Significant General Combining Ability Effects Research Articles

Combining ability and heterosis of selected sweetpotato (Ipomoea batatas L.) clones for storage root yield, yield-related traits and resistance to sweetpotato virus disease

Designed crosses using genetically diverse and complementary genotypes is useful to develop sweetpotato clones with improved agronomic traits. The objective of this study was to determine combining ability and heterosis among selected sweetpotato clones for number of storage roots per plant (NRPP), storage root yield (SRY), dry matter content (DMC) and resistance to sweetpotato virus disease (SPVD) for breeding. Eight selected genotypes were crossed using an 8 × 8 half diallel mating design to generate 28 families which were evaluated along their parents under field condition at three sites using a 6 × 6 lattice design with three replications. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant (P < 0.001) among families. Significant GCA × sites and SCA × sites effects indicated environmental effect on gene action and expression. Parental genotypes Simama and Gairo had positive and significant GCA effects for NRPP. The parents 03-03, Ukerewe and Simama had significant and positive GCA effects for SRY and DMC, respectively. Further, Ex-Msimbu-1 and Gairo displayed negative and significant (P ≤ 0.01) GCA effect for SPVD resistance. The genotypes Gairo, 03-03, Ukerewe, Simama and Ex-Msimbu-1 are promising parents for sweetpotato breeding to improve NRPP, SRY, DMC and resistance to SPVD. Further, the study selected best performing families namely: 03-03 × Simama, 03-03 × Resisto and Simama × Ex-Msimbu-1 which recorded the highest mean storage root yields of 16.1, 16.6 and 17.2 tons/ha combined with high DMC and resistant to SPVD for genetic advancement.

Combining ability, gene action and heritability of weevil resistance, storage root yield and yield related-traits in sweetpotato

The objective of this study was to determine general combining ability (GCA), specific combining ability (SCA), gene action and heritability of weevil (Cylass spp.) resistance, dry matter content (DMC), yield and yield-related components of newly developed sweetpotato clones. Six weevil resistant and six susceptible parents were crossed using a 6 × 6 factorial mating design. The resultant 36 families were evaluated at three locations using a 3 × 12 lattice design with two replications for weevil resistance and yield and related traits in western Tanzania. The GCA effect for females was significant except for percentage marketable root number (PMRN) and percentage marketable root yield (PMRY). Significant GCA effect of males were detected for all traits except PMRY. The SCA effect of families was significant for all traits. With a general predicted ratio (GPR) > 0.5, additive gene action controlled more the expression of total root number (TRN), root yield (RY), DMC, percentage infested root number (PIRN), percentage infested root yield and weevil damage score (WDS), whereas non-additive gene action controlled more the expression of PMRN and PMRY with a < 0.5 GPR. The narrow sense heritability for TRN, RY, DMC, PIRN and WDS were 0.24, 0.56, 0.84, 0.62 and 0.62, while the broad sense heritability for these traits were 0.58, 0.72, 0.93, 0.78 and 0.77, in that order. Four female parents and four male parents were identified as the best general combiners and 13 families recorded the best performance for the evaluated traits. The high heritability for most of the traits studded and presence of both additive and non-additive gene action for the traits suggests that genetic gain can be realized through hybridization and clonal selection in breeding programs. The selected parents and families are useful genetic resources for the development of sweetpotato genotypes resistant to weevils and enhanced root yield, yield components and DMC.

Test cross performance and combining ability of newly introduced quality protein maize (Zea mays) inbred lines for grain yield and agronomic traits evaluated in mid-altitude agro-ecological zones of Ethiopia

Development of quality protein maize (QPM) helps to reduce human malnutrition in areas where maize is the major protein source in the diet. The objective of this study was to estimate combining ability effects of QPM inbred lines for grain yield and yield-related traits. Twenty-one newly introduced QPM inbred lines were crossed with four single cross testers in a line × tester mating design and resulted in 84 F1 progenies. These F1 hybrids, including four checks, were evaluated in an 8 × 11 alpha lattice design with two replications at four locations during 2016. Mean squares due to location, crosses, general combining ability (GCA) and specific combining ability (SCA) were significant for most traits. However, the contributions of GCA sum of squares to the variation among the hybrids were larger than SCA sum of squares, suggesting that the traits were controlled predominantly by additive gene effects. Among the inbred lines, L3, L5 and L10 showed positive and significant GCA effects for grain yield and other agronomic traits. The lines can be used in synthetic variety development. Among crosses, only L3 × T3, L9 × T1 and L15 × T2 revealed positive and significant SCA effects for grain yield, implying the presence of heterosis in these particular crosses.

