Showing papers on "Heterosis published in 2000"

Inbreeding depression influences lifetime breeding success in a wild population of red deer (Cervus elaphus)

Abstract: Evolutionary and conservation biologists have a long-standing interest in the consequences of inbreeding. It is generally recognized that inbred individuals may experience reduced fitness or inbreeding depression. By the same token, relatively outbred individuals can have greater than average fitness, i.e. heterosis. However, nearly all of the empirical evidence for inbreeding depression comes from laboratory or domestic species. Inbreeding depression and heterosis are difficult to detect in natural populations due to the difficulties in establishing pedigrees. An alternative method is to correlate heterozygosity, which is measured using genetic markers, with a trait related to fitness. The typically studied traits, such as juvenile survival and growth rates, either cover only early life or are weakly correlated with lifetime breeding success (LBS). In this paper we show that heterozygosity is positively associated with male and female adult LBS in a wild population of red deer (Cervus elaphus) on the Isle of Rum, Scotland. To the authors' knowledge, this is the first time that inbreeding depression and/or heterosis have been detected for a trait highly correlated with overall fitness in both sexes in a wild population.

Local drift load and the heterosis of interconnected populations.

Abstract: We use Wright's distribution of equilibrium allele frequency to demonstrate that hybrids between populations interconnected by low to moderate levels of migration can have large positive heterosis, especially if the populations are small in size. Beneficial alleles neither fix in all populations nor equilibrate at the same frequency. Instead, populations reach a mutation-selection-drift-migration balance with sufficient among-population variance that some partially recessive, deleterious mutations can be masked upon crossbreeding. This heterosis is greatest with intermediate mutation rates, intermediate selection coefficients, low migration rates and recessive alleles. Hybrid vigour should not be taken as evidence for the complete isolation of populations. Moreover, we show that heterosis in crosses between populations has a different genetic basis than inbreeding depression within populations and is much more likely to result from alleles of intermediate effect.

Fine mapping of a quantitative trait locus (QTL) from Lycopersicon hirsutum chromosome 1 affecting fruit characteristics and agronomic traits: breaking linkage among QTLs affecting different traits and dissection of heterosis for yield

Abstract: The near-isogenic Line TA523, containing a 40-cM introgression at the bottom of chromosome 1 from Lycopersicon hirsutum acc. LA1777, affects several agronomically important traits. A set of recombinant lines (subNILs) derived from the original NIL TA523 were developed in order to fine-map, by substitution mapping, the genetic factors included within the original introgression. In the current experiment, TA523 showed redder, rounded, less pigmented shoulder, lower-weighted fruits and higher brix, whereas higher yield and brix*yield was observed only in the hybrid TA253×TA209 suggesting heterosis for these traits. By substitution mapping we mapped independent genetic loci affecting brix, yield and fruit shape, whereas fruit weight, shoulder pigmentation and external color mapped to a position coincident with the brix locus. Analysis of the subNILs revealed that the gene action of most of the QTLs was additive or nearly additive. The exception was for the yield QTL which was dominant (d/a=0.7), eliminating the possibility that yield increase is due to true overdominance at a single gene locus. However, no negative yield effects were detected in other regions of the introgressed segment, as would be predicted by a dominance complementation model. Therefore, epistatic interactions among genetic factors along the introgressed segment are suggested as the cause of yield heterosis. Results from this study, combined with previous experiments involving different tomato wild species, demonstrate that the base of chromosome 1 of tomato contains multiple QTLs affecting various agronomic and fruit traits and that these effects can not be attributed to the pleiotropic effects of a single locus.

Genetic distance as a predictor of heterosis and hybrid performance within and between heterotic groups in sunflower.

