Showing papers on "Diallel cross published in 2002"

Biplot Analysis of Diallel Data

Abstract: Diallel crosses have been used in genetic research to determine the inheritance of important traits among a set of genotypes and to identify superior parents for hybrid or cultivar development. Conventional diallel analysis is limited to partitioning the total variation of the data into general combining ability (GCA) of each genotype and specific combining ability (SCA) of each cross. In this paper we formulate a biplot approach for graphical diallel analysis. The biplot is constructed by the first two principal components (PCs) derived from subjecting the tester-centered diallel data to singular value decomposition. It displays the most important entry by tester patterns of the data and allows the following information to be extracted visually: (i) GCA of each genotype; (ii) SCA of each genotype; (iii) groups of parents with similar genetics; and (iv) superior hybrids. In addition, the biplot allows hypotheses to be formulated concerning the genetics of the genotypes. Three published diallel data sets of wheat (Triticum aestivum L.) and maize (Zea mays L.) were used to demonstrate the biplot approach and detailed procedures were provided for constructing and interpreting a biplot.

Forage Yield Heterosis in Alfalfa

Abstract: Increasing forage yields remains a top priority of most alfalfa (Medicago saliva L.) breeding programs, but yield trends suggest yield has stagnated over the past two decades. Little effort has been invested into capturing heterosis in alfalfa, but semihybrid breeding systems are a possible solutions to overcome forage yield stagnation. Development of alfalfa semihybrids will require identification of heterotic groups. Studies of crosses between dormant M. saliva ssp. saliva and M. saliva ssp. falcata suggest a heterotic pattern exists between the two subspecies. The objective of this study was to measure heterosis in elite sativa × falcata crosses (SFC) in relation to elite sativa × sativa crosses (SSC) and falcata × falcata crosses (FFC). Nine elite sativa clones and five falcata clones were crossed in a diallel mating design. Progeny were space planted in 1998 at Ames and Nashua, IA, and harvested for forage yield twice in 1998 and three times in 1999. A definite sativa-falcata heterotic pattern was observed. Sativa-falcata heterosis was observed at the subspecies, halfsib, and individual cross level calculated using subspecies comparisons, halfsib heterosis analysis, and combining ability analysis. On average, intersubspecific crosses yielded 18% more than the average of intrasubspecific crosses. The sativa-falcata heterotic pattern is a potentially useful resource in alfalfa breeding programs.

Genetic diversity in bread wheat, as revealed by coefficient of parentage and molecular markers, and its relationship to hybrid performance

Abstract: Variable results have been obtained in different crop species using geneticsimilarity (GS) estimates based on molecular markers and coefficient ofparentage (COP) to predict heterosis.This study was designed: i) to assess the level of GS among 40 breadwheat (Triticum aestivum L.) cultivars selected in Central and SouthEurope; ii) to compare GS with COP; iii) to correlate the estimates ofparental diversity with the heterotic effects detected on 149 F1hybrids obtained by crossing the 40 cultivars according to three matingdesigns.The parental cultivars and the F1 hybrids were grown in severallocations at normal seed density. Significant heterotic effects were detectedfor grain yield and other traits including quality attributes. The parentalcultivars were assayed for DNA polymorphisms using two classes ofmarkers: 338 RFLP and 200 AFLP® bands were scored. GS estimates werecomputed considering each molecular marker set separately (GSRFLP,GSAFLP) and together (GSTOT). Ample differentiation amongthe parental cultivars was detected with the two marker sets. Although theaverage GSTOT (0.43) was higher than COP (0.10), the twomeasurements were significantly correlated (r = 0.36, p < 0.01).Correlations between the different estimates of genetic diversity andF1 performance or mid parent heterosis for grain yield and otherrelated traits were in general low although statistically significant.A more detailed analysis was conducted on 28 F1 hybridsproduced in a half diallel cross of eight parental cultivars characterized byhigh heterotic effects for grain yield. The GS estimates based on RFLP,AFLP® markers and also on RAPD were partitioned into general andspecific components. Correlations with general and specific combiningability effects for the measured traits were in several cases statisticallysignificant but too low to be predictive and therefore exploitable in practicalbreeding.

