Genetic Resources for Tropical Areas: Achievements and Perspectives

This paper analyses the present status of tropical forage resources and their utilization in the development of novel cultivars based on the accumulated information from past decades of collecting, evaluation and whatever little breeding has been pursued. The situation of world collections of tropical forages is presented and discussed in the light of limited investment and dwindling resources. A cause for concern is the lesser priority assigned to conservation and manipulation of official tropical germplasm banks, such as CSIRO’S and CIAT’s. In order to assure the availability of tropical genetic resources for the future it is imperative that international efforts be undertaken to renew investments into organizing world databases, providing human and financial resources to maintain existing collections and that national and international research organizations be stimulated to act cooperatively in favor of a common goal. Perhaps by assigning value to biodiversity, the stimuli for national organizations to collect, conserve and exchange will come forth. In order to fully exploit genetic resources and guarantee continued diversity for selection, breeding activities need to be pursued. It is odd, however, that tropical forages have deserved such little input from breeding: most cultivars in use, are little more than selections from the wild, whereas the animals grazing those pastures have been bred for generations and many times using sophisticated methodologies. A survey of major Brazilian university curricula in agronomy and animal sciences provided a clue: only two of those have a forage breeding course at the graduate level and hardly any of those has a forage breeder in the staff. However, all of them have at least one animal breeding course in the required curriculum and animal breeders in their staff. If no forage breeders are being trained, genetic resources of forage plants will continue to be underutilized in the future. A vast body of information was generated in the past decade on characteristics and agronomic value of tropical forages. A scheme generally followed to develop new cultivars was presented in this paper and discussed using examples of a grass (Panicum maximum) and a legume (Stylosanthes). Forages as pastures for animal production in the tropics are ever so much more important than in the temperate zones, where some form of forage conservation or grain needs to be utilized to maintain animals over the winter. Meat is produced mostly from pasture-fed cattle in the tropics, which has an ecological appeal, contributes to competitiveness and gains public endorsement worldwide. Therefore the perspectives for developing new improved cultivars to yield better quality and produce meat more cost and energy efficiently are large. To achieve such goals, team work is essential such that breeders, agronomists, phytopathologists, etc. establish priorities closely linked with the demands of the producer, as to assure quick and easy adoption once the variety is released, without forgetting the requirements of the consumers. A form of involving the private sector in the development of the technology should be seriously considered in these times of diminished resources and plant protection laws

Grass and Forage Plant Improvement in the Tropics and Sub-Tropics

Key points 1. The majority of tropical and subtropical forage grass genera and/or species have not yet been collected, or need further collection to be representative of their natural distribution. 2. New biotechnological techniques will only result in the release of superior forage cultivars if supported by strong breeding programs. 3. More funding and investment in the formation of strong public research teams in forage conservation and improvement are needed to guarantee the sustainability of tropical and subtropical pasture-based livestock systems in the future. 4. The creation of a permanent international working group on tropical and subtropical forages is essential to assist the International Plant Genetic Resources Institute (IPGRI) in prioritising collection, conservation, evaluation and adoption in the tropical/subtropical world for the benefit of mankind

Evaluation of Guineagrass (\u3ci\u3ePanicum maximum\u3c/i\u3e Jacq) Hybrids in Brazil

Guineagrass (Panicum maximum Jacq.) is responsible for a high percentage of cattle finishing and milk production in Brazil, but presents problems of pasture degradability due to high soil fertility requirements and uneven production distribution. In order to search for new varieties to reduce these problems, over four hundred apomictic accessions of guineagrass and several sexual plants were introduced to Brazil in 1982. Agronomic evaluation took place at the National Beef Cattle Research Center of the Brazilian Agricultural Research Corporation (Embrapa Beef Cattle), in Campo Grande, MS, Brazil. Breeding of the apomictic species began in 1990 using sexual x apomictic crosses. Three sexual plants and five apomictic accessions were used in the crosses. Seventy-nine hybrids were evaluated in small plots, for forage yield, regrowth after cuts, flowering and vigor during three years. The best families were identified for each characteristic evaluated. Multivariate analysis using principal components grouped the hybrids into six clusters according to their production. Due to superior performance, hybrids in groups 6 and 2 (22 hybrids) were indicated for future regional trials in small plot evaluations and grazing studies, aiming at releasing new cultivars for pasture diversification in Brazil

Analysis of Genomic Affinity Between \u3cem\u3eBrachiaria Ruziziensis\u3c/em\u3e and \u3cem\u3eB. Brizantha\u3c/em\u3e Through Meiotic Behaviour

Genetic divergence between polyploid hybrids is displayed in chromosome pairing and in the rate of chromosome elimination due to differences in cell cycle between the two combined genomes (Sundberg et al. 1991). In Brachiaria, a genus of African grasses reaching continental proportions as a tropical pasture in Latin America, genome analysis has never been performed. The majority of accessions in this genus is polyploid and apomictic, which restricts breeding. The relative ease of obtaining fertile interspecific hybrids once ploidy barriers are overcome (Pereira et al. 2001) confirms the phylogenetic proximity among B. ruziziensis, B. decumbens and B. brizantha. Hybrids were synthesised using sexual artificial 4x as the female genitor and natural apomictic 4x as the pollen donors. Genome affinity is a pre-requisite for chosen genitors to produce fertile hybrids and plenty of viable seed to assure adoption of the new cultivar. Microsporogenesis of a hybrid between B. ruziziensis and B. brizantha is described in this paper, focusing on the behaviour of both genomes