Abstract: Heterosis is significant for seed yield and is one of the driving forces behind the hybrid seed industry in cultivated sunflower (Helianthus annuus L). Heterotic groups in sunflower, if any other than the female and male inbred-line groups exist, have not been well studied or described. The primary aims of this study were to assess the utility and validity of a series of proposed heterotic groups and estimate correlations between genetic distance, heterosis, and hybrid performance for seed yield in sunflower. Fortytwo female by male heterotic group (A × R) and 81 female by female heterotic group (A × B) single-cross hybrids were grown in Corvallis, Ore., and Casselton, N.D., in 1996 and 1997. Heterosis was significant for seed yield and plant height but not for seed oil concentration and days to flowering. Genetic distances were significantly correlated with hybrid seed yield when estimated from AFLP fingerprints (GD) (r = 0.63 for A × R and 0.79 for A × B hybrids), but not from coancestries (GC) (r = -0.02 for A × R and 0.54 for A × B hybrids). GD (R2 = 0.4) was a poor predictor of hybrid seed yield. The proposed heterotic groups in sunflower seem to have utility, but do not seem to be as strongly differentiated as those in corn (Zea mays L.). The highest-yielding hybrids were from the BC× RB heterotic pattern; however, several BC× BC hybrids (within-group hybrids) were among the top-yielding hybrids. The outstanding performance of certain BC× BC hybrids casts some doubt on the validity of the BC group. Substantial genetic diversity seems to be present within and between heterotic groups in sunflower.

Heterosis increases the effective migration rate.

Abstract: Individuals coming from the same subpopulation are more likely to share deleterious mutations at any given locus than hybrids formed between parents from different populations. Offspring of migrants therefore may experience heterosis and have higher fitness than resident individuals. This will, in turn, result in the immigrant alleles being present in higher frequencies than predicted from neutral expectations and thus a higher effective migration rate. In this paper we derive a formula to calculate the effective migration rate in the presence of heterosis. It is shown that the effect of heterosis on the migration rate can be substantial when fitness reduction within local populations is severe. The effect will be more pronounced in species with relatively short map lengths. Furthermore the heterosis effect will be highly variable throughout the genome, with the largest effect seen near selected genes and in regions of high gene density.

Genetic diversity in tropical maize inbred lines: heterotic group assignment and hybrid performance determined by RFLP markers.

Abstract: Tropical maize inbred lines, eight derived from a Thai synthetic population (BR-105) and 10 from a Brazilian composite population (BR-106), were assayed for restriction fragment length polymorphisms with 185 clone-enzyme combinations. The aim of this study was to investigate genetic distances among tropical maize material and their relationship to heterotic group allocation and hybrid performance. Genetic distances (GDs) were on average greater for BR-105 x BR-106 lines (0.77) than for BR-106 × BR-106 (0.71) and for BR-105 × BR-105 (0.69) lines. Cluster analysis resulted in a clear separation of BR-105 and BR-106 populations and was according to pedigree information. Correlations of parental GDs with single crosses and their heterosis for grain yield were high for line crosses from the same heterotic group and low for line combinations from different heterotic groups. Our results suggest that RFLP-based GDs are efficient and reliable to assess and allocate genotypes from tropical maize populations into heterotic groups. However. RFLP-based GDs are not suitable for predicting the performance of line crosses from genetically different heterotic groups.

Chromosomal regions involved in hybrid performance and heterosis: their AFLP®-based identification and practical use in prediction models

Abstract: In this paper, a novel approach towards the prediction of hybrid performance and heterosis is presented. Here, we describe an approach based on: (i) the assessment of associations between AFLP® 2 , 3 markers and hybrid performance and specific combining ability (SCA) across a set of hybrids; and (ii) the assumption that the joint effect of genetic factors (loci) determined this way can be obtained by addition. Estimated gene effects for grain yield varied from additive, partial dominance to overdominance. This procedure was applied to 53 interheterotic hybrids out of a 13 by 13 half-diallel among maize inbreds, evaluated for grain yield. The hybrid value, representing the joint effect of the genetic factors, accounted for up to 62.4% of the variation in the hybrid performance observed, whereas the corresponding efficiency of the SCA model was 36.8%. Efficiency of the prediction for hybrid performance was evaluated by means of a cross-validation procedure for grain yield of (i) the 53 interheterotic hybrids and (ii) 16 hybrids partly related to the 13 by 13 half-diallel. Comparisons in prediction efficiency with the ‘distance’ model were made. Because the map position of the selected markers is known, putative quantitative trait loci (QTL) affecting grain yield, in terms of hybrid performance or heterosis, are identified. Some QTL of grain yield detected in the present study were located in the vicinity of loci reported earlier as having quantitative effects on grain yield.