Sexual compatibility within and between olive cultivars

Abstract: SummarySelf- and cross-incompatibility of the olive cultivars Frantoio, Manzanillo, Kalamata, Pendolino, and Picual were investigated using a 5 × 5 diallel matrix. Pistils were collected seven days after controlled pollinations on the day of flower opening, and pollen tubes were detected by fluorescence microscopy. Diallel analysis showed significant specific combining ability, general combining ability and reciprocal effects between cultivars for pollen tube growth in the pistil. ‘Frantoio’ was cross-compatible, as either a male or female parent, with each of the other cultivars, but showed a high degree of self-incompatibility. ‘Manzanillo’, ‘Kalamata’, ‘Pendolino’, and ‘Picual’ were crossincompatible, and all except for ‘Manzanillo’, were self-incompatible. It is concluded that ‘Frantoio’ is a good general polleniser for the other cultivars investigated. Pollen tube growth decreased in discrete steps from stigma to upper style, and from upper style to lower style, with the result that only one, and rar...

Heritability estimates of bread wheat quality traits in the Western Cape province of South Africa

Abstract: The inheritance of wheat quality traits is complex due to the polygenic control of most of these characteristics. Furthermore, correlations and genotype × environmental interactions that exist among these characteristics, makes progress using conventional breeding procedures even more difficult. A diallel trial was carried out with parents and their F2progeny at Langgewens, South Africa, to determine the correlations, heritability and combining ability of the different quality characteristics. High narrow sense heritability was found for thousand kernel mass, flour extraction, breakflour yield, flour colour and hectolitre mass. Positive genetic correlations were observed between SDS sedimentation and falling number, mixograph development time and hectolitre mass, and loaf volume and flour protein content. Thus, genetic correlations, heritability and combining ability estimates can be used to design a selection strategy to improve quality traits.

Diallel Analysis of Leaf Shape Variations of Citrus Varieties Based on Elliptic Fourier Descriptors.

Abstract: The inheritance of citrus leaf shape was investigated by analyzing a diallel set of crosses of five citrus varieties/selections. Leaf contours were extracted by image processing, and described by elliptic Fourier descriptors. Mathematically independent shape characteristics were then identified by principal component analysis of the descriptors. The 1st, 2nd, 3rd and 4th components accounted for 51%, 20%, 10% and 6% of the total shape variation, and were good measures of the ratio of length to width, the position of the centroid, the curvature and the leaf wing size, respectively. Diallel analyses indicated that these components differed substantially in their mode of inheritance. The broad sense heritability was fairly high (>0.90) in the 2nd and 4th components and high (>0.70) in the 1st component, whereas the narrow sense heritability was high only in the 2nd component. There was no significant genetic effect in the 3rd component. The 1st, 2nd and 4th components showed over-, incomplete- and complete- dominance, respectively. The results indicate that elliptic Fourier descriptors can be successfully applied to the quantitative genetic analysis of citrus leaf shape.

Validity of a leaf inoculation test to assess the resistance to Phytophthora megakarya in a cocoa (Theobroma cacao L.) diallel mating design

Abstract: Cocoa pod rot, caused by different Phytophthora species, is rife in all production zones. Phytophthora spp. control is therefore a major challenge for world cocoa cultivation, and selection of resistant material is a priority research theme for many producing countries. Various genetic trials have been set up over many years in zones affected by the disease. In Cameroon, a 6x6 diallel mating design was set up to study heritability of the resistance trait. Field observations led to the classification of parents according to their ability to transmit resistance to their progenies. These field measurements were long and laborious, so a resistance test based on artificial leaf inoculations was developed. This article studies the correspondence between results obtained with the test and observations of rot rates in the field. There was a significant genetic correlation between pod rot rate in the field and leaf test data, so using this resistance test could shorten cocoa tree selection cycles.

