Significant Specific Combining Ability Effects Research Articles

Diallel Analysis of Wheat Resistance to Fusarium Head Blight and Mycotoxin Accumulation under Conditions of Artificial Inoculation and Natural Infection.

Breeding resistant wheat cultivars to Fusarium head blight (FHB), caused by Fusarium spp., is the best method for controlling the disease. The aim of this study was to estimate general combining ability (GCA) and specific combining ability (SCA) for FHB resistance in a set of eight genetically diverse winter wheat cultivars to identify potential donors of FHB resistance for crossing. FHB resistance of parents and F1 crosses produced by the half diallel scheme was evaluated under the conditions of artificial inoculation with F. graminearum and natural infection. Four FHB related traits were assessed: visual rating index (VRI), Fusarium damaged kernels (FDK), and deoxynivalenol and zearalenone content in the harvested grain samples. Significant GCA effects for FHB resistance were observed for the parental cultivars with high FHB resistance for all studied FHB resistance related traits. The significant SCA and mid-parent heterosis effects for FHB resistance were rare under both artificial inoculation and natural infection conditions and involved crosses between parents with low FHB resistance. A significant negative correlation between grain yield under natural conditions and VRI (r = -0.43) and FDK (r = -0.47) under conditions of artificial inoculation was observed in the set of the studied F1 crosses. Some crosses showed high yield and high FHB resistance, indicating that breeding of FHB resistant genotypes could be performed without yield penalty. These crosses involved resistant cultivars with significant GCA effects for FHB resistance indicating that that they could be used as good donors of FHB resistance.

ESTIMATION OF COMBINING ABILITY EFFECTS FOR YIELD AND FATTY ACID-RELATED TRAITS IN BRASSICA RAPA USING LINE BY TESTER ANALYSIS

Brassica rapa is an important oilseed crop in Pakistan. It is a rich source of oil and contains 40%–46% oil. In addition, its meal has 38%–40% protein. Given their high levels of erucic acid and glucosinolate, mustard and rapeseed oil is unhealthy as regular cooking oil. A dire need to exploit the genetic variability of rapeseed germplasm is necessary to improve the performance of cultivars. The line × tester analysis helped estimate various types of gene actions that are important to quantitative traits. The key to successful research is selecting suitable lines and testers and designing good mating patterns. Choosing and developing genotypes with high yield and fatty acid profiles are the major concern of rapeseed breeders. The current research on hybridization and evaluation of Brassica rapa accessions sought better harvest and its related traits from the selected germplasm. The combining ability effects determination used line × tester analysis in rapeseed. The accessions’ variability analysis exhibited extremely significant differences in yield and related traits. Recorded data for different morphological and yield-related qualities provided days till 50% flowering, the number of major branches per plant, and the number of secondary branches per plant had positive and significant general combining ability estimates, and all yield-related variables had extremely notable specific combining ability estimates. All the yield-related characteristics displayed a favorable and substantial connection in the examined germplasm. Among the lines, 28244, 40980, and 40981 occurred to be the best general combiners showing the additive gene action. The cross combinations, 40977 × 26283, 40979 × 26283, and 40981 × 26283, indicated significant specific combining ability effects, which showed the non-additive genetic effects of total variance due to the dominance and/or epistasis. The results suggested that the research material used in the remarkable study can benefit by improving yield and fatty acids-related components and can further enhance upcoming breeding programs based on strong particular combining ability impacts.

Heterosis and Combining ability analysis in F1 hybrids of bread wheat

Bread wheat (Triticum aestivum L.) is the most auspicious cereal food crop with regard to production, consumption, nutritional value, storage space, quality, adaptability and transportation. The all 15 F1 cross combinations and their parents were planted in a randomized block design (RBD) with three replications. Out of 15 cross combinations, only 10 show significant heterobeltiosis for early maturity over the standard check-in desirable direction. Five cross combinations PBW 343 x PBW 65, RAJ 2184 x PBW 65, PBW 343 x RAJ 2184, CPAN 3004 x RAJ 2184, HD 1981 x PBW 154 show significant positive heterobeltiosis whereas two cross combinations HD 1981 x PBW 154 and PBW 343 x PBW 65 show significant positive heterosis over commercial check for seed yield. The GCA (General combining ability) effects of the parent PBW343 showed significant positive effect for most of all the traits followed by CPAN3004, PBW154 and PBW65. Out of fifteen, two cross crosses, namely PBW 343 x PBW 65 and CPAN 3004 x RAJ 2184 showed a significant positive SCA (specific combining ability) effect for grain yield.