Mate choice in the face of both inbreeding and outbreeding depression in the intertidal copepod Tigriopus californicus

Abstract: In species vulnerable to both inbreeding and outbreeding depression, individuals might be expected to choose mates at intermediate levels of genetic relatedness. Previous work on the intertidal copepod Tigriopus californicus has repeatedly shown that crosses between populations result in either no effect or hybrid vigor in the first generation, and hybrid breakdown in the second generation. Previous work also shows that mating between full siblings results in inbreeding depression. The present study again found inbreeding depression, with full sibling mating causing significant fitness declines in two of the three populations assayed. In the mate choice assays, a single female was combined with two males. Despite the costs of both inbreeding and outbreeding, mate choice showed clear inbreeding avoidance but no clear pattern of outbreeding avoidance. This lack of outbreeding avoidance may be attributed either to the temporary increase in fitness in the F1 generation or to the absence of selection for premating isolation in wholly allopatric populations with infrequent migration. If this inability to avoid unwise matings is common to other taxa, it may contribute to the problem of outbreeding depression when allopatric populations are mixed together.

Heterosis in landrace-based topcross hybrids of pearl millet across arid environments

Abstract: This study quantified the magnitude of heterosis in pearl millet (Pennisetum glaucum) topcross hybrids produced by crossing 16 diverse landraces and three high yielding open-pollinating varieties on two homozygous male-sterile lines. Hybrids and pollinators were grown in 12 year ×;location combinations in India that were grouped into three zones. Genetic components of variance quantifying the differences among these hybrids were estimated. The hybrids showed a conspicuous heterosis for grain yield, earliness and biomass yield but not for straw yield. The level and direction of heterosis for time to flowering depended strongly on the earliness of the male-sterile line. In the terminal drought stress zone hybrids made on the early maturing male-sterile line 843A had the highest level of heterosis for grain yield (88%). This was partly due to escape from terminal stress. In the other two zones the heterosis for grain yield was on average 30%. Heterosis for biomass yield and biomass yield per day was on average also positive in all three zones. For all traits, except time to flowering and biomass yield per day, pollinator effects were the only significant source of variation. Differences between hybrids were mostly caused by additive genetic effects. Significant amount of heterosis observed in landrace-based topcross hybrids for grain yield and other productivity-related traits suggested that substantial improvement in pearl millet productivity in and environments can be obtained by topcrossing locally adapted landraces on suitable male-sterile lines.

Genetic Analysis of Quantitative Traits in Pepper (Capsicum annuum)

Abstract: ADDITIONAL INDEX WORDS. quantitative inheritance, vegetable breeding, wide crosses ABSTRACT. Inheritance of 10 quantitative traits related to plant and fruit development was studied in an intraspecific cross between a bell-type 'Maor' ( Capsicum annuum L. var. annuum (Grossum Group) 'Maor') and a small-fruited pungent chilli line 'Perennial' ( C. annuum var. annuum (Longum Group) 'Perennial'). Estimates of broad- and narrow-sense heritabilities, coefficients of genetic variance, and genotypic correlations were obtained from the segregation of 120 F 3 families in 2 years. Three of the traits analyzed, days to first ripened fruit, plant height, and pedicel length, exhibited heterosis and transgressive segregation. Days to first ripened fruit and total soluble solids had low narrow-sense heritabilities. The other traits studied had moderate to high narrow-sense heritability estimates. Most of the genetic variation associated with traits that affect the size of the fruit and its shape was additive. The highest genetic correlation coefficients among pairs of traits were found between fruit weight and each of the three width characters: fruit diameter, pericarp thickness, and pedicel diameter. In contrast, fruit weight had a low correlation coefficient with fruit length, indicating that the size of the pepper fruit in this cross was determined primarily by its width. type inbred 'Perennial' (

Influence of parentage upon growth in Ostrea edulis: evidence for inbreeding depression.

