Combiners For Grain Yield Research Articles

Study of gene action in different traits of maize (Zea mays L.)

A study was conducted on maize incorporating a total of 28 single crosses, eight parental lines and two standard checks to determine the combining ability and gene action. Among the eleven traits that were studied, the analysis of variance revealed that the mean squares due to genotypes, parents and hybrids were highly significant for all traits, except for 100 grain weight in case of parents, indicating the presence of an adequate amount of genetic variability. Onfurther analysis of variance for combining ability,the mean squares due to GCA and SCA were observed to be highly significant for almost all traits indicating the role of both additive and non additive components of genetic variance in the expression of all the studied traits.The  high gca effect for grain yield per plant was associated with high or average gcafor yield component traits for most parents, while the poor combiners for grain yield per plant were also poor combiners for other yield component traits.High sca effects were seen in a few cross combinations which were good specific combiners for grain yield per plant and yield component traits.Based on the gca effects some inbred lines were identified as good general combiners for various traits. This indicated that these parents could be utilized for developing synthetic variety.The inbred lines with desirable gca effects for grain yield and other agro-morphological traits could be inter-crossed to develop an improved base population and subsequent recurrent selection efforts would facilitate the derivation of elite lines excelling in desirable character.All ofthe cross combinations exhibiting desirable significant sca effect were having one parent as a good or average combiner for each of the eleven agro morphological traits studied.It was clear that these hybrids were the combinations of either  the parents as good general combiners or one of the parents as a good general combiner for yield and yield related traits. Hence, they can be used as a potential single cross hybrid combination and tested further.The crosses that show high sca effects indicate a preponderance of non-additive genes and can be used for heterosis breeding. Keywords: Maize, Combining ability, GCA and SCA

The Combining Ability for Grain Yield and Some Related Characteristics in Rice (Oryza sativa L.) Under Normal and Water Stress Conditions.

Drought is considered a major threat to rice production. This study aimed to determine the effects of drought stress on the estimates of heterosis and the combining ability of rice genotypes for the number of days to 50% heading, plant height, number of panicles per plant, panicle length, number of filled grains per panicle, and grain yield per plant. Field experiments were conducted at the Rice Research and Training Center, Kafr El Sheikh, Egypt, during the rice-growing season in 2018 and 2019. Eight rice genotypes (Giza178, Giza179, Sakha106, Sakha107, Sakha108, WAB1573, NERICA4, and IET1444) were crossed in a half-diallel cross in the rice-growing season in 2018, which yielded a wide range of variability in numerous agronomic traits and drought tolerance measurements. In 2019, these parents and their 28 F1 crosses were produced by employing a three-replication randomized complete block design under normal and water stress conditions. The results showed remarkable differences across the studied genotypes under normal and water stress conditions. Under both conditions, Sakha107 was the best general combiner for earliness and short stature. Giza179 and Sakha108 were the best general combiners for grain yield per plant and one or more of its characteristics. Furthermore, in both normal and water stress conditions, Giza179 exhibited the highest general combining ability effects for all attributes that were evaluated. Under normal and water stress conditions, the Giza179 × Sakha107 cross demonstrated substantial and desirable specific combining ability effects on all the examined traits, which suggested that it could be considered for use in rice hybrid breeding programs. Therefore, we recommend that these vital indirect selection criteria to be considered for improving rice grain yield under drought conditions.

Selection of Suitable Pearl Millet Hybrids for Arid and Semi-Arid Conditions through Combining Ability Analysis

Present investigation was carried out to study combining ability effects for grain yield and its component traits in 77 hybrids of pearl millet. From the results of GCA effects, it was revealed that a number of parents namely, ICMA 98222, ICMA 93333, ICMA 30199, ICMA 30201 (female parents), and BIB 481-500, BIB 561-570 and BIB 571-581 (male parents) were found to be good general combiner for grain yield and most of its component characters. On the basis of GCA effects, lines ICMA 98222, ICMA 88004, ICMA 93333, ICMA 30199, ICMA 30201 and testes BIB 571-580, BIB 561- 570, BIB 511- 520, BIB 481- 500, BIB 531- 540 were good general combiner for more than nine yield contributing characters. The SCA effects of the crosses namely, ICMA 97111 x BIB 561- 570, ICMA 98222 x BIB 481- 500, ICMA 88004 x BIB 501- 510 and ICMA 93333 x BIB 551-560 were significant and were identified as superior for seed yield and related traits over the environments. Therefore, these parents and hybrids were recommended for utilization in development of promising populations as well as hybrid development.

