across optimum and late sowing conditions. The main gene action type was found to be non-additive, especially incomplete dominance and over-dominance in both conditions. Narrow-sense heritability ranged from low to moderate whereas broad-sense heritability was recorded more than 60% for all of the studied traits in both generations and conditions. The average heterosis in F₂ population for all studied traits was lower than that in F₁ representing this fact that heterosis is generally related to the heterozygosity at the population level and poorly correlated with heterozygosity at the individual level.     

Genetic Analysis of Grain Yield and Other Traits of Early‐Maturing Maize Inbreds under Drought and Well‐Watered Conditions

Maize (Zea mays L.) is an important staple food crop in West and Central Africa (WCA). However, its production is constrained by drought. Knowledge and understanding of the genetics of hybrid performance under drought is invaluable in designing breeding strategies for improving maize yield. One hundred and fifty hybrids obtained by crossing 30 inbreds in sets using the North Carolina Design II plus six checks were evaluated under drought and well‐watered conditions for 2 years at three locations in Nigeria. The objectives of the studies were to (i) determine the mode of gene action controlling grain yield and other important agronomic traits of selected early inbred lines, (ii) examine the relationship between per se performance of inbreds and their hybrids and (iii) identify appropriate testers for maize breeding programmes in WCA. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P < 0.01) for grain yield and other traits under the research environments. The GCA accounted for 64.5 % and 62.3 % of the total variation for grain yield under drought and well‐watered conditions, indicating that additive gene action largely controlled the inheritance of grain yield of the hybrids. Narrow‐sense heritability was 67 % for grain yield under drought and 49 % under well‐watered conditions. The correlations between traits of early‐maturing parental lines and their hybrids were significant (P < 0.01) under drought, well‐watered and across environments. Mid‐parent and better‐parent heterosis for grain yield were 45.3 % and 18.4 % under drought stress and 111.9 % and 102.6 % under well‐watered conditions. Inbreds TZEI 31, TZEI 17, TZEI 129 and TZEI 157 were identified as the best testers. Drought‐tolerant hybrids with superior performance under stress and non‐stress conditions could be obtained through the accumulation of favourable alleles for drought tolerance in both parental lines.     

Combining ability and heterotic patterns of extra-early maturing white maize inbreds with genes from <Emphasis Type="Italic">Zea diploperennis</Emphasis> under multiple environments

Low soil nitrogen (Low N), Striga hermonthica and recurrent drought are major constraints to maize production and productivity in sub-Saharan Africa (SSA). Only a few extra-early maturing hybrids with combined tolerance to drought, Striga and low N have been commercialized in SSA. The objectives of the study were to determine the general combining ability (GCA) and specific combining ability (SCA) effects of grain yield and other traits, classify the inbreds into heterotic groups using the SCA effects of grain yield, and the heterotic group’s SCA and GCA of grain yield (HSGCA) methods, and examine the performance of hybrids under contrasting environments. Sixty-three extra-early white maize inbred lines containing genes from Zea diploperennis were crossed to four elite testers to obtain 252 single-cross hybrids and evaluated together with four checks at four locations for 2 years under drought, Striga-infested, low N and optimal environments in Nigeria. The GCA and SCA effects were significant (P ≤ 0.01) with preponderance of GCA over SCA effects for all measured traits indicating that additive genetic effects were predominant in the lines under all the contrasting environments. The HSGCA was more efficient than the SCA method in the classification of the inbreds into heterotic groups. The hybrids TZdEEI 74 × TZEEI 13 and TZdEEI 74 × TZEEI 29 were high yielding and most stable across research environments. These hybrids should be further evaluated in on-farm trials to confirm the consistency of performance for commercialization in SSA.     

Combining ability for rancidity and associated traits in pearl millet (Pennisetum glaucum)

Pearl millet occupies an important place in attaining nutritional security in marginal areas; however, as it develops off-flavours, it is less preferred by food industry. The objective of the current study was to determine the variations in rancidity-related traits and estimate the combining ability of inbreds and hybrids for these traits under varied environmental conditions. In this study, 32 hybrids were developed from eight lines and four testers using line × tester mating design and evaluated along with parents and checks 86M86 and HHB 67 for yield and rancidity-associated traits in three environments. The hybrids L7T2 and L6T1 are identified as promising hybrids for grain yield and rancidity. Higher variance due to specific combining ability and predictability ratio for grain yield and rancidity-associated characters indicate the predominance of non-additive gene action. The tester T1 recorded a significant negative GCA effect with low alcoholic acidity. A significant and positive SCA for grain yield was observed in L3T1 and L7T2, whereas for rancidity in L5T4. Alcoholic acidity showed a significant positive association with 1000 seed weight, lipase and lipoxygenase in parents and negative association with 1000 seed weight in hybrids.     

