Desirable SCA Effects Research Articles

Genetic Analysis for Popping Traits in Tropical Inbred Lines of Popcorn (Zea mays var. everta)

Aim: Combining ability studies in popcorn to identify superior parents for commercial hybrid breeding. Study Design: line x tester mating fashion. Place and Duration of Study: MRC, PJTSAU, Rajendranagar Hyderabad, between 2023-2024. Methodology: Popcorn (Zea mays var. everta) is a popular snack item both in India and other countries, the genetic base of popcorn germplasm is very narrow, and they resulted in few popcorn hybrids. In this study, a set of 44 popcorn hybrids obtained by crossing 22 inbred lines with two testers in line x tester fashion were evaluated along with parents and two standard checks i.e. Amber popcorn and BPCH-6. Results: Combining ability analysis implied significant differences among parents, crosses, parent’s v/s crosses for all the traits indicating variation in the selected lines of popcorn. For grain yield, lines PC 1, PC 116, PC 6-1, PC 12-2, PC 25, PC 201-1 and tester CML 451 were identified as good general combiners, whereas crosses, PC 1 x CML 451, PC 25-1 x CML 451, PC 71-1 x CML 451 and PC 5 x CML 286 showed high desirable sca effects for grain yield. The popping expansion trait in crosses viz., PC 22 x CML 451, PC 5 x CML 286, PC 72-2 x CML 451 displayed desirable sca effects. In addition to these hybrids PC 5 x CML 286 exhibited positive significant sca values along with high per se performance for both the traits. Conclusion: The lines which show desirable performance for yield and popping traits will be utilized in further development of popcorn hybrids.

Combining Ability Analysis and Genetic Studies of Stripe Rust Resistance in Bread Wheat Genotypes

A set of eighteen F1 and F2 experimental crosses were grown in a randomized complete block design (RCBD) with three replications. From lines, TD-1 was on top by showing greater and significant general combining ability (GCA) effects for maximum number characters including grain yield in both (F1 and F2) populations, while tester Benazir remained exceptional by showing higher and significant specific combining ability (GCA) effects for majority traits including grain yield in F1 and F2 populations, as a result, both parents would contribute significantly to the improvement of the bread wheat. Regarding the SCA effects in F1 population, the hybrids TD-1 × Pakistan-2013, TJ-83 × Benazir, and NIA-Sundar × NIA-Sarang and from F2 populations, the crosses TD-1 × Benazir, TJ-83 × Benazir, Kiran-95 × NIA-Sarang and NIA-Amber × Pakistan-2013 expressed desirable and maximum SCA effects for number of traits including grain yield, thus may be preferred in future wheat breeding programs. Disease reaction on selected 18 F2 populations was performed, the introgression stripe rust resistance showed single dominant gene. The genetic analysis reported the involvement of major genes for stripe rust resistance. These findings could be used to grow high-yielding wheat lines that could have a profitable yield in stripe rust-prone areas.

Combining ability of yellow maize (Zea mays) inbred lines for yield and agronomic traits

Present study was carried out during 2021 and 2022 at Field Crops Research Institute, Agricultural Research Centre, Giza, Egypt to estimate combining ability effects of newly developed 8 yellow maize (Zea nays L.) inbred lines using diallel cross fashion. The 28 maize hybrids were obtained by half diallel crosses at Ismailia Research Station in 2021 and evaluated at 3 locations, viz. Ismailia, Sids and Sakha Research stations in 2022 for yield and agronomic traits. Experimental results revealed that crosses mean square was significant for all the studied traits. Similarly, general and specific combining ability were significant for all the traits. Parental line P8 considered to be an excellent combiner for all traits studied except for, number of days to 50% silking and number of rows characters. The hybrid P5 × P8 possessed desirable SCA effects for a great number of studied traits. Besides, it recorded the heighest mean value for grain yield (12.55 t/ha) plus lowest ear position. As result, this cross P5×P8 could be recommended for releasing after extensive evaluation.

Combining Ability Studies of Promising Restorer Lines for Yield and Yield Components in Rice (Oryza sativa L.)

