Genetic studies for seed size and grain yield traits in kabuli chickpea

Seed size, determined by 100-seed weight, is an important yield component and trade value trait in kabuli chickpea. In the present investigation, the small seeded kabuli genotype ICC 16644 was crossed with four genotypes (JGK 2, KAK 2, KRIPA and ICC 17109) and F₁, F₂ and F₃ populations were developed to study the gene action involved in seed size and other yield attributing traits. Scaling test and joint scaling test revealed the presence of epistasis for days to first flower, days to maturity, plant height, number of pods per plant, number of seeds per plant, number of seeds per pod, biological yield per plant, grain yield per plant and 100-seed weight. Additive, additive?×?additive and dominance?×?dominance effects were found to govern days to first flower. Days to maturity and plant height were under the control of both the main as well as interaction effects. Number of seeds per pod was predominantly under the control of additive and additive?×?additive effects. For grain yield per plant, additive and dominance?×?dominance effects were significant in the cross ICC 16644?×?KAK 2, whereas, additive?×?additive effects were important in the cross ICC 16644?×?JGK 2. Additive, dominance and epistatic effects influenced seed size. The study emphasized the existence of duplicate epistasis for most of the traits. To explore both additive and non-additive gene actions for phenological traits and yield traits, selection in later generations would be more effective.     

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.     

Genetics of spike length in durum wheat

Gene effects were analyzed using mean spike length of 12 populations, viz., both parents, F₁, F₂, first back cross generation, BC₁ and BC₂, second backcross generations, BC₁₁,BC₁₂, BC₂₁ and BC₂₂ along with BC₁ self and BC₂ self derived by selfing BC₁ and BC₂populations of three crosses involving six diverse cultivars of Triticum durumto determine the nature of gene actions governing spike length through generation mean analysis under normal and late sown environments. The six-parameter model was adequate in most of the cases to explain genetic variation among the generation means under both the sowing environments. Additive (d) gene effect was significant in all the cases, whereas dominance (h) gene effect was not so frequently observed significant. Epistatic effects, particularly digenic types were predominant over additive and dominance effects in most of the cases under both normal and late sown environments except in the cross Cocorit 71 × A-9-30-1 (normal sown).Additive × dominance × dominance (y), trigenic interaction played significant role in controlling the inheritance of this trait in the cross HI 8062 × JNK-4W-128under late sown condition. Duplicate epistasis was observed in the cross HI 8062× JNK-4W-128 (normal sown). Non-fixable gene effects were of higher magnitude than fixable gene effects in almost all cases, confirmed the major role of non-additive gene effects to control the inheritance of spike length in durum wheat. Significant heterosis over better parent was not observed. Similarly, inbreeding depression was not commonly observed. Favourable and suitable environment must be considered before finalizing breeding programme for its simple inheritance to get desirable improvement for high grain yield. Hybridization systems, such as biparental mating and / or diallel selective mating, which exploit both additive and non-additive gene effects, simultaneously, could be useful in the improvement of spike length in durum wheat. This revised version was published online in July 2006 with corrections to the Cover Date.     

The mechanism of genetic control for low soil nitrogen (N) tolerance in common beans (Phaseolus vulgaris L.)

The study was conducted to determine the mode of inheritance and the genetic mechanisms associated with bean nitrogen use efficiency under low soil nitrogen. Eight widely grown and well adapted low soil N tolerant lines (CAL143, CIM9314-36, and AFR708) and non-tolerant varieties (E5, E8, GLP-2, CAL96, and SCAM80-CM/15) were crossed in a half diallel mating design. The parents and their F₁ generations were evaluated under low soil N and moderate soil N conditions. Significant genetic differences were observed for basal root length, root dry weight, nodule numbers, leaf area and grain yield for both N conditions. Inheritance of the traits associated with better performance under low soil N was found to be under both additive fixable and non-fixable genetic effects. Genotypes that had well-developed basal root systems performed better than those with less developed basal roots. F₁ hybrids from crosses between low N tolerant and non-tolerant parents performed better under nitrogen stressed conditions compared with those between susceptible parents. Hybrids involving CAL143 as one of the parents showed high levels of tolerance to low soil nitrogen conditions. Among parents, CAL143 showed the best performance for basal root length, root dry weight, nodule numbers, leaf area, and grain yield. This parent had highly significant GCA effects for the traits under both N conditions, except basal root length which was significant at Kabete and non-significant leaf area at Thika. The results show that CAL143 would be a good parent to use in a low soil N bean breeding program.     