Genetics of Resistance in F2 Soybean Populations for Adzuki Bean Bruchid (Callosobruchus chinensis)

Adzuki bean bruchid (Callosobruchus chinensis) is a significant pest of soybean in Uganda. To sustainably manage this pest, utilization of resistant soybean varieties is the key solution. Development of resistant varieties needs knowledge on modes of inheritance which is crucial in selection of parent materials. To identify parents, a study was initiated to determine the gene action and mode of inheritance of resistance to bruchids in soybean. Nine parental lines were crossed in a full-diallel at Makerere University Agricultural Institute, Uganda. The generated F1s were advanced to F2 and seeds were evaluated for response to bruchid infestation in a randomised complete block design. Ten seeds were infested with 10 randomly selected unsexed 1-3 day old bruchids. Genotypes showed significant differences in seed weight loss (swl), adult bruchid emergence (ABE) and Dobie susceptibility index (DSI) indicating that these parameters could be used to screen genotypes in genetic analysis. Mean squares of general combining ability (GCA) were significant (P &amp;lt; 0.05) for swl, DSI and number of ABE from the F2 seeds indicating additive gene action. Susceptibility parameters ABE and DSI showed significant specific combining ability (SCA) indicating non-additive gene action. Resistance was influenced by maternal effects indicating that direction of the cross was important. Genotypes S-Line 9.2 and S-Line 13.2A showed negative significant GCA effects for at least two of the susceptibility parameters indicating that they were the best parents for bruchid resistance breeding. The study established that additive, non additive and maternal effects governed the gene expression in soybean resistance to bruchids.

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

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

Heterosis and combining ability analysis of quality protein maize (Zea mays L.) inbred lines adapted to mid-altitude sub-humid agro-ecology of Ethiopia

Generation of information on heterosis and combining abilities of newly developed maize inbred lines is necessary for a successful hybrid and synthetic maize varieties development. Accordingly, this study was conducted to estimate the combining ability of QPM inbred lines for grain yield and yield related traits and to determine the magnitudes of standard heterosis for grain yield and yield related traits in line × tester QPM hybrids. Fifty test crosses together with two standard checks were evaluated using alpha lattice design with three replications at three mid-altitude sub humid trial sites (Bako, Hawassa and Jimma) in Ethiopia during 2016 main cropping season. Combined analysis of variance showed highly significant differences among the three locations for all the studied traits indicating the presence of considerable variation among locations for genotype performance. The interaction between sites and genotypes were highly significant and significant (P<0.05) for grain yield and ear height, indicating that the performances of the genotypes and crosses were not consistent for these traits. The significance of both general combining ability (GCA) and specific combining ability (SCA) mean square for some traits indicates the role of additive and non-additive gene action in the inheritance of the traits. However, for all the traits, the contribution of GCA variance was greater than the contribution of SCA variance, revealing the predominance of additive gene action in the inheritance of all the traits studied. L1 and L3 had significant positive GCA effects and are considered as good combiners for grain yield. In addition, L1 and L9 were good combiners for earliness. In this study, none of the crosses showed positive and significant standard heterosis for grain yield. Key words: General combining ability, grain yield, specific combining ability, standard heterosis.

Investigation on genetic control for yield and yield contributing traits in advanced generation of maize (Zea mays L.)