Background: The present inquisition was carried out at Regional Agricultural Research Station, Maruteru with a set of 30 experimental hybrids developed by crossing three male sterile lines with 10 testers in Line ´ Tester mating design during Kharif, 2022. Methods:The resultant 30 hybrids were studied in randomized block design with two replications along with the parents and hybrid check, HRI-174 during Rabi, 2022-23. Predominant non-additive gene action was found in the analysis of combining ability for lines, testers and line testers for grain production per plant, days to 50% flowering, days to maturity, ear bearing tillers per plant, filled grains per panicle and 1000-grain weight. Result:The results revealed RGL 5613 and MTU 2055 to be effective combiners for grain yield per plant, filled grains per panicle, spikelet fertility percentage and grain weight of one thousand grains. For five hybrids, the sca effects on grain yield per plant were large and favourable. These hybrids had recorded significantly higher grain yield perplant, more than 30 per cent, compared to the check, HRI-174, in addition to significant desirable sca effects for grain yield per plant.

Breeding Novel Rice Hybrids for Aerobic Ecology: A Way Out from Global Warming and Water Crisis

The development of novel rice hybrids is a prospectus area of research for enhancing grain yield to meet the growing population demands. An experiment was conducted in 2016–2017 to develop novel rice hybrids for aerobic ecology with lesser yield penalties than irrigated ecosystems, with the added advantage of reduced methane emissions and water budget as witnessed in irrigated systems. Based on the restorer-maintainer reaction and spikelet fertility (%), ten restorer lines were selected to cross with three CMS (Cytoplasmic male sterile) lines in the Line by Tester fashion in Yasangi (summer) season 2016–2017. They resulted in 30 experimental hybrids besides 13 parental lines (10 restorer lines and 3 B—lines of akin CMS lines) and checks (GK 5022, CR Dhan 201) assessed during the Vankalam (rainy) season 2017 at three different places/locations viz., Rajendranagar, Warangal, and Kampasagar. The outcome of the experiment was that two experimental hybrids viz., APMS-6A × HRSV-7 and IR-79156A × ATR-372, were categorized as stable hybrids with desirable sca (Specific combining ability) effects, heterosis (ranging from 7% to 13%) over best check GK 5022, along with an in-essence performance for yield and other yield attributing characters.

Assessing Combining Ability of Doubled Haploid Maize (Zea mays L.) Breeding Lines for Grain Yield and Yield Components under Heat Stress Condition

Maize (Zea mays L.), a leading cereal worldwide and staple food of many countries, is a multipurpose crop used for human food, animal feed and industry purposes. Maize has wider genetic adaptability to grow under different agro-ecological environments. 29 and 48 DH lines derived from MPS 1 and MPS 2, respectively, were crossed with more than one testers belonging to opposite heterotic in L x T fashion. The resultant double haploid testcrosses, and their parents were evaluated along with checks during kharif (in South Asia: the autumn crop sown at the beginning of the summer rains) 2019 at three locations. Among female lines of MPS1, DH line ZL19337 was identified as good general combiner and registered significant negative GCA effect for days to 50 per cent anthesis and days to 50 per cent silking. While, DH lines ZL19641 and ZL19357 recorded significantly positive GCA for plant height and grain yield, respectively. Among female lines of MPS 2, DH line ZL19492 was identified as good general combiner and recorded significant negative GCA effects for days to 50 per cent anthesis, and days to 50 per cent silking. Similarly, DH lines, ZL19534 and ZL19572 were identified as good general combiners for grain yield and ear position, respectively. Among testers of MPS1, ZL1840 was identified as the good general combiner for days to 50 per cent anthesis, days to 50 per cent silking and plant height and CAL14113 for ear height and grain yield. Similarly, VL1010996 was identified as the good general combiner for days to 50 per cent anthesis, days to 50 per cent silking, plant height, ear height, ear position and grain yield in MPS 2. Hybrid ZH2063 exhibited desired SCA effects for days to 50 per cent anthesis and days to 50 silking and ZH2010 was identified as a good specific combiner for days to 50 per cent anthesis and grain yield in MPS 1. Hybrid ZH20158 recorded desirable SCA effects for the trait days to 50 silking, While, ZH20251 and ZH20183 were identified as good specific combiners for plant height and grain yield in MPS 2.

