Involvement of higher order interactions addressing complex polygenetically controlled inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot] resistance in pearl millet [Pennisetum glaucum (L.) R.Br.]

Inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot]resistance was studied using generation mean analysis in pearl millet [Pennisetum glaucum (L.) R.Br.]. Eleven basic generations, namely, P₁, P₂, F₁, F₂, B₁, B₂, B₁F₂, B₂F₂, L₁, L₂ and L₃ of three crosses involving six diverse lines for downy mildew incidence were evaluated under artificial epiphytotic conditions over two environments. The downy mildew incidence was best fitting for digenic, trigenic and tetragenic ratios when fitted into classical Mendelian ratios demonstrating involvement of two or more genes. Digenic and trigenic interaction models were adequate in the case of crosses I and III respectively, to account for the total variability in generation means. Unlike severity, comparative estimates of gene effects over two environments were mostly consistent in all crosses for prevalence. Most of the epistatic and major gene effects were found significant in all crosses for both the disease traits. Non-allelic interactions particularly at three-gene loci viz., w (additive × additive × additive) and y (additive × dominance × dominance) in cross II and all trigenic interactions in cross III were predominant. Duplicate dominance (cross I) and complementary epistasis (crosses II and III) were observed for both the traits revealing inconsistency of gene effects over crosses. The gd₁ (interaction of additive gene effect with e₁) and gh₁(interaction of dominant gene effect with e₁) were significant in crosses I and II, indicating interaction of additive and dominance gene effects with environments. Thus a breeding method that can mop up the resistant genes to form superior gene constellations interacting in a favorable manner against pathotype I would be more suitable to accelerate the pace of resistance improvement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimation of additive, dominance and digenic epistatic interaction effects for certain yield characters in Vigna sesquipedalis Fruw

Inheritance of yield and yield contributing characters were investigated using generation mean analysis, utilising the means of six basic populations viz., P₁, P₂, F₁, F₂, BC₁P₁ and BC₁P₂ in four crosses of Vigna sesquipedalis. The analysis reiterated that the importance of dominance (h) gene effects for pod yield/plant and pods/plant as compared to additive (d) gene effects. However, significant and positive additive effects were noticed for pod yield/plant, pods/plant, pod weight and seed weight in different crosses. The three types of gene interactions (additive, dominance and epistasis) were significantly involved for pods/plant in cross KU 7 ×KU 8. Among the digenic epistatic interactions, both additive ×additive (i) and dominance × dominance (l) contributed more for pod yield/plant and pods/plant, however, it varied among the crosses. Populations having earliness can be developed as indicated by reducing dominance effects. Pedigree selection and heterosis breeding is suggested to exploit the fixable and non fixable components of variation respectively in Vigna sesquipedalis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to Fusarium head blight in the wheat lines 'CJ 9306' and 'CJ 9403'

Fusarium head blight (FHB or scab) caused by Fusarium graminearum is a worldwide serious disease in wheat. Exploitation and genetic studies of elite resistance sources can speed up the development of resistant cultivars. To characterize the inheritance of host plant resistance in two new lines, ‘CJ 9306’ and ‘CJ 9403’, developed from a recurrent selection programme in China, six generations P₁, P₂, F₁, F₂, B₁ and B₂ of four crosses and 137 F_{6 : 7} recombinant inbred lines (RILs) from one cross were evaluated in the greenhouse for scab resistance using single‐floret inoculation. The data of area under disease progress curve (AUDPC) in F₂, backcross (BC) and RIL populations exhibited mono‐modal distributions without clear‐cut demarcations and skewing towards resistance. An additive–dominance model was well‐fitted, additive effects played a predominating role, and dominance effects were also significant. Continuous distributions with two major peaks and one minor peak for the number or percentage of scabby spikelets (NSS or PSS) in segregating populations implied the existence of major genes or quantitative trait loci (QTL) for resistance. The estimates of broad‐sense and narrow‐sense heritabilities based on the six‐generation experiment were 56–76% and 26–67% respectively. The estimates of broad‐sense heritabilities based on anova with RILs were 89–90%. These two improved lines with excellent scab resistance and good agronomic traits are of interest for wheat breeding and production.     