Physical Impediment Towards Digestive Breakdown in Leaf Blades of Brachiaria Brizantha

Consumption of grasses is influenced by the physical properties of forages which confer resistance to digestive breakdown. Such barriers may be the proportion of indigestible tissues, girder structure and epidermal cell arrangements. Anatomical factors, if identified early are invaluable tools in breeding and selection programmes for forages of high quality. The objective of this study was to verify which anatomical attributes might be interfering in the physical resistance to rumen breakdown in Brachiaria brizantha ecotypes

Evaluation of \u3ci\u3eBrachiaria brizantha\u3c/i\u3e Ecotypes under Grazing in Small Plots

An intense search for new cultivars amongst recently collected and introduced ecotypes from Africa is in effect since 1988, at the National Beef Cattle Research Center, of the Brazilian Agricultural Research Corporation (Embrapa Beef Cattle). After agronomic evaluations of a large collection, 21 ecotypes were pre-selected for multilocational trials and from these, eight were elected for evaluation under grazing. The objective of this trial was thus to evaluate the persistence and carrying capacity of these eight new Brachiaria brizantha ecotypes after two years of grazing. The experimental design was a randomized complete block with nine treatments and two replicates. The experimental area was divided into 18 paddocks of 1000 m2. They were grazed according to a deferred flexible system. After two years, it was possible to select four ecotypes, which were indicated for animal performance trials aiming at releasing at least one of them as a new cultivar in 2002

Animal Performance and Productivity of New Ecotypes of Brachiaria Brizantha in Brazil

Brazil has the competitive advantage of a very dynamic and cost effective animal production system on pastures over other countries. The pursuit for more productive forages that will result in higher quality beef at a lower cost is then justified. Brachiaria is the most important forage genus utilised in Brazil, thus an intense search for new cultivars amongst collected and introduced ecotypes from Africa is underway. Following agronomic evaluation of this material in plots, 8 pre-selected Brachiaria ecotypes were tested under intermittent grazing in paddocks (Euclides et al., 2001). Continuing on the process of cultivar development, two out of the eight, selected for superior agronomic characteristics were compared to the standard cultivar Marandu, under grazing and the results are presented in this paper

Selecting New \u3ci\u3eBrachiaria\u3c/i\u3e for Brazilian Pastures

Brazilian beef production relies heavily on cultivated pastures, of which about 80% are planted mainly to two Brachiaria cultivars. The narrowness of diversity associated with reproduction by apomixis of most plants in this genus prompted an intense search for new cultivars amongst recently collected and introduced ecotypes from Africa. This paper reports results for a three-year evaluation of 21 pre-selected ecotypes in two typical Cerrado ecosystems. Plots, replicated four times, were seeded in rows and cut every 6 weeks during the rainy season followed by a cut in the middle and one at the end of the dry season. Significant differences were found between ecotypes, seasons and years for total, leaf or leaf + stem dry matter production, percentage of leaves, leaf: stem ratio and regrowth rate. Ecotypes differed in the two ecosystems for percentage of leaves, leaf: stem ratio and regrowth. Superior ecotypes (BRA004308, 003361, 002844, 003204, 003441) could be identified and were equally advantageous in both ecosystems

Evaluation of tropical forages managed for stockpiling purposes

Conduziu-se um experimento objetivando-se determinar espécies adequadas ao manejo para a produção de feno-em-pé e as melhores épocas para diferimento e utilização. Comparou-se sete espécies de gramíneas em parcelas sub-subdivididas, com duas repetições. As parcelas principais foram constituídas pelas gramíneas, as sub parcelas pelas épocas de vedação e as subsubparcelas pelas de utilização. Quanto à produção de matéria seca verde (MSV) destacam-se (P < 0,01) Brachiaria decumbens, B. humidicola e Cynodon plectostachuys. Essas três gramíneas, independente da época de vedação, apresentaram decréscimos (P < 0,05) nas percentagens de MSV, no conteúdo de proteína bruta e na digestibilidade in vitro da matéria seca, durante o período de utilização. Apesar do decréscimo na percentagem de MSV estas mantiveram disponibilidade de MSV superior a 2000 kg/ha, durante todo o período. A melhor época da vedação para a B. humidicola foi janeiro e para B. decumbens e C. plectostachuys janeiro e fevereiro. Entretanto, para as duas últimas, caso a utilização seja no final da estação seca, é recomendável vedá-las em marçoAn experiment was conducted with the objectives of determining species of grasses adapted to stockpiling as well as establishing the best dates for deferment and utilization of the forage accumulated. Seven grass species were studied in a randomized block with split-split-plot design, in two replications. The grass species constituted the main plots, the deferring months the sub-plots and the utilization months the sub-sub-plots. Brachiaria decumbens, B. humidicola and Cynodon plectostachuys were superiors (P < 0.01) to the others, in terms of green dry matter (GDM). All three grasses, irrespective of diferring dates, showed reductions (P < 0.05) in green matter percentage (GMP), crude protein content and dry matter in vitro digestibility towards the later utilization dates. However, despite the reductions in GMP they were able to maintain over 2000 kg/ha of available GDM, at all utilization dates. The most adequate month for diferring B. humidicola was January, and for 8. decumbens and C. plectostachuys both January and February. However, if the two latters are to be used in the late dry season, they should be deferred in March