Diallel analysis among new yellow maize inbred lines for grain yield and other agronomic traits

Yellow maize (Zea mays L.) is one of the important sources of animal feed in Egypt. The national maize programmes uses conventional crop breeding methodology, which depends on the development inbred lines of maize from open pollinated varieties or other heterogeneous sources. The objective of this study was to assess the general and specific combining ability for nine yellow maize inbred lines and their crosses for grain yield and other morphological traits, under Egyptian conditions. Nine new yellow maize inbred lines, derived from different yellow maize sources, were crossed in a half diallel mating scheme in 2020 summer season, at Gemmeiza Agricultural Research Station Gharbia Governorate in Egypt. The resulting 36 crosses, along with two commercial check hybrids (SC 168 and Pioneer SC 3444), were evaluated at three locations, i.e. Gemmeiza, Mallawy and Sids Agricultural Research Stations of the Agricultural Research Center (ARC), in 2021 summer season in Egypt. Overall, the additive gene effects played a major role in the inheritance of days to 50% silking, plant and ear heights; while the non-additive gene effects were mostly responsible for controlling the inheritance of grain yield. The parental inbred lines (P1 and P2) possessed significant (P<0.05) negative estimates of GCA effects for days to 50% silking towards earliness. The best general combiners were inbred lines P2 and P6 for plant and ear height, and these inbred lines would be good combiners for breeding to short hybrids and low ear placement. Crosses (P1xP9 and P3xP4) had desirable SCA effects and significantly out-yielded the two checks.

Assessment of grain quality traits in rice under normal and water deficit condition

The main objective of this study was to assess the combining ability for rice grain quality to recognize the most desirable genotypes for rice breeding programs. A half diallel cross was made among eight rice genotypes. The obtained 28 F1 and their parents were evaluated in two separate irrigation experiments; the first experiment was irrigated every four days (normal condition). The second experiment was irrigated every ten days (a stress condition). The two experiments were designed in randomized complete block design with three replications. The results indicated that water deficit treatment significantly reduced all the studied traits except for amylose content % was increased under stressed treatments. General combining ability mean squares were highly significant for all the studied features except gelatinization temperature under drought irrigation. Specific combining ability mean squares were highly significant for grain elongation % under both conditions and amylose content % under water deficit; this indicates the importance of additive and non-additive genetic effects in the inheritance of these traits. Two crosses, Sakha106 × Sakha107 and Sakha106 × Sakha108 had the highest desirable mean values for hulling (%), milling (%), head rice, and gelatinization temperature, also lowest amylose content under both conditions. Three crosses, Giza 179 X Sakha 107, Giza 179 X Sakha 108, and Sakha 106 X Sakha 108, had the highest mean values of grain elongation % under both conditions. The cross Sakha107 × sakha108 showed highly significant positive desirable SCA effects for hulling (%) milling (%) gelatinization temperature and grain elongation. The varieties Sakha 107 and Sakha108 were the best general combiners and could be used in breeding programs for improving all the studied traits under both conditions.

General and Specific Combining Ability of Quality Protein Maize (Zea mays L.) Inbred Lines for Major Foliar Diseases, Grain Yield and Other Agronomic Traits Evaluated at Mid-altitude Agroecology of Ethiopia

Abstract: Despite the fact that maize is a crucial cereal crop for food security, several foliar diseases are the main threats and limitations maize production in Ethiopia, resulting in low yields, particularly quality protein maize (QPM). Accordingly, national maize research program of Ethiopia has released QPM maize varieties adapted to the mid-altitude, low moisture stress and highland agro-ecologies of the country. Nonetheless, the market share of these varieties is generally small due to these reason and other features that have limited their adoption by farmers. General and specific combining ability analysis is one of the powerful instruments in identifying the best combiners that may be used in crosses to accumulate biotic resistance and productive alleles. A line x tester analysis involving 36 crosses generated by crossing 9 selected maize inbred lines with 4 testers were evaluated for different desirable agronomic traits during 2019/2020 main season at Bako and Jimma. The purpose of the experiment were to determine the GCA and SCA combining ability of QPM inbred lines, adapted to mid altitude agroecology of Ethiopia for grain yield and major foliar diseases. The crosses were evaluated in alpha lattice design replicated 3 times. For analysis of days to silking interval, days to maturity, turcicum leaf blight, grey leaf spot, common rust disease severity index, and grain yield were recorded. Analyses of variances showed significant mean squares due to crosses for almost all the traits studied. GCA mean squares due to lines and testers were significant (P<0.05 or P<0.01) for most studied traits. SCA mean squares were also significant for most attributes and major foliar maize diseases across locations. The comparative importance of GCA and SCA variances observed in the current study for most studied traits. Inbred lines L1, L2, L5 and L8 exhibited negative and highly significant GCA effects for husk cover. From this conduct it can be decided that better performing hybrids, inbred lines with desirable GCA and cross combinations with desirable SCA effects for grain yield, major foliar maize diseases and other traits were successfully identified.