Resistance to Aspergillus ear rot and aflatoxin accumulation in maize F1 hybrids

Abstract: Unacceptable levels of contamination by aflatoxin, a carcinogenic toxin, produced by Aspergillus flavus Link:Fr can halt the sale and shipment of maize (Zea mays L.) grain. Our objectives were to: (i) determine the relative resistance to A. flavus and aflatoxin accumulation in F 1 hybrids produced by crossing promising resistant maize inbreds, regardless of heterotic pattern; (ii) investigate the genetic basis of resistance for this subset of inbreds through diallel analysis; and (iii) determine which inbreds are the most promising sources of resistance for molecular marker mapping and breeding programs. Two historically important inbreds and six inbreds tentatively associated with reduced ear rot and inhibition of aflatoxin production were crossed in all combinations. The resulting F 1 hybrids were evaluated for two years. Ears were inoculated 20 to 24 d after midsilk by a pinboard method and a mixture of conidia of Aspergillus flavus Link:Fr. isolates. Individual ears from each plot were rated by scoring the percent visible rot in the inoculated area. Aflatoxin B 1 levels in harvested ears were determined by an indirect competitive ELISA. The highest level of resistance for ear rot and aflatoxin accumulation was detected for resistant inbred x resistant inbred F 1 hybrids, but they were not significantly different from many resistant inbred x historically important inbred F 1 hybrids. Diallel analysis indicated general combining ability (GCA) effects for ear rot and aflatoxin levels were highly significant among hybrids overall, and for the inbreds Tex6 and Oh516. The results indicate that Tex6 and Oh516 are promising resistance sources for molecular marker mapping and breeding programs in diverse genetic backgrounds.

Diallel Analysis of Winter Wheat at Two Nitrogen Levels

Abstract: Price reduction and environmental concerns advocate a lower use of nitrogen (N) fertilizer on the wheat (Triticum aestivum L.) crop. It is a common hypothesis that hybrids would be more valuable in stressed environments such as limited fertilizer conditions. The objective of this study was to assess heterosis and combining ability at two N levels. Seven winter wheat cultivars were used to produce a 7 × 7 diallel cross without the reciprocals. The 21 F1 hybrids and parental lines were tested in replicated plots over 2 yr without N fertilizer (NO) or with 150 kg N ha -1 (N+). The diallel analysis was conducted according to Griffing with year, genotype, and treatment as fixed effects. Mid-parent heterosis for grain yield was +12.2%** at NO and +8.9%** at N+ in 1997 and +1.7% ns at NO and -0.4% ns at N+ in 1998. This was directly related to high mid-parent heterosis for above-ground dry weight in 1997 (+11.2%** at NO and +10.9%** at N+) and low heterosis in 1998 (+1.2% ns at NO and + 0.0% ns at N + ). General (GCA) and specific (SCA) combining ability effects were always significant. The GCA/SCA ratio ranged from 3.6 to 14.8. The GCA x N level interaction was generally significant indicating different parental contributions at low or high N levels. The SCA x N level interaction was never significant. There was a tendency toward higher GCA/SCA ratio at NO than at N+. The choice of parents will be dependent upon the N level under which the new hybrids will be grown.

Heterosis of Agronomic Traits in Alfalfa

Abstract: Increasing forage yields remains a top priority of most alfalfa (Medicago sativa L.) breeding programs. Studies of crosses between dormant to moderately dormant M. sativa subsp. sativa and M. sativa subsp. falcata suggest a heterotic pattern for yield exists between the two subspecies. However, other agronomic traits need to be considered in addition to yield, especially when trying to develop breeding material from nonadapted sources. The objective of this study was to quantify the agronomic performance of sativa × falcata crosses (SFC) in relation to sativa × sativa crosses (SSC) and falcata × falcata crosses (FFC). Nine elite sativa clones and five falcata clones were crossed in a diallel mating design. Progeny were space planted in 1998 at Nashua and Ames, IA. During the 1999 growing season, winter injury, spring regrowth, vigor, growth habit, maturity, height, midseason regrowth, and autumn regrowth were measured. The 14 parental genotypes differed for general combining ability (GCA) for all traits; specific combining ability (SCA) was noted for height, maturity, winter injury, and vigor. Sativa × sativa crosses were superior to FFC for all traits except winter injury and vigor. Sativa × falcata crosses per se had slightly increased agronomic performance over the expected mid-subspecies for many traits. Most of the hybrids are intermediate to SSC and FFC, suggesting potential agronomic weaknesses of falcata germplasm in a breeding program. Improving regrowth, height, and growth habit of falcata breeding material would likely be needed to create commercially successful sativa–falcata semihybrid cultivars.