Genetic analysis of parental lines and identification of heterotic hybrid combinations in rice (Oryza sativa L.)

Thirty hybrids along with their parents (B and R lines) and standard checks viz., MTU 1001 and 27P63 were evaluated for grain yield and related traits to study combining ability and heterosis in rice. The mean performance of the hybrids for most of the characters was found higher than that of parents. The analysis of variance revealed significant differences among lines, testers and hybrids for most of the characters studied. SCA variances were found lower than GCA variances for most of the characters and average degree of dominance was far from unity indicating the predominance of additive gene action for these traits. However, for effective bearing tillers and spikelet fertility the average degree of dominance was very near to unity inferring the predominance of non-additive genetic components for these traits. The gca effects revealed that the lines, RNR 25783 and RP 5980-109-12-9-27 had significant gca effects in desired direction for yield and yield attributing traits whereas the tester, CMS 59A was a good general combiner. SCA effects showed that the hybrid, JMS 13A × RNR 19361 was found to be good specific combiner for grain yield per plant and spikelet fertility. Similarly, the hybrids, CMS 59A × SYE 503-78-34-2, CMS 46A × WGL 347 and JMS 13A × RP 5980-109-12-9-27 were identified as good specific combiner for grain yield and yield contributing characters. Based on heterotic estimates, five hybrids viz., CMS 59A × RNR 25783, CMS 59A × WGL 14, JMS 13A × RNR 25783, CMS 59A × RNR 25776, JMS 13A × RP 5980-109-12-9-27 were identified as promising with more than 5% and 20% yield advantage over hybrid and varietal checks, respectively.

Estimation of combining ability and heterosis for yield and its component traits for identification of promising red rice (Oryza sativa L.) hybrids developed from new WA-based CMS lines and red kernel breeding lines

Combining ability analysis and heterosis enables plant breeders in anticipating improvement in productivity through hybridization and selection. In this study, line × tester mating design was used to develop 42 red rice hybrids by utilizing newly developed six WA-based CMS lines and seven testers selected from red kernel breeding lines at Zonal Agricultural Research Station, V.C. Farm, Mandya during kharif, 2018. The phenotypic performance of hybrids along with parents and checks were evaluated for grain yield and yield contributing traits. Analysis of variance revealed that variance due to the line × tester was significant for almost all the characters studied. Combining ability analysis revealed the predominance of non-additive gene action for most of the characters studied. On the basis of gca effects, CMS 2 among the lines and MO-21 among testers were identified as good general combiners for most of the traits studied. High sca effects were observed in the crosses, viz., CMS-1 × ME-19, CMS-2 × IET-14757 and CMS-4 × MSN-98 and they were also found to be the best combinations for grain yield and its component traits. The crosses CMS 5 × MSN-10-3, CMS 2 × ME-19 and CMS 5 × IET-14757 exhibited high mean grain yield and high standard heterosis over the standard commercial check KRH-4. These hybrids further need to be evaluated in multi-location trails for commercial exploitation of heterosis in red rice hybrid breeding program. Keywords: Hybrid rice, CMS, Combining ability, Heterosis, GCA, SCA &nbsp

Heterosis and combining ability for floral and yield characters in rice using cytoplasmic male sterility system