Combining ability analyses of grain yield and kernel micronutrient content in maize (Zea mays)

The present study was aimed to assess the general combining ability of parents and specific combining ability of their crosses for yield and yield related traits. Nine inbred lines were crossed with two testers using line × tester mating design. Nine lines, two testers and 18 experimental hybrids were evaluated along with two checks in this study for grain yield and protein content, besides kernel micronutrients (phosphorous, caicium and iron) during kharif 2019 in a randomized block design at experimental farm of BAC, Sabour. The line CLQRCY44 and HKI1532 were found as good general combiner for grain yield and quality traits followed by DHOLI inbred 55 and CLO2450. Lines DHOLI inbred 55 and CML451 were found as good general combiner for earliness, lines CLQRCY44, CLO2450 and DHOLI 55 for quality traits like protein content, calcium content, phosphorous and iron content. Among the crosses, HKI1532 × 95IOWA (67.43 q/ha), LM13 × SUWAN (65.87 q/ha) and CML425 × SUWAN (63.30 q/ha) were the promising crosses for grain yield. CLO2450 × SUWAN and LM13 × SUWAN exhibited highly significant and desirable SCA effects for grain yield. CLO2450 × 95IOWA exhibited highly significant and desirable SCA effects for protein content. HKI1532 × 95IOWA (67.43 q/ha) was the promising hybrid for grain yield and micronutrient content. Therefore, these crosses can be utilized for developing high yielding micronutrient enriched hybrid varieties in maize (Zea mays L).

Estimation of Combining Ability and Heterosis for Wheat Yield and Its Components under Water Stress Conditions

DROUGHT is a worldwide problem which controls the crop productivity. Six Egyptian bread wheat varieties were crossed in a 6x6 half diallel in 2018/19 season. Parents and their fifteen F1 crosses were evaluated under normal irrigation (N), mid water stress (MS) and severe water stress (SS) during 2019/20 in three field experiments. Results showed that the analysis of variance were significant for all the studied traits. The highest mean values were recorded under all irrigation treatments as well as the combined analysis with the crosses P1x P2, P1 x P3, P1 x P5, P2 x P3, P3 x P5 and P5 x P6 for grain yield per plant. Mean squares for both general (GCA) and specific (SCA) combining ability estimates were highly significant for all studied traits. GCA/SCA ratio was greater than unity for most traits. The parental P1 exhibited positive and significant GCA effects for number of kernels per spike, grain yield per spike and grain yield per plant. The highest desirable SCA effects were obtained with the crosses P3 x P5 and P4 x P5 for grain yield per plant under stresses conditions. Positive significant heterosis were detected by the crosses P1 x P3, P2 x P3, P3 x P5, P4 x P5 and P5 x P6 for number of spikes per plant, number of kernels per spike, grain yield per spike, 1000-grain weight and grain yield per plant at N, MS, SS conditions and the combined data.

Molecular markers and GGE biplot analysis for selecting higher‐yield and drought‐tolerant maize hybrids

AbstractImproving maize (Zea mays L.) genotypes for higher productivity and tolerance to drought stress depends mainly on physiological and molecular markers. Therefore, this study aims at breeding maize for drought tolerance and high potentiality by selection based on molecular markers, photosynthetic parameters; and easy graphic methods that help in selecting elite genotypes across diverse environments. An 8 × 8 half diallel analysis was used at two locations involving drought and normal irrigation treatments to study parental genetic diversity (GD) and combining ability (general combing ability [GCA] and specific combining ability [SCA]) in F1 of maize. Fingerprinting of parents was made using simple sequence repeat (SSR) markers. Fifty‐eight alleles were ranged from two to five alleles per locus with an average of 0.63 alleles per locus. The average of polymorphic information content (PIC) was 0.63. Cuvette temperature (oc) was lowest by the cross L14 × L36. The cross L8 × L34 expresses the highest value for Quantum sensor (μmol m–2 s–1), net CO2 assimilation rate and chlorophyll content. As for leaf diffusive resistance (LDR) four crosses exhibited significant desirable LDR values. Concerning rate of leaf transpiration (LTR) (μg cm−2 S−1) the cross (L5 × L104) gave the lowest value. Most hybrids exhibited desirable values for drought susceptibility index. For grain yield plant–1, five F1 crosses, that is, L5 × L34, L8 × L14, L8 × L14, L30 × L104, and L36 × L104 expressed the most desirable SCA effects. These crosses are promising in maize breeding programs. Based on GGE biplot analysis, genotype nos. 8 and 10 exhibited the highest grain yield plant−1 and ranked the first across all environments.