Performance of testers with contrasting provitamin A content to evaluate provitamin A maize for resistance to Aspergillus flavus infection and aflatoxin production.

In sub-Saharan Africa (SSA), millions of people depend on maize as a primary staple. However, maize consumers in SSA may be exposed to malnutrition due to vitamin A deficiency (VAD) and unsafe aflatoxin levels, which can lead to serious economic and public health problems. Provitamin A (PVA) biofortified maize has been developed to alleviate VAD and may have additional benefits such as reduced aflatoxin contamination. In this study, maize inbred testers with contrasting PVA content in grain were used to identify inbred lines with desirable combining ability for breeding to enhance their level of resistance to aflatoxin. Kernels of 120 PVA hybrids generated by crossing 60 PVA inbreds with varying levels of PVA (5.4 to 51.7 µg/g) and two testers (low and high PVA, 14.4 and 25.0 µg/g, respectively) were inoculated with a highly toxigenic strain of Aspergillus flavus. Aflatoxin had a negative genetic correlation with β-carotene (r= -0.29, p < 0.0001) and PVA (r = -0.23, p < 0.0001), indicating that hybrids with high PVA content accumulated less aflatoxin than those with low to medium PVA. Both general combining ability (GCA) and specific combining ability (SCA) effects of lines and testers were significant for aflatoxin accumulation, number of spores, PVA, and other carotenoids, with additive gene actions playing a prominent role in regulating the mode of inheritance (GCA/SCA ratio >0.5). Eight inbreds had combined significant negative GCA effects for aflatoxin accumulation and spore count with significant positive GCA effects for PVA. Five testcrosses had combined significant negative SCA effects for aflatoxin with significant positive SCA effects for PVA. The high PVA tester had significant negative GCA effects for aflatoxin, lutein, β-carotene, and PVA. The study identified lines that can be used as parents to develop superior hybrids with high PVA and reduced aflatoxin accumulation. Overall, the results point out the importance of testers in maize breeding programs to develop materials that can contribute to controlling aflatoxin contamination and reducing VAD.

HETEROTIC GROUPING WITH COMBINING ABILITY AND GENE ACTION IN SESAMUM INDICUM L. USING LINE × TESTER ANALYSIS

Line × tester analysis is an efficient method to evaluate many entries for GCA (general combining ability) and SCA (specific combining ability) effects. Fifteen lines and three testers of sesame (Sesamum indicum L.) gained evaluation for shattering, yield, and oil quality traits. Crossing selected tolerant and sensitive accessions in line × tester fashion ensued, with the resultant F1, parent material, and commercially cultivated varieties sown in the field to ascertain the genetic mechanisms to assess heterosis manifestation and generation turnover. Combining ability analysis exhibited variable direction and magnitude of GCA effects among line and testers and SCA effects among crosses. The lines SG-41, G-43, and SG-50 and testers SG-60 and SG-1 were the best general combiners. Crosses SG-44 × SG-60, SG-50 × SG-60, SG-103 × SG-14, SG-103 × SG-60, SG-110 × SG-14, SG-50 × SG-1, and SG-113 × SG-60 had a positive significant SCA effect for maximum yieldrelated traits. SG-39 × SG-60, SG-44 × SG-60, and SG-50 × SG-60 had positive significant SCA effects for maximum oil-related qualities. Crosses SG-41 × SG-1, SG-41 × SG-60, SG-43 × SG-60, SG-50 × SG-14, and SG-50 × SG-60 had positive and significant heterosis over the mid-parent, a better parent, and commercial hybrids for most of the traits. Conditioning on secondary branches, flower initiation, capsule length, and 1000-seed weight were by non-additive genetic effect, with all the other parameters under the control of additive gene action. The variance ratio of GCA to SCA showed less than unity; in contrast, the additive genetic variance was more than the dominant variance for all traits except for secondary branches, flower initiation, capsule length, and 1000-seed weight. The association of traits based on correlation and path analyses suggested that plant height, oil content, and 1000-seed weight can serve as criteria for selecting sesame for a future breeding program.

