Combining ability analysis was carried out in the F1 and F2 generations of a 10 × 10 parents half diallel for peduncle length and flag leaf area in spring wheat under three environments. The mean squares for both general combining ability (GCA) and specific combining ability (SCA) were significant for peduncle length in both the generations, indicating the involvement of both additive and non-additive gene actions in the inheritance. However, the high values of GCA variance showed the greater importance of additive gene action in the inheritance of this trait. Flag leaf area was observed to be controlled by non-additive gene action. The environment played a significant role in the expression of both the traits. The GCA × environment interaction exhibited greater sensitivity in all cases than the SCA × environment interaction. The varieties Kharchia 65 and Durgapura 65 emerged as desirable general combiners for peduncle length, whereas Pavon and Moncho had high mean performance for flag leaf area. These parents could be used as donors in future breeding to develop a physiologically efficient wheat genotype with high production. The crosses Moncho × Brochis and Durgapura 65 × Raj 821 were the most desirable specific combinations for flag leaf area and Kharchia 65 × Chiroca for both the traits. Desirable transgressive segregants can be expected from these crosses. Diallel selective mating or bi-parental crossing could be useful for the genetic improvement of these physiological traits.
Gene effects were analysed using mean stomatal number and specific leaf weight of 12 populations, consisting of both parents (P
, first backcross generations (BC
), second backcross generations (B
) and backcross selfed generations (B
s and B
s) of four crosses involving three drought-tolerant and three drought-susceptible cultivars of
L. to determine the nature of gene action governing stomatal number (SN) and specific leaf weight (SLW) through generation mean analysis in moisture stress (E
) and moisture non-stress (E
) environments. The digenic epistatic model was found to be inadequate for stomatal number and the additive-dominance model was found to be adequate for specific leaf weight in most of the crosses. Additive gene effects were predominant for SLW, while for SN both additive and dominance components of variance were important. Epistatic effects, particularly the additive × dominance (j) type of interaction, were present for both the characters. The duplicate type of epistasis was observed for stomatal number in the cross VL421/HS240 in the moisture stress environment. Significant heterosis was observed for the crosses Hindi 62/HS240 and VL421/HS240 over the standard check (SC) in the moisture stress environment (E
) for both the characters. Genotype-environmental interactions and/or differential gene expression appeared to account for the different results found between environments. Hybridization systems, such as biparental mating and/or diallel selective mating, could be useful for the improvement of these traits, which would help in identifying drought-tolerant progenies.
Authors:F. S. Pelser, M.T. Labuschagne, B. Wentzel, and A. van Biljon
The mixograph performs certain rheological measurements during dough mixing and is a good predictor of wheat end-use quality. The aim of this study was to determine the expression and the heritability of mixing characteristics measured with Mixsmart® software and some quality characteristics in hard red spring wheat parents and their F1 progeny. Six parents varying in midline peak time and envelope peak time were crossed in a half diallel design. Parents and progeny were planted in three different environments. General combining ability (GCA) was a significant source of variation for the measured characteristics, and parents differed widely in terms of GCA effects. Midline-development time, -peak integral and -peak time showed high narrow sense heritability. Envelope peak-integral and -tail width displayed high narrow sense heritability for some, but not all locations. High GCA:SCA (specific combining ability) ratios indicated the prevalence of additive gene effects for midline-development time, -peak integral and -peak time, indicating that these characteristics are largely genetically determined, and that selection for them should lead to genetic gain.
Authors:B. R. Bakheit, A. A. El-Shiemy, F. S. Sedek, and A. A. Ismail
The present study was carried out during the three successive growing seasons of 1996, 1997 and 1998 to estimate the additive, dominance and epistatic components of genetic variation for the yield, yield components and wilt infection by using ninety triple test cross families and their parents, F1 and F2 in four sesame crosses. A randomized complete block design with three replications was used. The results indicated that mean squares of the genetic analysis of variance and the overall epistatic gene effects for the crosses showed highly significant differences for all studied characters. The [i] type (additive × additive) was considered as a major component of the overall epistatic effects for 1000-seed weight in the TTC3 cross, wilt infection percentage in TTC3 and TTC4, number of capsules/plant in TTC1, TTC2 and TTC4 and seed yield/plant in all crosses. The ratio of (H/D)1 for all crosses confirms the presence of partial dominance for all studied traits. The direction of dominance was positive and significant for wilt infection in TTC4, oil percentage in TTC1 and TTC4, number of capsules/plant and 1000-seed weight in TTC2 and seed yield/plant in all four crosses. The results also revealed that the highest proportion of recombinant lines was obtained for number of capsules/plant, 1000-seed weight and oil percentage in the TTC2 cross and for seed yield/plant in TTC3.