Abstract: Summary Genetic variability for growth was analysed in three populations of Ostrea edulis, selected for resistance to the protozoan parasite Bonamia ostreae. This study was undertaken first to determine the potential for selection for growth in populations that have never been selected for this character, and second to estimate heterosis versus inbreeding depression. Growth was monitored in culture for 10 months. The selected populations (namely S85-G3, S89I-G2 and S89W-G2), their crossbred population and a control population were composed of full-sib families whose parents were already genotyped using five microsatellite markers. This genotyping allowed the estimation of genetic relatedness among pairs of parents. The parents’ relatedness was then correlated with the growth performance of their ospring within each of the three populations, and inbreeding depression was estimated. The population eect for growth was highly significant, with the crossbred population having the highest growth rate, followed by S89I-G2 and S89W-G2, S85-G3 and the control population. The within-populations family eect was also highly significant, indicating, as well as the high value for heritability at the family level (between 0‐57 and 0‐92), that a potential for a further selection for growth still exists within the three populations. Estimates of inbreeding depression (relative to the mean, for complete inbreeding) were high (1 for S891-G2, 0‐44 for S89W-G2 and between 0‐02 and 0‐43 for S85-G3), which correlates with the apparent heterosis for growth observed in the crossbred population. These results are discussed in the context of the future management of the selected populations.

Inbreeding depression by recessive deleterious genes affecting female fecundity of a haplo-diploid mite

Abstract: The effect of inbreeding on haplo-diploid organisms has been regarded as very low, because deleterious recessive genes on hemizygous (haploid) males were immediately purged generation by generation. However, we determined such recessive genes to decrease female fecundity in a population of Schizotetranychus miscanthi Saito which is known in the Acari as a subsocial species with haplo-diploidy. In mother–son inbreeding experiments, there was no depression in egg hatchability nor in the larval survival of progeny over four generations. There was, on the other hand, significant inbreeding depression in the fecundity with increasing f-value. Crosses between two lineages, one having deleterious effects on the fecundity and the other having no such effects, established during the inbreeding, revealed heterosis, and backcrosses showed that the depression was caused by deleterious recessive(s). These results strongly suggest the existence of some deleterious genes governing only the traits of adult females in wild populations of haplo-diploid organisms.

Breeding Potential of European Flint and U.S. Corn Belt Dent Maize Populations for Forage Use

Abstract: Information about appropriate breeding populations and the type of forage maize (Zea mays L.) hybrids that should be developed for cooler regions of Europe is scarce. Our objectives were to determine the potential, performance, and heterosis of flint (F) and dent (D) populations as base germplasm for developing silage maize hybrids. Four U.S. Corn Belt dent populations which had been selected for early maturity and four European flint populations were included in our study. The eight populations, the 28 possible crosses among them, and topcrosses to inbreds A632 and EC18 were evaluated for stover, ear, and whole plant dry matter yield (DMY), as well as stover and whole plant dry matter content (DMC), digestible organic matter (DOM), and add detergent fiber (ADF) content in northwest Spain. Means of F x D population crosses for stover and ear DMY (6.98 and 8.71 Mg ha -1 , respectively) were greater than those of D x D crosses (6.12 and 8.05 Mg ha -1 , respectively) and F × F crosses (6.03 and 7.64 Mg ha -1 , respectively). Average heterosis of whole plant DMY was greater for the F × D crosses (2.16 Mg ha -1 ) than for the D × D and F x F crosses (0.23 and 0.56 Mg ha -1 , respectively). No significant heterosis was found for DOM and ADF of the stover and whole plant fractions. The only exception was a negative average heterosis of population BSSS-M for stover DOM. Results suggest that forage maize hybrids should be developed from the F x D heterotic pattern. Breeding strategies should include selection for stover DOM for both parent lines and hybrids because favorable recessive genes may be involved in this trait.