Heterosis and combining ability of iron, zinc and their bioavailability in maize inbred lines under low nitrogen and optimal environments

Iron (Fe) and zinc (Zn) nutrient enrichment of staple crops through biofortification can contribute to alleviating micronutrient deficiency in sub-Saharan Africa. A line × tester mating design was used to determine the general combining ability (GCA), specific combining ability (SCA) and heterosis for grain yield, iron, Zn and phytic concentration of six lines crossed with three testers. Lines and testers were selected for high, intermediate and low mineral content. The F1 hybrids and parental lines were evaluated under low nitrogen (N) and optimum conditions across four environments over two seasons. Under low N conditions, Fe and Zn concentration in grain, and grain yield of genotypes were reduced by 9%, 9%, and 59%, respectively. However, phytic acid concentration in grain was increased by 10% under low N conditions. Both additive and non-additive gene effects were important in controlling Fe, Zn and phytic acid concentration in grain and grain yield of maize under both N conditions. The preponderance of GCA effects indicates the importance of additive gene effects in the inheritance of grain yield. Line GCA effects were more sensitive to N conditions across the environments than the tester GCA. High and significant positive SCA effects for grain yield, Fe and Zn content under low N conditions, would be a good indicator of possible heterosis in these traits. Hybrid CBY101 LM-1600 × CBY358 LM-1857 had high and significant positive SCA for grain yield under low N conditions and is a promising candidate for production in low N environments. CBY358 LM-1857 (tester) and CBY102 LM-1601 (line) are a good general combiners for Fe, Zn and GY can be used as parents in future maize hybrid breeding programs to develop high-yielding maize genotypes with high Fe and Zn content.

Genetic studies in pearl millet (Pennisetum glaucum L.)

The present investigation on “Studies on heterosis for yield and its components in pearl millet (Pennisetum glaucum L.)” was conducted during Kharif-2020, at Department of Agriculture Botany, Vasantrao Naik Krishi Vidyapeeth, Parbhani, National Agricultural Research Project, Aurangabad and College of Agriculture, Golegaon. The experimental material included in the present study comprised of five females (lines) and twelve restorers (testers) and sixty crosses. The experimental material was evaluated for twelve characters viz; days to 50% flowering, days to maturity, earhead length (cm), earhead girth(cm), number of nodes per plant, plant height(cm), total number of tillers per plant, number of effective tillers per plant, Fe content (ppm), Zn content (ppm), grain yield per plant (g) and grain yield per hectare (kg). The hybrids 02888A x 15006R, 02333A x 15006R, 00444A x 15351R, 99111A x 15020R and 99111A x 15713R exhibited high mean values for grain yield per plant and highly significant specific combining ability effects and wider adaptation across the environments. These hybrids could be utilized to exploit heterosis for grain yield. The hybrids 00444A x 15351R, 99111A x 15020R, 00111A x 15713R and 02888A x 15392R were found early for days to maturity. The hybrids 02888A x 15006R, 00444A x 15351R and 02333A x 15351R were found to contain high Fe content, whereas 99111A x 15020R, 02333A x 15351R and 02333A x 15020R had high Zn content.

Combining ability studies of grain Fe and Zn contents of pearl millet (Pennisetum glaucum L.) in West Africa.

