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FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais O estudo da dinâmica do perfilhamento na primavera permite conhecer os mecanismos pelos quais a gramínea forrageira retoma a sua rebrotação, após as condições de clima adversas vigentes no inverno. O objetivo com este trabalho foi determinar o efeito da altura e da roçada do pasto previamente diferido sobre o perfilhamento da Brachiaria brizantha cv. Marandu syn. Urochloa brizantha cv. Marandu (capim-marandu) durante a primavera e o inicio do verão. Quatro condições do pasto ao término do inverno foram avaliadas: baixo (15,1 cm e 4.600 kg/ha de MS), médio (23,2 cm e 5.940 kg/ha de MS), alto (31,4 cm e 7.640 kg/ha de MS) e alto/roçado (31,3 cm e 7.200 kg/ha de MS, porém roçado para 8 cm). O delineamento foi inteiramente casualizado, com três repetições. Em outubro, os pastos baixo e alto/roçado tiveram taxa de aparecimento de perfilho (TApP) e índice de estabilidade de perfilhos (IE) superiores aos pastos médio e alto. Nos demais meses, a TApP e o IE foram iguais para todas as condições de pastos. O IE foi muito alto em outubro, reduziu em novembro e dezembro e voltou a aumentar em janeiro. Em outubro, a taxa de mortalidade de perfilho (TMoP) foi menor no pasto baixo, intermediária naqueles médio e alto, e maior no pasto alto/roçado Em janeiro de 2014, o percentual de perfilho jovem foi maior nos pastos médio e alto, em relação aos baixo e alto/roçado, contrariamente ao observado para a percentagem de perfilho maduro. Em janeiro de 2014, a percentual de perfilho velho foi maior no pasto alto, intermediário nos pastos baixo e médio e menor no pasto alto/roçado. O pasto de capim-marandu diferido e mais baixo ao término do inverno apresenta maior perfilhamento e estabilidade da população de perfilhos na primavera, em comparação aos pastos altos. A roçada do capim-marandu alto no fim do inverno não compromete a estabilidade da população de perfilhos no pasto na primavera. The study of the dynamics of tillering on spring allows to know the mechanisms by which the forage plant resumes its regrowth, after the adverse weather conditions prevailing in winter. The objective of this work was to determine the effect of the height and mowed of the previously deferred pasture about the tillering of Brachiaria brizantha cv. Marandu syn. Urochloa brizantha cv. Marandu (capim-marandu) during the spring and the early the summer. Four pasture conditions at the end of winter was evaluited: short (15,1 cm e 4.600 kg/ha de DM), medium (23,2 cm e 5.940 kg/ha de DM), tall (31,4 cm e 7.640 kg/ha de DM) and tall/mowed (31,3 cm e 7.200 kg/ha de DM, however mowed to 8.0 cm). A completely was randomized design, and with three replications. In October, low and high/mowed pastures had tiller appearance rate (TApR) and stability index of the tiller population (SI) greater that medium and tall pastures. In the remaining months, TApR and SI were the same for all pasture conditions. SI was very high in October, declined in November and December and increased again in January. In October, the tiller mortality rate (TMoR) was lower in the low pastures, intermediate in the medium and high pastures, and greater in the high/mowed pastures. The percentage of young tillers was greater in the medium and tall pastures, in relation to the short and tall/mowed, a pattern of response contrary to that observed for the percentage of mature tillers. The percentage of old tillers was greater in the tall pastures, intermediate in the short and medium pastures, and lower in the tall/mowed pastures. Deferred and shorter marandu palisadegrass pastures at the end of winter showed greater stability of the tiller population and tillering in early spring compared to tall pastures. The mowing of marandu palisadegrass at the end of winter does not compromise the stability of the tiller population from spring. Dissertação (Mestrado)

Background and AimsPlant modelling can efficiently support ideotype conception, particularly in multi-criteria selection contexts. This is the case for biomass sorghum, implying the need to consider traits related to biomass production and quality. This study evaluated three modelling approaches for their ability to predict tiller growth, mortality and their impact, together with other morphological and physiological traits, on biomass sorghum ideotype prediction.MethodsThree Ecomeristem model versions were compared to evaluate whether tillering cessation and mortality were source (access to light) or sink (age-based hierarchical access to C supply) driven. They were tested using a field data set considering two biomass sorghum genotypes at two planting densities. An additional data set comparing eight genotypes was used to validate the best approach for its ability to predict the genotypic and environmental control of biomass production. A sensitivity analysis was performed to explore the impact of key genotypic parameters and define optimal parameter combinations depending on planting density and targeted production (sugar and fibre).Key ResultsThe sink-driven control of tillering cessation and mortality was the most accurate, and represented the phenotypic variability of studied sorghum genotypes in terms of biomass production and partitioning between structural and non-structural carbohydrates. Model sensitivity analysis revealed that light conversion efficiency and stem diameter are key traits to target for improving sorghum biomass within existing genetic diversity. Tillering contribution to biomass production appeared highly genotype and environment dependent, making it a challenging trait for designing ideotypes.ConclusionsBy modelling tiller growth and mortality as sink-driven processes, Ecomeristem could predict and explore the genotypic and environmental variability of biomass sorghum production. Its application to larger sorghum genetic diversity considering water deficit regulations and its coupling to a genetic model will make it a powerful tool to assist ideotyping for current and future climatic scenario.