Genetic components of pod shattering in soybean

Abstract: Half diallel crosses among ten pure breeding lines of soybean were made in 1997 and 1998 to study the inheritance of pod shattering in soybean. Evaluation for pod shattering among F2 segregating populations was carried out in an oven set at 80 °C for 12 hours. Diallel analysis was carried out to estimate genetic parameters and detect presence of non allelic interaction of genes affecting pod shattering. Hayman's diallel analysis indicated significant variation of Wr + Vr and Wr – Vr over arrays, suggesting epistatic gene action. Similarly results from a joint regression coefficient over replications were significantly (p < 0.05) different from unity and zero, suggesting presence of non allelic interaction of genes. The intercept was positive, suggesting partial dominance for the shattering trait. Both general combining ability (GCA) and specific combining ability (SCA) effects were significant (p < 0.05).

Heterosis in soybeans for seed yield components and associated traits

Abstract: The objective of this research was to quantify heterosis of agronomic traits and evaluate direct and indirect correlations among seed yield and other traits. A diallel involving six parents was grown in two localities. Seed yield (PG), one-hundred seed weight (PCS), number of pods per plant (NV), weight of aerial part of the plant (PPA), harvest index (IC) and number of seeds per pod (NGV) were evaluated. Positive values of heterosis were detected for all traits. Estimates of heterosis components were significative for most traits, showing effects of aditivity and dominance. The specific heterosis was more important than the variety heterosis, mainly in the locality Anhembi. MTBR-95-123800 presented the best potential per se and as parent in crosses, but it was excelled by some of the hybrids in the two localities. Number of pods per plant demonstrated to be suitable for indirect selection for PG.

Genetic studies of selection criteria for productive and stable peas

Abstract: In this study we investigated the genetic determinism of criteria suitable for breeding for seed yield and yield stability in dry pea (Pisum sativumL.) using a diallel cross involving eight genotypes. Seven criteria related to plant and seed development were evaluated including: onset of flowering, node of first flower, leaf appearance rate, rate of progression of flowering, number of podded nodes on the main stem, mean dry seed weight per podded node and number of basal branches per plant. Most of these traits measured are related to timing of seed set and are thought to be critical in determining yield stability. We combined different diallel analyses (Hayman,1954; Griffing, 1956) with a Principal Component Analysis, to divide the parental lines into groups sharing similar genetic control for the traits studied. We found that the two main groups, defined according to their genetic control of node of first flower, also differed for all the others characters and, in particular, did not reach the same levels of productivity. These results indicated that crosses within the group with the highest productivity, but between lines with differing development and architectural features, could be a good starting point for breeding high-yield pure lines.

Heterosis for Flowering Time and Agronomic Traits among Early Open-pollinated Sweet Corn Cultivars

Abstract: ADDITIONAL INDEX WORDS. Zea mays, maize, maturity, combining ability ABSTRACT. Heterosis in corn (Zea mays L.) usually results in earlier flowering, larger plants, and increased yield. In extremely early sweet corn the effect of heterosis on flowering time may be reduced or eliminated due to developmental and physiological requirements for vegetative growth before the transition to reproductive phase. The objective of this study was to determine the level of heterosis and the combining ability for flowering time and other agronomic traits in a diallel cross of six very early open-pollinated sweet corn cultivars. The diallel was grown in 1995 and 1996. Hybrids and parents averaged over hybrids differed for silk date, plant height, ear height, 10-ear weight, ear length, and 100-kernel weight but did not differ for row number and ear width. Heterosis for silk date was significant, but the difference between parents and hybrids was very small, 0.5 day. No hybrids were earlier than the earliest parent, and average midparent heterosis was -0.8%. In contrast midparent heterosis was significant and relatively high for 100-kernel weight (10.0%), ear length (12.9%), ear height (8.6%), plant height (9.0%), and 10-ear weight (28.2%). The traits with low heterosis had very high general combining ability/specific combining ability ratios while these ratios were much smaller in traits with high heterosis. Heterosis for many of the traits, including 10-ear weight, was higher than published values. Conversely, heterosis for flowering time was small, compared to other traits in this study and to published values for silk date, indicating that this extremely early germplasm may be at or near the limit for flowering time under the photoperiod and temperatures typical of summer in Madison, Wis. (43.05°N, 89.31°W).