Developing high-yielding rice genotypes is decisive to ensure global food security with current population growth and the threat of environmental pressures. Cytoplasmic male sterility (CMS) system provides a valuable approach for commercial exploitation of heterosis and producing high-yielding and quality hybrid rice. Three CMS lines and ten diverse restorers were crossed using line × tester mating design. The obtained thirty F1 hybrids and their thirteen parents were evaluated. Yield traits as well as certain floral traits characters that influence the efficiency of crossing and hybrid seed production as the duration of floret opening (min), stigma exsertion (mm), stigma length (mm), opening floret angle, and anther length (mm) were assessed. Highly significant variations were detected among parents, crosses, and parents vs. crosses for all the studied traits. The CMS line L2 and the restorer T5 were determined as good combiners for stigma exsertion, stigma length, opining floret angle, and duration of floret opening. Besides, the hybrids L1 × T1, L1 × T3, L2 × T2, L2 × T5, L3 × T4, L3 × T5, and L3 × T9 exhibited positive SCA effects for most floral traits. Moreover, the CMS lines L1 and L3 as well as the restorers T1, T2, T3, T6, and T9 were identified as good general combiners for grain yield and certain related traits. The hybrids L1 × T1, L1 × T5, L1 × T7, L2 × T3, L2 × T4, L2 × T5, L2 × T10, L3 × T1, L3 × T2, and L3 × T6 displayed positive SCA effects for grain yield and one or more of its attributes. Both additive and non-additive gene effects were involved in the governing inheritance of all evaluated traits. The biochemical variations among the certain evaluated genotypes were further studied. The esterase and peroxidase isozymes were applied for verifying the genetic diversity at the protein level among the used CMS lines, restorers, and their crosses. All the applied isozymes displayed polymorphism for the parents and their crosses. The banding pattern and intensity differences provided accurate results on the reliable variability among the tested genotypes.

Molecular Genetic Diversity and Combining Ability for Some Physiological and Agronomic Traits in Rice under Well-Watered and Water-Deficit Conditions.

Water deficit is a pivotal abiotic stress that detrimentally constrains rice growth and production. Thereupon, the development of high-yielding and drought-tolerant rice genotypes is imperative in order to sustain rice production and ensure global food security. The present study aimed to evaluate diverse exotic and local parental rice genotypes and their corresponding cross combinations under water-deficit versus well-watered conditions, determining general and specific combining ability effects, heterosis, and the gene action controlling important traits through half-diallel analysis. In addition, the research aimed to assess parental genetic distance (GD) employing simple sequence repeat (SSR) markers, and to determine its association with hybrid performance, heterosis, and specific combining ability (SCA) effects. Six diverse rice genotypes (exotic and local) and their 15 F1 hybrids were assessed for two years under water-deficit and well-watered conditions. The results revealed that water-deficit stress substantially declined days to heading, plant height, chlorophyll content, relative water content, grain yield, and yield attributes. Contrarily, leaf rolling and the sterility percentage were considerably increased compared to well-watered conditions. Genotypes differed significantly for all the studied characteristics under water-deficit and well-watered conditions. Both additive and non-additive gene actions were involved in governing the inheritance of all the studied traits; however, additive gene action was predominant for most traits. The parental genotypes P1 and P2 were identified as excellent combiners for earliness and the breeding of short stature genotypes. Moreover, P3, P4, and P6 were identified as excellent combiners to increase grain yield and its attributes under water-deficit conditions. The hybrid combinations; P1 × P4, P2 × P5, P3 × P4, and P4 × P6 were found to be good specific combiners for grain yield and its contributed traits under water-deficit conditions. The parental genetic distance (GD) ranged from 0.38 to 0.89, with an average of 0.70. It showed lower association with hybrid performance, heterosis, and combining ability effects for all the studied traits. Nevertheless, SCA revealed a significant association with hybrid performance and heterosis, which suggests that SCA is a good predictor for hybrid performance and heterosis under water-deficit conditions. Strong positive relationships were identified between grain yield and each of relative water content, chlorophyll content, number of panicles/plant, number of filled grains/panicle, and 1000-grain weight. This suggests that these traits could be exploited as important indirect selection criteria for improving rice grain yield under water-deficit conditions.