Inheritance of stalk rot resistance in cauliflower (Brassica oleracea var. Botrytis L.)

Summary The inheritance of resistance in cauliflower to stalk rot (Sclerotinia sclerotiorum (Lib.) de Bary) was investigated in population from six generations of six crosses. Disease incidence was recorded on 4 parents, 6 F^s ₁, 6 F^s ₂ and 12 back-crosses in a screenhouse under artificially created epiphytotic conditions. Resistance to stalk rot in this set of parents was found to be polygenic and under the control of recessive genes and due primarily to additive gene action. A breeding strategy emphasizing recurrent selection should lead to improvement in resistance.     

Inheritance of grain filling duration in spring wheat

The genetic basis of grain-filling duration (GFD, days from anthesis to maturity) in six spring wheat hybrids involving nine varieties (‘Son-alika’/‘Bobwhite’, ‘Sonalika’/‘Glennson 70’, ‘Lelija’/‘Bobwhite’, ‘Lelija’/‘Mitacore’, ‘Buckbuck’/‘Dugoklasa’, and ‘Vesna’/‘Radu?a’) and their F₁, F₂, BC₁, and BC₂ generations was studied in the field near Sarajevo, Yugoslavia. Parental means differed in four of the six crosses. Generation mean analyses of genetic effects indicated that an additive-dominance model was sufficient for only two crosses: Lel/Bow and Lel/Mco. One or more types of epistasis were significant in the remaining crosses. The F₁ and F₂ means were either intermediate, closer to the mean of the parent with the longer GFD, or closer to the mean of the Parent with the shorter GFD. Even though different modes of gene action controlled GFD among the six crosses, the heritabilities were reasonably high (narrow sense, 39-59) range for six crosses), indicating that progress could be made from selection in these crosses for either long or short GFD. The parents were selected to have a range in days from planting to anthesis and to maturity. The relationship between dates of anthesis or maturity and GFD was not consistent, but the two latest-maturing varieties had the longest GFD, indicating that anthesis or maturity dates are not a good criteria for choosing parents for modifying GFD. Additive genetic effects predominated in the crosses studied here, but epistasis involving dominance gene action was sufficiently important. To eliminate confounding epistatic dominance effects and to take advantage of favourable additive × additive effects during selection for GFD, a breeding strategy involving rapid approach to homozygosity followed by selection after the achievement of homozygosity was suggested.     

Inheritance of culm number in two uniculm x multiculm wheat crosses

Summary Effective utilization of uniculm wheat (Triticum aestivum L.) germplasm in breeding programs requires an understanding of the inheritance of the uniculm character. The parents, F₁, F₂, and first generation backcrosses (B₁ and B₂) of two crosses, each utilizing a uniculm spring wheat line and a locally adapted winter wheat cultivar, were space planted in an experiment to acquire information regarding the genetic control of culm number. Significant F₁ deviations from midparent values revealed the presence of substantial non-additive gene effects. The scaling tests of Mather and the joint scaling test detected the presence of epistasis. Hayman's six-parameter model revealed that a negative dominance effect provided the major contribution to variation in culm number, while additive x additive and dominance x dominance gene effects were of considerable importance.     