Inheritance of resistance to the panicle-feeding bug Eurystylus oldi and the sorghum midge Stenodiplosis sorghicola in sorghum

Abstract: A study of the inheritance of sorghum resistance to head-bug Eurystylusoldi and midge Stenodiplosis sorghicola has been conducted from anF1-based complete diallel involving four parental lines (namely head-bugresistant Malisor 84-7 & 87W810, and susceptible S 34 & ICSV 197).The trial was conducted at Samanko, Mali, under both natural and artificialhead-bug infestation, in one date of sowing (DOS) in 1995 and two DOSin 1996. Head-bug visual damage scores (under both types of infestation)were indicated and analyzed in all these trials. Head-bug numbers underartificial infestation on the two DOS of 1996, and midge damage scoreunder natural infestation on the second DOS of 1996 were recorded. Allfour parents confirmed their expected level of resistance to head-bugs,while ICSV 197 confirmed its resistance to midge. Diallel analyses showedthat general combining ability (GCA) and thus additive gene effects werevery important in the inheritance of resistance to both pests. Specificcombining ability and maternal effects were generally of minor importance.Mean performance of the parents and their GCA effects were linked, whichsuggests high heritability. Head-bug resistant parents, Malisor 84-7 &87W810, with high per se resistance and negative GCA shouldtherefore be used in breeding for resistance to this pest, while for a similarreason, ICSV 197 should be used in breeding for midge resistance. Resultsconcerning independance between resistance to head-bugs and to midge,are also discussed.

Inbreeding depression of 28 maize elite open pollinated varieties

Abstract: The study of inbreeding depression is important for breeding strategies such as use of inbred progenies or extraction of inbreed lines. A diallel of 28 maize open-pollinated varieties was evaluated in 10 environments in the early 1990s. At the same time, S1 populations for each of the 28 varieties were evaluated in the same 10 experiments (environments). Yield reductions of the populations from S0 to S1 (mean of the 10 environments), varied from 34.6% (CMS-01) to 59.2% (CMS-30), with an average of 49.1%. Inbreeding depression was greater in populations with a wider genetic base, which had never been exposed to inbreeding (CMS-30, BR-107, PH4, Cunha, Saracura, Nitrodent, and Nitroflint). Inbred lines with greater yield means should be obtained from the BR-105, BR-111, CMS-01, CMS-03, BR-106, CMS-14c, and CMS-28 populations. The use of parameter estimates generated by analysis of inbreeding depression, allow to make inferences about frequencies of deleterious alleles in the population. The frequencies of favorable alleles in the parents can be obtained by diallel analysis. The association of these two types of information, can provide a better interpretation of the genetic parameters and also can improve the process of selection of parents for either an intra- or an inter-populational breeding program.

Genetic analysis of growth curves for a woody perennial species, Pinus taeda L.

Abstract: Inheritance of growth curves is critical for understanding evolutionary change and formulating efficient breeding plans, yet has received limited attention. Growth curves, like other characters that change in concert with development, often have higher heritability than age-specific traits. This study compared genetic parameters of height-growth curves with those of age-specific heights for a conifer, Pinus taeda L. Growth curves were fitted with: (1) a linear regression model, and (2) a non-linear model based on Richards' function using two sources of height data: two six-parent diallel tests assessed at age 2 to 10 years and two tests from a nested mating design with 222 parents assessed at 1 to 25 years. Additive genetic control of growth-curve parameters was moderate (h2 = 0.06 to 0.26) and slightly lower than that for age-specific heights. Additive variance exceeded dominance variance for rate and shape parameters, but not for the asymptote. Genetic correlations among growth-curve parameters were high. Early selection on height was as efficient as selection on growth-curve parameters.