The new stem rust strain, Puccinia graminis f. sp. tritici — Ug99, has been a rising threat since the alarm was rung in Uganda in 1998. The genetic and breeding dimensions of research against this disease include the development of vigorous molecular markers, the identification and introgression of multiple resistance genes, the translocation of alien chromosomes, the enrichment of breeding lines with crossability alleles and the development of interspecific hybrids. Resistance genes have been identified in the primary wheat gene pool and in alien sources such as Aegilops spp., Dasypyrum villosum, Secale cereale, Hordeum vulgare and Oryza spp. and some of these sources have been used to confer resistance as a function of single or multiple gene effects. Realizing the potential disaster if Ug99 and related variants break out in other regions, wheat-producing countries are characterizing their germplasm and improving their stem rust race tracking systems. Equally important is “appropriate genetic management”, i.e. the use of currently effective resistance genes in such a way that the evolution and adaptation of new virulence will be deterred. This review will summarize the recent research advances and future perspectives in setting effective genetic barriers vis-à-vis the seemingly intractable spread and evolution of Ug99.
Authors:A.O. Kolawole, A. Menkir, E. Blay, K. Ofori, and J.G. Kling
Two improved tropical maize composites, TZL COMP3 and TZL COMP4; representing complementary heterotic pools have been subjected to four cycles of reciprocal recurrent selection (RRS) for two decades to enhance varietal cross performance. The objectives of this study were to evaluate the effect of selection on genetic gain in heterosis for grain yield and other agronomic traits of these composites. Ten parental populations representing the C0 to C4 of each composite and their crosses plus a varietal check were evaluated in a trial at eight environments in Nigeria. Grain yield of the varietal crosses increased with selection by 3.1% cycle–1. Mean grain yields of the C4 × C4 varietal cross exceeded that of a popular improved reference variety by 23%. Selection also reduced anthesis-silking interval, improved ear characteristics, phenotypic appeal and resistance to foliar diseases. Mid-parent heterosis (MPH) increased from 4% at C0 × C0 to 24% at C4 × C4. The average rate of genetic gain in heterosis for grain yield in population crosses was 3.1% possibly because of presence of non-additive gene effects. The results of our study present the potential usefulness of the advanced selection cycle as sources of diverse inbred lines with improved combining ability as well as improved varietal crosses that can be multiplied and deployed in areas with limited market access.
The fruit yield and quality of hot pepper, Capsicum annuum L., is very low in Ethiopia mainly due to the lack of improved cultivars. The objective of this study was to evaluate the combining ability for yield and yield contributing characters in order to apply an appropriate breeding methodology for the improvement of yield and the contributing characters. Seven diverse cultivars, two local cultivars and five introduced promising inbred lines, were crossed in a half-diallel. The parents and F1s were grown at Melkasa Agricultural Research Center in 1999 and 2000. The experiment was arranged in a randomized complete block design with three replications of ten plants per row. The green fruit yield and eight yield contributing characters were recorded from eight plants in each replication. The analysis of variance and estimates of GCA and SCA were significant for most of the characters studied. Significant GCA and SCA values were recorded for most of the characters, revealing that both additive and non-additive gene effects were involved in genetic control. A lower average degree of dominance was also recorded for some of the characters. Although none of the parents was a good general combiner for all the traits, some parents showed high GCA effects for some of the economic traits, suggesting that these parental lines could be considered simultaneously while formulating a breeding programme for improving fruit yield and yield contributing characters. The majority of the crosses also depicted significant SCA effects in the desirable directions.