Elucidation of gene action and combining ability for grain and forage yield and contributing traits in sorghum [Sorghum bicolor (L.) Moench

The present investigation was undertaken to achieve information on gene action and combining ability in sorghum [Sorghum bicolor (L.) Moench]. The experimental material consisted of eleven parents and their 28 Line × Tester crosses. The evaluation was carried out during Kharif, 2020 at Sorghum Research Station, S. D. Agricultural University, Deesa. The ratio of σ2D/σ2H being more than unity was found for days to flowering, which suggested a more significant role of additive genetic variance in the inheritance of this trait. In contrast, the rest of the yield and its component traits showed non-additive genetic variance. The gca effects indicated that parents, SR 3019, CSV 31 and GJ 43 were found as good general combiners for grain yield per plant. While, parents DS 156, CSV 31 and SPV 2682 were good general combiners for dry fodder yield per plant and its contributing traits. Based on estimates of sca effects, the most promising hybrids for grain yield per plant were viz., SR 2980 × CSV 31, SR 3019 × SPV 2573 and DSF 117 × SPV 2682, whereas for dry fodder yield per plant were viz.,SR 3048 × CSV 31, GJ 43 × SPV 2573 and DSF 168 × SPV 2573. The good general combiners for yield and contributing traits can be utilized in intensive crossing programme and select transgressive segregants for desired characters in segregating generations to develop superior lines. Keywords: L × T analysis, Gene action, combining ability, Grain yield, Dry fodder yield

Study of combining ability analysis on half diallel crosses in water stress of wheat (triticum aestivum L.)

Combining ability analysis was performed in a 10 x 10 half diallel cross of ten bread wheat genotypes for yield and its contributing traits. The experiment was conducted in 2013–2014 and 2014–2015 at Crop Research Centre, Sardar Vallabhbhai Patel University of Agriculture & Technology, Modipuram, Meerut, UP. Combining ability revealed that both general and specific combining ability variances were responsible for all the traits. Thus, additive and non-additive gene action was important in controlling the inheritance of all the traits. The variance due to gca was equal to that part of genetic variance which is due to additive and additive x additive effects, while variances due to sca was ascribed to non-additive components of variance that include dominance and epistatic variance. On the basis of overall gca effects, the best general combiners were WH-147, RAJ-3765, WH-730, NP-846, HUW-468, UP-2382 for maximum number of characters under normal and water stress condition. On the basis specific combining ability effects, five crosses viz., HUW-234 x RAJ-3765, HUW-234 x HUW468, WH-730 x C-306, C-306 x HD-2967 and DBW-17 x UP-2382 in normal condition, and WH-147 x WH-730, WH-147 x HD-2967, RAJ-3765 x HUW-468, RAJ-3765 x WH-730 and WH-730 x UP-2382 in water stress condition were found as good specific combiner for grain yield per plant.

Combining ability studies for lodging resistance and yield traits in rice

General and specific combining ability effects of parents and hybrids were studied for lodging resistance and for yield in rice. Twelve F1 hybrids were developed by crossing four lines (lodging genotypes) with three testers (lodging resistant) in the L x T pattern. The analysis of variance was highly significant, indicating the genetic diversity of parents and the importance of both additive and non-additive gene actions in the inheritance of traits investigated. Significant sca effects for different traits indicated a preponderance of non-additive gene action. Among parents, lines viz., Ponmani, Uma and Gouri were found to be good combiner for grain yield per plant and lodging resistance. Among the hybrids viz., Ponmani x Uma, Prathyasha x Pournami and Prathyasha x Gouri were the best cross combinations. Thus, specific parents and crosses can be used effectively in crop improvement programs. Key words: Combining ability, lodging resistance, rice, yield, gca and sca

Combining ability and heterosis studies in different crop sites for yield and yield contributing traits in sorghum (Sorghum bicolor (L.) Moench)

Forty eight hybrids, utilizing six male sterile lines and eight restorers of Sorghum (Sorghum bicolor (L.) Moench) were evaluated for general and specific combining ability, variance components and standard heterosis. Among the lines ICSA 427 and ICSA 433 and testers ICSR 13009 and ICSR 13031 were found to be good general combiners for grain yield per plot and other yield contributing traits. The estimates of σ2gca and σ2sca suggested a non-additive genetic variance for all the traits studied. Most of the cross combinations showed higher magnitude of specific combining ability effects volving high × high (H × H) and high × low (H × L) combining ability effects of lines and testers for grain yield per plot and other yield contributing traits. The estimates of standard heterosis for grain yield per plot ranged from -49.53 and -50.46 (ICSA 435 × ICSR 13004) to 41.96 and 39.35 (ICSA 433 × ICSR 13043) over CSV-41 and CSH-16, respectively. Out of 48 cross combinations, six registered highly significant positive heterosis (over CSV-41 and CSH-16) for grain yield per plot. Key words: Sorghum, male sterility, heterosis, combining ability.