Combining ability analysis for yield and yield components and quality traits in Indian mustard [Brassica Juncea L. (Czern & Coss)

Combining ability analysis was performed in a 10× 10 half dialle cross in Indian mustard genotypes for yield and quality traitsduring 2017-18 and 2018-19 at the agriculture research farm R.B.(PG) college Mudi, Agra and IFTM university,Lodhipur Rajput Moradabad.In this study, 45 F1 hybrid and their parents were evaluated for 14 quantitative and qualitative traits. The parents used namely, NRCHB -101, DRMR- IJ- 31, Kanti, Urvashi, Pusa mustard- 25 (NPJ-112), Pusa mustard-26 (NPJ-113), Pusa mustard- 27 (EJ-17), CS- 54, RH- 406, RH -749. The results indicated that both additive and non-additive type of gene actions were responsible in expression of all the 14 characters. Parental genotypes viz., RH -749, RH -406 and CS -54, showed high GCA effects for seed yield per plant and most of the important characters except days to 50% flowering and days to maturity. The other parent’survashi, PM -27, DRMRIJ- 31, NRCHB -101 showed high GCA effects for the remainingtraits. Out of 45 crosses only three crosses RH- 406 × RH -749, PM- 26 × RH -406 and PM -26 × RH -406 had desirable and significant SCA effects with high per se performance for seed yield per plant in F1,s generation. The present study indicated that genetic improvement in the Indian mustard would be achieved by using selected promising crosses having significantly high SCA values coupled with high per se performances.

Combining ability analysis of common bean (Phaseolus vulgaris L) genotypes for resistance to bean fly (Ophiomyia spp.), and grain yield and component traits

The bean fly (Ophiomyia spp.) is the most destructive insect pest of common bean (Phaseolus vulgaris L.) causing significant yield losses. The objectives of this study were to determine the combining ability effects and deduce gene action controlling the inheritance of bean fly resistance and agronomic traits among common bean genotypes, and to select superior genotypes for breeding. Eight selected complementary parents were crossed using a half-diallel mating design to derive new families. Parents and 28 F2 families were evaluated in two locations using were evaluated in two locations using a 6 × 6 lattice square design with two replications. Bean fly resistance parameters such as bean fly damage severity (BDS), pupae count (PC) and plant mortality rate (PMR) and agronomic traits such as days to 50% flowering (DTF), days to maturity (DTM), number of pods per plant (NPP), number of seed per pod and grain yield (GYD) were collected. Results revealed significant genotype × location interaction effects on resistance parameters and agronomic traits allowing selection of unique families adapted to different production environments. There were negative correlations between grain yield (GYD) and bean fly damage severity (p < 0.01, r = − 0.60), pupa count (p < 0.01, r = − 0.34) and plant mortality rate (p < 0.01, r = − 0.53), implying that direct selection for bean fly resistant genotypes would improve GYD. Genotypes A429 and A55 exhibited negative general combining ability (GCA) effects for bean fly damage parameters and positive GCA effects for GYD. Good combiners for number of pods per plant (NPP) and GYD were the genotypes A55, MW365 and Sinoni, while MW466 exhibited desirable GCA effects for days to 50% flowering (DTF) and days to 90% maturity (DTM). These parental lines with desirable GCA effects for bean fly resistance and agronomic traits were selected for future breeding. Families such as Sinoni/A55, Kabanima/A55 and MW365/Kabanima showed desirable BDS, PC and PMR (SCA) effects for bean fly resistance and grain yield. Families such as Kabanima/A55, Sinoni/A55 and NUA45/MW365 exhibited desirable and significant SCA effects for traits such as NPP, number of seeds per pod (NSP) and GYD. Families with desirable SCA effects will be utilised in selecting desirable recombinant inbred lines and breeding populations for improving bean fly resistance and agronomic performance. The Baker’s ratios indicated that additive gene effects were more important for bean fly resistance and GYD. Recurrent selection would be the best strategy for improving bean fly resistance and grain yield using this germplasm.