Genetic analysis of low-temperature tolerance during germination in tomato, Lycopersicon esculentum Mill.

The genetic basis of low-temperature tolerance during germination of tomato seed was investigated using two approaches. First, a cold-tolerant (PI 120256) and a cold-sensitive tomato cultivar (UCT5) and their reciprocal F₂, F₃ and BC₁ progeny (total of 10 generations) were evaluated for germination at a low (11 ± 0.5°C) and a high (control) temperature 20 ±0.5° C) Weighted least-square regression analysis indicated that in the low-temperature treatment most of the variation resulted from additive genetic effects, and dominance and epistatic interactions were nonsignificant. Partitioning of the total genetic variance into those attributable to the effects of embryo, endosperm, testa and the cytoplasm indicated that additive effects of endosperm and embryo could individually account for 80% and 77% of the total variance, respectively. In the control treatment, greater than 60% of the variation could be explained by individual additive effects of endosperm or embryo and ? 27% of the variation could be explained by embryo dominance effects. Across generations, there was a positive correlation (r = 0.78, P < 0.01) between germination in the control and low-temperature treatments and there were no significant genotype × temperature interactions. The results indicate the presence of similar or identical genes with predominantly additive effects on germination under both low and high temperatures. In the second approach, the effectiveness of directional phenotypic selection to improve tomato cold tolerance during germination was evaluated by selecting (in an F₂ population of the same cross) the fastest germinating seeds under low temperature and comparing the germination of the selected F₃ progeny with germination of an unselected F₃ population. The results indicated that selection was highly effective and significantly improved germination performance of the progeny; a realized heritability of 0.74 was obtained for low-temperature tolerance during germination. It is concluded that in these tomato lines germination under low temperature is genetically controlled, with additivity being the major genetic component, and thus the trait can be improved by phenotypic selection.     

Generation mean analysis of resistance to downy mildew in adult muskmelon plants

Downy mildew (Pseudoperonospora cubensis) is the most devastating disease in muskmelon (Cucumis melo). A generation mean analysis study was designed to determine the types of gene action and estimate the heritability for resistance to downy mildew in four selected crosses of muskmelon. Generation mean analysis revealed that genetic dominance may be of greater importance for expression of resistance to downy mildew in both greenhouse and field experiments and in all the crosses. The F₁ mean was significantly lesser than the mid-parent value and skewed towards resistant parent in all the crosses. Negative sign associated with gene effects indicated, in those crosses, that disease level could be decreased in relation to midparent. All the crosses expressed significant and positive additive (d) gene effects. Dominance (h) and dominance × dominance (l) gene effects had opposite sign in all crosses and both experiments, which implied duplicate type of gene action. High mid-parent heterosis in all the crosses indicated strong dominance effects (as combination of parental alleles) for resistance to downy mildew. In all the crosses, both resistant and susceptible parent contributed one or more dominant/partially dominant factors for resistance. Estimates of broad-sense heritability were high and relatively consistent in both experiments. The two different screening experiments showed that fixable gene effects (d + i) were lower than the non-fixable gene effects (h + l) in all the crosses indicating greater role of non-additive effects in the inheritance of resistance to downy mildew. Resistance to downy appeared to be controlled mainly by dominance effects, therefore the inbred lines IIHR 121 and IIHR 122 could be used strategically to exploit heterotic effects.     

Genetic impacts of fiber sugar content on fiber characters in Sea Island cotton, Gossypium barbadense L.