Breeding for resistance to ear rot of maize caused by Stenocarpella maydis (Berk) Sutton. 1. Evaluation of selection criteria

Abstract: The objective of this study was to provide a better understanding of the interrelationship between methods of screening for resistance to ear rot, caused by Stenocarpella maydis. The inheritance of resistance as well as genetic and phenotypic correlation of various selection criteria were investigated. A complete diallel cross of 10 inbred lines, ranging from resistant to susceptible, was evaluated at each of three localities, representative of different environments within the South African maize production area. Plants were artificially inoculated twice during the vegetative stages of plant development. Resistance to ear rot was found to be controlled by additive gene effects, with low dominance and interaction effects. Significant genetic correlations existed between various characteristics relating to disease incidence, with high heritability and highly correlated responses. The incidence of rotted ears was the most practical and reliable method to select for resistance. However, the simultaneous use ...

Heterotic relationships among European maize inbreds.

Abstract: European flint maize (Zea mays L.)cannot be considered an uniform group of germplasm based on its origin and area of adaptation. However, maize breeders have not taken full advantage of the variability within the European flint germplasm. The objective of this work was to study the heterotic relationships among European maize inbreds from different origins. Nine European flint inbreds were crossed in a diallel that was evaluated in three environments in northwestern Spain. The variability within the European flint germplasm and the agronomic value of some inbreds could be utilized for maize breeding programs as an alternative to the systematic introduction of U.S. dent germplasm that is narrowing the germplasm base of breeding programs even in places where it is poorly adapted. Some European flint inbreds may also be valuable sources of earliness (F7 and EP42), resistance to root lodging (EA1070), and yield (EP42).These results suggest that, within the European flint germplasm, there could be some heterotic patterns, such as ‘north-central Europe × southern Europe’, which could provide an alternative to the heterotic pattern ‘European flint × U.S. dent’.

Genetic control of quality traits of lucerne (Medicago sativa L.)

Abstract: An important objective in lucerne breeding is the improvement of feeding value. An understanding of the inheritance of digestibility and cell wall related traits would facilitate the breeding of varieties with higher feeding value. The aim of this experiment was first to determine the genetic control of dry matter digestibility and related biochemical and morphological traits, and to assess phenotypic and genetic correlations between these traits. Quantitative genetic parameters were estimated for enzymatic solubility, neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), protein content, plant height, and leaf-to-stem ratio. A 7 × 7 diallel design with reciprocals and without selfing among parents from different populations and a 7 × 7 factorial design within the 'Flamande' population were studied. In the diallel study, effects due to general combining ability (GCA) were higher than those due to specific combining ability (SCA) for all characters tested. In the factorial study, the F1 progeny effect was significant for all characters. The male effect was highly significant for all traits and higher than the female effect except for plant height. The additive variance was higher than the dominance variance for all characters except for plant height. The inheritance was predominantly additive. The highest narrow- sense heritabilities were found for NDF and ADF and leaf-to-stem ratio. As a consequence, NDF or ADF would be more efficient selection criteria than enzymatic solubility in a breeding program for improved feeding value. In both mating designs, NDF, ADF, and ADL were positively correlated with one another and negatively with enzymatic solubility and protein content. Additional keywords: combining ability, additive variance, dominance variance, heritability, within- and among- population genetic variation. A ro y t rn F

Inheritance of drought tolerance in Maize

Abstract: Summary To investigate the genetic properties of some physiological and agronomical characters in maize, a six-parent diallel cross, excluding reciprocals, was grown in a randomized complete block design with three replications under two different environments (irrigated and rainfed) in the Research Station of Dezful, Iran. High narrow-sense heritability estimates were observed for relative water loss, excised leaf water retention, number of seed per plant, seed weight and number of ear per plant. Additive gene action was found to be predominant for relative water loss, excised leaf water retention, seed weight and number of ear per plant. The results of combining ability analysis revealed that the genotype kl515 was the best general combiner for improvement of osmoregulation, and kl 8 x kl264 and kl 9 x kl264 were the best specific combination for improvement of osmotic adjustment and stress tolerance index.