Diallel Analysis of Eight Yellow Maize Inbred Lines for Earliness and Grain Yield

Combining ability for grain yield and other traits were evaluated in a half diallel fashion in maize. Eight yellow maize inbred lines were crossed in half diallel fashion excluding the reciprocals during the summer season of 2018 at Gemmeiza station, the resulting 28F1 were evaluated along with check SC168 at two locations (Gemmeiza and Sids) in 2019 summer season. A randomized complete block design (RCBD) with four replications was used. Mean squares of GCA and SCA were highly significant for all the studied traits at combined data, except SCA for ear diameter. The non-additive gene effects were most responsible for controlling the inheritance of days to 50% silking, plant height, ear length and grain yield. While the additive gene effects had the important role in the inheritance of ear height and ear diameter. The parents; P6 and P7 were significant for general combiner for yield and p 4 for earliness. The crosses P3 xP7, P5 x P8 andP6 x P7 had desirable SCA effects for earliness. Meanwhile, the crosses P2 xP8, P3 x P6, P4 x P5 and P5 x p 7 showed high SCA effect for grain yield. The single crosses; P2 xP7, P2 x P8,P3 x P6, P5 x P7, P6 xP7 andP7 x P8 had desirable mean values for earliness and grain yield.

Combining Ability of White Maize Inbred Lines Via Line X Tester Analysis

Combining ability analysis was conducted using line x tester design for seven inbred lines of maize which were crossed to three single crosses as testers at Ismailia Agricultural Research Station during 2016 growing season. In 2017 season, 21 crosses in addition to one check hybrid were evaluated at three locations. Highly significant differences were found between the locations for all studied traits. Mean squares due to crosses, their partitions and their interaction with locations were significant or highly significant for all studied traits, except for lines and lines x testers for number of ears/plant and testers for number of rows/ear. The best inbred lines for general combining ability effects were Gz-8093, Gz-8092 and Gz7253 for earliness and Tep-6240 for grain yield. the tester SC 131 was the best general combiner for days to 50% silking toward earliness, grain yield, number of ears/plant, ear length and ear diameter. The cross Gz-8093 x SC131 had the desirable SCA effects for all traits also. The additive gene effects were more important than the non-additive gene effects in inheritance of days to 50% silking, number of ears/plant, ear length and ear diameter while, the non-additive was more important than additive for grain yield, number of rows/ear and number of kernels/row. The non-additive gene effects were more affected by environment than additive gene effects for all traits except for number of ears/plant. The cross Gz-8093 x SC131 highly significantly outyielded to the TWC 324, suggesting the use of this cross in maize breeding programs.

Combining ability effects in CGMS based pigeonpea [Cajanus cajan (L.) mill sp.] hybrids

The objective of present study is to estimate the Combining Ability effects in CGMS based parents and crosses to find out promising cross combinations for seed yield and its components. The experimental material comprised of 40 crosses along with 13 parents (5 lines and 8 testers) and a standard check BDN 716. The experiment was laid out in Randomized Block Design with two replications. The observations were recorded on eleven characters for evaluation. The analysis of variance revealed that there were significant differences among the parents and crosses for all the characters studied. The estimates of GCA effects revealed that BDN 2004-4 B, BSMR 736 B, BDNHR 1 and BDNHR 35-8 were the good general combiners for number pods per plant and grain yield per plant. The line BDN 2004-3 B and the tester BDNHR 21-1-1 and BDNHR 36-7 have registered significant negative GCA effects for days to 50 per cent flowering and for days to maturity the negative GCA effects recorded by line BDN 2004-3 B and BSMR 736 B and testers BDNHR 24-1-1-1 and BDNHR 36-7. The crosses BDN 2004-4 A x BDNHR 35-8 and BSMR 736 A x BDNHR 22-1-1 had high per se performance and desirable significant SCA effects for grain yield and other components.

