BackgroundIn tropical countries, losses caused by bovine tick Rhipicephalus (Boophilus) microplus infestation have a tremendous economic impact on cattle production systems. Genetic variation between Bos taurus and Bos indicus to tick resistance and molecular biology tools might allow for the identification of molecular markers linked to resistance traits that could be used as an auxiliary tool in selection programs. The objective of this work was to identify QTL associated with tick resistance/susceptibility in a bovine F2 population derived from the Gyr (Bos indicus) × Holstein (Bos taurus) cross.ResultsThrough a whole genome scan with microsatellite markers, we were able to map six genomic regions associated with bovine tick resistance. For most QTL, we have found that depending on the tick evaluation season (dry and rainy) different sets of genes could be involved in the resistance mechanism. We identified dry season specific QTL on BTA 2 and 10, rainy season specific QTL on BTA 5, 11 and 27. We also found a highly significant genome wide QTL for both dry and rainy seasons in the central region of BTA 23.ConclusionsThe experimental F2 population derived from Gyr × Holstein cross successfully allowed the identification of six highly significant QTL associated with tick resistance in cattle. QTL located on BTA 23 might be related with the bovine histocompatibility complex. Further investigation of these QTL will help to isolate candidate genes involved with tick resistance in cattle.

Napier grass (Pennisetum purpureum Schum.) is an important forage crop in tropical areas although little is known about its genome information, and few molecular markers have been developed for this species. This work aimed to check the viability of cross‐species amplification of microsatellite markers between pearl millet (Pennisetum glaucum) and Napier grass and to evaluate the genetic diversity among Napier grass germplasm accessions. Fifty‐four microsatellite markers previously described in pearl millet were tested against Napier grass, and 30 markers (55.5%) showed successful cross‐amplification. From them, 18 microsatellite markers were selected to study the genetic diversity in the Embrapa Active Germplasm Bank of Napier Grass (Embrapa‐BAGCE). A total of 180 alleles were identified by these selected microsatellite markers in 107 Napier grass accessions and four pearl millet samples. The average similarity coefficient (Dice) calculated among the Embrapa‐BAGCE accessions was 0.651, ranging from 0.254 to 1.0. Some accessions showed similarity coefficients equal to one, indicating that they have common progenitors or that they might be the same accessions with different denomination. To our knowledge, this work is the first to describe microsatellite markers in Napier grass and represents a significant advance regarding the use of molecular markers in this species.

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ABSTRACT. Frequencies of κ-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 κ-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 κ-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.

Pasture is the main food source for more than 200 million cattle heads in Brazil. Although Brazilian forage breeding programs have successfully released well-adapted, high-yielding cultivars over the years, the use of genomic tools in these programs is currently limited. These tools are required to tackle the main challenges for tropical forage breeding in Brazil. In this context, this note lists the main research priorities raised at the workshop "Breeding Forages in the Genomic Era", which are necessary to accelerate the use of genomic tools for next-generation breeding of tropical forages and allow breeders to increase genetic gains. Additionally, an online discussion forum (hosted at http://www. cnpgl.embrapa.br/genfor) has been launched to strengthen collaborations among research groups. The research priorities and more synergistic collaborations will assist researchers and decision-makers in delivering a sustainable increase in production of animal products, especially beef and milk, which are required to feed a rising world population.