Twenty five cross progeny of maize developed by Plant Breeding Division of BARI were evaluated by determining general combining ability (GCA) and specific combining ability (SCA) effects following line × tester design involving five female lines and five testers for grain yield and other yield contributing traits. Highly significant genotypic variances specified inclusive inconsistency existed among the genotypes. None of the lines showed significant GCA effects for all the characters, but the line Pac-60/S4-3 and Pac-60/S4-9 showed negative GCA effect for days to 50% tasseling and silking which is desirable to develop early variety. Additionally, the line Pac-60/S4-9, Pac-60/S4-18 and Pac-60/S4-21 showed negative GCA effect for plant and ear height which is also desirable to develop dwarf variety. Nevertheless, none of the cross showed significant SCA effect for any character studied, but crosses Pac-60/S4-21×BIL-113, Pac-60/S4-21×Utn/S4-15, Pac-60/S4-18×Utn/S4-8, Pac-60/S4-3×BIL-113, Pac-60/S4-3×Utn/S4-18, Pac-60/S4-9×Utn/S4-15, Pac-60/S4-9×BIL-113 and Pac-60/S4-21×Utn/S4-10 had higher yield with positive SCA effects. However, considering yield data along with lodging percentage, five crosses namely Pac-60/S4-21×BIL-113, Pac-60/S4-21×Utn/S4-15, Pac-60/S4-21×Utn/S4-10 Pac-60/S4-9×Utn/S4-15 and Pac-60/S4-3×BIL-113 showed better performance.Bangladesh J. Agril. Res. 42(4): 715-724, December 2017

Combining Ability for Grain Yield Performance among CIMMYT Germplasm Adapted to the Mid-Altitude Conditions

The International Centre for Maize and Wheat Improvement (CIMMYT) develops maize (Zea mays L.) inbred lines and hybrids yearly that have several breeding and commercial attributes. However, no genetic analysis has been done on the recently developed inbred lines for yield performance under drought and low-N stress. The objectives of this study were to identify lines with positive general combining ability (GCA) effects for grain yield under stress environments and to identify the best single-cross hybrids with the highest specific combining ability (SCA) effects. Analysis of variance combined across sites showed significant mean squares for genotypes, locations and genotype by environment interaction (GEI) for grain yield. GCAlines, SCA and components of interaction effects were significant across sites. Additive genetic variance was more important than dominance variance in determining yield performance across locations indicating that selection based on grain yield under drought and low-N stress can be effective. Average grain yield across the eight locations ranged from 1.61 t ha-1 to 10.63 t ha-1 while narrow sense heritability for grain yield was 52.6% across sites and was slightly lower under managed drought and low-N stress. The testers CL115807 and CL106622 showed positive and significant GCA effects for yield performance under drought and low-N stress respectively. The best tester across all sites was CL115793 and line CZL0713 had consistently positive GCA effects for grain yield across sites. CML536 × CL115802 and CML312 × CL106508 were the best single crosses under low nitrogen stress sites while hybrid CML312 × C323-45 showed the highest positive SCA effects across sites. In conclusion, our results show that CIMMYT has new lines that have desirable adaptive attributes when grown under drought and low nitrogen stress environments in the mid-altitude region; hence these can be adopted for hybrid, synthetic and OPV formation.

Study of combining ability analysis for seed cotton yield, yield contributing and fibre quality traits in Desi cotton (Gossypium arboreum L.)