Heterosis and combining ability vis-à-vis association for green fruit yield and component traits involving male sterile lines in chilli (Capsicum annuum) under wet temperate zone of North Western Himalayas

Fourteen genetically diverse inbred lines comprising of four genic male sterile lines and 10 often pollinated lines as testers were crossed following ‘line × tester’ mating design to generate 40 F₁s. These F₁s, parents and check ‘CH-27’ were evaluated in α-lattice square design, replicated thrice during summer seasons of 2020 and 2021. The male sterile line DPChMS 9-2 was good general combiner for marketable fruit yield and eight other component traits while testers namely, DPCh 10, PBC 535, VVG, Him Palam Mirch-2 and DPCh 40 showed significant GCA for majority of yield related traits. The hybrids DPChMS 9-2 × HPM-2, DPChMS 9-2 × DPCh 40, DPChMS 9-2 × DPCh 101, DPChMS 9-2× VVG and DPChMS 26-1× HPM-1 were the most desirable based on specific combining ability (SCA) and economic heterosis for fruit yield and other important traits. Heterosis was positively correlated with SCA indicating prediction of potential hybrids can be made based on both these parameters simultaneously. Present study provides an opportunity to exploit top hybrids for stability and commercial cultivation.     

Combining ability estimates for yield and fibre quality traits in 4 × 13 line × tester crosses of Gossypium hirsutum

The aim of this study was to estimate the general combining ability of the parents and specific combining ability of hybrids considered for the development of high yielding and better quality cultivars. Seventeen genotypes and 52 F₁ hybrids obtained by crossing 4 lines and 13 testers in line × tester mating system during 2003 were sown in randomized complete block design in 2004. Line × Tester analysis revealed significant GCA and SCA effects for all the traits except fibre elongation. Preponderance of non-additive gene action was obtained for seed cotton yield per␣plant and majority of its component traits including fibre traits. Among the parents: PIL-8 for days to 50% flowering, CCH-526612 for boll weight, CITH-77 for number of open bolls per plant and CNH-36 for seed cotton yield per plant were detected with higher general combining ability. Parent, CCH-526612 for 2.5% span length, fibre strength and fibre elongation and AKH-9618 for micronaire value, fibre strength and fibre elongation were good combiners for fibre quality traits. The F₁s achieved high seed cotton yield by producing more number of open bolls. The high yielding hybrids with acceptable fibre quality traits were: CISV-24 × LH-1995, H-1242 × PIL-8 and RS-2283 × SGNR-2 deducted with significant SCA effects for seed cotton yield and fibre characteristics; 2.5% span length and fibre strength. These cross combinations involved at least one parent with high or average GCA effect for a particular trait.     

Estimates of combining ability for resistance of winter rye to Fusarium culmorum head blight

Summary Head blight caused by Fusarium culmorum and F. graminearum is damaging in all winter rye (Secale cereale L.) growing areas. For hybrid breeding, the relative magnitude of general (GCA) and specific combining ability (SCA) is a crucial parameter for developing appropriate selection procedures. Forty single-cross hybrids were produced by crossing six and seven inbred lines of the Petkus and Carsten gene pool, respectively, in a factorial design. Hybrids were evaluated in two years with artificial F. culmorum inoculation. Resistance traits were head blight rating and grain weight relative to the non-inoculated control. Both resistance traits were closely correlated across both years (r-0.8, P=0.01). Significant genotypic variation was found for both traits with medium to high estimates of heritability (h²=0.6-0.8). Components of variance for GCA were, across years, 10 and 6 times larger than those for SCA for head blight rating and relative grain weight, respectively. Significant SCA effects were found for 15 to 20% of all cross combinations across both traits in each year. SCA effects were, however, inconsistent over years leading to a high SCA-year interaction. In conclusion, resistance to Fusarium head blight among the interpool hybrids tested was conditioned mainly by additive gene action that could be utilized by recurrent selection in multi-environment trials.Abbreviations GCA general combining ability - SCA specific combining ability     

Combining ability, heterotic patterns and genetic diversity of extra-early yellow inbreds under contrasting environments