Natural selection for grain yield in dry bean populations bred by the bulk method

Abstract: Three dry bean harvests are possible in some regions of Brazil that differ significantly in temperature, rainfall and day length conditions. Thus in breeding programs, generation advance using the bulk method can be carried out in these three periods. It is questionable whether under conditions such as these the action of natural selection would contribute to an increased frequency of individuals considered superior by breeders. The present study assessed six segregating populations, for up to 17 successive generations to check the effects of natural selection during inbreeding. Six populations were generated from a partial diallel: one group consisting of two early maturity cultivars, ESAL 686 and Manteigao Fosco was crossed to a second group of three cultivars with medium maturity, Carioca MG, Milionario and Ouro. The six populations plus the five parents were assessed in experiments using a randomized complete block design, in three locations: Lavras, where in breeding started from the F2 generation; Lambari and Patos de Minas, from the F3 generation. A linear regression equation was fitted to the parents and hybrids mean data in each location, considering grain yield as the dependent variable (y) and generations (F2 = 1, F3 = 2, etc.) as the independent variable. Genetic progress was estimated from the differences between the linear regression coefficients of the hybrids (bi)and the mean of the b coefficient of their respective parents (bj). The (bi-bj) were positive in all cases, showing that natural selection acted in all the segregating populations and contributed to an average increase in grain yield of 2.5% per generation over the mean of the parents.

Inheritance of Resistance to Colletotrichum acutatum Simmonds on Runners of Garden Strawberry and its Backcrosses

Abstract: Two half diallel mating designs were conducted to study the inheritance of resistance to Colletotrichum acutatum Simmonds on runners of strawberry. The main design included six genotypes representing a range of responses to the pathogen: 'Chandler' (very susceptible); FL 87-210 (tolerant); MS/US 541 (very resistant); NC 92-01 (Fragaria chiloensis Duch.) (resistant); NCH 87-10 (tolerant-susceptible); and NCC 89-39 (susceptible). The cross 'Chandler' x MS/US 541 was absent. The secondary test included 'Chandler' and selections FL 87-210 and NC 85-01 (Fragaria virginiana Duch.) (very resistant) as parents. Griffing's methods 4 and 2, model I, were used to test for combining ability in the main and secondary tests, respectively. General combining ability and specific combining ability were highly significant in all analyses. This study indicated that nonadditive effects are more important than additive effects in the inheritance of resistance of runners to anthracnose. The frequency distribution of lesion lengths within progenies suggests that resistance to C. acutatum on runners is quantitative. Therefore, breeding for resistance should be accomplished using progeny testing followed by individual selection within progenies.

Combining ability for nitrogen use in a selected set of inbred lines from a tropical maize population

Abstract: Tolerance rather than resistance, is the crop response mechanism sought by maize breeders for cultivation under low levels of nitrogen. Although improved nitrogen use is in intensive research by maize breeders, little is known about its inheritance on tropical maize germplasm. The objectives of this study were to evaluate the N use through yield and other traits, and to determine the importance of general (GCA) and specific (SCA) combining ability effects in the inheritance of N use, for yield, using a diallel of crosses among a selected set of tropical maize lines under two levels of N. A comparison of relative magnitudes of GCA and SCA for ear yield (EY) suggests that this trait was governed more by dominance than additive gene action, and the contribution of additive genes for nitrogen utilization efficiency decreases under N nutrient shortage. Since, for this set of lines, only non additive effects were significant for this trait, the lines with favorable SCA could be used as donors of N use efficiency in a hybrid development program. The line L2 was identified as being the most suitable combining overall parents in this study for improving EY. The crosses L 3 x L 7, L 1 x L 2 and L 7 x L 10 showed to be promising combinations based on the significant SCA effects for lines and hybrids development. The results of this study can enhance the use of promising inbred lines in a program focused on developing hybrid that efficiently can take up and uses nitrogen.