The present investigation entitled “Study on heterosis and combining ability for yield, its components and fibre characters in Desi cotton ( Gossypium arboreum L.)” was undertaken to estimate general combining ability effects (GCA) of the parents and specific combining ability effects (SCA) of the crosses. The experimental material comprised of 24 F 1 hybrids obtained by crossing 4 lines with 6 testers in line x tester mating system. Sum total of 36 treatments consisting of 24 crosses, 10 parents and three standard checks were sown in Randomized Complete Block Design. The analysis of variance for combining ability revealed significant general combining ability effects (GCA) and specific combining ability effects (SCA) for all the traits. Among ten parental lines, most of the lines were found to be best general combiner, which had significant general combining ability (GCA)effect for seed cotton yield and its contributing characters including fibre quality traits. Analysis of variance for means revealed significant differences for all the eighteen characters studied. Among females, PA 741 was found to be the best general combiner for 3 characters viz ., days to 50 per cent flowering, days to 50 per cent boll bursting and days to maturity had significant GCA effects. The female PAIG 77 was the best general combiner for three characters viz ., number of bolls per plant, number of seeds per plant and boll weight. The female PA 809 was the best general combiner for 2.5 per cent span length, fibre fineness/micronaire, fibre strength, uniformity ratio and short fibre index. Among males, AKA 2004-29 found to be best general combiner for days to 50 per cent flowering, days to 50 per cent boll bursting, days to maturity and ginning outturn. Male parent ARBAS 1301 was also found to be best general combiner for number of sympodia per plant, number of bolls per plant,number of seeds per boll, seed cotton yield per plant, lint index, seed index, plant height, 2.5 per cent span length, fibre fineness, short fibre index and fibre strength. Male parent GAM 162 found to be best genral combiner for ginning outturn, 2.5 per cent span length and short fibre index whereas, CNA 1016 for boll weight. There was close agreement between per se performance and GCA as well as SCA effects for most of the characters. Observations on various characters indicated that the crosses showing high heterosis and high SCA effects had high per se performance and they involved at least one high combining parent. The combinations PAIG 77 x ARBAS 1301, PA 734 x ARBAS 1301, PA734 x CNA 1016, PA 809 x ARBAS 1301 and PA 741 x JLA 0614 showed significant and desirable SCA effects for most of the yield and fibre quality traits studied, indicating potential for exploiting hybrid vigor in breeding programme.

Combining Ability Analysis for Achene Yield and Related Components in Sunflower (Helianthus annuus L.)

AbstractFor determination of best general and specific combiners for achene yield and related components, a study on a 7×7 diallel fashion in sunflower was conducted at experimental field of Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan. The data were recorded on quantitative traits; days to maturity, plant height, stem diameter, head diameter, number of leaves, Achene per head, achene yield per plant, 100-achene weight, filled achene percentage and oil contents and subjected to Analysis of variance and combining abilities. The accessions were significant for studied traits except oil contents. The accessions A-544, A-554 and A-552 showed significant general combining ability effects days to maturity, plant height, stem diameter, head diameter, number of leaves and filled achene, achene per head and achene yield per plant. The best cross combination A-546×A-560 showed significant specific combining ability effects for number of leaves and filled achene percentage. Among reciprocal crosses, the cross A-560×A-534 proved best for plant height and stem diameter while A-548×A-546 for number of leaves and achene per head.

Combining ability estimates in maize (Zea mays L.) Through line × tester analysis

Eighteen advanced S4 lines of maize extracted from NK46 were evaluated through line × tester method by using two testers for grain yield and its components. General combining ability (GCA) and specific combining ability (SCA) effects of crosses were determined to evaluate the prospective inbred lines. Highly significant genotypic differences for all of six characters, i.e. days to 50% tasselling, Days to 50% silking, plant height, ear height, 1000 kernel weight, and yield indicated presence of wide range of variability among the genotypes for those traits. Non-additive gene action was predominant. Four lines for days to 50% tasselling, one for days to 50% silking, two for plant height, one for ear height, three for 1000 kernel weight, and four for yield were found with significant GCA effects in desired direction. For days to tasselling, days to silking, plant height and ear height, none of 36 cross combinations confirmed significant SCA effects. Five combinations showed significant positive SCA effects for 1000 kernel weight. For yield two crosses showed significant positive SCA. Considering the results of present study, based on GCA and SCA analysis of observed characters seven lines namely, NK46-2, NK46-4, NK46-10, NK46- 13, NK46-18, NK46-43 and NK46-44 were selected for further breeding programBangladesh J. Agril. Res. 42(3): 425-436, September 2017

Combining ability, heterosis, and genetic distance among nine elite American Pima cotton genotypes (Gossypium barbadense)

