Symmetric pollen mitosis I and suppression of pollen mitosis II prevent pollen development in Brachiaria jubata (Gramineae)

Microsporogenesis and pollen development were analyzed in a tetraploid (2n = 4x = 36) accession of the forage grass Brachiaria jubata (BRA 007820) from the Embrapa Beef Cattle Brachiaria collection that showed partial male sterility. Microsporocytes and pollen grains were prepared by squashing and staining with 0.5% propionic carmine. The meiotic process was typical of polyploids, with precocious chromosome migration to the poles and laggards in both meiosis I and II, resulting in tetrads with micronuclei in some microspores. After callose dissolution, microspores were released into the anther locule and appeared to be normal. Although each microspore initiated its differentiation into a pollen grain, in 11.1% of them nucleus polarization was not observed, i.e., pollen mitosis I was symmetric and the typical hemispherical cell plate was not detected. After a central cytokinesis, two equal-sized cells showing equal chromatin condensation and the same nuclear shape and size were formed. Generative cells and vegetative cells could not be distinguished. These cells did not undergo the second pollen mitosis and after completion of pollen wall synthesis each gave rise to a sterile and uninucleate pollen grain. The frequency of abnormal pollen mitosis varied among flowers and also among inflorescences. All plants were equally affected. The absence of fertile sperm cells in a considerable amount of pollen grains in this accession of B. jubata may compromise its use in breeding and could explain, at least in part, why seed production is low when compared with the amount of flowers per raceme

Análise financeira e de sensibilidade de sistemas de produção de leite em pastagem Financial and sensitivity analysis of milk production systems under pasture

Realizou-se neste estudo uma análise econômica de sistemas de produção para vacas em lactação manejadas em pastagem de capim-mombaça recebendo diferentes fontes de suplementação volumosa durante a época seca do ano. As suplementações fornecidas foram: pastagem de aveia-preta, cana-forrageira com ureia e silagem de sorgo. Utilizaram-se como indicadores econômicos o valor presente líquido (VPL) e a taxa interna de retorno (TIR). Para cada sistema de produção estudado, foi construído um fluxo de caixa, com sua particularidade e índices de desempenhos produtivo e reprodutivo, obtidos experimentalmente. Os fluxos de caixa foram construídos mensalmente para um período de 12 anos e os VPL dos sistemas foram calculados aplicando-se taxas de desconto de 6, 8, 10 e 12% ao ano. Com uma taxa anual de desconto de 8%, todos os sistemas de produção foram viáveis financeiramente. O capital investido apresentou TIR anuais de 11,91% para pastagem de aveia-preta, 9,43% para cana-forrageira e ureia e 8,46% para silagem de sorgo. O item de maior impacto nos resultados econômicos dos sistemas, de acordo com a análise de sensibilidade, foi o preço de venda do leite produzido.<br>An economical analysis of milk production systems was made with lactating cows on Mombaça grass pasture receiving different sources of roughage supplementation during the dry season. The supplementations were: black oat pasture, forage sugarcane with urea and sorghum silage. The economical indicators used were: net present value (NPV) and internal rates of return (IRR). For each production system studied one cash flow was used with their particularities and productive and reproductive performances index, obtained experimentally. The cash flows were built monthly, for a 12 years period and the NPV of the systems were calculated applying discount rates of 6, 8, 10 and 12% a year. At an annual discount rate of 8% all the production systems were financially viable. The invested capital showed annual IRR of 11.91% for black oat pasture, 9.43% for forage sugarcane and 8.46% for sorghum silage. The sensitivity analysis showed that the milk selling price had greatest economic impact on the profitability of the systems

Soil flood tolerance of seven genotypes of Panicum maximum Jacq.

The soil flood tolerance of seven genotypes of Panicum maximum Jacq. (PM11, PM34, PM40 and PM45, and the commercial cultivars Massai, Mombaça and Tanzânia) was evaluated in plants subjected to two conditions: flooded and not flooded, during a period of 14 days. Flooding significantly decreased the total and above ground biomass of PM40 and PM45. For cultivar Tanzânia, flooding decreased these two variables and also root biomass. The root, total and above ground relative growth rates were significantly reduced by flooding in cultivar Tanzânia, while in PM45 only the above ground relative growth rate was reduced. Cultivar Tanzânia showed significant differences for all variables analyzed, thus was not flood tolerant, as well as PM40 and PM45. It could be concluded that Massai, PM34, Mombaça and PM11 were the most flood tolerant genotypes.<br>Avaliou-se a tolerância ao alagamento do solo em sete genótipos de Panicum maximum Jacq. As plantas foram submetidas a duas condições: alagado e não alagado, avaliadas por um período de 14 dias. O alagamento reduziu a produção de biomassa seca da parte aérea e total (para PM40, PM45, p < 5%). Para a cv. Tanzânia (p < 1%), além destas variáveis, reduziu a biomassa da raiz. Quanto à taxa de crescimento relativo total sob alagamento em relação à testemunha foi significativa apenas para PM45 (p < 5%), na parte aérea e para a cv. Tanzânia (p < 1%) na taxa de crescimento relativo da raiz, parte aérea e total; a cv. Tanzânia apresentou diferenças significativas em todas as variáveis analisadas, não sendo tolerante ao alagamento, assim como PM40 e PM45; Massai, Mombaça, PM11 e PM34 são tolerantes ao alagamento, sendo que o mais tolerante foi a cv. Massai

Molecular genetic variability, population structure and mating system in tropical forages

Microsatellite (SSR) markers were developed for the following tropical forage species, using accessions available from the plant genetic resources (PGR) collections held by EMBRAPA (Brazilian Agricultural Research Corporation): Brachiaria brizantha, B. humidicola, Panicum maximum, Paspalum spp., Stylosanthes capitata, S. guianensis, S. macrocephala, Calopogonium mucunoides and Centrosema spp. The markers were used to analyze population structure and genetic diversity, evolution and origin of the genetic variability in the center of origin, mating systems and genetic resources in EMBRAPA’s germplasm bank. The results shed light on the amount of genetic variation within and between populations, revealed the need in some cases for further plant collection to adequately represent the species in PGR collections, allowed us to assemble core collections (subsets of the total collections) that should contain most of the available diversity and (in the case of the legumes) showed the need to avoid unwanted outcrossing when regenerating conserved material. The data will allow plant breeders to better select accessions for hybrid production, discriminate between genotypes and use marker-assisted selection in breeding programs. Our results will also underpin the construction of genetic maps, mapping of genes of agronomic interest and numerous other studies on genetic variability, population structure, gene flow and reproductive systems for the tropical forage species studied in this work