Micronutrient malnutrition is a major challenge in Africa, where half a million children die each year because of lack of micronutrients in their food. Pearl millet is an important food and fodder crop for the people living in the Semi-Arid regions of West Africa. The present study was conducted to determine the stability, combining ability, and gene action conditions of the high level of Fe and Zn content in grain and selected agronomic traits. Hence, eight genotypes were selected based on the availability of grain Fe and Zn contents and crossed in a full diallel mating design. Progenies from an 8 × 8 diallel mating along with the parents were evaluated in an alpha lattice design with three replications in three locations for two years. The parental lines Jirani, LCIC 9702 and MORO, had positive significant general combining ability (GCA) effects for grain Fe concentration, while Jirani and MORO had positive significant GCA effects for grain Zn concentration. For the specific combining ability (SCA), among the 56 hybrids evaluated, only the hybrids LCIC 9702 × Jirani and MORO × ZANGO had positive significant SCA effects for grain Fe concentration across locations, and for grain Zn concentration, the hybrids Gamoji × MORO, LCIC 9702 × Jirani, and ICMV 167006 × Jirani had positive significant SCA effects. The reciprocal effects were significant for grain Zn concentration, grain yield, flowering time, plant height, test weight, and downy mildew incidence, suggesting that the choice of a female or male parent is critical in hybrid production. Grain Fe and Zn concentration, flowering time, plant height, panicle length, panicle girth, panicle compactness, and downy mildew incidence were found to be predominantly under additive gene action, while grain yield and test weight were predominantly under non-additive gene action. A highly positive correlation was found between grain Fe and Zn concentrations, which implies that improving grain Fe trait automatically improves the grain Zn content. The stability analysis revealed that the hybrid ICMV 167006 × Jirani was the most stable and high-yielding with a high level of grain Fe and Zn micronutrients.

DEVELOPMENT OF HIGH-YIELDING SESAME (SESAMUM INDICUM L.) GENOTYPES UNDER DROUGHT STRESS CONDITIONS

Ten drought-tolerant and six sensitive lines with their resultant crosses emerged from crossing in the Line × Tester mating design, then evaluated at the maturity stage in the field. Data recorded for morphological and physiological parameters took place, as well as, for drought tolerance and yieldrelated traits. Recorded data followed analysis to access the variability in germplasm and general and specific combining ability effects. Combining ability analysis exhibited variable direction and magnitude of specific combining ability effects among crosses and general combining effects among line and testers. Results showed the breeding material had genetic variability that can serve in developing drought-tolerant and high-yielding genotypes of Sesamum indicum L. The testers 93004 and 96019 and Lines 90005 and 96006 revealed the best general combiners under normal and drought stress. Results of SCA indicated that 95001 × 97005, 97007 × 97001, 95010 × 93004, TH-6 × 96019, and 90005 × 96014 exhibited to have positive significant specific combining ability effects for most of the traits under control and drought stress conditions that can undergo further evaluation for growing under drought conditions. The fresh and dry weight of seedlings and 1000-seed weight traits proved useful as selection criteria in developing drought-tolerant types in sesame.

Combining ability and heritability analysis of sweetpotato weevil resistance, root yield, and dry matter content in sweetpotato

Efficient breeding and selection of superior genotypes requires a comprehensive understanding of the genetics of traits. This study was aimed at establishing the general combining ability (GCA), specific combining ability (SCA), and heritability of sweetpotato weevil (Cylas spp.) resistance, storage root yield, and dry matter content in a sweetpotato multi-parental breeding population. A population of 1,896 F1 clones obtained from an 8 × 8 North Carolina II design cross was evaluated with its parents in the field at two sweetpotato weevil hotspots in Uganda, using an augmented row-column design. Clone roots were further evaluated in three rounds of a no-choice feeding laboratory bioassay. Significant GCA effects for parents and SCA effects for families were observed for most traits and all variance components were highly significant (p ≤ 0.001). Narrow-sense heritability estimates for weevil severity, storage root yield, and dry matter content were 0.35, 0.36, and 0.45, respectively. Parental genotypes with superior GCA for weevil resistance included “Mugande,” NASPOT 5, “Dimbuka-bukulula,” and “Wagabolige.” On the other hand, families that displayed the highest levels of resistance to weevils included “Wagabolige” × NASPOT 10 O, NASPOT 5 × “Dimbuka-bukulula,” “Mugande” × “Dimbuka-bukulula,” and NASPOT 11 × NASPOT 7. The moderate levels of narrow-sense heritability observed for the traits, coupled with the significant GCA and SCA effects, suggest that there is potential for their improvement through conventional breeding via hybridization and progeny selection and advancement. Although selection for weevil resistance may, to some extent, be challenging for breeders, efforts could be boosted through applying genomics-assisted breeding. Superior parents and families identified through this study could be deployed in further research involving the genetic improvement of these traits.