American Pima cotton (Gossypium barbadense L.) is grown in the southwest United States, and no Pima cotton hybrid is commercially grown. In this study, six commercial Pima cultivars (Pima S-7, Pima S-6, Phy 76, BR 007, DP 340, and DP 744) and three elite germplasm lines (SI 1331, 93252, and 8810) were crossed in a diallel mating scheme without reciprocals, and their 36 F2 and F3 progeny were planted in replicated tests at two locations (L) in 2004–2005. Yield and fiber traits were analyzed using Griffing’s Model 1, Method 2 diallel analysis. Genetic distance (GD) of parent lines was determined using 661 AFLP molecular markers. Across locations, significant genotype (G) and general combining ability (GCA) effects were detected for yield, boll size, lint percent, micronaire, 2.5% fiber length, fiber strength, and elongation. Significant specific combining ability (SCA) effects were detected for yield, micronaire, and strength. Lint yield and the yield components- boll size and lint percent exhibited significant G × L interactions. Significant GCA × L interactions occurred for yield and lint percent. Yield, boll size, and micronaire also had significant SCA × L interactions. No significant GCA or SCA by L interactions were detected for fiber length, strength, and elongation. The mean mid-parent heterosis (MPH) of the 36 hybrids in lint yield was low in F2, but non-existent in F3. Among the nine parents, Pima S-7 and DP 340 had the highest and significant positive GCA effects for lint yield, lint percent, and boll weight across tests. Only several F2 hybrids with Pima S-7 and DP 340 as one parent displayed some levels of useful heterosis in lint yield in the two locations, as compared to Pima S-7 as the check. MPH for other agronomic and fiber quality traits was low to non-existent in both generations. The average GD of the parents were not significantly correlated with their GCA effects, and GD between parents was also not correlated with SCA and MPH of their hybrids, with the exception of lint yield at the Las Cruces location where a significant negative correlation was obtained. However, GD of the parents was correlated with the performance of hybrids in lint yield, fiber length, fiber strength and elongation in one or two tests. This study represented one of the first studies to estimate heterosis, combining ability, and their relationship with genetic distance of parents in a representative subset of Pima cotton genotypes.

Combining ability of sugarcane genotypes based on the selection rates of single cross families

Abstract This study evaluated the genetic potential of parents used in sugarcane genetic breeding programs based on the performance of previously conducted single crosses. The average selection rate of each family, predicted using Best Linear Unbiased Prediction (BLUP) procedure, was used as a surrogate to the cross performance in the initial evaluation phase. Data analysis was performed using Griffing’s method IV adapted for the available set of crosses to detail the general combining ability (GCA) and specific combining ability (SCA) effects. Significant GCA effects were detected, which demonstrated the possibility of selecting parents based on this parameter. SCA had a higher coefficient of determination than GCA. In conclusion, the selection rate is an effective indicator for evaluation of the combining ability of parents in the first selection stage of a sugarcane breeding program.

Combining ability studies exploiting gynoecy in cucumber (Cucumis sativus L.)

Twelve F1 hybrids of cucumber derived from a top cross involving twelve monoecious parents and a stable gynoecious inbred (EC 709119) as female parent were evaluated in randomized block design (RBD) with three replications to assess general combining ability (GCA). Significant GCA effects were observed for all the characters except days to first male flower anthesis. The estimates of GCA effects revealed that none of the parents exhibited good GCA for all the characters together. Among 12 parents, CS123 was observed as the good general combiner for fruit yield per vine, length of main vine, branches per plant, number of harvests, duration of the crop, fruits per plant and number of seeds per fruit. The parents, CS128 and IC 538186 were general good combiners for earliness. The parent CS127 was found to be superior for fruit length, weight and girth.

Genetic components of agronomic traits in maize landraces and their hybrid progeny

Knowledge of the genetic components of agronomictraits is an important factor to characterize landraces of maize tomake them useful in plant breeding programs. The objective of thiswork was to know the genetic action and combining ability of severalagronomic traits of five maize races and their crosses. Maize landracesanalyzed were Jala, Tuxpeno, Celaya, Pepitilla and Dulce. Plantheight, days to male and female flowering date after planting, anddry matter and grain yields were recorded. Those variables showedhighly significant differences among genotypes. With the exceptionof dry matter yield, the other variables showed significant generalcombining ability effects (GCA). Statistically, plant height and femaleflowering date did not show specific combining ability (SCA)differences. Pepitilla x Dulce and Jala x Tuxpeno crosses, and Jalaand Celaya parents, were the best dry matter and grain yields. Plantheight, male and female flowering dates, and grain yield were controlledby additive genes. On the other hand, dry matter yield showednon-additive gene action.