A genetic model with additive effect, dominant effect, additive × additive effect, and their interaction with environment effect (GE) was employed to analyze the 2-year data of F₁ and F₂ hybrids from 5 × 4 diallel cross, whose parents were Sea Island cotton with different fruit branch types. Unconditional and conditional genetic variances were analyzed to demonstrate genetic impacts of fiber sugar content on fiber characters. Results of unconditional genetic variances showed that dominance × environment interaction effect and additive × additive epistatic effects mainly controlled the genetic variation of fiber sugar content, and environment influenced the inheritance of fiber sugar content. Fiber uniformity, fiber elongation, and fiber micronaire were mainly controlled by dominance × environment effects. Fiber strength was mainly controlled by the interaction of additive × additive epistatic effects and the environment. Analysis of correlation coefficients indicated that the varieties or hybrids with high-fiber sugar content had short fiber, low-fiber uniformity, strength, and fineness, which indicated the close co-variation between fiber quality traits and fiber sugar content. Relatively better fiber quality traits could be obtained effectively through selecting parents with low-fiber sugar. Fiber sugar content of different parents had different genetic effect on fiber quality traits.     

Inheritance of Bolting in Three Sugar Beet Crosses after Different Periods of Vernalization

The induction of bolting after different periods of vernalization was studied in the parental, F₁, F₂ and backcross generations (F₂× P₁ and F₂× P₂) of three crosses between five sugar beet lines. The parental lines represented different levels of bolting resistance. The populations were evaluated in replicated field or greenhouse trials. Generation mean analysis was used to quantify the genetic effects of bolting. The additive (d) parameter was predominant for those levels of cold treatment that stimulated the bolting to occur. The dominance (h) parameter was also shown to be important in most cases. In one cross, the additive × additive (i) type of epistasis was significant. The chances of detecting genetic effects are increased by exposing the plants to vernalization conditions which maximize the difference between two parental lines of each cross. Hence, it would be sensible to exploit both additive and non-additive genetic effects in any selection programme.     

Genetics of resistance to early blight (Alternaria solani Sorauer) in tomato (Lycopersicon esculentum L.)

The genetic nature of early blight resistance in tomato was studied in three crosses at seedling and adult plant stages. A six generation mean analysis of the cross Arka Saurabh (susceptible) × IHR1939 (resistance) and its reciprocal cross revealed that the resistance to early blight was conferred by recessive polygenes at both seedling and adult plant stages. This polygenic early blight resistance revealed the importance of additive and additive × additive gene effects at seedling stage and higher magnitude of dominance and dominance× dominance gene effects at adult plant stage. Evaluation of parents, F₁, F₂ and backcross generations of IHR1816 (resistance) × IHR1939 (resistance) revealed that the early blight resistance genes in IHR1816 (Lycopersicon esculentum NCEBR-1) and IHR1939 (Lycopersicon pimpinellifolium L4394) are independent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combining ability and heritability of soybean resistance to groundnut leaf miner

Groundnut leaf miner (GLM) (Aproaerema modicella) (Deventer) is one of the most destructive pests of soybean and groundnuts. In this study, the mode of inheritance, general combining ability (GCA), specific combining ability (SCA) effects, maternal effects of resistance to GLM and grain yield ha^?1 were determined. Thirteen soybean parental genotypes and 81 F₂ populations were evaluated for resistance to GLM in a 5?×?19 alpha lattice diallel design with two replications under natural GLM infestation in northern (Arua) and eastern (Iki-iki) Uganda during September to December 2016 rainy season. Highly significant differences were observed among parental genotypes and F₂ populations for GLM incidence, severity, and grain yield. The estimates of GCA effects were significant for GLM incidence and severity scores but not for the number of larvae per plant and grain yield ha^?1. SCA effects were non-significant for all the studied traits, suggesting that GCA effects were the major component responsible for soybean resistance to GLM with additive gene effects being more important for these traits. Baker’s ratio ranged from 0.44-1.0 for most of resistant traits except number of larvae per plant and grain yield ha^?1. The results indicated also that cultivars Maksoy1 N, PI615437, PI578457A and NIIGC4.1-2 were good combiners against GLM incidence and severity. Parent PI615437 was a good combiner for grain yield and Maksoy1 N?×?PI615437 was a superior cross for grain yield and against GLM incidence. There were no maternal effects for the inheritance of resistance to GLM. The study provides a basis for understanding patterns of inheritance of soybean resistance to groundnut leaf miner for an efficient breeding program.     

