Heterosis Effects Research Articles

Genetic analysis of first lactation production and fertility traits in Karan Fries cattle

The present investigation encompasses the genetic analysis of first lactation production and fertility performance of Karan Fries cattle. Data were collected on 1,988 cows maintained at National Dairy Research Institute (NDRI), Karnal, Haryana over a period of 34 years (1978 to 2012). Least squares analysis was carried out to study the effect of non-genetic factors, viz. season of first calving (SC), period of first calving (PC), genetic group (GG) and age at first calving group (AFCG) on first lactation fertility and production traits. Least squares means of age at first calving (AFC), first calving to first service (FCFS), first service period (FSP), first lactation length (FLL), first calving interval (FCI), first lactation 305 day or less milk yield (F305MY), first lactation total milk yield (FTMY), milk yield per day of first lactation length (MY/FLL), milk yield per day of first calving interval (MY/FCI) and first lactation daughter pregnancy rate (FDPR) were 957.48±6.54 days, 79.46±3.58 days, 130.03±4.43 days, 347.02±5.51 days, 415.47±5.21 days, 3,213.91±47.61 kg, 3,760.49±74.27 kg, 10.49±0.12 kg/day, 9.14±0.13 kg/ day and 0.33±1.42, respectively. Overview of least squares analysis regarding first lactation traits indicated that most of the non-genetic factors excepting AFC group, significantly affected the performance of the animal. Results revealed the superiority of F1 over other GG of Karan Fries cows indicating a significant effect of heterosis. Heritability estimated by both analysis of variance and average information restricted maximum likelihood methods indicated that the fertility traits were less affected by additive gene action; the estimates for production traits indicated higher role of additive gene action. Both phenotypic and genetic correlation estimates indicated antagonistic association between fertility and production traits.

Vigor híbrido en cruzamientos de líneas endocriadas de gusanos de seda (Bombyx mori L)

Productive characteristics of hybrids, from the crossing of a FA-UBA line and other one of a European origin, have been assessed. Three quantitative variables have been measured: length and weight of the entire cocoon and of the cocoons without pupa. Weight and silk weight of 20000 cocoons and raw silk percentage were also determined. This data was analyzed through ANOVA and several comparisons were performed for each variable analyzed. For all the variables tested, highly significant differences were found between genotype media (breeds and hybrids). For the three features tested, the heterosis effect was very strong. For the cocoon length (mm) the differences were de following: 30.2 parental average vs. 36.05 the direct hybrid and 34.53 the reciprocal hybrid. For the entire cocoon weight (g): 1.17 parental average vs. 1.57 the direct hybrid and 1.54 the reciprocal hybrid. For the bark weight: 0.21 parental hybrid vs. 0.30 the direct hybrid and 0.29 the reciprocal hybrid. The raw silk percentage was between the species ranges (16 to 24%) but the hybrid average turned to be higher than the parents average. The hybrids silk production was 39% higher than the parents production media. In conclusion, the crossing of the two lines used showed strong heterosis effect for all the variables analyzed.

0355 The effect of heterosis on pulmonary arterial pressure on beef cattle

0355 The effect of heterosis on pulmonary arterial pressure on beef cattle

Genetic group and heterosis on morphometric measurements during the growth of male beef cattle

In the present study, the effects of genetic group and heterosis on body measurements of purebreds (Charolais - C and Nellore - N), first-generation crossbreds (G1) (1/2C1/2N and 1/2N1/2C), and second-generation crossbreds (G2) (3/4C1/4N and 3/4N1/4C) males from rotational crossbreeding were evaluated at 8, 12, 18, and 24 months of age. Among the purebreds, the Nellore displayed greater rump height than the Charolais. The Charolais had greater thoracic perimeter than the Nellore, however this difference decreased gradually with advancing age, being equal between the two genetic groups at 24 months. For width of the rump, ischial opening and thoracic perimeter crossbred animals showed higher values than the purebred animals at all ages, but less pronounced at eight months of age. For all morphometric measurements, with exception of rump height, the differences of crossbreds males in relation to the purebreds, were more evident in relation to the Nellore. Heterosis was significant for morphometric measurements in male beef cattle. Morphometric measurements showed high correlation with each other and with body weight, thereby indicating that they are good indicators of body development.