Information on the combining ability, heterotic patterns and genetic diversity of maize (Zea mays L.) inbreds is crucial for the success of a hybrid program targeting the stress environments of West Africa (WA). Studies were conducted in 2011 at four locations in Nigeria to (i) determine the combining ability of 20 extra-early yellow inbred lines, (ii) classify the inbred lines into heterotic groups, and (iii) determine the genetic diversity among the lines. General combining ability (GCA) effects were greater than specific combining ability (SCA) effects across test environments suggesting that additive gene action was more important than the nonadditive in the set of inbred lines. The lines were classified into four heterotic groups based on SCA effects, and three groups based on heterotic groups’ specific and GCA, the GCA effects of multiple traits of inbred lines and molecular markers. TZEEI 79, TZEEI 67, and TZEEI 81 were the best inbred testers while TZEEI 95 × TZEEI 79 was the best single-cross tester. TZEEI 88 × TZEEI 66 and TZEEI 96 × TZEEI 73 were identified as ideal hybrids for further testing, promotion for adoption and commercialization in WA.     

Construction of a crop—wild hybrid population for broadening genetic diversity in cultivated sunflower and first evaluation of its combining ability: the concept of neodomestication

The genetic base of sunflower elite lines is very narrow, due to many years of selection and breeding. To broaden the genetic diversity of the cultivated sunflower, in 1995 73 wild sunflower populations were crossed with 3 cultivated lines (Testers), and 219 hybrid offspring’s were evaluated in the field. GCA and SCA effects were computed suggesting for all traits a genetic potential for improvement through selection. Study of the hybrids revealed that the wild accessions bear different genetic abilities to combine with the testers for traits of morphological architecture, phenology and yield (seed weight and seed oil). The variance due to GCA and SCA showed that gene action was additive for days to flowering, branching and plant height. Genotypes derived from the same geographic origin may have either good or poor general combing ability. The correlation between GCA and per se genotype performance was positive for all traits except for seed oil content. This was the first attempt to evaluate wild-cultivated hybrids in sunflower on a large scale and will be the starting point for the management of hybrid Helianthus annuus populations for breeding. GCA and SCA estimations will facilitate the definition of strategies to manage and exploit the natural diversity for this crop.     

Genetic analysis of thrips resistance in cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> [L.] Walp.)

Flower bud thrips, Megalurothrips sjostedti is the most severe field pest of cowpea that causes massive flower abortion which eventually results to substantial yield reduction in Africa. There is paucity of information on the mode of gene actions controlling inheritance of resistance to flower bud thrips in cowpea in the literature. The objectives of study were to assess the genetic variability for thrips resistance among the cowpea germplasm, determined the mode of inheritance of genes that conferred resistance and both broad and narrow-sense heritability estimates for the inheritance of thrips resistance in cowpea. Twelve cowpea lines were used in crosses in the screen house at IITA, Ibadan. The mating was accomplished using North Carolina design II to generate 48F₁ hybrids, which were eventually evaluated with the parents. Data on number of peduncles, number of pods and number of thrips per flower were recorded and subjected to analysis of variance using random model by SAS 9.2. Significant variability was observed for most agronomic and thrip-adaptive traits among the cowpea germplasm, parental-lines and F₁ genotypes evaluated. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P < 0.01) for number of pods per plant and other traits under the research environment. The GCA effect accounted for 68.82–80.07% of the total variation among hybrids for all traits except days to flowering; SCA explained less than 50% of the total variation. Narrow-sense heritability estimates ranged from 7.53 (days to flower) to 63.92% (number of peduncles per plant). Additive gene action largely controlled the inheritance of yield components and other traits under thrips infestation and these traits were moderately heritable.     

Inheritance of resistance to Fusarium wilt and yield traits in pigeonpea

Fusarium wilt is the main pigeonpea production constraint in Malawi. The purpose of the study was to understand the nature and mechanism of inheritance of F. wilt resistance, yield and secondary traits in pigeonpea. 48 crosses were generated in a 12 lines × 4 testers mating scheme. Some F₁ plants were selfed for segregation analysis for inheritance pattern of resistance, while others were evaluated for resistance, yield and secondary traits. There were significant variations among F₁ plants for F. wilt, days to 50 % flowering, seed/pod, and number of secondary branches. Specific combining ability (SCA) effects were predominant for F. wilt, days to 50 % flowering and number of secondary branches. The general combining ability (GCA) effects, mainly due to maternal genotypes, were preponderant for yield and other secondary traits. The significance of GCA and SCA effects suggested that variations were due to additive gene action in both the testers and parental lines arising from their interactions, and the dominance effects due to interactions of the parental lines. The χ² analysis suggested dominant patterns of inheritance for wilt in most of the F₂ populations. The segregation ratios of 3:1, 15:1, and 9:7 suggested the involvement of single or two independent/complementary dominant genes in the test donors. Involvement of a few genes governing wilt resistance suggested the ease of breeding for this trait. Pedigree breeding method would be recommended for incorporating various traits in pigeonpea.     