Combining ability and gene action analysis for yield and yield attributing traits in pearl millet [Pennisetum glaucum (L.) R. Br.

A diallel mating design excluding reciprocal was practised among 8 diverse parents and their 28 crosses to access the gene action and combining ability in pearl millet during kharif 2019. The statistical results of analysis of variance showed highly significant differences due to genotypes for all the traits under study indicating the parents and their hybrids under study have sufficiently high amount of genetic variability. Moreover, division of mean sum of square due to genotypes showed that the differences among eight parental genotypes were significant for all the yield related attributes. Among the 8 parents, 16317, 15708 and 15851 were considered as good general combiner for character viz. grain yield. Apart from grain yield per plant, the parent 16317 was also good combiner for days to flowering, days to maturity, ear head length and ear head girth, harvest index, test weight and protein content. The cross 17548 × 15388 was the finest specific combiner for grain yield per plant followed by 15851 × 15725 and 15725 × 16110. An inspection of per se performance as well as sca effects of crosses revealed that the 17548 × 15388 and 15851 × 15725 found best crosses for grain yield per plant and its component characters. So, these crosses are advised to further study for commercial exploitation. The proportion of σ2gca / σ2sca was below unity for all the traits under study, which suggested considerable action of non-additive genetic variance in the governance of these characters.

Combining Ability Study for Grain Yield and Agronomic Traits of Quality Protein Maize (Zea mays L.) Inbred Lines Adapted to Mid-Altitude Agroecology of Ethiopia

In spite of the importance of quality protein maize to alleviate protein deficiency, almost all maize varieties cultivated in Ethiopia are normal maize varieties, which are devoid of lysine and tryptophan. Perusing the combining ability of QPM inbred for grain yield and its components is vital to design appropriate breeding strategies for the development of nutritionally enhanced maize cultivars. A line x tester analysis involving 36 crosses generated by crossing 9 elite maize inbred lines with 4 testers were evaluated for different desirable agronomic traits during the 2019 main season at BNMRC and JARC. The experiment was conducted using alpha lattice design with 3 replications. The objectives were to determine the combining ability of quality protein maize inbred lines, adapted to mid altitude agroecology of Ethiopia for agronomic traits. The crosses were evaluated in alpha lattice design replicated 3 times. 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 across locations. The comparative importance of GCA and SCA variances observed in the current study for most studied traits indicated the preponderance of additive genetic variance in governing these attributes. Only L3 was the best general combiner for grain yield. Inbred line L3, for days to anthesis and L5 for days to silking had negative and significant GCA effects. L5 and L6 displayed negative and significant GCA effects for plant and ear height. Crosses, L2xT4, L3xT4, L4xT4, L5xT2, L6xT3, L7xT2, L9xT1 and L9xT4 were good specific combiners for grain yield. In general, these genotypes help as a source of promising alleles that could be used for forthcoming breeding work in the development of quality protein maize cultivars with desirable traits.

Genetic Analysis of Yield Attributes in Rice for Water Deficit Under Egyptian Conditions التحليل الوراثى لصفات المحصول فى الارز للاجهاد المائى تحت الظروف المصرية

Rice parental genotypes with good combining abilities provide an efficient tool to enhance rice yield under water deficit conditions. Using 15 F1 hybrids derived from a half diallel mating involving six parental genotypes, two experiments were carried out during 2019 and 2020 growing seasons to investigate the genetic analysis and combining ability for yield and its components under irrigated (E I) and water stress (E II) environments. Eight agronomic traits were studied over a period of two seasons, and cluster analysis based on 16 SSR primers found that the genotypes under study differed greatly in terms of variation. Overall, all yield attributes have been significantly affected by water deficit and was governed by both additive and non-additive gene actions. Based on the mean values and GCA effects, Gaori and IET1444 are suitable for incorporation of earliness and drought tolerance traits. Obviously that Gaori, IET1444, IRAT 170 and WAB 450 would serve as good general combiners for grain yield attributes under (E II) conditions. Due importance should be given for six combinations viz, Giza 177 x IRAT 170, Giza 177x Gaori, Sakha 101x IRAT 170, Sakha 101x IET 1444, Gaori x WAB 450 and IET 1444x WAB 450 to identify as new genotypes with high grain yield under water deficit condition. There might be a great possibility to get the best new combinations through crossing genotypes with highest genetic distance. Therefore, these findings should be considered when selecting elite genotypes for developing superior new rice crosses under water-stress conditions.