English

Maize (Zea mays L.) has a range of uses, from animal to human feed and can be consumed in nature, or as feedstock material in the preparation of starches, flours, canjicas, breads, beverages and porridges. This study aimed to determine the linear associations, estimates of genetic parameters and heterosis of bioactive and micronutrients compounds in maize. The experimental design was randomized blocks, the treatments consisted of six open pollinated varieties (OPVs) of maize: Dente de Ouro Roxo (P1), BRS Missões (P2), Caiano Rajado (P3), AL 25 (P4), Bico de Ouro (P5), Argentino Branco (P6) and five hybrids maize derived from crosses, P2 x P1, P3 x P1, P4 x P1, P5 x P1 e P6 x P1. Linear high and positive associations are expressed between the seed width and hundred kernel weight, between the antioxidants DPPH and ABTS radical, and through the manganese and zinc. The genetic parameters determine the progenies and the parent-average relationship are superior to the length, width and acidity of seeds, total phenols and copper. The heritability in a wide sense expressed is greater for the traits: acidity seeds, antioxidant DPPH radical and copper. The heritability in a restricted sense is superior to the traits length, width and acidity of seeds, carotenoids and sodium content. The traits thickness and color of seeds, total phenols, antioxidant ABTS radical and zinc are increased through the effects of intervarietal heterosis in maize. Estimates of genetic parameters obtained can be used in genetic maize breeding programs, in order to obtain biofortified genotypes using bioactive compounds and micronutrients. Key words: Zea mays L., enriched cereals nutritionally, genetic variability, plant breeding.

Combining Ability of Plant Height and Yield components in Indian Mustard (Brassica junceaL.Czern & Coss.) under Salt affected Soil using Line×Tester Analysis

Line × tester analysis of twenty lines and three testers of Indian mustard (Brassica juncea L. Czern & Coss.) cultivars were used to estimate general combining ability (GCA), specific combining ability (SCA) effects, high parent heterosis and narrow-sense heritability estimate for plant height, yield components and seed yield. Significant variance of line x tester for the traits like pods per plant and seed yield indicating non additive genetic effects have important role for controlling these traits. Significant mean squares of parents v/s crosses which are indicating significant average heterosis were also significant for all the traits except seeds per pod. High narrow-sense heritability estimates for all the traits except seeds per pod exhibited the prime importance of additive genetic effects for these traits except seeds per pod. Most of the crosses with negative SCA effect for plant height had at least one parent with significant negative or negative GCA effect for this trait. For most of the traits except pods per plant, the efficiency of high parent heterosis effect was more than SCA effect for determining superior cross combinations.

Gene flow among Hancornia speciosa (Apocynaceae) varieties and hybrid fitness

The fate of hybrids and the temporal and spatial dynamics of hybrid zones depend on hybrid fitness in comparison to non-hybrids. We studied cross-pollination among Hancornia speciosa varieties and compared progeny fitness in a nursery to address whether hybrid fitness differed from non-hybrids and whether maternal and paternal taxa contribute differentially to offspring fitness. This species has edible fruit pulp that is used as a raw material for candies, ice cream, and juice by small- and medium-sized enterprises in Central-West and Northeast Brazil. We genotyped 258 adults from a germplasm collection and 320 seeds using seven microsatellite loci to estimate genetic parameters and determine pollen donors. Fitness components, days to shoot, growth rate (mm/day), leaf width (mm), leaf length (mm), stem diameter (mm), and plant height (cm) were analyzed in 200 individuals. Genetic diversity and polymorphism did not differ neither between adults and progeny arrays nor among the four varieties. Genetic differentiation among varieties (F CT = 0.019, p < 0.001) and among populations within varieties (F SC = 0.053, p < 0.001) was significant but low. We detected mating among the four varieties, and no self-pollination was observed in parentage analysis, confirming that H. speciosa is self-incompatible with a high outcrossing rate (t m = 0.990, SE = 0.007). No significant effect of heterosis or exogamic depression was detected for any fitness component, but maternal contribution significantly affected plant height.

