Positive Specific Combining Ability Effects Research Articles

Assessment of combining ability for targeted traits in periwinkle (Catharanthus roseus (L.) G. Don) through diallel analysis

Catharanthus roseus (L.) G. Don is a vital summer season perennial semi shrub and multipurpose drought resilient flower crop of the tropical region of the Indian subcontinent. This industrially dominant crop is primarily availed as border, bedding and pot culture in landscaping; and also cultivated for its anti-cancer alkaloid compounds enriched plant parts. Hence, the present study was focused to explore diversity. Six inbred lines of periwinkle were crossed in full-diallel fashion with an objective of identifying superior cross-combinations for high general, specific and reciprocal combining ability. The analysis of variance for combining ability was highly significant for growth and flowering traits indicated existence of both additive and non-additive gene actions. However some traits showed only additive effect due to non-significant general combining ability. The parental lines of Vi-13–2 and Vi-15–2 expressed superior general combining effects for flower yield and considered as good general combiners for crossing programmes. The cross combinations Vi-15–1 × Vi-14–3 and Vi-16 × Vi-15–2 exhibited significantly positive specific combining ability effects for flower yield and considered as good specific direct combiners. High specific direct cross combiners necessitate poor × good, good × good and poor × poor parental combinations and can be contribute additive × dominance, additive × additive, dominance × dominance and epistatic gene interactions. The specific reciprocal cross combiners identified as Vi-14–3 × Vi-29 and Vi-14–3 × Vi-13–2 with superior expression in the reciprocal magnitudes for various traits might be due to cytoplasmic effects. The current investigation is designed to identify the best performing inbred lines for ornamental utilization as well as lines that can be exploited as parents in subsequent crosses.

Selection of inbreds with better combining ability is instrumental in developing CMS-based heterotic hybrids in tropical carrot (Daucus carota L.)

Abstract Carrot is an important vegetable crop worldwide valued for its fleshy edible roots of varied colours. Owing to its highly cross-pollinated nature and small flower size, cytoplasmic male sterility (CMS) is being utilized for hybrid development. Among different types of male sterility, petaloid CMS is widely used for hybrid carrot breeding globally. This study aimed to develop selection criteria for parents in developing heterotic F1 hybrids using CMS lines. A large number of agro-morphological traits and Simple Sequence Repeats (genomic-SSRs) were used to assess the diversity among parental lines. We developed 60 F1 hybrids by crossing four petaloid CMS lines and 15 testers in line × tester mating design and evaluated them in replicated randomized block design trial for four vegetative and 11 economic traits. The mean squares of all the traits in line × tester interactions were significant. The estimates of genetic components of variance indicated predominance of non-additive gene action except for root maturity, root length and core diameter. The hybrids with highest per se performance also had significant positive specific combining ability effects. The root yield and root weight showed highest heterosis percentage (33%). The best performing heterotic hybrids were DCatH-5392, DCatH-700 and DCatH-9892. Correlation between genetic distance and relative heterosis of economic traits indicated no significant association and thus genetic distance could not be used to predict heterosis. As most of the yield-related traits were controlled by non-additive gene action, heterosis breeding could be potentially used along with combining ability analysis to reduce time in selection of best parents and crosses in tropical carrot.

Combining Ability and Heterosis among Bottle Gourd [Lagenaria siceraria (Molina) Standl.] Selections for Yield and Related Traits under Drought-Stressed and Non-Stressed Conditions

Bottle gourd [Lagenaria siceraria (Molina) Standl.] is cultivated for multiple utilities, including as a leafy vegetable, for fresh and dried fruits and seeds. It is an under-researched and -utilized crop, and modern varieties are yet to be developed and deployed in sub-Saharan Africa (SSA). There is a dire need for pre-breeding and breeding of bottle gourds for commercialization in SSA. Therefore, this study aimed to determine the combining ability and heterosis among selected genotypes of bottle gourd for fruit yield and related traits under drought-stressed and non-stressed conditions to select the best parents and hybrids. Eight preliminarily selected and contrasting parents with drought tolerance were crossed using a half-diallel mating design. The 8 parents and 28 crosses were evaluated under non-stressed (NS) and drought-stressed (DS) conditions across two growing seasons (2020/21 and 2021/22) using a 6 × 6 alpha lattice design with three replicates. Data were collected on fruit yield and related traits and subjected to analysis of variance, combining ability and heterosis analyses. Significant (p < 0.05) specific combining ability (SCA) and general combining ability (GCA) effects were computed for fruit yield per plant (FYPP). The SCA × environment and GCA × environment interaction effects were highly significant (p < 0.001) for FYPP and SYPP. The results suggest that genetic effects were affected by the test environment. Parental genotypes BG-58 and GC recorded positive and significant GCA effects for FYPP under the DS condition, whereas GC recorded positive and significant GCA effects for FYPP under the NS condition. The two genotypes are ideal breeding parents for population development to select genotypes with high fruit and seed yields. Crosses BG-27 × BG-79, BG-79 × BG-52, BG-79 × BG-70, BG-80 × BG-70, BG-80 × GC, and BG-70 × GC recorded high and positive SCA effects for FYPP and SYPP under DS condition. Crosses BG-81 × BG-52, BG-81 × GC, BG-27 × BG-79, BG-27 × GC, BG-79 × GC, BG-80 × BG-70, BG-81 × BG-58, BG-27 × BG-80, BG-27 × BG-58, BG-79 × BG-52, BG-52 × BG-58, BG-80 × BG-58, and BG-58 × BG-70 recorded high and positive SCA effects for FYPP and SYPP under NS condition. Crosses BG-80 × BG-58, BG-27 × BG-79, BG-79 × BG-52, BG-27 × BG-52, and BG-52 × BG-80 showed high and positive mid- and better-parent heterosis under DS condition for FYPP and SYPP. Crosses BG-27 × GC, BG-79 × GC, BG-27 × BG-58, and BG-27 × BG-79 showed high and positive mid- and better parent heterosis under NS condition for FYPP and SYPP. The newly selected families are recommended for multi-environment evaluation forrelease and commercialization in South Africa or similar agroecologies.