Genetic Analysis of Developmental Traits in Chickpea

Chickpea (Cicer arietinum L.) is an important legume crop in India. The present study was conducted to investigate the inheritance of several developmental traits in three crosses of chickpea, viz., WFWG III’בT20’, ‘T88’בBold Seeded’, and ‘NP34’בP1528-1-1’, each having seven generations. The seven generations were P₁, P₂, F₁, B₁, B₂, F₂, and F₃. The experimental lay-out was randomized complete block design with three replications. Data were acquired on days to flowering (DF), days to maturity (DM), plant height in cm (PH), number of primary branches (PB), and number of secondary branches (SB). Generation mean analysis was used to estimate the genetic components; narrow sense heritability was estimated using variance components; and correlation analysis to estimate correlation coefficients among different traits. Genetic differences were found in all three crosses for all traits studied. Additive, dominance, and epistatic effects were found for many traits'. Duplicate epistasis was observed for all traits except number of PB. Higher order interactions and/or linkage were detected for DM and SB. For many traits the relative magnitudes of the genetic effects differed among crosses, thus the extrapolation to other crosses may be difficult. The inheritance becomes more complex as the fate of the character is decided at a later stage in the life cycle. Positive heterosis was observed for some traits, but the exploitation of this component may not Feasible since stable male sterile lines are not available. Early maturity and high yield ‘may be selected independently because of the absence of any significant correlation between these two traits.     

Heterosis and epistasis in rapeseed estimated from generation means

Summary Heterosis and epistasis in spring oilseed rape (Brassica napus L.) was analysed by comparing generation means for ten agronomic traits. Parents, F₂, F₃ and F₆ generations of four crosses with Swedish and French material were investigated. The F₂ was 11% higher in yield, earlier in flowering time, and slightly later in maturation when compared with the parents. Randomly derived single seed descent lines had an 8% lower yield, were later flowering and maturing than the parents in F₆. This poorer average performance of recombinant lines is explained by the loss of favourable epistatic interactions present in the parents.     

Inheritance of resistance to race F of broomrape in sunflower lines of different origins

A new race F of broomrape overcomes all known resistance genes in cultivated sunflower, but recently, sources of resistance against race F have been developed. The objective of the present research was to study the inheritance of resistance to race F in crosses between 12 resistant sunflower breeding lines, derived from three different sources of resistance, and the susceptible male‐sterile line P‐21. Parental lines and F₁, F₂, F₃ and BC₁ generations were evaluated for broomrape resistance. Segregations in the F₂ and BC₁ to resistant parent approached resistant to susceptible ratios of 1: 15 and 1: 3, respectively, in most of the crosses, suggesting a double dominant epistasis. However, segregations of 3: 13 and 1: 1 for F₂ and BC₁, respectively, indicating a dominant‐recessive epistasis, were also found. The F₃ data confirmed these results. Owing to the recessive nature of this resistance, it must be incorporated into both parental lines for developing resistant hybrid cultivars.     

Development of an appropriate breeding scheme for tolerance to Empoasca kraemeri in common bean

Summary Significant advances in increasing tolerance to the leafhopper Empoasca kraemeri Ross & Moore in common bean have been obtained using a new breeding scheme where yield under leafhopper attack is the principal selection criterion in the evaluation of progenies. However, to further refine this breeding scheme, a study was conducted to determine whether selection for nonprotected yield would be more effective in early versus late generations. Two selection strategies were compared. In Strategy I, early generation selections in the F₂ and F₃ were compared to Strategy II where late generation selections were made in the F₄ and F₅, with the F₂ and F₃ generations advanced using single pod descent and bulk practices, respectively. Yield trials of the F₆ lines from both selection strategies were conducted under nonprotected and insecticide protected treatments. No significant differences were detected between the two selection strategies. However, Strategy II did produce advanced lines with greater nonprotected yields than did Strategy I, with the best F₆ line, in three out of four crosses, coming out of Strategy II. Late generation selection is recommended over early generation selection. Results of the new leafhopper breeding scheme, based on yield, are compared to the old breeding scheme where selections were made using visual selection practices in early generations.     