Genetic Linkage Map Construction and QTL Analysis of Two Interspecific Reproductive Isolation Traits in Sponge Gourd.

The hybrids between Luffa acutangula (L.) Roxb. and L.cylindrica (L.) Roem. have strong heterosis effects. However, some reproductive isolation traits hindered their normal hybridization and fructification, which was mainly caused by the flowering time and hybrid pollen sterility. In order to study the genetic basis of two interspecific reproductive isolation traits, we constructed a genetic linkage map using an F2 population derived from a cross between S1174 [L. acutangula (L.) Roxb.] and 93075 [L. cylindrica (L.) Roem.]. The map spans 1436.12 CentiMorgans (cM), with an average of 8.11 cM among markers, and consists of 177 EST-SSR markers distributed in 14 linkage groups (LG) with an average of 102.58 cM per LG. Meanwhile, we conducted colinearity analysis between the sequences of EST-SSR markers and the genomic sequences of cucumber, melon and watermelon. On the basis of genetic linkage map, we conducted QTL mapping of two reproductive isolation traits in sponge gourd, which were the flowering time and hybrid male sterility. Two putative QTLs associated with flowering time (FT) were both detected on LG 1. The accumulated contribution of these two QTLs explained 38.07% of the total phenotypic variance (PV), and each QTL explained 15.36 and 22.71% of the PV respectively. Four QTLs for pollen fertility (PF) were identified on LG 1 (qPF1.1 and qPF1.2), LG 3 (qPF3) and LG 7 (qPF7), respectively. The percentage of PF explained by these QTLs varied from 2.91 to 16.79%, and all together the four QTLs accounted for 39.98% of the total PV. Our newly developed EST-SSR markers and linkage map are very useful for gene mapping, comparative genomics and molecular marker-assisted breeding. These QTLs for interspecific reproductive isolation will also contribute to the cloning of genes relating to interspecific reproductive isolation and the utilization of interspecific heterosis in sponge gourd in further studies.

Hybrid breeding boosted molecular genetics in rye

The history of rye (Secale cereale L.) breeding began from the first targeted selections made in Germany by the Probsteier Seed Cooperative around 1850, and over 150 years of breeding yielded a tremendous amount of results. Rye has also long been used as cytological subject due to its low number of chromosomes and their size. However, genetic findings in rye up to the early 1980s were rather scant. About 120 genes could be assigned to seven linkage groups. However, since then development of new methods such as C-banding procedures, in situ DNA hybridization, enzymology and molecular marker techniques achieved an enormous progress. Particularly, the latter of these was driven by the agronomic success of hybrid breeding in rye. The basic genetic knowledge resulting from intra- and interspecies genetic diversity assay and phylogenetic studies in the Secale genus used nuclear and cytoplasmic molecular markers to facilitate successful selection of parents for hybrid breeding and hence contribute to improvement of heterosis effect. The main achievements in rye hybrid breeding and genetic mechanisms exploited for different hybrid breeding strategies are discussed. The exploitation of landraces or wild rye species gene pools via advanced backcross QTL analysis or introgression libraries to increase the heterosis effect is a prospective strategy of marker-assisted hybrid breeding in rye. Prediction of hybrid performance can also be improved significantly by marker-assisted selection and genomic selection based on genome-wide marker data. The findings in rye genetics (including phylogenetic, mapping and population studies) are reviewed in their relation with the hybrid breeding purposes and demands. Overall, about 450 morphological and biochemical traits are mapped throughout the the genome plus about 5,000 DNA markers. They are not only associated with individual chromosome or segments but also efficiently used for comparative mapping (evolutionary studies), introgression monitoring, QTL tagging, and marker-assisted selection.