Selection for high yield and quality in half-diallel bread wheat F2 populations (Triticum aestivum L.) through heterosis and combining ability analysis

The study was carried out to evaluate the combining ability and heterosis of seven parents and their 21 half-diallel F2 populations for yield and quality traits during the 2013-14 season in the randomized complete block design with three replications. Significant differences were observed among the genotypes, GCA (general combining ability) and SCA (specific combining ability) effects for all traits, except spike length. The best combiner parents were identified as Esperia and Pehlivan for grain yield, and Flamura85, Aldane and Selimiye for quality traits because of significant GCA and per se performance. The ranges of best parent heterosis were -12.71 to 8.23% for plant height, -15.46 to 8.36% for spike length, -16.62 to 24.80% for number of grains per spike, -23.61 to 36.50% for grain weight per spike, -17.13 to 8.84% for harvest index and -44.26 to 15.83 for grain yield, -17.61 to 8.38% for thousand grain weight, -18.55 to 8.44% for wet gluten content, -33.80 to 24.78% for gluten index, -20.24 to 15.23% for Zeleny sedimentation value, -15.58 to 10.00% for quality index and -8.96 to 6.87 for grain protein content. The three (Slm/Phl, F85/Slm and F85/Esp) and seven (F85/Phl, Sb/Fs, Fs/Slm, Esp/Slm, Fs/Phl, Esp/Sb and Sb/Slm) of F2 populations are offered a good opportunity in base material for selection of potential because of significant SCA effects and best parent heterosis for grain yield and quality traits respectively.

Combining Ability and Gene Action Controlling Agronomic Traits for Cytoplasmic Male Sterile Line, Restorer Lines, and New Hybrids for Developing of New Drought-Tolerant Rice Hybrids.

This study aimed to identify new rice lines and hybrids that are tolerant to water deficit and produce high yields under water stress conditions. A line × tester mating design was used to study the lines and testers’ general combining ability (GCA) effects. The specific combining ability (SCA) of the hybrid rice combinations was measured under three different irrigation regimes; 6, 9, and 12 days. The study was carried out at the experimental farm of Sakha Agricultural Research Station, Sakha, Kafr El-Sheikh, Egypt, during the 2018 and 2019 rice growing seasons. Due to the genotypes and their partitions to the parents and the crosses, the mean squares were highly significant for all studied traits under the three irrigation regimes. The additive gene effects play an important role in expressing most of the studied traits. Therefore, the selection procedures based on the accumulation of the additive effect would be successful at improving these traits and the grain yield. The cytoplasmic male sterile (CMS) line G46A (L1) was the best combiner for most yield component traits in the three irrigation regimes. The newly devolved restorer lines T11, T1, T2, T5, T4, and T3, as well as the new hybrids L2 × T10, L2 × T6, L1 × T7, L1 × T5, L1 × T3, L2 × T7, L2 × T9, L2 × T8, L2 × T4, L1 × T4, L2 × T2, L1 × T8, L1 × T9, and L2 × NRL 10, showed good, desirable values of the studied traits such as earliness of flowering, short plant height, number of panicles/plant, panicle length, number of spikelets/panicle, number of filled grains/panicle, panicle weight, 1000-grain weight, hulling percentage, milling percentage, head rice percentage, and grain yield under the irrigation regimes of 6, 9, and 12 days. The hybrids L2 × T10, L2 × T6, L1 × T7, and L1 × T5, showed significant positive SCA effects for grain yield, under all three irrigation regimes.