Neste ensaio foram avaliados os parâmetros de densidade populacional, taxas de emissão e de mortalidade, proporção de perfilhos florescidos e acúmulo de matéria seca de forragem para a espécie Cynodon spp. cultivar Tifton 85. Os tratamentos corresponderam a quatro situações de altura do pasto (5, 10, 15 e 20 cm) mantidas constantes por ovinos sob regime de lotação contínua e taxa de lotação variável. O delineamento experimental foi o de blocos completos casualizados com quatro repetições. Foram utilizadas áreas (@ 0,0176 m²) delimitadas por anéis plásticos (PVC), onde todos os perfilhos existentes foram marcados com pequenas argolas plásticas coloridas e contados a cada avaliação. As taxas de acúmulo de matéria seca foram avaliadas utilizando-se a técnica da gaiola de exclusão, com mensuração da massa de forragem a cada 21 dias. Houve efeito (P0,10) de tratamento sobre as taxas de acúmulo de forragem.The aim of this study was to verify patterns of tiller population density, tiller appearance and mortality rates, proportion of flowering tillers and herbage dry matter accumulation for Cynodon spp. (cv. Tifton 85). Treatments corresponded to four "steady state" conditions characterised by sward surface heights of 5, 10, 15, and 20 cm, maintained by sheep grazing under continuous stocking and variable stocking rate. Treatments were allocated to experimental units (400 m² each) according to a completetely randomised block design with four replication. Tillering evaluations consisted of tagging and counting all tillers present and new tillers emerging within two 15 cm diameter plastic rings (PVC) per experimental unit. Herbage accumulation was measured using exclosure cages rotated every three weeks. There was a time effect (P0,10).

International audience; Extreme climatic events are expected to increase in frequency and magnitude as a consequence of global warming. Grasslands cover a large proportion of the European continent and contribute to both agricultural production and ecosystem services through inter and intraspecific genetic variability. This study analysed the effects of summer droughts and heat waves on the persistence and production of perennial forage grasses. Mediterranean and temperate populations of Dactylis glomerata L. and Festuca arundinacea (Schreb.) were compared at both Mediterranean and temperate sites in France. By manipulating canopy temperatures and water availability, grass swards in the field were subjected to cumulative summer and spring water deficits (CSSWD) ranging from 329 to 707 mm to test different projected climatic conditions and extreme summer events. Under controlled summer heat waves (621 days at a mean daily canopy temperature higher than 3035 degrees C), there was no increase in membrane damage to surviving aerial tissues. Plant stress was thus mainly generated through greater soil water deficit. Under the greatest CSSWD, annual biomass production was reduced on average by 60% and 30% with temperate and Mediterranean populations, respectively. Thresholds for a significant increase in summer tiller mortality were seen at CSSWD higher than 450 mm for temperate populations and 550 mm for Mediterranean populations. The latter displayed lower predawn leaf water potentials in summer and recovered through intense tillering in the subsequent seasons. Under the most extreme CSSWD, fewer than 20% of tillers of temperate populations survived and their nitrogen uptake ability was drastically altered. The higher potential productivity of Mediterranean populations in winter was associated with greater frost sensitivity. The identification of thresholds for vulnerability and the determination of the role of genetic diversity will improve the management of plant resilience and the design of new plant material to cope with climate change.