Cadmium accumulation characteristics of F1 hybrids by reciprocal hybridizing of Solanum nigrum in two climate-ecology regions.

Different ecotypes of crop hybridization can produce heterosis effects and have wide applications in plant breeding. In this study, seedlings of cadmium (Cd) hyperaccumulator Solanum nigrum were collected from two different climate-ecology regions of the western Sichuan Basin, China, to carry out reciprocal hybridizing and to study the Cd accumulation characteristics of F1 hybrids of S. nigrum. In the two pot experiments (high and low soil Cd concentration), the biomass and Cd extraction of reciprocal hybridizing F1 hybrids were higher than those of the parents, but the Cd content in different organs was lower than those of the parents. These results indicate that the biomass and Cd extraction of F1 hybrids show over-parent heterosis, and the Cd content shows hybrid weakness. In the field experiment, the variety of the biomass, Cd content, and Cd extraction of reciprocal hybridizing F1 hybrids were the same as the pot experiments, and the Cd extraction by shoots of reciprocal hybridizing F1 hybrids increased by 17.20 and 23.08%, relative to the two higher parents. Therefore, the reciprocal hybridizing S. nigrum of different climate-ecology regions could be efficiently used to improve the phytoremediation ability of S. nigrum to Cd-contaminated soil.

Crossbreeding in beef production: meta-analysis of breed means to estimate breed-specific effects on leather properties

The objective of this study was to discern opportunities for improving leather-making properties of hides originating from beef production systems based on indigenous Afrikaner cattle via crossbreeding. Data were previously unpublished breed means from purebred Afrikaner, Brahman, Charolais, Hereford and Simmental, top-crosses of Brahman, Charolais, Hereford, and Simmental sires on (1) Afrikaner dams producing F1 progenies and (2) Brahman × Afrikaner, Charolais × Afrikaner, Hereford × Afrikaner, and Simmental × Afrikaner F1 females producing both backcross and three-breed cross progenies. Hide yield (%), leather yield (dm2/kg), force 20% extension (Mpa), extension grain crack (%), extension break (%), force break (Mpa), slit tear force (N/mm), distension grain crack (%), and force grain crack (N/mm) were evaluated. Breed direct effects and individual heterosis, but not maternal effects, may be important for most of these traits. Direct effects due to the exotic breeds reduced hide yield but generally improved leather properties relative to the indigenous Afrikaner. For both hide and leather yields, individual heterosis effects arose primarily from indicus × taurus crosses with the Hereford × Brahman effect being most pronounced. Thus, there may be opportunities to improve leather yield and quality through crossbreeding relative to the straightbred Afrikaner. A top-cross mating plan may be recommended to enhance production by subsistence level farmers having access to Afrikaner females, provided that management can ensure appropriate use of the terminal sires.

Utilization of Plant Genetic Resources in Peanut Breeding Program of Bulgaria

Based on study of some morphological indices, responsible for productivity in 97 breeding lines Arachis hypogea L. with Bulgarian origin, a linear regression model of the plant, that is characterized with high seed yield, was established. The breeding program requires the identification of direct and indirect effects on productivity. By application of the Path Coefficient Analysis,it has been found that the higher yield plants must have low and extensive bush (i&gt; 2,0). The local accessions of peanuts are characterized by a lower index of the bush (i &lt;2,0). For this purpose, 399 genotypes with different geographical origin were introduced from USDA (USA) in 2008. Based on the evaluation of foreign accessions by height and width of the plant, seed yield from one plant and resistance to Fusarium, four genotypes were selected. They were included in crosses with Bulgarian varieties and lines of Valencia type. The heterosis expressions and some genetic effects of progenies were studied.The results show that heterosis effect in F1at some of the progenies in connection withyield of the fruit and seeds are inherited without epistatic effect. The inbred depression in F2is an indication of homozygosity in respect of allelic pairs defining yield.