Combining Ability of Drought-Tolerant Bread Wheat Genotypes for Agronomic and Physiological Traits

A combining-ability analysis is key to select desirable parents and progenies with enhanced response to selection under water-limited environments. The objective of this study was to determine combining ability for agronomic and physiological traits among distantly related drought-tolerant bread wheat (Triticum aestivum L.) genotypes under well-watered (WW) and terminal-drought (TD) conditions to determine their genetic merit for breeding. Ten heat- and drought-tolerant wheat genotypes were crossed in a half-diallel mating design to generate 45 F1s, which were evaluated under WW and TD moisture regimes in rainout shelter (RS) and greenhouse (GH) environments. The following agronomic traits were assessed: days to 50% maturity (DTM), plant height (PH), spike length (SL), number of productive tillers (TN), spikelets number per spike (SPS), number of grains per spike (GPS), grain yield (GY) and thousand-kernel weight (TKW); and physiological traits (stomatal conductance (SC) and chlorophyll content index (CCI)). Variances attributable to general combining ability (GCA) and specific combining ability (SCA) were significant (p &lt; 0.05) for GY, DTM, PH, SL, SPS, GPS, TKW and CCI. The parental genotypes LM72, LM81 and LM95 with positive and significant GCA effects on GY were selected to make crosses to develop high-yielding wheat genotypes for water-limited environments. Crosses LM71 × LM02, LM71 × LM81, LM82 × LM02, LM82 × LM81, LM22 × LM100, LM22 × LM81 and LM95 × LM22 were selected with positive and significant SCA effects for GY. The selected parents and crosses are valuable genetic resources for breeding and genetic advancement.

Combining ability for yield and yield components in okra [Abelmoschus esculentus (L.) Moench

Combining ability analysis was carried out for fruit yield and its components in okra. Both general a combining ability (GCA) and specific combining ability (SCA) variances were highly significant for almost all the characters indicating the importance of both additive and non-additive gene actions. Parents and F1 hybrids differed significantly for general combining ability and specific combining ability effects for all the characters respectively.The highest GCA effect for total fruit yield per plant recorded in Punjab Padmini.The highest significant positive SCA effect was observed in the cross VRU-109 x Arka Anamika. Among the parents Punjab Padmini, VRU-109, VarshaUpahar proved to be the good general combiner and VRU-109 x Arka Anamika was the good specific combiner for most of the yield and yield attributing traits followed by Punjab Padmini x ZARS.

Combining Ability for Growth, Yield and Related Traits In Cucumber (Cucumis Sativus L.) Under Subtropical Conditions of Garhwal Himalayas

To assess the combining ability for quantitative and qualitative traits in cucumber a full diallel set of 7 parents and their 42 F1’s was evaluated at Horticultural Research Centre, Department of Horticulture, H.N.B. Garhwal University, Srinagar (Garhwal), Uttarakhand, India during 2015 and 2016. The mean sum of squares due to general combining ability (GCA) was of significant differences at 1 % level for almost all the characters. The variance due to specific combining ability (SCA) was found highly significant at 1 % level for almost all the characters. Results from general combining ability studies revealed that the parent, New Manipur-1 showed significant GCA effect in desired direction for maximum characters viz., length of vine, days to first fruit harvest and number of fruits per vine. The cross combinations, Seven Star x New Manipur-1 for length of vine, Swarna Purna x Seven Star for days to first fruit harvest; K-90 x Seven Star for number of fruits per vine and the cross PB-Naveen x Swarna Purna for total fruit yield per vine showed significant SCA effect in desired direction and found to be superior specific cross combinations. Bangladesh J. Bot. 50(4): 1003-1010, 2021 (December)

Estimation of gene action, combining ability and heterosis for yield and yield contributing traits in sorghum [Sorghum bicolor (L) Moench

