DNA elimination in embryogenic development of Pennisetum glaucum x Pennisetum purpureum (Poaceae) hybrids.

Interspecific hybridization between Napier grass (Pennisetum purpureum), which is widely grown in Brazil for cattle forage, and pearl millet (Pennisetum glaucum) has been used as a breeding strategy for the development of improved cultivars. However, the hybrid between these two species is sterile due to its triploid condition (2n = 3x = 21 chromosomes), which hinders its use in crop breeding programs. It is known that genomic alterations result from the hybridization process. In order to measure the loss of DNA during embryo development, we used flow cytometry to estimate the nuclear DNA content of triploid and tetraploid embryos produced by interspecific hybridization between Napier grass and pearl millet. The triploid and tetraploid hybrids had a mean DNA content of 4.99-4.87 and 5.25-4.84 pg, at 10 and 30 days after pollination, respectively. The mean reduction in DNA content was higher in the tetraploid hybrids. The flow cytometry results revealed progressive genomic instability in these triploid and tetraploid hybrids, with this instability causing significant alterations in the DNA content of the hybrids.

Quantitative trait loci affecting lactose and total solids on chromosome 6 in Brazilian Gir dairy cattle.

Fourteen Brazilian Gir sire families with 657 daughters were analyzed for quantitative trait loci (QTL) on chromosome 6 affecting lactose and total solids. Cows and sires were genotyped with 27 microsatellites with a mean spacing between markers of 4.9 cM. We used a 1% chromosome-wide threshold for QTL qualification. A QTL for lactose yield was found close to marker MNB66 in three families. A QTL for total solid yield was identified close to marker BMS2508 in three families. A QTL for lactose percentage, close to marker DIK1182, was identified in two families. A QTL for total solid percentage, close to marker MNB208, was identified in four families. These QTLs could be used for selection of animals in dairy production systems.

High degree of genetic diversity among genotypes of the forage grass Brachiaria ruziziensis (Poaceae) detected with ISSR markers.

The grasses of the genus Brachiaria account for 80% of the cultivated pastures in Brazil. Despite its importance for livestock production, little information is available for breeding purposes. Embrapa has a population of B. ruziziensis from different regions of Brazil, representing most of existing variability. This population was used to initiate an improvement program based on recurrent selection. In order to assist the genetic improvement program, we estimated the molecular variability among 93 genotypes of Embrapa's collection using ISSR (inter-simple sequence repeat) markers. DNA was extracted from the leaves. Twelve ISSR primers generated 89 polymorphic bands in the 93 genotypes. The number of bands identified by each primer ranged from two to 13, with a mean of 7.41. Cluster analysis revealed a clearly distinct group, containing most of the B. ruziziensis genotypes apart from the outgroup genotypes. Genetic similarity coefficients ranged from 0.0 to 0.95, with a mean of 0.50 and analysis of molecular variance indicated higher variation within (73.43%) than among species (26.57%). We conclude that there is a high genetic diversity among these B. ruziziensis genotypes, which could be explored by breeding programs.

Quantitative trait loci affecting milk production traits on bovine chromosome 6 in zebuine Gyr breed.

Fourteen Brazilian dairy Gyr sire families with 657 daughters were analyzed for quantitative trait loci (QTL) on chromosome 6 by using a daughter design for 5 economic traits: milk, fat, and protein production, fat and protein percentage. The cows and sires were genotyped for 27 microsatellites with average spacing between markers of 4.9 cM. In the analyses across 14 families, for the largest significant families, and within family, a QTL was located for milk yield and fat yield close to marker BMS2508 at the 5% chromosome-wide significance level across families and 1% chromosome-wide within families. For fat percentage, a QTL near DIK4482 was identified at the 5% chromosome-wide significance level when all families were analyzed together and at the 1% chromosome-wide significance level within the largest significant families. The different analyses yielded results that were generally consistent for milk yield, fat yield, and fat percentage. The order of the markers in the derived map was consistent with that in the consensus map. Some QTL and candidate genes in dairy cattle for milk production traits are probably preserved in Bos taurus and Bos indicus.

On the search for markers of tick resistance in bovines.

Genetic differences in susceptibility to ticks (Rhipicephalus (Boophilus) microplus) are considerable in bovines. Here, mapping, association and gene expression approaches were employed to further advance our understanding of the molecular basis of tick resistance. A B. taurus x B. indicus F2 population was developed by Embrapa and 382 individuals were measured for parasitic load. Scanning of all chromosomes is in progress. Quantitative trait loci (QTL) for tick load were mapped to chromosomes 4, 5, 7, 10, 14, 18 and 23 out of the 20 chromosomes scanned and were dependent on the season in which the phenotype was scored. In the candidate gene approach, females from the genetic groups Nelore (NE--184), Canchim x Nelore (CN--153), Aberdeen Angus x Nelore (AN--123) and Simmental x Nelore (SN--120) were evaluated under natural infestation. Microsatellite markers close to the genes for interleukin 2 (IL2), interleukin 4 (IL4) and interferon gamma (IFNG) were analysed. Tick counts were associated with the marker for interleukin 4 (P < 0.05) in three genetic groups. Differences in cytokine mRNA levels of naive versus infested Nelore calves as well as between resistant versus susceptible cows from NE, CN and AN genetic groups were also investigated. Comparison of cytokines from infested and naïve animals showed downregulation of IL2. When resistant cows were compared to susceptible animals, IL8 was downregulated. These results reinforce the multiloci nature of tick resistance and the need to consider QTL and environment interactions.