Breed and heterosis effects for milk yield traits at different production levels, lactation number and milking frequencies

ABSTRACTThe objective of this study was to evaluate the effects of production level (PL) and lactation number (LN) on the expression of breed, and heterosis for yield traits in cows milked once (OAD) or twice daily (TAD) in New Zealand. Records were used from 35,192 Friesian (F), 31,118 Jersey (J) and 88,606 crossbred (F × J) cows that calved in spring between 2008 and 2012. With an average LN of five, F cows had a higher milk yield (592 kg in OAD and 909 kg in TAD), fat yield (2.1 kg in OAD and 6.3 kg in TAD) and protein yield (11.9 kg in OAD and 19.5 kg in TAD) compared with J cows. Expressed as a percentage, heterosis effects for milk yield traits ranged from 4.1%–7.6% for production traits, and were similar across milking frequencies. In absolute values, however, heterosis was different for fat and protein yield only in first-lactation cows, and no differences were found in milk yield. In a second analysis, breed effects, defined as F–J, increased as PL of the herd increased in both OAD and TAD systems. The highest expressions of heterosis were found at medium (5.9%–6.4%) and low (5.2%–6.8%) PL in cows milked OAD and TAD, respectively. However, in absolute values, the greatest heterosis was observed at high PL in the population milked TAD. The estimates of breed and heterosis obtained in this study can be used for simulation studies to evaluate the profitability of crossbreeding systems under OAD and TAD milking systems in New Zealand dairy farms, at different PL.

Breed genotype effect on ewe traits during the pre-weaning period in hair sheep under the tropical Mexican conditions

The present study was carried out on a commercial farm in southwest of Mexico to determine breed group effects of hair sheep (Pelibuey, Dorper, Katahdin, and Blackbelly and their crosses) and their genetic components (breed additive, breed maternal and heterosis effects on litter weight at birth, adjusted litter weaning weight at 60 days, and lambing interval. The dataset included records from 1821 four-purebred ewes and crossbreed groups (representing 9 different crosses between the four pure breeds). In total, there were 6371 lambing events from 2007 to 2013. The first model included the effects of breed, parity, litter size, season of lambing, year of lambing and season×year interaction. Those significant effect (P<0.05) were included in the models to estimate the breed additive, breed maternal and heterosis effects. Breed additive and breed maternal effects were expressed as deviations from the Pelibuey breed. Breed, parity and litter size were significant sources of variation for all the traits (P<0.05), but season and year interaction were significant only for litter birth and weaning weight (P<0.05). Heterosis effect was only observed for adjusted litter weaning weight at 60 days of age for the Pelibuey×Katahdin crossbred ewes (P<0.05). Under the conditions of this study, direct heterosis and maternal effects between the four breeds studied has shown no significant effect on these traits. Non-genetic factors had a greater influence on the traits studied than the genetic makeup of the ewe.

Hybrid performance and heterosis in strawberry (Fragaria × ananassa Duchesne), regarding acidity, soluble solids and dry matter content in fruits

AbstractA top‐cross‐mating design among 29 S4 inbred lines and tester (cultivar ‘Dukat’) was carried out to study their breeding value in terms of general combining ability (GCA). The objectives of this study were to evaluate the acidity, soluble solids and dry matter contents in fruits of progeny F1 in comparison with S4 inbred lines as well as the cultivars (S0); identify strawberry genotypes with high value of GCA for use in cultivar development; and determine mid‐parent heterosis regarding S4 inbred lines and cultivated strawberry. The 2‐year observations showed statistically significant differences between tested genotypes in terms of the studied traits. The highest breeding value based on GCA was estimated for Chandler 123‐5 for soluble solids and dry matter content, and Kent 7‐6 for acidity. Estimated mid‐parent heterosis had positive and negative values. The highest heterosis in terms of extract and dry matter content (26.71% and 17.50%, respectively) occurred in the offspring Chandler 123‐5 × ‘Dukat’, but as regards acidity in hybrid Chandler 123‐22 with cv. ‘Dukat’. The study of genetic divergence by dendrograms may help to identify parents suitable for obtaining hybrids with higher heterosis effects.