Genetic Potential of Tropically Adapted Exotic Maize (Zea mays L.) Heat-Tolerant Donor Lines in Sub-Tropical Breeding Programs

Breeding for heat stress tolerance became a priority in sub-Saharan Africa (SSA), as projections are showing an increase in frequency, duration, and severity. In this study, 14 heat stress tolerant-donor lines (HSTDLs) sourced from CIMMYT-India (males) were crossed with 15 locally adapted elite lines (females) developed within the CIMMYT-Zimbabwe maize-breeding program using the North Carolina Design II mating scheme. The resultant 175 single crosses were evaluated alongside five commercial hybrids and adjacent to the trial of parental lines used in the crosses across two locations representing heat stress and optimal environments in Zimbabwe. The design II analysis showed significant (p < 0.01) general combining ability (GCA) effects for exotic heat donor lines and specific combining ability (SCA) effects on grain yield under heat stress, optimal conditions, and across locations; demonstrating additive and non-additive genetic inheritance of grain yield. High Baker’s ratios observed in this study indicate predominance of additive over non-additive gene effects. Three exotic HSTDLs, namely CAL14138, CAL152, and CAL1440, exhibited significant (p < 0.001) and positive GCA effects under heat stress conditions. The results imply that these exotic lines could serve as valuable genetic resources for introgression of heat tolerant alleles into local maize populations for accelerated yield genetic gains. Single crosses, DJ265-15 × VL1018816 and DJ267-9 × CAL1440, exhibited positive and significant (p < 0.01) and (p < 0.05) SCA effects for grain yield under heat stress conditions, respectively. These crosses can be used for further breeding and can contribute to grain yield performance under heat stress conditions. The exotic HSTDLs, CAL14138, CAL152, and VL109126 showed superior per se performance under heat, optimal conditions, and across environments. Overall data demonstrate the potential of exotic HSTDLs for improving the adaptation of maize to heat stress in sub-tropical breeding programs.

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.

Combining Ability and Heterosis Study for Grain Yield And Yield Contributing Traits of Maize (Zea Mays L.)

The nature of combining ability and heterosis were studied in an 8×8 diallel cross excluding reciprocals in maize for grain yield and yield contributing characters. Significant estimates of general combining ability (GCA) and specific combining ability (SCA) variances suggested the importance of both additive and non-additive gene actions for the expression of the traits studied. The variances for GCA Was found significant for days to pollen shedding, days to silking, plant height, ear height, 1000- grain weight and yield. SCA was significant for all the characters except yield. Non-significant SCA variance for yield suggests that this trait was predominantly controlled by additive type of gene action. Variances due to GCA were much higher in magnitude than SCA for all the characters indicating preponderance of additive gene effects for the inheritance of these traits. Parents CML431 (P4) and CML285 (P6) were the best general combiner for both high yield and parent CLG1837 (P7) and CML429 (P8) for earliness and dwarf plant type. Seven crosses CL02450×CML451 (P1×P5), CL02450×CLG1837 (P1×P7), CML551×CML431 (P2×P4), CML223×CML451 (P3×P5), CML431×CML451 (P4×P5), CML431× CML429 (P4×P8) and CML285× CLG1837 (P6× P7) exhibited positive SCA effects for grain yield. Considering, BARI Hybrid Maize-9 (BHM-9) as check, the percent heterosis for grain yield varied from -46.17 to 12.14%. Two crosses CML551×CML431 (P2×P4) and CML285× CLG1837 (P6× P7) exhibited significant and positive heterosis 12.14 and 10.77%, respectively over the check BHM-9 suggested their benefit cost ratio (BCR) study for developing high yielding hybrid varieties.&#x0D; Bangladesh J. Agril. Res. 47(1): 81-90, March 2022

Assessment of Inbred Lines of Field Corn for Yield And Yield Attributes Through Line × Tester Method