Combining ability of tropical maize inbred lines under drought stress conditions

Abstract: Among the environmental stresses, drought is considered the main source of maize grain yield instability in tropical areas. Anthesis-silking interval (ASI) is used as an efficient phenotypic index for water stress tolerance and has also been used in breeding programs aiming to increase yield stability under water stress. This phenotypic index is also an important tool to be used in cultivar development, in relation to the emergence of silk hairs, since the ASI is totally independent from the differences in genotype cycles. The objective of this study was to evaluate the genetic potential of six maize inbred lines from the Embrapa Maize and Sorghum breeding program, selected for drought tolerance by using grain yield. The F 1 ’s and reciprocals from a diallel crosses, plus three hybrids checks, were evaluated under two irrigated systems: well-watered conditions during all growth stage and water-stressed conditions where irrigation was suppressed during the flowering period. The means over the checks were 15% and 5% higher than the means of all F 1 ’s hybrids in the experiments under non-stress and stress conditions, respectively. Under water-stressed conditions, yield means were 45.6% and 40.4% low for the checks and F 1 ’s , respectively, when compared to well-watered condition. The results for mean grain yield showed a great potential for the genetic material used in the ecological condition studied. Under well-watered conditions, the F1‘s L1147 x L10.1.1; L6.1.1 x L8.3.1 and L1147 x L13.1.2 and the reciprocal cross L13.1.2 x L1147 presented the highest specific combining ability effect values. For both conditions, general combining ability effects of the inbred line L6.1.1 showed the highest value and the inbred lines L10.1.1 and L1147 the lowest ones. Under water stress, the specific combining ability effects were not significant among F 1 ’s and reciprocals, indicating similar performances for crossing combinations among the evaluated lines. The grain yield means of the checks were similar to the means of the F 1 ’s in both environments. Among the hybrid checks, the single cross presented a higher grain yield than the three-way and double-crosses hybrids, in both well-watered and under water-stress conditions.

Genetic basis of plant height and its degree of indetermination in mungbean (Vigna radiata (L.) Wilczek).

Abstract: The genetic basis of plant height at various growth stages and the degree of indetermination of plant height in six mungbean genotypes (NM 92, 6601, NM 89, VC 1560D and VC 3902A) were assessed through half diallel cross. Cultivars, 6601 and NM 92, were the best general combiner for pre-flowering dry matter accumulation and minimum increase in plant height from first flower to 90 % pods maturity, respectively. For these traits, the combination NM 92×NM 89 was the best specific combiner of all the crosses. Both additive and dominant gene effects controlled the inheritance of plant height at first pod and to 90 % pods maturity, degree of indetermination of plant height (DDh) from first flower to first pod maturity (DDhl), DDh from first flower to 90 % pods maturity (DDh2) and DDh from first pod maturity to 90 % pods maturity (DDh3). Plant height at first flower was additively inherited. The additive gene action was predominant as compared to dominant gene action for all the traits examined. High narrow and broad sense heritability estimates for DDh2 showed that better response to selection is possible for the development of mungbean genotypes with minimum increase in plant height during post-flowering development.

Genetic analysis combining ability and heterotic studies for yield, its components, and fibre quality traits in upland cotton

Abstract: This thesis embodies genetic analysis, combining ability, heritability, genetic advance and heterotic effects for different productive and quality traits of complete diallel cross of six cotton (Gossypium hirsutum L.) cultivars viz; CIM-109, CIM-240, CIM-1100, FH-682, BH-36 and CRIS-9 having diverse genetic origin. The detailed studies were based on data for F1 and F2 generations. The single plant selections made in F2 generation were also studied in F3 and F4 generations through plant progeny row method. Hayman's diallel analysis for genetic components of variation and Griffing's approach were employed to study the general combining ability (GCA), specific combining ability (SCA), the nature of gene action and their interactions for exploring possibilities of isolating useful recombination

Heterosis and its components in crosses among high quality protein maize populations

Abstract: The objective of the present study was to investigate heterosis in high quality protein maize populations of distinct grain type groups. Agronomic traits and reaction to some leaf diseases of 19 yellow grain populations were assessed in a partial diallel grown in four environments. For grain yield trait, only variety effects and average heterosis were significant, indicating that the best intervarietal hybrids can be predicted using the means of the parental populations. The BR 473 and CMS 52 flint populations, the CMS 474 and ZQP 103 dent populations are recommended for an inter-group reciprocal recurrent selection program. In a decreasing order of preference, the dent type CMS 474, ZQP 103 and ZQP 101 populations and the flint type BR 473, CMS 455C, CMS 453, CMS 52, CMS 455 and CMS 458 are recommended to form composites.