Estimates of genetic and crossbreeding parameters for milk components and potential yield of dairy products from New Zealand dairy cattle

ABSTRACTMilk composition can vary significantly among individual cows and breeds, and the dairy products that can be made from that milk are limited by available milk components. The objective of this research was to estimate genetic and crossbreeding parameters for lactation yields of milk, fat, protein and lactose, and use these to determine potential yields of dairy products from New Zealand dairy cattle. A mass-balance milk-processing model was used to estimate yields of milk products for 4310 first lactation heifers that produced milk in the 2010–2011 dairy season. Estimates of heritability for yields of whole and skim milk powders were moderate (0.31). Heterosis effects for product yield per lactation was significant only for cheese and butter production (P < 0.05). The use of genetic parameters and correlations for dairy product yield could increase the rate of gain for specific product yields, but have to be evaluated in conjunction with other traits of interest in breeding worth.

TO 135TH ANNIVERSARY FROM THE DATE OF BIRTH OF ZHEGALOV S.I. – AN ESTABLISHER OF NATIONAL SCHOOL FOR BREEDING AND SEED INDUSTRY OF VEGETABLE CROPS

On the second of October, in 1881, Sergey Ivanovich Zhegalov, an establisher of national breeding and seed production of vegetable crops was born in a little village Vasilkovo of Vyazemskogo uezda. He was a founder and a first director of Gribovskaya Vegetable Breeding Station. This year marked by 135th anniversary from the date of birth of the outstanding scientist. All the time at All-Russian Research Institute of Vegetable Breeding and Seed Production (VNIISSOK), its scientific leader and mastermind is honored and remembered for his heritage that is still preserved and augmented. This scientist was at the beginning of plant breeding science and became the first who brought scientifically proved methods into agricultural plant science. The process of newplant- form-producing and development of new more qualified breeding forms through distant crossing, hybridization, heterosis effect, are the problems which interested the mind of Zhegalov and always were the sense of his life. These problems still remain in these days, where his ideas are embodied in scientific program of the institute covering theoretical researches for development of innovation method needed for creation of new highly qualified breeding plant material regarded as a source for nearest breeding practice and seed production. At VNIISSOK the richest plant collection with important genes and donor genotypes of productivity, fast ripening, high quality, resistance to biotic and abiotic stresses is created in Cucurbitaceae, Solanaceae, Alliaceae, Fabaceae, root vegetables, Brassicas, leafy crops, aromatic and medicinal crops and ornamental crops. Core plant collection is substantially extending by means of introduction of new crops and non-traditional ones as well. The specialist-breeders of VNIISSOK have developed over 800 cultivars and hybrids F1 of vegetables, melons and gourds, aromatic plants, ornamental plants, non-traditional. 546 accessions out of 118 crops have been included into State Register of Breeding Achievements of Russian Federation in 2016.