Estimates of Combining Ability for some Quantitative Traits During Different Sowing Dates in Rice

Half diallel crosses among six genotypes of rice (Oryza sativa L.) as well as their parents were cultivated in a randomized complete block design to investigate general combining ability (GCA) effects of parents and specific combining ability (SCA) effects of crosses during different sowing dates. Analysis of variance in diallel analysis exhibited highly significant (P < 0.01) for most studied traits at the four sowing dates. The mean squares due to GCA and SCA were also highly significant for all studied traits during the four sowing dates, indicated that the importance of the both additive and dominance gene actions for these traits. Variances due to GCA were greater than these due to SCA for days to heading, panicle length and panicle weight traits during the second, third and fourth sowing dates and for grain yield/plant during the first and second sowing dates. However, the values of SCA variances were higher than the values of GCA variances for the other studied traits through the other studied sowing dates. Results showed significant differences among all the crosses means and their respective parental values for all examined traits at the four sowing dates. The most of parents and their F1 crosses were displayed significant or highly significant GCA and SCA effects either negative for days to heading or positive for the other studied traits at the four sowing dates. Concerning the four sowing dates, the variety Giza 179 was the best general combiner for days to heading, grain yield/plant, number of panicles/plant and 1000-grain weight traits while, the genotype CT 9882 was the best general combiner for panicle length and panicle weight traits. The best specific combinations during the four sowing dates were the cross Giza 178 x CT 9882 for days to heading and number of panicles/plant traits, the crosses Giza 178 x Sakha 105, Giza 178 x Sakha 106 and Giza 178 x Giza 179 for grain yield/plant and 1000-grain weight traits and the cross Giza 179 x CT 9882 for panicle weight and panicle length traits. Cluster analysis based on all studied traits resulted into two clusters from genotypes through all sowing dates in rice. The first cluster included the two exotic genotypes (CT9882 and CT 9506). The second cluster containing four genotypes, further divided into two sub clusters. Sub cluster-I containing the most earlier rice genotypes (Sakha105 and Sakha106). The Egyptian indica rice varieties (Giza178 and Giza179) were grouped together. The results of cluster analysis suggested that there is genetic diversity among the six genotypes for all studied traits. Hybridization among these genotypes in the two groups provided more possibility to having more genetic diversity and could be used in breeding programs to achieve maximum heterosis as well as earliness and yield improvement in rice. Generally, the parents involved in the previous combinations and the best crosses could be use in initiated the breeding program for growing at early sowing dates (first and second sowing dates) of rice crop in the north of Egypt.

Combining Ability of Plant Height and Yield components in Indian Mustard (Brassica junceaL.Czern &amp; Coss.) under Salt affected Soil using Line×Tester Analysis

Line × tester analysis of twenty lines and three testers of Indian mustard (Brassica juncea L. Czern &amp; Coss.) cultivars were used to estimate general combining ability (GCA), specific combining ability (SCA) effects, high parent heterosis and narrow-sense heritability estimate for plant height, yield components and seed yield. Significant variance of line x tester for the traits like pods per plant and seed yield indicating non additive genetic effects have important role for controlling these traits. Significant mean squares of parents v/s crosses which are indicating significant average heterosis were also significant for all the traits except seeds per pod. High narrow-sense heritability estimates for all the traits except seeds per pod exhibited the prime importance of additive genetic effects for these traits except seeds per pod. Most of the crosses with negative SCA effect for plant height had at least one parent with significant negative or negative GCA effect for this trait. For most of the traits except pods per plant, the efficiency of high parent heterosis effect was more than SCA effect for determining superior cross combinations.