Genetic Analysis of Resistance to Phytophthora Root Rot in Tomato (Lycopersicon esculentum Mill.)

The resistant accession, LA1312, and the susceptible cultivar ‘Peto 343′, were crossed to develop F₁, F₂ and BC₁ populations for genetic analysis of resistance in tomatoes to Phytophthora parasitica Dastur, the causal agent of Phytophthora root rot. There was no maternal effect on resistance. Generation means analysis indicated that tolerance to Phytophthora root rot was under genetic control with both simple (additive and dominance) and digenic interaction (additive × additive and additive × dominance) effects contributing to the total genetic variation among generation means. Weighted least square regression analysis indicated that the majority (ca. 96 %) of the genetic variation could be explained by simple additive effects alone. Narrow sense heritability was estimated as 0.22. Based on effective factor formulae, at least five effective factors controlled the resistance. Implications for breeding procedures are discussed.     

Generation mean analysis of phosphorus‐use efficiency in freely nodulating soybean crosses grown in low‐phosphorus soil

Freely nodulating soybean genotypes vary in their phosphorus (P) uptake and P‐use efficiency (PUE) in low‐P soils. Understanding the genetic basis of these genotypes’ performance is essential for effective breeding. To study the inheritance of PUE, we conducted crosses using two high‐PUE genotypes, two moderate‐PUE genotypes and two inefficient‐PUE genotypes, and obtained F₁, F_2, BC₁ and BC₂ populations. The inheritance of PUE was evaluated using a randomized complete block design. A generation mean analysis of phenotypic data showed that PUE was heritable, with complex inheritance patterns and the presence of additive, dominance and epistatic gene effects. Seed P, shoot P, root P, P‐incorporation efficiency and PUE were largely quantitatively inherited traits. There were dominance, additive × additive and dominance × dominance gene effects on PUE, grain yield, shoot dry weight, 100‐seed weight, root dry weight and shoot dry matter per unit P for populations grown under low‐P conditions. Dominance effects were generally greater than additive effects on PUE‐related indices. These PUE indices can be used to select P‐efficient soybean genotypes from segregating populations.     

Genetic effects of embryo and endosperm for four malting quality traits of barley

Seed of seven cultivars of two-rowed barley (Hordeum Vulgare L.) and F2 seed from a half-diallel set of crosses among the cultivars were malted in two years to obtain data on diastatic power (DP), alpha-amylase activity (αAA), beta- amylase activity (βAA) and malt nitrogen (N) content. Embryo and endosperm genetic effects on the traits were studied by using a genetic model including genotype × environment interaction for malting quality characters. Variation of the four malting quality traits was affected by gentic effects and environmental interaction. Performance of DP and βAA was mainly controlled not only by endosperm dominance effects but also by embryo genotype × environment interaction and endosperm dominance × environment interaction. Variation of αAA and malt N content was controlled by both embryo and endosperm genetic effects, but the embryo dominance and endosperm additive effects contributed a major part to the total genetic effects. Significant interaction variances (embryo additive × environment and dominance × environment and endosperm dominance × environment) were also observed for αAA and malt N content. Diastatic power was related positively to βAA. Malt N content was associated positively with DP, largely because of the relationship between malt N and βAA. No obvious phenotype association between DP and αAA was found. General narrow-sense heritabilities of αAA and malt N content were 26.1% and 27.8%, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of plant height using two immortalized populations of “CRI12 × J8891” in Gossypium hirsutum L.