PARTICULARITIES OF WHITE HEAD CABBAGE F1 HYBRID BREEDING FOR PRIDNESTROVIAN MOLDAVIAN REPUBLIC CONDITIONS

A model of late maturing F1 hybrid of white head cabbage for long-term storing and suitable for national recipe “golubci” have been developed based on requirements for varieties and F1 hybrids grown in the South in the conditions of drought, high temperatures and low air humidity. Combining ability of seven self-incompatible inbred lines of white head cabbage was studied by the system of full diallel crosses in conditions of Pridnestrovian Moldavian Republic. These lines were developed on the base of heat tolerant varieties ‘Biruchekutskaya’, ‘Volna’, ‘Lada’, ‘Moldavanka’ and ‘Kharkovskaya Zimnyaya’ bred in the south. Out of 42 hybrid combinations studied 15 significantly surpassed in productivity the variety ‘Zavadovskaya’ that is traditionally grown by local farmers for pickling and recipe “golubci”. High GCA effects for productivity showed the following breeding lines: Bu1, Ml3 and Kl5. Polygenes, controlling the high yield ability, mainly were dominant and single-directed, however the correlation between yield ability and GCA effect was middle, r=0.63±0.35. No correlation was observed in breeding line between GCA effect and truly heterosis effect in hybrid combinations (r=0.19). Disease resistance analysis revealed lines Bu1 and Kl5 that had shown resistance to Fusarium yellows. Two hybrid combination Kl5xBu1 and Ml3xBu1 were highly tolerant to thrips attacks according to analysis of all promising hybrid combinations, carried out in natural infection background. Weak correlation was observed between the number of damaged leaves in cabbage head and dry matter content, r=0.41±0.21, and also there is no correlation revealed with sugar contents, ascorbic acid and nitrate content. High tolerance of hybrids with participation of line Bu1 explained the partial dominance nature of the trait. Hybrid combinations Kl5xBu1 and Ml3xBu1 called ‘Batal’ and ‘Shedevr’, respectively, included in registry of Moldova and PMR.

Genetic parameters and crossbreeding effects of fat deposition and fatty acid profiles in Iberian pig lines.

The aim of this study was to estimate the genetic and environmental parameters and crossbreeding effects on fatty acid and fat traits in the Iberian pig. Our final goal is to explore target selection traits and define crossbreeding strategies. The phenotypes were obtained under intensive management from 470 animals in a diallelic experiment involving Retinto, Torbiscal, and Entrepelado lines. The data set was composed of backfat thickness at the fourth rib (BFT), intramuscular fat (IMF) in the longissimus thoracis (LT), and the fatty acid profile for IMF and subcutaneous fat (SCF) traits. Data were analyzed through a Bayesian bivariate animal model by using a reparameterization of Dickerson's model. The results obtained showed an important genetic determinism for all traits analyzed with heritability ranging from 0.09 to 0.67. The common environment litter effect also had an important effect on IMF (0.34) and its fatty acid composition (0.06-0.53) at slaughter. The additive genetic correlation between BFT and IMF (additive genetic correlation [] = 0.31) suggested that it would be possible to improve lean growth independent of the IMF with an appropriate selection index. Furthermore, the high additive genetic correlation ( = 0.68) found between MUFA tissues would seem to indicate that either the LT or SCF could be used as the reference tissue for MUFA selection. The relevance of the crossbreeding parameters varied according to the traits analyzed. Backfat thickness at the fourth rib and the fatty acid profile of the IMF showed relevant differences between crosses, mostly due to line additive genetic effects associated with the Retinto line. On the contrary, those for IMF crosses were probably mainly attributable to heterosis effects. Particularly, heterosis effects were relevant for the Retinto and Entrepelado crosses (approximately 16% of the trait), which could be valuable for a crossbreeding system involving these lines.

EFEK HETEROSIS DAN AKSI GEN UKURAN BUAH PADA HIBRIDA PEPAYA

Fruit size is an important character in determining the quality of papaya fruit. Domestic consumers prefer small or medium size papaya fruit, while for the desirable fruit slices are large one. Assembly papaya varieties based on fruit size can be done through conventional breeding. The objectives of this study were to determine the effects of heterosis and gene action on the fruit size character of the papaya hybrid. The research was conducted at KP. Sumani Tropical Fruit Research Institute, Solok, West Sumatra in 2010-2011. This research used a randomized block design with 25 treatments (20 hybrids and five elders papaya) and repeated three times. The results showed that in general the heterosis effect on fruit size (weight, length and girth of the fruit) was found below 50%. Heterosis effect can decrease and increase the size of the fruit because the value is negative and positive. The negative excess of dominant gene action resulting in smaller sizes of F1 than the average of both parents or youngest parents. Therefore, crosssing BT3 x BT2 had the smallest fruit size. Positive excess of dominant gene action i.e crossing BT1 x D, BT4 x BT1 and D x BT3 resulted in bigger fruit size than two parents. Keywords: Gene action, Heterosis, Hybrid, Papaya