Combining ability analysis of cassava (Manihot esculenta Crantz) genotypes for cassava mosaic disease in Zambia

Despite the importance of cassava as a staple crop in Luapula province and other regions of Zambia, there is a lack of information on the resistance to diseases and associated combining ability of the locally cultivated cassava cultivars. Therefore, this study was carried out in 2010/2011 to: identify progeny with resistance to cassava mosaic disease (CMD); evaluate the performance of F1 progeny for agronomic traits and determine general combining ability and specific combining ability for resistance to CMD. A total of 809 genotypes comprising of parents and progeny were developed through controlled crossing and evaluated using α-lattice design. The general combining ability (GCA) and SCA mean squares (MS) were highly significant (P<0.001) for CMD. The total sum of squares (SS) for CMD was mainly accounted for by specific combining ability (SCA) effects (67.9%). Bangweulu a local highly susceptible cultivar had the most negative, significant (P<0.001) GCA effect among the landraces. In summary, the results indicated that the local landraces (Bangweulu and Kampolombo) used as parents can be sources of CMD resistance.

Combining ability for yield and oil quality traits in Indian mustard [Brassica juncea (L.) Czern &amp; Coss] using line × tester analysis

ABSTRACT : Ten lines and four testers of Indian mustard [Brassica juncea (L.) Czern & Coss.] genotypes were used to estimate general combining ability (GCA) and specific combining ability (SCA) effects estimate for yield and oil quality traits. For all the quantitative and quality traits, the mean sum of squares due to line/tester was highly significant, proving that the parental lines used in present investigation are comprising the diverse genetic background. Among the lines and testers, good general combiner RH-30, RAURD 214, EC 401574 and Rajendra Sufalam have exhibited desirable negative and significant GCA effect for days to 50 per cent flowering and days to maturity, whereas positive and significant GCA effect for number of primary and secondary branches per plant, siliqua per plant, siliqua length, 1000 seed weight, biological yield per plant, oleic acid, oil content and seed yield per plant, indicating the presence of additive gene action or additive x additive interaction effects. On the basis of desirable SCA effects for yield, oil and its component traits were found best cross combinations RAURD 153/ JD-6, EC 401574/Rajendra Sufalam, RAURD 170/JD-6 and RAURD 214/Rajendra Sufalam. The cross combinations EC 401574/Rajendra Sufalam, RAURD 214/Pusa Bold and RAURD 172/ Pusa Bold with highly significant economic heterosis and SCA effects, reflected presence of both additive and non-additive gene effects responsible for increase in grain yield over economic parents.

Genetic variation in sorghum as revealed by phenotypic and SSR markers: implications for combining ability and heterosis for grain yield

AbstractHybrid breeding relies on selection of genetically unrelated and complementary parents for key traits. The objective of this study was to examine genetic variation and identify unique sorghum genotypes using phenotypic and simple sequence repeat (SSR) markers and to determine their relationships with combining ability and heterosis for grain yield. A total of 32 landraces and four cytoplasmic male sterile (CMS) lines were phenotyped using 25 agro-morphological traits and genotyped with 30 polymorphic SSR markers. The landraces were crossed with four CMS lines using a line × tester mating design. The 128 hybrids, 36 parentals and four check varieties were field-evaluated using a 12 × 14 alpha lattice design with three replications. General combining ability (GCA), specific combining ability (SCA) and heterosis for grain yield were determined. Genetic distance estimates ranged from 0.39 to 0.60 and 0.50 to 0.79, based on phenotypic and SSR markers, respectively. Landraces 72572, 75454, 200654, 239175, 239208, 244735A and 242039B and CMS lines ICSA 743 and ICSA 756 displayed positive and significant GCA effects for grain yield. Based on the SCA effects of yield, lines were classified into three heterotic groups aligned to the different cytoplasmic systems of testers. Lines with high GCA effects rendered hybrids with highly significant SCA effects with high mid-parent heterosis (MPH) for grain yield. Both marker systems were effective in demarcating sorghum genotypes that provided desirable cross-combinations with high combining ability effects and MPH for grain yield. The selected genotypes are recommended as potential parents for sorghum hybrid breeding in moisture stress environments.