Estimates of additive and dominance effects for Fusarium head blight resistance of winter triticale

The most effective strategy to control Fusarium head blight (FHB), a devastating disease of small‐grain cereals, is breeding resistant cultivars. This resistance study of F₁ crosses, F₂ and backcross generations of triticale estimates heterosis, general and specific combining ability (GCA, SCA), additive and dominance effects and compares parents with segregating generations. The genetic material consisted of 10 parents with their 45 F₁ crosses and of six parents with their 15 F₂ progeny and backcrosses to each parent. Genotypes were grown in various environments and artificially inoculated with an aggressive isolate of F. culmorum. FHB was assessed, by visual rating, as the mean of four to five individual ratings of disease development. Heterosis for FHB was of little importance. The correlation between the FHB rating of F₁ crosses and their mid‐parent performance was close. GCA was the predominant source of variation, although the significance of the SCA variance also implied non‐additive allelic interaction. The preponderance of additive gene effects is encouraging for increasing resistance by a recurrent selection programme. The relationship between the GCA effect of a parent and its per se performance was close, which gives the possibility of predicting FHB resistance in F₁ crosses. Additive effects were predominant in the F₂ progeny and also in the backcrosses. Transgressive segregants could not be detected. Searching for them should be postponed to the F₃ or later generations.     

Identification of stable restorers and genetics of fertility restoration in late‐maturing pigeonpea [Cajanus cajan (L.) Millspaugh]

A total of sixty‐six germplasm lines were crossed with five CMS lines, where two belong to A₄ cytoplasm, while other three belong to A₂ cytoplasm. On the basis of pollen fertility test as well as good pod setting, of 330 hybrids, 34 restorer lines were observed in ICPA 2043 and 19 in ICPA 2092. Thirteen germplasm lines restored fertility in both the A₄ CMS lines, viz. ICPA 2043 and ICPA 2092; however, none of the lines restored fertility in A₂ CMS lines. For confirmation of result, restoration competence of identified lines tested subsequently 2 years at two different temperatures. The segregation patterns for fertility restoration studied in F₂ and BC₁F₁ generations of selected ten crosses. Six crosses indicated the involvement of two major genes with recessive epistasis, three crosses confirmed dominant epistasis, and one cross indicated the involvement of duplicate recessive epistasis. The obtained results from this study will hasten the future three‐line breeding programme and lead the hybrid technology to the farmers' field with the better exploitation of CMS lines.     

Inheritance of drought resistance related traits in two crosses of groundnut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

Groundnut (Arachis hypogaea L.) is an important oilseed crop grown in more than 100 countries across wide range of environments. Frequent occurrence of drought is one of the limiting factors adversely affecting groundnut productivity, especially in rainfed areas, and hence genotypes having high water use efficiency (WUE) under limited available water need to be developed. In groundnut, WUE is correlated with SPAD chlorophyll meter reading (SCMR) and specific leaf area (SLA). These two traits, SCMR and SLA, can be used as surrogate traits for selecting for WUE. In order to improve SCMR and SLA, and in turn WUE in groundnut, a good knowledge of the genetic system controlling the expressions of these traits is essential for the selection of the most appropriate and efficient breeding procedure. The present investigation was conducted to determine the gene action controlling the inheritance of SCMR and SLA in two crosses, ICG 7243 × ICG 9418 and ICG 6766 × Chico, and their reciprocals. Six generations of each cross (P₁, P₂, F₁, F₂, BC₁P₁, and BC₁P₂) were evaluated for SCMR and SLA at two stages of the crop growth viz., 60 and 80 days after sowing (DAS). For SCMR at 80 DAS, additive effects were important in both the crosses whereas predominance of dominance effects with duplicate epistasis was observed for SCMR at 60 DAS and SLA at both stages in both the crosses. Predominance of additive effect for SCMR at 80 DAS suggested effective selection could be practiced even in early generations whereas for SCMR at 60 DAS and SLA at both stages in both crosses, it would be better to defer selection to later generations. Further, recording of SCMR and SLA should be done between 60 and 80 DAS for screening the germplasm lines for drought tolerance.     