Plant height is an important plant architecture trait that determines the canopy structure, photosynthetic capacity and lodging resistance of upland cotton populations. To understand the genetic basis of plant height for marker-assisted breeding, quantitative trait loci (QTL) analysis was conducted based on the genetic map of recombinant inbred lines (RILs) derived from the cross “CRI12 × J8891” (Gossypium hirsutum L.). Three methods, including composite interval mapping, multiple interval mapping and multi-marker joint analysis, were used to detect QTL across multiple environments in the RILs and in the immortalized F₂ population developed through intermating between RILs. A total of 19 QTL with genetic main effects and/or genetic × environment interaction effects were identified on 15 chromosomes or linkage groups, each explaining 5.8–14.3 % of the phenotypic variation. Five digenic epistatic QTL pairs, mainly involving additive × additive and/or dominance × dominance, were detected in different environments. Seven out of eight interacting loci were main-effect QTL, suggesting that these loci act as major genes as well as modifying genes in the expression of plant height. The results demonstrate that additive effects, dominance and epistasis are all important for the genetic constitution of plant height, with additive effects playing a more important role in reducing plant height. QTL showing stability across environments that were repeatedly detected by different methods can be used in marker-assisted breeding.     

Genetics of grain yield and other agronomic characters in t'ef (Eragrostis tef Zucc. Trotter). I. Generation means and variances analysis

Quantitative genetics of grain yield and other agronomic characters of t'ef (Eragrostis tef) were studied using the F₁, F₂, BC₁, and BC₂ of the cross Fesho × Kay Murri. The study was carried out to estimate gene effects controlling the inheritance of grain yield and related agronomic characters. Significant additive [d] and dominance × dominance [l] interaction effects were detected for grain yield. The variations of yield per panicle and panicle weight were explained in terms of [d], dominance [h], and additive × additive [i] interactions. Non-allelic gene interactions were also detected for kernel weight, harvest index, tiller number, plant height, days to heading and days to maturity. The simple additive-dominance model explained the variation for panicle length, culm diameter and plant weight, allowing unbiased estimates of additive (D) and dominance (H) variance components. Large dominance variances (H) were estimated for grain yield, yield per panicle, and panicle weight. The additive variances for plant height, panicle length, days to heading and days to maturity were higher than the respective dominance variances. High narrow-sense heritability (h²) values (> 0.50) were estimated for plant height, panicle length, days to heading and days to maturity. The lowest h² (0.09) was obtained for kernel weight for which there was little variability. Since grain yield and several important agronomic characters of t'ef are influenced by non-allelic gene interaction, it is advisable to delay selection for yield to later generations with increased homozygosity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combining ability analysis of earliness and yield of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) genotypes in Uganda

Potato (Solanum tuberosum L.) is a major food and cash crop mainly grown by small-scale farmers in the highland regions of Uganda. Changing global weather patterns require varieties that are able to grow within the short rainfall cycles and yield optimally under the prevailing conditions. The objectives of this study were to estimate the combining ability effects for early maturity, yield and yield related traits in potato. Eighteen F¹ families generated from two sets of 12 parents using a North Carolina Design II were evaluated for days to 50% flowering, leaf senescence, yield and yield related traits in two different locations. Both additive and non-additive genetic effects influenced the expression of traits. However, additive genetic effects were predominant over the non-additive for most of the traits. The GCA/SCA ratios were 0.68 and 0.78 for days to 50% flowering and average tuber weight. Broad sense heritability estimates were 0.70 for total tuber weight and 0.78 for days to 50% flowering. The predominance of additive genetic effects imply that, genetic gains can be achieved through different selection methods and traits transferred to the respective progenies. Parents Rwangume, 396,038.107, 395,011.2, NKRK19.17, 393,077.54, Kimuri, and 392,657.8 had desirable GCA effects for the number of days to flowering and yield related traits. Families of Rwangume?×?NKRK19.17, 393,077.54?×?395,011.2, 396,038.107?×?Rwangume and 396,038.107?×?395,011.2 had desirable SCA effects for yield and number of days to 50% flowering. The selected parents and families will be subjected to further clonal evaluation and selection.     