Estimating gene action,combining ability and heterosis for grain yield and agronomic traits in extra-early maturing yellow maize single-crosses under three agro-ecologies of Ghana

Maize (Zea mays L.) is the most important cereal crop produced in Ghana. However, yield of the crop is generally low, producing just about 1.7 t/ha. The low yield is attributed to continuous use of local/unimproved varieties. Generally, hybrid varieties have proven to out-yield the local/unimproved varieties due to improved vigour. Development of hybrid varieties depend on good understanding of combining ability and inheritance of important quantitative traits such as grain yield (GY). 45 half-diallel crosses generated from 10 extra-early maturing yellow inbred lines were evaluated in 2015 under rain-fed conditions. The objectives were to determine the genetic control, breeding value and estimate heritability for GY and agronomic traits of the inbred lines under contrasting growing environments in Ghana. General combining ability (GCA) and specific combining ability (SCA) were important in the inheritance of GY and agronomic traits of the inbred lines. However, GCA was more important than SCA across environments to suggest that additive gene action was more important than non-additive gene action in the inheritance of GY and agronomic traits in the inbred lines. High broad-sense heritability, for GY and other agronomic traits indicated preponderance of additive gene action in trait expression, thus, selection based on phenotypic expression could be feasible. Inbred lines P1, P4 and P8 were good combiners for high GY. The genotype, P4 × P8, was identified as the ideal and most yielding single-cross hybrid across research environments and should be further tested on-farm before commercialization.     

Advanced cycle pedigree breeding in sunflower. II: combining ability for oil yield and its components

Combining ability is one of the most important information breeders use to identify superior inbred lines on the basis of their performance in hybrid combinations. The objectives of our study were (i) to quantify the importance of general combining ability (GCA) and specific combining ability (SCA) variances for seed yield, oil content and oil yield; and (ii) estimate GCA and SCA effects of seed yield, oil content and oil yield of inbred lines developed from advanced cycle pedigree breeding populations in sunflower. A total of 109 female S₃ cytoplasmic male sterile (CMS) lines from four bi-parental populations in advanced cycle pedigree breeding were crossed with two testers to form 218 testcross hybrids (TCHs). The TCHs were then evaluated in three environments. Variance component analysis results showed predominance of σ²gca over σ²sca for seed yield and oil yield indicating that superior TCHs can be identified based on positive and significant GCA effects of the female lines. For oil content σ²sca was predominant over σ²gca indicating that selecting for TCHs with high oil content would be best among line × tester combinations and not among female S₃CMS lines per se. The proportion of GCA and SCA effects in the best five TCHs in each breeding population also confirmed the predominance of GCA effects over SCA effects for seed yield and oil yield while for oil content both GCA and SCA effects appear to be important, with SCA effects having more influence than GCA. The best selection strategy would therefore be to capture the GCA in the early stages of inbreeding and then SCA for the few unique combinations when lines are almost fixed.     

Genetic analysis of mechanisms associated with inheritance of resistance to sheath rot of rice

Understanding genetic mechanisms controlling inheritance of disease resistance traits is essential in breeding investigations targeting development of resistant genotypes. Using North Carolina design II, 32 F₁ hybrids were generated by crossing eight susceptible to four resistant parents and submitted for field evaluation. The analysis of general and specific combining ability (GCA and SCA) indicated involvement of additive and non‐additive gene action controlling inheritance of horizontal resistance to sheath rot of rice. High GCA/SCA ratio and high heritability estimates revealed additive effects and were more predominant than none additive ones. The level of dominance indicated dominant genes was more important than recessive genes. Estimates of GCA and SCA analysis suggested that crop improvement programmes should be directed towards selection of superior parents or good combiners, emphasizing on GCA. As far as source of resistance is concerned, most promising genotypes were Cyicaro, Yunertian and Yunkeng. The predominance of additive genetic effects together with the relevance of dominant genes suggested possibilities of improving the resistance by introgression of resistance genes through recurrent selection coupled with phenotypic selection.     