Genetic similarity and relationships of DNA fingerprints with performance and with heterosis in Japanese quail lines from two origins and under reciprocal recurrent or within-line selection for early egg production

Abstract: DNA fingerprints of Japanese quail male and female pure line breeders were obtained with probes 33.6, 33.15, and R18.1 and they yielded a total of 59 scoreable bands. Bandsharing (0 < BS < 1) was calculated within and between six quail lines of two origins, and under reciprocal recurrent (AA and BB), within-line (DD and EE) or no (PP and FF) selection. Twenty one pair types were compared. BS was 0.30 higher within line than between lines. BS with the control line was smaller for reciprocal recurrent selection lines than for lines under individual selection. Bandsharing between the two reciprocal recurrent selection lines was 0.19 lower than between lines under individual selection. These results indicate that the two selection methods had different effects on the genetic constitution of the lines, in agreement with previous observations made from the analysis of biochemical polymorphisms with the same set of birds. Egg production and weight traits of pure and crossbred progeny from fingerprinted quail were obtained and compared, and a linear relationship with the measure of bandsharing was estimated. No significant regression coefficient of performance on BS was found over all progeny genetic types. Heterosis from individual matings could also be estimated under the two selection methods since the same birds were parents of both pure and crossbred performance-tested quail. The association of heterosis with the difference between BS of parents of the purebreds and BS of parents of their half-sib crossbreds was favourable and significant for early production traits in lines DD and EE, but no relationship was found in lines AA and BB. These results indicate that the high level of heterosis obtained through reciprocal recurrent selection, and the heterosis observed under within-line selection may have, partly at least, a different genetic determinism. Therefore, the relationship of heterosis with BS may also depend on the past history of selection in the lines.

Genetic variation of inbred lines of maize detected by SSR markers.

Abstract: Simple sequence repeats (SSRs) were used to detect genetic variation among 21 maize(Zea mays L. ) inbred lines. Forty-three SSR primers selected from 69 primers gave stable amplification profiles, which could be clearly resolved on 3% Metaphor agarose gel, and produced 127 polymorphic amplified fragments.The average number of alleles per SSR locus was 2.95 with a range from 2 to 7. The polymorphism information content (PIC) for the SSR loci varied from 0.172 to 0.753 with an average of 0.511. Genetic similarities among the 21 lines ranged from 0.480 between the combination of Zhongzi451 vs. K12 up to 0.768 between CA156 vs. Ye478. The cluster analysis showed that 21 inbred lines could be classified into two distinct clusters with several subclusters, which corresponded to the heterotic groups determined by their pedigree information.Eight SSR primers, which had high level of polymorphism, could allow a rapid and efficient identification of 21 inbreds. Consequently, SSR markers could be used for measuring genetic variation of maize inbred lines and assigning them to heterotic groups.

Evidence of epistatic effects on weaning weight in crossbred beef cattle.