The combining ability of four tomato genotypes (Lycopersicon esculentum Mill.) for salt tolerance was determined by investigating the progeny from a 4 × 4 diallel cross. Sixteen progenies (F1s, selfs and reciprocals) were evaluated at three levels of salinity (0%, 1.0%, 1.5%) in a complete block design with four replications under greenhouse conditions. The analysis of the genetic component revealed that the mode of inheritance of salt tolerance appeared to be different to that of plant characters and salinity levels as measured by plant height and fruit yield components. However, the fruit count was consistently controlled by additive gene effects. The specific crosses Moneymaker (MM) × Red Alert (RA) and Ailsa Craig (AC) × Gardener's Delight (GD) produced the highest yield. The small-fruited parents, Red Alert and Gardener's Delight, had higher general combining ability value for salt tolerance than the large-fruited, Ailsa Craig and Moneymaker, for fruit yield components. RA and GD were superior parents in transmitting salt tolerance. The study revealed that plant selection could be used to improve varietal performance for salt tolerance. It is also suggested that the potential variation in commercial cultivars could be exploited to improve adaptability to more saline growing conditions till resistant cultivars are developed through crosses with the wild species or genetic transformation with optimum management practices.
Authors:J. Kumar, A. Kumar, M. Kumar, S.K. Singh, and L. Singh
In order to study the inheritance pattern of morpho-physiological traits in bread wheat, a 10×10 diallel cross, excluding reciprocals was made and grown in a randomized complete block design (RCBD) with three replications. Observations were recorded on Days to 75% flowering (DF), Days to maturity (DM), Duration of reproductive phase (DRP), Plant height (cm) (PH), Effective tiller/plant (TLS), No. of spikelets per spike (SLS), No. of grains per spike (GS), Grain weight per spike (g) (GW), Spike length (cm) (SL), Biological yield per plant (g) (BY), Harvest index (%) (HI), 1000-Grain weight (g) (TGW), Spike density (SD), Canopy temperature depression (°C) (CTD), Chlorophyll intensity (%) (CI), Chlorophyll fluorescence (Fv/Fm) (CF), Protein content (%) (PC), Grain yield per plant (g) (GY). Highly significant differences were observed among the genotypes for all traits. The resulted 45 F1s and their F2s used for study the nature of gene for grain yield and its contributing traits in bread wheat. The result indicated that considerable gene action and average degree of dominance respond to achieving significant result for grain yield and its component traits. In both the generations F1s and F2s, grain yield per plant (g) was governed by non-additive gene action based on combining ability analysis, (σ2 g/σ2 s)0.5 [GCA and SCA variance ratio] and (H1/D)0.5 [Degree of dominance] were exhibited over dominance type average degree of dominance for grain yield and its component traits in both generations. Genetic analyses of the traits confirm the involvement of both additive and non-additive gene effects in governing the inheritance.
Authors:S. Sareen, N. Bhusal, G. Singh, B.S. Tyagi, V. Tiwari, G.P. Singh, and A.K. Sarial
Heat stress is a matter of a great concern for the wheat crop. Heat stress usually either hastens crop development or shortens the grain filling duration, which severely reduces grain yield. Being a complex trait, understanding the genetics and gene interactions of stress tolerance are the two primary requirements for improving yield levels. Genetic analysis through generation mean analysis helps to find out the nature of gene actions involved in a concerned trait by providing an estimate of main gene effects (additive and dominance) along with their digenic interactions (additive × additive, additive × dominance, and dominance × dominance). In the present investigation, we elucidated the inheritance pattern of different yield contributing traits under heat stress using different cross combinations which could be helpful for selecting a suitable breeding strategy. Thus six generations of five crosses were sown normal (non-stress, TS) and late (heat stress, LS) in a randomized block design with three replications during two crop seasons. The model was not adequate for late sown conditions indicating the expression of epistatic genes under stress conditions. The traits i.e. Days to heading (DH), Days to anthesis (DA), Days to maturity (DM), Grain filling duration (GFD), Grain yield (GY), Thousand grain weight (TGW), Grain weight per spike (GWS) and Heat susceptibility index (HSI) under heat stress conditions were found under the control of additive gene action with dominance × dominance interaction, additive gene action with additive × dominance epistatic effect, dominance gene action with additive × additive interaction effect, additive and dominance gene action with dominance × dominance interaction effect, additive gene action with additive × dominance epistatic effect, additive gene action with additive × additive interaction effect and dominance gene action with additive × additive interaction effect, respectively.