Combining ability effects, heterosis and gene action of selected sorghum lines for yield and yield contributing traits were assessed. Twenty hybrids were synthesized involving five lines and four testers through L x T mating design. The hybrids, parents and check variety CO 30, were evaluated in a randomized complete block design with three replications and seventeen traits were recorded. The analysis of variance for combining ability revealed that the mean sum of squares due to general combining ability was significant for all the traits. The ratio of σ2gca/ σ2sca revealed that non-additive gene action predominated in all the traits. On the basis of gca effects and per se performance of the parents viz., CO(S) 28, SPV 759 and IS 9807 exhibited significantly superior gca value and identified as a good general combiner for yield and yield contributing traits. The hybrids viz., CO(S) 28 x IS 18551, SPV 2424 x IS 9807 and CO 30 x SPV 759 showed significant specific combining ability effects, significant and higher heterosis of all the three types and per se performance for studied traits. These hybrids were identified as promising hybrids and can be commercially exploited for heterosis breeding programmes. Key words: Sorghum, per se, GCA, SCA and Heterosis

Unveiling combining ability and heterotic grouping of newly developed winter maize (Zea mays) inbreds

Pooled analysis of the test-crosses evaluation of 61 newly developed maize (Zea mays L.) inbred lines usingtwo inbred testers namely BML-6 and BML-7 during rabi 2016-17 and 2017-18 at ICAR-IIMR Regional Centre,Begusarai revealed significant variation among genotypes, general combining ability (GCA) and specific combiningability (SCA) effects for all the traits. Out of 61 inbred lines, 29 exhibited significant positive GCA effect for grainyield with maximum GCA effect value of 25.64. Inbred lines, viz. IMLSB-1299-5, IMLSB-406-2, IMLSB-334B-2,IMLSB-814-2 and IMLSB-285-1 were identified as the best general combiners on the basis of GCA effects whichcan be utilized to a greater extent in hybrid breeding programme. Out of 29 inbred lines with significant positive GCAeffects, 12 and 17 lines also showed significant positive SCA effects with tester, BML-7 and BML-6 respectively, thuswere classified into two heterotic groups ‘A’ and ‘B’, respectively. Out of 122 test-crosses, 14 exhibited significantand positive heterosis for yield over three national checks. The information generated on the heterotic grouping willhelp in further streamlining the available germplasm into heterotic pools and thereby augmenting the national hybridbreeding programme.

Combining ability of soybean (Glycine max L.) yield performance and related traits under water-limited stress conditions

Development of improved genotypes requires acquiring adequate information on genetic background and nature of gene action for planning appropriate breeding and selection strategies. This study was aimed at obtaining estimates of general and specific combining ability, identifying the best combiners in developing drought tolerant genotypes and determining gene action of soybean traits. Six genotypes were crossed using the North Carolina II mating design to form eight families, of which Makwacha and Nasoko were regarded as males and TGX1990-137F, TGX1987-23F, 1988-70F and Tikolore were regarded as females. Two-hundred F2 progeny and six parents were evaluated in the field under non-water-limited stress (non-WLS) and water-limited stress (WLS) conditions across 2 sites during the 2018 dry season in a split-plot layout. Water-regimes were allocated to main plots and genotypes to subplots in a randomized complete block design with 3 replications. Significant genotype and water regime effects were found for seed yield and yield components. Most progeny ranked higher than parents under WLS conditions for all traits. Significant general combining ability (GCA) and specific combining ability (SCA) effects for all traits indicated that both additive and non-additive gene effects were important for trait expression under WLS conditions. Both GCA and SCA effects significantly interacted with water regime effects, demonstrating the need for testing of potential progeny across varied WLS levels to determine stable genotypes. Parents and F2 progeny with significant positive GCA and SCA effects, respectively, under WLS were identified as potential material for inclusion in the breeding program for drought tolerance.

ESTIMATION OF HETEROSIS AND COMBINING ABILITY FOR YIELD AND FIBER QUALITY TRAITS BY USING LINE X TESTER ANALYSIS IN COTTON (Gossypium barbadense L.)