Abstract: Weaning weights (WW; N=1962) of 20 genotypes comprising purebred, F1, backcrosses, crisscrosses, F2, F3 and F4 generations of inter se combinations of Brahman (B) and Hereford (H) were used to estimate (direct and maternal) additive, joint additive, heterotic and epistatic effects and their interactions with environment. Results are from additional data, plus data previously presented by Arthur et al. (1999) where experimental details can be found. For brevity, only estimates for the 15 genotypes produced in Grafton (subtropical NE of NSW) are presented here. At this location, there were 5 dam genotypes: H, B, firstcross BxH (F1), backcross BxF1 or HxF1 mated to sires H, B or F1. Covariates for joint additive (genes for adaptation and genes for high metabolism) effects on WW are calcu-lated by proportion B x proportion H and conceptua-lized as complementarity or "profit heterosis" (Kinghorn, 1993). Dickerson (1974) defined coefficient of recombination loss as the average fraction of independently segregating pairs of loci in gametes from both parents which are expected to be non-parental combinations; numerical values for these coefficients and for hetero-zygosity in stabilized synthetic populations are equal. Given all the intermediate genotypes in the present work, individual and maternal coefficients of epistasis (E and E) were calculated as the average hetero-zygosity in parents of an individual and of the dam. The best possible model, with respect to the genetic components, is the genotypic model (GM), when the effects of each of the 15 genotypes are estimated and the best possible (100%) fit is reached. A more parsimonious representation in terms of genetic components is needed. The benchmark model (BM) contains 4 genetic para-meters: individual additive, maternal additive, indi-vidual heterosis and maternal heterosis. This is a com-monly used model in analysis of crossbred data and it explained 75.7% of the variation amongst genotypes. The full model (FM) required 8 parameters to be estimated and the 4 extra ones to the BM are: individual joint-additive, maternal joint-additive, E and E. FM could explain 90.1 % of the variation between genotypes. About 60% of the lack-of-fit or total distance (24.3%) between BM and GM can be reduced by fitting FM. Part of the remaining distance between FM and GM (9.9%) may be due to sampling errors in the estimation of each of the 15 points and part to other genetic effects. The estimation of all genetic components, showing severe multicollinearity on this data structure, was possible since ridge regression (λ=10) was used. Individual additive effects were small for WW: 0.8 kg advantage for pure B calves in comparison with pure H (if all other genetic components were the same) but maternal additive was much larger: 6.9kg. Individual and maternal joint additive effects were positive indicating that intermediate genetic compositions are complementary. The individual jointadditive benefit of a .5B .5H was 1.3 kg with respect to either purebred. If the dam was .5B .5H then the benefit was 3.3 kg with respect to either pure dam. Individual heterosis was estimated as 19.4 kg (9.8%) for a F1 calf and maternal heterosis as 26.0 kg (13.1%) for a F1 dam. Maximum epistatic loss occurs in F2 individuals and it was estimated as -9.5 kg (4.8%). This reduction in WW was independent of the one observed due to reducing heterozygosity from 1.0 to 0.5 (from F1 to F2). F2 calves still perform well because their F1 dam expresses maximum maternal heterosis. But F2 dams show full epistatic loss, estimated as -12.6 kg (6.4%). It is easy to realize the importance of considering epistatic effects for genetic evaluation if, for example, progeny of a given sire out of F1 or out of F2 dams are compared. Even if reduction in heterosis is considered in the BM, margin for error is large. Koch et al. (1985), working with advanced genera-tions of crosses among Angus and Hereford cattle, found that heterosis retained in F3 vs. F1 indicated that net epistatic effects were relatively negligible for weaning weight. Differences between their results and epistasis estimates found in this study may arise from different interpretations of Dickerson's recombination loss. Their coefficients for individual "two-locus additive x additive epistatic effects in parental breeds" were all equal in F1, F2 and F3; and the same for maternal epistatic effects in F2 and F3. The design of the present set of experiments allowed for the verification that more heterozygosity in one generation is concomitant with higher frequency of recombinant configurations in the gametes; therefore, more epistatic effects in the next generation. Currently used BM captures basic features of the surface from the GM while FM provides a better fit. Similar benefits and gains in accuracy can be expected if E and E are added to the models in: (1) predicting results of advanced generations of designed crossbred populations; and (2) acrossor multibreed genetic evaluation analysis.

Provenance hybridization in a diallel mating scheme of maritime pine (Pinus pinaster). II. Heterosis

Abstract: Maritime pine (Pinus pinaster Ait.) is a species characterized by a discontinuous natural range with populations as a rule of small size and growing in heterogeneous environments. Ten provenances belonging to the three biosystematic groups of the species (Atlantic, Mediterranean, and North African) were crossed using a diallel scheme. Parental provenances and their hybrids were tested and measured for height growth at age 1, 2, 3, 8 and 13, as well as for insect resistance and stem crookedness in a trial in southwestern France. The results show a decrease in the variance of heterosis for height growth with age. Heterosis measured as the relative superiority of the hybrid to the midparent varies from -10% to 42% at age 1 and between 2 and 20% at age 13. There is no age effect on the mean value of heterosis, which amounts to 9.7% at age 1 and 8.4% at age 13. The value of heterosis was then compared with the genetic distance of parental provenances measured with various traits and markers (phenotypic traits,...

Identification of RFLP markers linked with heading date and its heterosis in hexaploid wheat

Abstract: Recombinant inbred lines (RILs) from a cross between hexaploid wheat (T. aestivum cv. Chinese Spring (CS) and T. spelta (Sp)) were used for RFLP analysis of heading date and heterosis. Fourteen RFLP markers linking with heading date were identified; two were localized on chromosome 1A, one on 2A, three on 2B, one on 2D, four on 5A, two on 7A and one unlinked but reported to be on group 2. All of these markers may be attributable to genes for earliness per se. However, the markers in the chromosomes of 1A and 7A are new to this study. RILs were crossed with (tim)-CS, the alloplasmic CS with T. timopheevi cytoplasm, and the heterosis from earlier-parent and mid-parents were calculated for the F1s to examine the heterotic effect toward earliness on heading date. Five and two RFLP markers were associated with heterosis from the earlier-parent and mid-parents, respectively. They were distributed on the chromosomes of homoeologous groups 1 and 2.