Combining Ability for Quantitative Traits Under Normal And Heat Stress Conditions in Maize (Zea Mays L.)

Investigation was carried out to ascertain the genetic architecture for heat tolerance and yield components from diallel crosses in maize (Zea mays L.). The combining ability in both the normal and heat stress conditions revealed highly significant mean squares due to general combining ability (GCA) and specific combining ability (SCA) in both the direct and reciprocal crosses for all the characters except for anthesis-silking interval in normal condition of the reciprocal crosses. Estimate of components of variance for 13 characters revealed higher SCA variance than that of GCA and reciprocal crosses for all the characters. CML 411 was good general combiner for grain yield in both the conditions, whereas, CML 306 and CML 307 were good general combiners in heat stress condition, and CML 164, CML 304 and CML 305 were average general combiners in normal condition. On the basis of high yield, high SCA and at least high GCA of seed parent, the CML 411*CML 305 and CML 411*CML 307 were identified as promising hybrids for normal and heat stress conditions, respectively. Bangladesh J. Bot. 50(3): 659-669, 2021 (September)

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).

English

Maize (Zea mays L.) is the most important cereal crop on which many smallholder farmers in sub-Sahara Africa (SSA) depend on as a sole source of calories, proteins, and vitamins. However, conventional maize is deficient in two essential amino acids, lysine, and tryptophan. Thereafter, Quality Protein Maize (QPM) developed to combat protein malnutrition. In SSA low soil nitrogen is also the most limiting factor in maize production and productivity. To determine the combining ability of QPM inbred lines for grain yield and other agronomic traits under low and optimum N environments, 121 genotypes generated using 11 QPM inbred lines in a complete diallel mating design with 5 checks were evaluated under both low and optimum N environments at 3 locations in the 2018 cropping season. Significant differences were observed among the genotypes for major characters under both low and optimum N environments. Under low and optimum N environments, non-additive gene actions were more important than additive gene action for grain yield, number of ears per plant, plant and ear height, ear length and diameter. Under low N environments, more contributions of reciprocal effects than GCA effects were observed for number of ears per plant, plant aspect, ear diameter. Parental lines TL156579, TL156583, and TL148288 were considered as a good general combiner for grain yield under low N environments. Parental line TL156612 showed higher positive GCA effects when used as female while parental line TL156612 showed higher negative GCA effects when used as a male parent for grain yield under low N environments.   Key words: Complete diallel, general combining ability, low soil nitrogen, lysine, optimum soil nitrogen, quality Protein maize, reciprocal effect, tryptophan.

Using of GGE biplot in determination of genetic structure and heterotic groups in wheat (Triticum aestivum L.)

The present study was undertaken to analyze diallel data using GGE biplot model to gather information about genetic interrelationships among parents and identification of heterotic combinations for yield and yield components in bread wheat varieties. For this purpose, 8 bread wheat genotypes tested across in half-diallel crosses design, GGE biplot technique was used. Parents included the genotypes of Kouhdasht, Karim, Ehsan, Mehregan, N-92-9, Line 17, N80-19 and Atrak. The hybrids obtained from the one-way cross (28 hybrids) in agricultural years of 2016-17 were evaluated as randomized complete block design in two replications on the research farm of Gonbad Kavous University. The evaluated traits included the grain yield, weight of spike grains, number of grains in spike and number of spikes. Additive main effects and genotype × environment interaction (GGE) were employed in the evaluation of genotypes; analyses showed significant (P< 0.01) G × E, (genotype × environment interaction) with respect to plant seed yield. GGE biplot analysis showed that Karim was as the best general combiners for grain yield, number grain per spike and grain weight per spike, whereas Ehsan had the highest GCA effects for number of spikes. Ehsan and Karim had higher specific combining ability than other genotypes. The studied genotypes for this trait were divided into two heterotic groups where the first group included the genotypes of Kouhdasht, N-92-9, N80-19 and Atrak and the second group contained the genotypes of Line 17, Mehregan and Karim. Mehregan line had a weak combining ability with all testers and N-92-9 had also more power than others. Based on the biplot, the Karim genotype with high general adaptation was introduced as the ideal genotype in terms of grain yield, spike number, grain number per spike and grain weight, so the Karim genotype can be adapted to obtain high yield hybrids.