A line × tester analysis comprising forty eight test-crosses generated by crossing 24 S3 inbred lines derived from commercial maize hybrid 981 with two testers. Heterosis study of these crosses against two standard checks was evaluated at Bangladesh Agricultural Research Institute, Gazipur during rabi 2015-16. The objectives of the study were to estimate general and specific combining ability effects of the inbred lines and to assess the test cross performance and estimate the amount of standard-heterosis of the hybrids for grain yield and yield related characters. Highly significant genotypic differences were observed indicated wide range of variability present among them. Five lines viz. Line 11, Line 14, Line 17, Line 24 and Line 30 were good general combiner for grain yield and possessed high means. Nine crosses showed (Line 18 × BIL22, Line 23 × BIL22, Line 27 × BIL22, Line 7 × BIL28, Line11 × BIL28, Line14 × BIL28, Line 24 × BIL28, Line 25 × BIL28 and Line 30 × BIL28) significant and positive specific combining ability effect for grain yield. The information on the nature of gene action with respective variety and characters might be used depending on the breeding objectives. These crosses, Line 24× BIL28 (11.40 t/ha), Line 18 × BIL22 (11.30 t/ha) and Line 25 × BIL28 (11.20 t/ha) showed higher yield, could be utilized in maize breeding activities. Estimation of heterosis was carried out using two commercial hybrids BARI Hybrid Maize-9 (BHM-9) and NK-40. The percent heterosis for grain yield varied from -23.39 to 4.6% against BHM-9. Among the 48 crosses, 13 crosses exhibited significant positive heterosis for grain yield.&#x0D; Bangladesh J. Agril. Res. 46(4): 469-489, December 2021

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.

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.

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 OF WATERLOGGING TOLERANCE IN WHEAT (TRITICUM AESTIVUM L.)

The mean performance and combining abilities of cross combinations derived from a complete diallel mating and their parents were evaluated under waterlogging conditions. Analysis of variance for combining abilities indicated significant GCA (general combining ability) and SCA (specific combining ability) for single spike yield, SPAD (soil plant analysis development) and leaf area; GCA for NDVI (normalised differences vegetation index) and SCA for Fe and Mn contents in roots and membrane thermal stability. The parents Stendal, Beşköprü and Pamukova 97 were the best combiners in terms of waterlogging tolerance, while Beşköprü × Pamukova 97, Pamukova 97 × Beşköprü, Stendal × Pamukova 97, Stendal × Beşköprü and Beşköprü × Hanlı were identified as the best cross combinations, with high positive specific combining ability effects for most waterlogging related characters.

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.

Study of genetic architecture for yield related traits in pearl millet [Pennisetum glaucum (L.) R. Br.]

The investigation on study of genetic architecture for yield related traits in pearl millet [Pennisetum glaucum (L.) R. Br.] was carried out with an aim to study the combining ability and gene action for yield and yield contributing characters. The combination JMSA 20102 × 42182 R recorded highest magnitude of sca effect followed by JMSA 20071 × 42182 R, ICMA 08444 × GP-5 R, ICMA 03666 × GP-5 R and JMSA 20102 × 30133 R for grain yield per plant. Similarly, the combinations JMSA 20071 × 30133 R (ear head girth), ICMA 08444 × GP-5 R (number of effective tillers per plant), ICMA 05888 × GP-5 R (ear length), ICMA 03666 × 41530 R (test weight), JMSA 20071 × 42182 R (days to flowering, days to maturity), JMSA 20071 × 41530 R (plant height), JMSA 20102 × 42182 R (grain yield per plant, harvest index, protein content and zinc content) and JMSA 20102 × 41530 R (iron content) exhibited highly significant and maximum sca effects for the respective characters. The hybrid JMSA 20102 × 42182 R and ICMA 03666 × GP-5 R showed high per se performance and significant positive specific combining ability effect for grain yield per plant and some other important characters. Thus, these hybrids could commercially be exploited through heterosis breeding programme after testing in multi-location trials.

Combining Ability of Selected Soybean [Glycine max (L.) Merrill] Parental Lines

Background: The success of hybridization programme depends on the combining ability of parental lines. Methods: Seven soybean genotypes and all their partial diallel crosses in the F2 generation were evaluated in a randomized complete block design at two locations in Nigeria, during the 2017-2018 growing season. Result: Analysis of variance showed that both environments and genotypes were significantly different for all measured traits. The genotype TGx 1988-5F was the best general combiner for earliness in flowering and poding, while TGx 1448-2E was the best general combiner for number of pods/plant and seed yield/plant. Crosses having significant and positive specific combining ability effect for number of pods/plant and seed yield/plant were TGx 1485-1D × TGx 1448-2E and TGx 1988-5F × TGx 1989-19F, respectively. Genotypes TGx 1988-5F and TGx 1448-2E exhibiting good general combining ability for earliness and seed yield/plant, are thus, promising for utilization in the future hybridization programme for soybean improvement.

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.

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.