Objetivou-se estabelecer estratégias de manejo do pastejo, sob lotação contínua, que otimizem o padrão natural de perfilhamento da Brachiaria decumbens cv. Basilisk. Duas estratégias de manejo do pastejo foram estudadas: em uma, o pasto foi mantido com 25 cm de altura média durante todo o período experimental; e na outra foi mantido em 15 cm de altura média durante o inverno, com aumento para 25 cm a partir do início da primavera. Adotou-se o esquema de parcelas subdivididas em delineamento em blocos casualizados com quatro repetições. Consideraram-se como fator primário as estratégias de manejo do pastejo, caracterizadas pelas alturas médias em que os pastos foram mantidos durante as estações do ano (inverno, primavera e verão) e, como fator secundário, as medidas ao longo do período experimental. A taxa de aparecimento de perfilho (4,7%), a taxa de mortalidade (4,7%) e o índice de estabilidade (0,998) foram menores no inverno. Nesta estação, contudo, a taxa de sobrevivência de perfilho foi maior (95,3%). Em comparação aos pastos mantidos com 25 cm, aqueles manejados com 15 cm de altura média no inverno apresentaram maiores taxas de aparecimento de perfilho (34,2%) e índice de estabilidade (1,065). O florescimento do capim-braquiária ocorreu apenas no verão e com pouca intensidade (0,5%). A otimização da renovação de perfilhos no pasto de B. decumbens cv. Basilisk sob lotação contínua ocorre com seu rebaixamento para 15 cm no início do inverno e seu posterior aumento para 25 cm no início da primavera. The experiment was conducted to establish management strategies of grazing under continuous stocking that optimize the natural pattern of tillering of Brachiaria decumbens cv. Basilisk. Two strategies of grazing management were studied: in one, the grass was maintained with 25-cm mean height throughout the experimental period, and in the other, 15-cm mean height during the winter, rising to 25 cm from beginning of spring. The split-plot in randomized block design with four replications was adopted. The strategies of grazing management corresponded to primary factor, characterized by average heights of pastures during the seasons of the year (winter, spring and summer). The seasons corresponded to secondary factor and consisted of measures over experimental period. The rates of tillers appearance (4.7%), death (4.7%) and stability index (0.998) were lower in winter. During this season, however, the tiller survival rate was higher (95.3%). Compared with pastures maintained at 25 cm, those managed with 15 cm in winter had higher tiller appearance rate (34.2%) and stability index (1.065). The signalgrass flowering occurred only in the summer and with low intensity (0.5%). Optimization for renewal of tillers in B. decumbens cv. Basilisk pasture under continuous stocking occurs with its decrease to 15 cm at the beginning of winter and subsequent increase to 25 cm in early spring.

Understanding the impacts of intensity and selection of grazing on the performance of grasses is important in the management of grazing areas. It is especially important in semi-arid environments where. apart from moisture. the levels at which grasses are utilized has a major influence on their persistence in the environment. The effects of selective defoliation and height of defoliation (5cm and 10cm stubble heights) on the performance of the grass, Themeda triandra, were investigated in a field experiment for two growing seasons. Performance was measured as tiller production, rate of production. tiller mortality, herbage yield and quality. Tiller production was greater (81 tillers per plant) under non-selective defoliation than under selective defoliation (49 tillers per plant) in the 1995/1996 season. Tiller mortality was higher (66.45%) under heavy selective defoliation than under nonselective defoliation (21.98%). Herbage yield, apart from the control treatment, was high (13.6g per plant) under light non-selective defoliation. Heavy selective defoliation reduced the nutrient levels (e.g. levels of soluble carbohydrates under heavy selective defoliation were 6g kg–1 glucose compared to 20g kg–1 glucose under light non-selective defoliation). African Journal of Range & Forage Science 17(1, 2&3): 52-59

Neste ensaio foram avaliados os parâmetros de densidade populacional, taxas de emissão e de mortalidade, proporção de perfilhos florescidos e acúmulo de matéria seca de forragem para a espécie Cynodon spp. cultivar Tifton 85. Os tratamentos corresponderam a quatro situações de altura do pasto (5, 10, 15 e 20 cm) mantidas constantes por ovinos sob regime de lotação contínua e taxa de lotação variável. O delineamento experimental foi o de blocos completos casualizados com quatro repetições. Foram utilizadas áreas (@ 0,0176 m²) delimitadas por anéis plásticos (PVC), onde todos os perfilhos existentes foram marcados com pequenas argolas plásticas coloridas e contados a cada avaliação. As taxas de acúmulo de matéria seca foram avaliadas utilizando-se a técnica da gaiola de exclusão, com mensuração da massa de forragem a cada 21 dias. Houve efeito (P0,10) de tratamento sobre as taxas de acúmulo de forragem. The aim of this study was to verify patterns of tiller population density, tiller appearance and mortality rates, proportion of flowering tillers and herbage dry matter accumulation for Cynodon spp. (cv. Tifton 85). Treatments corresponded to four "steady state" conditions characterised by sward surface heights of 5, 10, 15, and 20 cm, maintained by sheep grazing under continuous stocking and variable stocking rate. Treatments were allocated to experimental units (400 m² each) according to a completetely randomised block design with four replication. Tillering evaluations consisted of tagging and counting all tillers present and new tillers emerging within two 15 cm diameter plastic rings (PVC) per experimental unit. Herbage accumulation was measured using exclosure cages rotated every three weeks. There was a time effect (P0,10).