The present study was carried out at Seds Agricultural Research Station, Cotton Research Institute, Agricultural Research Center, Egypt, during 2019 and 2020 seasons. This investigation was carried out to estimate heterosis, combining ability, proportional contributions, genetic components and heritability estimates of some characters for six Egyptian cotton varieties as lines i.e, Giza 80, Giza 86, Giza 90, Giza 93, Giza 94 and Giza 95, while, the other three genotypes used as testers were Karshenky, Ustraly 13 and Pima S4, using line x tester analysis. In 2020 season a randomized complete block design with three replications was carried to evaluate all genotype (nine parents and their 18 F1s crosses) for some genetic parameters. The results indicated that mean squares due to the genotypes, parents, parents vs. crosses, crosses, lines, testers and Line x Tester were highly significant for all studied traits, except boll weight, seed index and lint index at tester and fiber strength for Line x Tester. The following crosses demonstrated the best heterosis relative to mid- and better-parent, i.e, Giza 80 x Karashenky, Giza 86 x Ustraly 13 and Giza 86 x Pima S4 for most yield studied traits and the crosses Giza 93 x Karashenky and Giza 93 x Ustraly 13 for most fiber quality traits. The results revealed that the lines Giza 86 and Giza 94 were significant and positive desirable GCA effects for most yield traits. Giza 93 had significant desirable GCA effects for all fiber traits, in this respect, the results of testers showed that Pima S4 had significant desirable for some yield and fiber traits. However, estimates of specific combining ability (SCA) effects for crosses Giza 86 x Ustraly 13, Giza 90 x Pima S4, Giza 93 x Karshenky and Giza 95 x Pima S4 were significant desirable SCA effects for most yield traits, while, the crosses Giza 90 x Pima S4, Giza 93 x Karshenky and Giza 95 x Pima S4 were significant desirable SCA effects for most fiber traits. The results showed that proportion contribution of lines was higher than of lines x tester interaction contribution and testers for all studied traits. The non-additive of genetic parameters was larger than additive genetic variance with respect to all studied traits except lint percentage, seed index, lint index and upper half mean. The highest broad sense heritability estimates was observed in case of UHM with values of 88.47% and the lowest was for fiber strength with value of 32.24%, while for narrow sense heritability, it was ranged from 8.04% to 49.03% for boll weight and upper half mean, respectively. Generally, Giza 86 and Giza 94 could be used in breeding programs for improving high yielding varieties, while Giza 93 could be considered as excellent parent for breeding programs to produce new varieties characterized with best fiber properties.

Assessment of Combining ability for some Grain Yield and Quality Traits in Rice (Oryza sativa L.) by using Griffing Method and Biplot Analysis

During 2017 growing season, half diallel crosses were made among six genotypes of rice. The obtained 15 F1 and their parents were evaluated during 2018 growing season to analyze the general combining ability (GCA) and specific combining ability (SCA). For all studied characters, the mean squares due to GCA and SCA were highly significant, indicating the importance of the behaviour of both additive and dominance gene in the heredity of these characters. Variances due to GCA were greater than these due to SCA for all studied traits, except milling and grain elongation. Giza 178 and Giza179 possessed highly significant GCA effects for earliness, panicle length, number of filled grains panicle-1, grain yield plant-1 and hulling. IET1444 was good combiner for cooking traits, beside panicle length and number of tillers plant-1. Seven crosses viz., Giza178xIET1444, Sakha 106x Giza 179, Sakha 105x Giza 179, IET1444x WAB880-SG, Giza178xGiza179, Sakha105xSakha106, and Sakha105xGiza178 evidence positive and significant SCA effects for grain yield plant-1. The cross, Sakha 105xGiza179 recorded significant SCA effect in favourable direction for seven traits viz., days to 50%heading, panicle length, number of filled grains/panicles, grain yield plant-1, milling, grain elongation, and amylose content. Sakha105x Sakha106 rice hybrid showed desirable either negative or positive directions and significant SCA effects for days to 50%heading, plant height, grain yield plant-1, gelatinization temperature and grain elongation. Concerning results obtained by biplot analysis, found agreement between two methods of griffing and biplot for analyzing the half-diallel in determining the best parents and hybrids.