Improving sweet sorghum for enhanced juice traits and biomass

Sweet sorghum (Sorghum bicolor [L.] Moench) is a prospective bioethanol feedstock source. Four high-biomass and sweet sorghum male lines and three grain sorghum female lines were intercrossed using Design II mating. Parents and hybrids were evaluated to (a) identify genetic sources to improve biofuel traits, and (b) determine the inheritance of biofuel and morpho-agronomic traits. Total soluble sugars (TSS) per plant were determined using juice weight (JW) and Brix (°Bx). Plant height (PH), biomass (BM) and stalk diameter (SD) were also measured. Mean hybrid performance for PH, JW, TSS and BM was higher than the male parent means. Three male parents exhibited positive and significant general combining ability (GCA) for at least three traits. Among males, PI185672 showed the highest GCA for PH, °Bx and BM, while No. 08 exhibited the greatest GCA for JW and TSS. Most hybrids exhibited overdominance-driven high-parent heterosis for all traits except SD. Trait broad-sense heritability ranged from 0.71 (BM) to 0.93 (PH). Results revealed that biofuel traits could be substantially improved through breeding, which will contribute to enhanced bioethanol production.     

Combining ability and gene action for maturity and agronomic traits in different heterotic groups of maize inbred lines and their diallel crosses

Combining ability information is necessary for selection of suitable advanced lines for hybridization and identification of promising hybrids for development of improved varieties. A number of 14 maize (Zea mays L.) inbred lines and 91 related crosses were evaluated over two years, 2008 and 2009, in a temperate-zone of Iran. The objectives of the study were to identify the best general and specific combiners, heterosis and type of gene actions responsible for agronomic traits. Except for grain yield and growing degree day to milky, significant general (GCA) and specific (SCA) combining ability were observed for all traits. The Baker ratio for plant height (0.15), ear height (0.26), growing degree day to milky stage (0.04), and grain yield (0.002) showed the predominance of non-additive gene effects in the expression of these traits. The heterosis observed for grain yield, grain number, pollination period, ear and plant height was considerably higher than that observed for other traits. The correlations (r) of F₁ means and SCA effects were positive and significantly higher than that of r (F₁, mid-parents) and r (F₁, heterosis) for all the traits except cob percent, growing degree days to silking, and physiological maturity. MO17, K3547/5, and K3615/2 had negative GCA effects for growing degree day to milky stage and maturity. Among hybrids, MO17 × K3653/2, B73 × K3651/2, and K3545/6 × K3493/1 with positive SCAs for pollination period and grain yield had also negative SCA effects for degree day to silking and milky stages. Therefore, the use of these inbred lines and hybrids increases the response to selection for increasing grain yield and early maturity in maize.     

Hybrid performance and heterosis in spring bread wheat, and their relations to SSR-based genetic distances and coefficients of parentage

Development of hybrids is considered to be a promising avenue to enhance the yield potential of crops. We investigated (i) the amount of heterosis observed in hybrid progeny, (ii) relative importance of general (GCA) versus specific (SCA) combining ability, and (iii) the relationship between heterosis and genetic distance measures in four agronomic traits of spring bread wheat. Eight male and 14 female lines, as well as 112 hybrids produced in a factorial design were grown in replicated trials at two environments in Mexico. Principal coordinate analysis based on Rogers' distance (RD) estimates calculated from 113 SSRs revealed three different groups of parents. Mid-parent heterosis (MPH) for grain yield averaged 0.02 t ha⁻¹ (0.5%) and varied from −15.33% to 14.13%. MPH and hybrid performance (F1P) were higher for intra-group hybrids than for inter-group hybrids, with low values observed in inter-group crosses involving two non-adapted Chinese parents. Combined analyses of variance revealed significant differences among parents and among hybrids. Estimates of GCA variances were more important than SCA variances for all traits. Tight correlations of GCA with line per se performance, and mid-parent value with F1P were observed for all traits. In contrast, correlations of MPH with RD and coefficient of parentage were not significant. It was concluded that the level of heterosis in spring wheat was too low to warrant a commercial exploitation in hybrids. SSRs proved to be a powerful tool for the identification of divergent groups in advanced wheat breeding materials.     