Análise dialélica para avaliação de híbridos interpopulacionais de cajueiro

Abstract: The objectives of this work were to obtain information related to the components of means of cashew tree (Anacardium occidentale L.) populations, through partial diallel analysis, and verify the potential per se of two distinct groups of parents, one of them made up by clones of dwarf cashew tree (CCP06, CCP76, CCP09 e CCP1001) and the other one by common cashew tree (CP07, CP12, CP77, CP96 e BTON), and the heterosis of their respective hybrid combinations. A randomized complete block experimental design with four replications was used. The traits evaluated were plant height, canopy diameter, number of cashew nut/plant, cashew nut yield, mean weight of cashew nut, mean weight of kernel and weight of kernel/weight of cashew nut ratio. It was found that parent effects and heterosis were important components of the means of the populations under study for all traits. Among the heterotic components, average heterosis presented itself as the most important, pointing out the presence of dominance and marked genetic divergence between the two groups. Only for the traits nuts number and yield the specific combining ability was significant. Hybrid combinations CCP76 x CP07, CCP09 x BTON and CCP09 x CP77 are the most promising, enabling establishment of base populations for breeding programs of cashew tree.

Cultivar heterosis between sweet and Spanish field corn

Abstract: Field corn (Zea mays L. var. mays) cultivar heterosis could improve sweet corn ( Zea mays L. var. rugosa Bonaf) heterotic patterns. Two Spanish field corn ( Su) and two sweet corn (su) heterotic patterns have been reported previously. The objective of this study was to determine which sweet x field corn crosses could be used to improve sweet corn heterotic groups. A diallel among three sweet corn cultivars ('Country Gentleman', 'Golden Bantam', and 'Stowell's Evergreen') that are representative of the variability among modern sweet corn cultivars, and three field corn synthetic cultivars ('EPS6(S)C3', 'EPS7(S)C3', and 'EPS10') representing the heterotic patterns involving Spanish field corn, was evaluated for 2 years at two locations in northwestern Spain. Differences in heterosis effects ( hjj') and average heterosis (h) were significant for all traits except grain moisture. Differences for cultivar heterosis ( hj) and specific heterosis (sjj') were significant for grain yield, plant height, and kernel row number. 'EPS6(S)C3' had lower sjj' for yield in crosses to 'Golden Bantam' than to 'Stowell's Evergreen', while 'EPS7(S)C3' had higher sjj' in crosses to 'Golden Bantam' than to 'Stowell's Evergreen'. The best crosses to establish enhanced sweet corn heterotic patterns involving Spanish maize would be 'Golden Bantam' x 'EPS6(S)C3' and 'Stowell's Evergreen' x 'EPS7(S)C3'. New sugary 1 cultivars would require preliminary cycles of intrapopulational recurrent selection for agronomic performance and flavor prior initiating an interpopulational recurrent selection program to enhance heterosis.

Progeny mean, heterosis and heterobeltiosis in Solanum tuberosum x tuberosum and S. tuberosum x andigena families under a short day sub-tropic environment

Abstract: Solanum tuberosum x tuberosum (TxT) families were compared withS. tuberosum x andigena (TxA) families as progeny mean, heterosis and heterobeltiosis for ten important agronomic characters by evaluating 72 cross combinations (36 of TxT and 36 of TxA, from 18 common female parents), for three successive seedling and clonal generations under short day sub-tropic conditions. TxA families had more vigorous progenies, higher tuber yield, higher number of tubers, larger tubers and better general impression than TxT families. The TxA families were inferior to the TxT families for characters such as tuber colour and uniformity of tuber colour, but their progeny means were within the acceptable range. High progeny means of TxA families were associated with high heterosis and high heterobeltiosis in these families, although there were a few exceptions. High mean performance for tuber yield and tuber number were associated with high variance of these traits in TxA families. It is concluded that, unlike under long day environments, andigena adapted to short days can be used advantageously for exploiting heterosis in the potato breeding programmes of short day subtropic environments.