Apical Development and Growth of Barley under Different CO2 and Nitrogen Regimes

Increases in atmospheric carbon dioxide (CO₂) concentration have stimulated interest in the response of agricultural crops to elevated levels of CO₂. Several studies have addressed the response of C₃ cereals to CO₂, but the interactive effect of nutrient supply and CO₂ on apical development and spikelet set and survival has not been investigated thoroughly. Hence, an experiment was conducted in the greenhouse to evaluate the effect of high (700 μmol CO₂mol^?1 air) and low (400 μmol mol^?1) levels of atmospheric CO₂ on apical development, spikelet set and abortion, and pre- and post-anthesis growth in spring barley (Hordeum vulgare L.) grown under high N (0.3 g N pot^?1 before sowing ?1–0.11 g N pot^?1 week^?1) and low N (0.3 g N pot^?1) regimes. The plants were grown in 5 L pots. Development of spike was hastened due to CO₂ enrichment, and the C+ plants pollinated few days earlier than the C— plants. Carbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinated 10 days later and matured 2 weeks later when compared with plants under low N. Carbon dioxide enrichment did not affect the number of spikelets at anthesis. Excess N decreased spikelet abortion and the increased maximum number of spikelets under both [CO₂]. Barley plants did not tiller when grown in low [CO₂] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appeared in other treatments, may have contributed to this. Carbon dioxide enrichment increased the C concentration of plants, but decreased the N concentration under high N regime. Both the C and N concentration of plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9 % under high N regime and by 21 % under low N regime. Under high [CO₂] increased kernel number on tiller spikes, and increased kernel weight both on main stem and on tiller spikes resulted in a 23 % increase in kernel yield under low N regime and 76 % increase in kernel yield under high N regime. The rate of N application influenced growth and yield components to a greater extent than CO₂ enrichment. At maturity, plant dry matter, kernel weight, the number of kernels per spike, and the number of spikes per plant were higher under high N regime than under low N regime. Long days (16 h), low light intensity (280 μmol m^?2s^?1), and at constant temperature of 20 °C high [CO₂] increased kernel weight and the number of kernels on tiller spikes under high and low N application rate, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.     

Inheritance of β-carotene concentration in durum wheat (Triticum turgidum L. ssp. durum)

Despite being one of the important characteristics in determining pasta quality in durum wheat (Triticum turgidum ssp. durum), there is no direct report on inheritance of β-carotene concentration. The objectives of this study were to determine the inheritance of β-carotene concentration and the number of genes involved in six crosses of durum. For the cross PDW-233 (P₁) × Bhalegaon-4 (P₂), F₁, F₂, BCP₁ and BCP₂ populations were developed. For all other crosses, only the F₁ and F₂ populations were developed. β-carotene concentration was determined for all populations and parents of each cross grown at Hol, Maharastra, India. The cross PDW-233 × Bhalegaon-4 was also evaluated at Dharwad, Karnataka, India. Low β-carotene concentration was partially dominant in most of the crosses. Broad sense heritability was 67 and 91% at Dharwad and Hol, respectively, for the cross PDW-233 × Bhalegaon-4 and varied from 74 to 93% for the other five crosses indicating the presence of additive gene effects. The frequency distributions of the trait in the F₂ populations were not normal and were skewed towards the lower parent. Segregation of β-carotene concentration in the six F₂ populations indicated that at least two major genes and two or three minor genes with modifying effects govern the trait. Analysis of variance indicated that environment had comparatively little influence on the trait and this should allow for easy selection. The joint scaling test revealed additive × additive, additive × dominance and dominance × dominance epistatic interactions in the cross PDW-233 × Bhalegaon-4. These authors contributed equally.     

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.     

Genetic analysis of yield and its components in vegetable cowpea (Vigna unguiculata L. Walp)

The F2 and backcrosses of a cross between two vegetable cowpea (Vigna unguiculata L. Walp) varieties with contrasting characteristics were evaluated for pod yield and its components, with the aim of understanding the genetic basis of these characteristics. A four-parameter model incorporating the additive, dominance and additive × additive genetic components fitted the data for pod yield and clusters per plant. The additive and additive × additive effects were positive and were larger than the dominance component. The relatively large additive and the predominantly positive dominant effects suggest that selection would be effective. Pod weight had high broad (84%) and narrow sense heritability (75%) and can be effectively selected for in the early generations. The study suggested that vegetable cowpea improvement programs should focus on selecting for clusters per plant and average pod weight in the early generations, while selection for dry pod yield could be delayed to later generations. It was concluded that pods per plant may be a useful selection criterion in multi-location trials aimed at selecting for stability of yield. This revised version was published online in July 2006 with corrections to the Cover Date.