Genetic polymorphism of the kappa-casein gene in Brazilian cattle.

Frequencies of kappa-casein gene alleles were determined in 1316 animals from the Brazilian Bos indicus genetic groups (Sindhi cows, Gyr sires, Gyr cows, Guzerat sires, Guzerat cows, Nellore sires, and Gyr x Holstein crossbreds) by means of polymerase chain reaction-restriction fragment length polymorphism analysis using two independent restriction nucleases (Hinf I and HaeIII). The genotyping of kappa-casein alleles (A and B) is of practical importance, since the B allele is found to correlate with commercially valuable parameters of cheese yielding efficiency. The frequencies of the B allele of kappa-casein among breeds ranged from 0.01 to 0.30. The Sindhi breed had the highest frequency for the B allele (0.30), while the frequencies of this allele in other breeds ranged from 0.01 to 0.18. A wide variation in the B allele frequency among B. indicus breeds was found suggesting that molecular selection for animals carrying the B allele could impact breeding programs for dairy production.

Association of BoLA-DRB3.2 alleles with tick (Boophilus microplus) resistance in cattle.

Losses caused by bovine tick burdens in tropical countries have a tremendous economic impact on production systems. Besides reducing production, this parasite can cause death in the most susceptible animals. The use of commercial acaricides has been the major method of control, but their misuse has led to tick resistance to many chemicals. More recently, vaccines have been used in some countries without solving the problem completely. An alternative could be the development of resistant animals and the use of genetic markers and candidate genes that could help with the enormous task of selecting resistant animals. The bovine lymphocyte antigen genes (BoLA) have been shown to be associated with some parasitic infestations and disease incidence. Thus, the objective of the present study was to determine the association of BoLA-DRB3.2 alleles with tick resistance in cattle. The study was conducted on 231 F2 (Gyr x Holstein) animals that were artificially infested with 10,000 tick larvae. Log of tick count +1 was used as the dependent variable in a mixed animal model with allele substitution effects in addition to fixed effects of year and season at tick count, sex of calves, age of animal at tick count, hair type (short-straight, short-curl, long-straight, and long-curl), coat color (white, >75% white, 50- 75% white, and 25-50% white), and additive genetic, permanent environmental and residual effects as random. Females showed fewer ticks than males. Animals with short-straight hair were more resistant to tick infestation than animals with long-curl hair, and animals with whiter coat color also had fewer ticks. An association between BoLA alleles and lower tick number was found for alleles DRB3.2 *18, *20 and *27 at the 5% significance level. Also, one allele (DRB3.2*16) showed an association at the 10% level. Allele *27 was the most frequent in the population (30.7%), followed by alleles *16 (10.8%), *20 (8.7%) and *18 (2.4%). These results suggest that BoLA-DRB3.2 alleles could be used to help in the selection of animals resistant to tick infestation. However, further studies involving a larger population of cattle in combination with other BoLA genes may help to understand the mechanisms of resistance to parasites.

Association of BoLA-DRB3.2 alleles with tick (Boophilus microplus) resistance in cattle

Losses caused by bovine tick burdens in tropical countries have a tremendous economic impact on production systems. Besides reducing production, this parasite can cause death in the most susceptible animals. The use of commercial acaricides has been the major method of control, but their misuse has led to tick resistance to many chemicals. More recently, vaccines have been used in some countries without solving the problem completely. An alternative could be the development of resistant animals and the use of genetic markers and candidate genes that could help with the enormous task of selecting resistant animals. The bovine lymphocyte antigen genes (BoLA) have been shown to be associated with some parasitic infestations and disease incidence. Thus, the objective of the present study was to determine the association of BoLA-DRB3.2 alleles with tick resistance in cattle. The study was conducted on 231 F2 (Gyr x Holstein) animals that were artificially infested with 10,000 tick larvae. Log of tick count +1 was used as the dependent variable in a mixed animal model with allele substitution effects in addition to fixed effects of year and season at tick count, sex of calves, age of animal at tick count, hair type (short-straight, short-curl, long-straight, and long-curl), coat color (white, >75% white, 50- 75% white, and 25-50% white), and additive genetic, permanent environmental and residual effects as random. Females showed fewer ticks than males. Animals with short-straight hair were more resistant to tick infestation than animals with long-curl hair, and animals with whiter coat color also had fewer ticks. An association between BoLA alleles and lower tick number was found for alleles DRB3.2 *18, *20 and *27 at the 5% significance level. Also, one allele (DRB3.2*16) showed an association at the 10% level. Allele *27 was the most frequent in the population (30.7%), followed by alleles *16 (10.8%), *20 (8.7%) and *18 (2.4%)...