Combining Ability and Gene Action Controlling Grain Yield and Its Related Traits in Bread Wheat under Heat Stress and Normal Conditions

High temperature is a major environmental stress that devastatingly affects wheat production. Thenceforth, developing heat-tolerant and high-yielding wheat genotypes has become more critical to sustaining wheat production particularly under abrupt climate change and fast-growing global population. The present study aimed to evaluate parental genotypes and their cross combinations under normal and heat stress conditions, exploring their diversity based on dehydration-responsive element-binding 2 gene (DREB, stress tolerance gene in response to abiotic stress) in parental genotypes, and determining gene action controlling yield traits through half-diallel analysis. Six diverse bread wheat genotypes (local and exotic) and their 15 F1 hybrids were evaluated at two different locations under timely and late sowing dates. Sowing date, location, genotype, and their interactions significantly impacted the studied traits; days to heading, chlorophyll content, plant height, grain yield, and its attributes. Cluster analysis classified the parents and their crosses into four groups varying from heat-tolerant to heat-sensitive based on heat tolerance indices. The parental genotypes P2 and P4 were identified as an excellent source of beneficial alleles for earliness and high yielding under heat stress. This was corroborated by DNA sequence analysis of DREB transcription factors. They were the highest homologies for dehydrin gene sequence with heat-tolerant wheat species. The hybrid combinations of P1 × P5, P1 × P6, P2 × P4, and P3 × P5 were detected to be good specific combiners for grain yield and its attributes under heat stress conditions. These designated genotypes could be used in wheat breeding for developing heat-tolerant and climate-resilient cultivars. The non-additive genetic variances were preponderant over additive genetic variances for grain yield and most traits under both sowing dates. The narrow-sense heritability ranged from low to moderate for most traits. Strong positive associations were detected between grain yield and each of chlorophyll content, plant height, number of grains/spike, and thousand-grain weights, which suggest their importance for indirect selection under heat stress, especially in early generations, due to the effortlessness of their measurement.

Evaluation and Classification of Yellow Maize Inbred Lines Using Line X Tester Analysis Across Two Locations

Ten yellow maize inbred lines and three testers were top crossed in line × tester scheme in 2019 season. The resulted 30 top crosses with two check hybrids were evaluated at two locations in 2020 growing season to assess mean performance, general and specific combining ability and their interaction with locations as well as elucidate type of gene action. The recorded data were days to 50% silking, plant height, ear height, ear length, ear diameter, No. of rows/ear, No. of kernels/row and grain yield (ardab/fed). The results showed that, the mean squares due to locations (Loc), genotypes (G), crosses (Cr.), G × Loc and Cr. × Loc interactions were significant for all the studied traits. Highly significant differences were observed among the evaluated lines (L), testers (T) and its corresponding hybrids for all traits. non-additive gene action gave an important role in the inheritance of all the studied traits. The inbred lines L2, L4 and L6 showed the best desirable GCA effects for earliness, L6, L7 and L10 for shortness and L4, L5, L6, L7 and L9 for lower ear placement. Whereas the inbreeds L3, L6 and L7 were the best general combiners for grain yield. The crosses L2×T1, L8×T1, L1×T2, L7×T2, L3×T3, L6×T3 and L10×T3 had the best SCA effects for grain yield. The ten inbred lines were classified into three different heterotic groups using HSGCA method. These groups could be used for selecting the best parents for making crosses in maize breeding programs.