Combining ability and testcross performance of drought‐tolerant maize inbred lines under stress and non‐stress environments in Kenya

Drought and poor soil fertility are among the major abiotic stresses affecting maize productivity in sub‐Saharan Africa. Maize breeding efforts at the International Maize and Wheat Improvement Center (CIMMYT) have focused on incorporating drought stress tolerance and nitrogen‐use efficiency (NUE) into tropical maize germplasm. The objectives of this study were to estimate the general combining ability (GCA) and specific combining ability (SCA) of selected maize inbred lines under drought stress (DS), low‐nitrogen (LN) and optimum moisture and nitrogen (optimum) conditions, and to assess the yield potential and stability of experimental hybrids under these management conditions. Forty‐nine experimental three‐way cross hybrids, generated from a 7 × 7 line by tester crosses, and six commercial checks were evaluated across 11 optimum, DS and LN sites in Kenya in 2014 using an alpha lattice design with two replicates per entry at each site. DS reduced both grain yield (GY) and plant height (PH), while anthesis–silking interval (ASI) increased under both DS and LN. Hybrids ‘L4/T2’ and ‘L4/T1’ were found to be superior and stable, while inbreds ‘L4’ and ‘L6’ were good combiners for GY and other secondary traits across sites. Additive variance played a greater role for most traits under the three management conditions, suggesting that further progress in the improvement of these traits should be possible. GY under optimum conditions was positively correlated with GY under both DS and LN conditions, but GY under DS and LN was not correlated. Our results suggest the feasibility for simultaneous improvement in grain yield performance of genotypes under optimum, DS and LN conditions.     

Relationship between phenotypic and genetic diversity of parental genotypes and the specific combining ability and heterosis effects in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The purpose of the study was to evaluate the relationship between the genetic distances (GD) and phenotypic distances (PD) of parents and the specific combining ability (SCA) and heterosis effects. The experiment comprised 18 parental genotypes of wheat (Triticum aestivum L.) and 76 F₂ hybrids, obtained after crossing in a line × tester scheme. Parents and hybrids were examined in a field experiment conducted in a block design with three replications. SCA as well as mid-parent heterosis effects were estimated for selected morphological and technological traits. PDs and GDs were investigated between pairs of parental genotypes. GD between parental genotypes was evaluated by using randomly amplified polymorphic DNA markers. Heterosis was observed in all hybrids, and protein content exhibited the highest heterosis among the seven examined traits. The relationship between PD and GD as well as the SCA and mid-parent heterosis effects were evaluated using correlation coefficient. The correlation between PD, SCA and heterosis were low and not significant for the examined traits, whereas the correlation between SCA, heterosis and GDs were significant for protein content and rheological properties. The results indicate that GDs between parents can be used to predict performance of hybrids for selected technological traits.     

Diallel analysis of barley for resistance to leaf stripe and impact of the disease on genetic variability for yield components

Barley breeders in Syria attempting to develop barley (Hordeum vulgare L.) cultivars resistant to barley leaf stripe (BLS) disease caused by Pyrenophora graminea Ito & Kuribayashi [anamorph Drechslera graminea (Rabenh. Ex. Schlech. Shoem.)]. Information on the combining ability for BLS resistance in Syria is not available. This study was conducted to evaluate, in 10 genetically diverse barley parents, general combining ability (GCA) and specific combining ability (SCA) effects towards the determination of the genetic basis of disease resistance and to estimate genetic variability for yield components and its modification by BLS. Ten parental genotypes varying in their reactions to BLS were crossed in a half-diallel mating design to generate 45 full-sib families. The families and the parents were inoculated with P. graminea and evaluated for resistance in replicated field tests (three inoculated and three non-inoculated plots). The parents chosen showed wide variations for resistance to BLS. Genetic component analysis showed significant effects for both GCA and SCA for resistance to BLS, suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. GCA effects were more important than SCA effects. Resistant parents exhibited high negative GCA indicating that additive gene effects were more predominant, and suggesting their prime suitability for use in barley breeding programs to improve resistance to BLS. Narrow-sense heritability was 58% and broad-sense heritability was 99% indicating that selection for BLS resistance should be effective in these crosses. A high genetic variability for the agronomic traits studied was observed. Yield components decreased significantly in inoculated plants and more pronounced in diseased plants. Significant GCA was observed for all traits. Values for GCA were, in some cases, significantly modified by BLS. This indicates that attention must be paid to the danger of drawing conclusion in quantitative genetics studies dealing with both diseased and healthy plants. Two genotypes, Banteng and Igri, had high negative GCA effects and are promising parents for enhancement of BLS resistance.