Genetics of grains per spike in durum wheat under normal and late planting conditions

Parental, F₁, F₂, BC₁, BC₂, BC₁₁, BC₁₂, BC₂₁, BC₂₂, BC₁ self and BC₂ selfed generations of three crosses involving six cultivars of durum wheat (Triticum durum Desf.) were studied for grains per spike under normal and late sown environments to analyze the nature of gene effects. A 10-parameter model did not fully account for the differences among the generation means. In two cases more complex interactions or linkage were involved in the inheritance of grains per spike in durum. Both digenic and trigenic epistatic interactions had a role in controlling the inheritance of grains per spike, however, trigenic interactions contributed more than digenic interactions. Non-fixable gene effects were many times higher than fixable ones in all three crosses and in both sowing environments indicating a major role of non-additive gene effects in the inheritance of this trait. Duplicate epistasis between sets of three genes under both environments was recorded for the cross Raj 911 × DWL 5002. Epistatic interactions, particularly the trigenic ones, contributed the maximum significant heterosis. Epistatic interactions involving dominance in the F₂ generations caused significant inbreeding depression. Selective diallel mating and/or biparental mating could be used for amelioration of grains per spike in durum wheat.     

Genetic analysis of photosynthesis‐related traits in faba bean (Vicia faba) for crop improvement

Increasing productivity through improvement of photosynthesis in faba bean breeding programmes requires understanding of the genetic control of photosynthesis‐related traits. Hence, we investigated the gene action of leaf area, gas exchange traits, canopy temperature, chlorophyll content, chlorophyll fluorescence parameters and biomass. We chose inbred lines derived from cultivars 'Aurora' (Sweden) and 'Mélodie' (France) along with an Andean accession, ILB 938, crossed them (Aurora/2 × Mélodie/2, ILB 938/2 × Aurora/2 and Mélodie/2 × ILB 938/2), and prepared the six standard generations for quantitative analysis (P₁, P₂, F₁, F₂, B₁, and B₂). Gene action was complex for each trait, involving additive and dominance gene actions and interactions. Additive gene action was important for SPAD, photosynthetic rate, stomatal conductance and F_v/F_m. Dominance effect was important for biomass production. It is suggested that breeders selecting for productivity can maximize genetic gain by selecting early generations for canopy temperature, SPAD and F_v/F_m, then later generations for biomass. The information on genetics of various contributing traits of photosynthesis will assist plant breeders in choosing an appropriate breeding strategy for enhancing productivity in faba bean.     

Inheritance pattern of mungbean yellow mosaic disease resistance and gene action for different traits in mungbean (Vigna radiata (L.) Wilczek) under protected and unprotected field conditions

Understanding of mungbean yellow mosaic disease resistance is crucial to develop resistant varieties to combat worldwide threat of the disease epidemics. This study was aimed to determine nature of disease resistance in terms of number of genes governing it and genetics of related traits. Experimental site was located on 31.43°N and 73.06°E with an elevation of 186 m, and evaluation trials were conducted during spring season due to high disease epidemics in this season. Two contrasting genotypes, that is, NM 6‐68‐2 (resistant) and NM 1‐32‐1 (highly susceptible), were crossed to raise six populations, that is, P₁, P₂, F₁, F₂, BC₁ and BC₂ for evaluation under protected and unprotected field conditions using chi‐square test and generation mean and variance analysis. It was discovered that disease resistance was governed by two major genes with additive effects. Disease resistance can easily be incorporated through backcrossing and direct selection following hybridization. Direct selection should be practised at earlier generation for plant height, chlorophyll contents and number of seeds per pod due to preponderance of additive effects whereas at later generations for seed yield per plant, 100 seed weight, harvest index, number of pods per plant and pod length due to involvement of duplicate epistasis.     

Comparison of two crossing and four selection schemes for yield, yield traits, and slow rusting resistance to leaf rust in wheat