Heterotic Groups, Gene Action and Heterosis Among Maize Inbred Lines Selected for the Major Agro-ecologies of Rwanda

Maize breeding programmes exploit inbred lines with superior combining ability for grain yield and other agronomic traits to create competitive hybrids. Therefore, the objectives of this study were to determine heterotic groups of locally developed maize inbred lines, their heterotic relationships, with exotic testers as well as the gene action controlling grain yield. Nineteen maize inbred lines were crossed to four testers, based on a line x tester mating scheme resulting in 76 test crosses. These crosses were evaluated together with four checks in 10 x 8 α-lattice design across four locations in 2015B and 2016A seasons. Both additive and non-additive gene action were important for grain yield with preponderance of additive gene action. The most desirable GCA effects for grain yield were realized in inbred line 8 while the highest desirable SCA effects were displayed by the test cross 18xT1. Generally, most of the inbred lines exhibited positive heterosis with all testers. However, there was more aligning firstly towards tester T2 and then to T3. The highest heterosis was displayed by the combination of inbred line 8 with 3. Regardless of the heterotic grouping method applied, the inbred lines were discriminated into different heterotic groups; two and nine heterotic groups were identified based on standard heterosis and SCA effects; respectively. The information generated would be useful in optimizing the maize hybrid breeding programme in Rwanda and for other researchers for high yielding maize variety development.

Determining the Combining Ability and Gene Action for Rice Yellow Mottle Virus Disease Resistance and Agronomic Traits in Rice (Oryza sativa L.)

Selecting genetically diverse and complementary parental lines and superior crosses are pre-requisites in developing improved cultivars. The objectives of this study were to determine the combining ability effects and gene action conditioning rice yellow mottle virus disease (RYMVD) resistance and agronomic traits in rice (Oryza sativa L.). Ten parental lines and their 45 F2 progenies were field evaluated in three locations using a 5 × 11 alpha lattice design with two replications. The genotype × site interaction effects were significant (p &lt; 0.05) for the number of tillers (NT), number of panicles per plant (NPP), number of grains per panicle (NGP), percentage of filled grains (PFG), thousand grain weight (TGW), RYMVD resistance and grain yield (GY). The analysis of general and specific combining ability (GCA and SCA) indicated involvement of both additive and non-additive gene action governing inheritance of traits. High GCA/SCA ratio estimate revealed additive genetic effect was predominant. Parental lines Mwangaza, Lunyuki, Salama M-57, Salama M-19, IRAT 256 and Salama M-55, which had negative GCA effects for RYMVD, and families such as SARO 5 × Salama M-55, IRAT 245 × Rangimbili, Rangimbili × Gigante and Rangimbili × Mwangaza, which had negative SCA effects for RYMVD, were selected for RYMV resistance breeding. The crosses Rangimbili × Gigante, Gigante × Salama M-19 and Rangimbili × Salama M-55 were selected due to their desirable SCA effects for GY. The predominance of additive gene effects for agronomic traits and RYMVD resistance in the present breeding populations suggested that rice improvement could be achieved through gene introgression using recurrent selection.

Estimation of Gene Action and Heterosis in F1 And F2 Diallel Crosses among Seven Genotypes of Field Bean

Heterosis, gene action, combining ability (GCA and SCA) effects and variances were studied in 21 F1 and F2 crosses derived from 7x7 half diallel scheme of field bean. To detect prospective and efficient material for immediate use in breeding programs to enhance field bean productivity. F1 and F2 with parents were arranged in RCBD with 3 replicates to evaluate seed yield and its components traits in 2018/2019 season. Mean squares (MS) for genotype and its partitioning (parent, crosses and parent vs crosses) were significant for all studied traits in both generations. P1xP5 and P3xP6 exhibited significant heterotic effect for seed yield plant-1 in F1 and F2 generations. Significant GCA and SCA MS were found for all studied traits, where proportion of additive was great for most traits in both generations, reveling predominance of additive gene effects. P2 (Sakha 2), P5 (M-13), P7 (M-1017) in F1 and P6 (M-148) in F2 were good combiners for seed yield and at least one of its components. More than 25 % of studied crosses showed positive and significant SCA effects for seed yield in F1 and F2 generations. The cross P1xP5 showed desirable SCA effects in both generation for seed yield and resistance to chocolate spot disease%. Significant and larger values of dominance component (H1) than additive were obtained for all studied traits resulting in more values of (H1/D)0.5 which were exceeded unity in both generations. Low narrow-sense heritability was exhibited in both generations for all traits, indicating that presence of non-additive genetic effects.