The most important breeding objectives in crop improvement are improving grain yield, grain quality, and resistances to various biotic and abiotic stresses. The objectives of our study were to compare two crossing and four selection schemes for grain yield, yield traits, and slow rusting resistance to leaf rust (Puccinia recondita) based on additive genes in wheat (Triticum aestivum), and to identify the most efficient crossing and selection methodologies in terms of genetic gains and cost efficiency. Segregating populations were derived from 18 simple crosses and the same number of top (three-way) crosses. Half of the crosses were derived from Yecora 70 and the other half from Veery #10 as the common leaf rust susceptible parents. The four selection schemes were: pedigree, modified bulk (F₂ and F₁-top as pedigree, selected lines in F₃, F₄, F₂-top, F₃-top as bulk; and pedigree in F₅ and F₄-top populations), selected bulk (selected plants in F₂, F₃, F₄, F₁-top, F₂-top and F₃-top as bulk; and pedigree in F₅ and F₄-top populations), and nonselected bulk (bulk in F₂, F₃, F₄, F₁-top, F₂-top and F₃-top; and pedigree in F₅ and F₄-top populations). A total of 320 progeny lines, parents and checks were tested for grain yield, other agronomic traits and leaf rust resistance during the 1992/93 and 1993/94 seasons in Ciudad Obregon (Sonora State, Mexico) which represents a typical high yielding irrigated site. The influence of the type of cross and the selection scheme on the mean grain yield and other traits of the progenies was minimal. The selection of parents was the most important feature in imparting yield potential and other favourable agronomic traits. Moreover, the highest yielding lines were distributed equally. Progeny lines derived from Veery #10 crosses had significantly higher mean grain yield compared to those derived from the Yecora 70 crosses. Furthermore, a large proportion of the highest yielding lines also originated from Veery #10 crosses. Mean leaf rust severity of the top cross progenies was lower than that of the simple cross progenies possibly because two parents contributed resistance to top cross progenies. Mean leaf rust severity of the nonselected bulk derivatives was twice that of lines derived from the other three schemes. Selected bulk appears to be the most attractive selection scheme in terms of genetic gains and cost efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Prediction of F6 line performance from F3 families in spring oilseed rape. I. Yield and other agronomic traits

Summary The reliability of a selection among crosses based on a cross prediction in early generations was investigated in spring rapeseed. The performance of the parents, the F₂ generation, and random F₃ lines from four crosses were used to predict the probability of finding superior recombinant lines. These predictions were made for two years and compared with the observed performance of F₆ lines in the second of these two years and in an additional year. Predicted and observed performances coincided reasonably for the characters plant height, standability, maturity and an index calculated from seed yield, oil content and protein content. For seed yield and flowering time, the predictions were very unreliable. In conclusion, prediction methods may be useful in rapeseed breeding, if quality traits are of major commercial interest.     

Investigations into the breeding system of cauliflower

In experiments to study the effect of inbreeding, I₁ progenies of summer cauliflower showed a trend towards increase in plant weight over their non-inbred commercial parents. Curd quality, however, showed no significant improvement.As summer cauliflower varieties tended to behave as pure lines, studies were made on F₁'s from crosses between five commercial varieties. The main results of hybridisation were an increase in earliness, and a slight, though significant increase in curd size over the parental varieties. It is suggested that summer cauliflowers have attained a state of homozygous balance, which could be emulated in the autumm and winter types, by selection of self-compatible individuals.     

The inheritance of quantitative traits in Brassica napus ssp. rapifera (swedes): Augmented triple test cross analyses of production characters

Two F₂ triple test crosses, augmented with F₃s, produced from crosses between different inbred lines of swedes (Brassica napus ssp.rapifera L.) were assessed in field trials at Dundee in 1988 and 1989,respectively. This paper reports the analyses of resistance to powdery mildew, neck length, growth cracks, sugar content and hardness; analyses of yield have been published previously. Additive genetical variation was found for all traits while non-additive variation was less important, the highest degree of dominance being 0.44 for hardness. There was evidence of additive × dominance and dominance × dominance epistasis for mildew and additive × additive epistasis for neck length and hardness. Significant,consistent reciprocal differences were found and these were particularly large for neck length and growth cracks. Sugar determination was carried out on the basic generations of the second cross, the parental lines of which showed large differences in concentration of glucose, fructose and sucrose. Directional dominance was found for high glucose but not for fructose or sucrose. The implications of these results for swede breeding are discussed and it is proposed that inbred cultivars would be a more practical option than F₁ hybrids. This revised version was published online in August 2006 with corrections to the Cover Date.