Tropical Grass Pastures Research Articles

Low canopy cover in a sown Digitaria eriantha Steud. pasture improves establishment of Trifolium subterraneum L.

ABSTRACTIn the summer-dominant rainfall zone of inland northern New South Wales and southern Queensland, tropical grass-temperate legume mixed pastures can provide forage for grazing livestock for most of the year; however, the effect of canopy cover and its interaction with ground cover for regeneration of Trifolium subterraneum (subterranean clover) are not known. An experiment was conducted using established Digitaria eriantha with two levels of canopy cover (defoliated to 0.1 m and undefoliated) and four levels of ground cover (ranging from bare to 75%). Plots were oversown with subterranean clover seed in May–June, and legume establishment and spring herbage production were assessed. Low rainfall throughout the experiment resulted in poor clover establishment and production but seedling densities were significantly higher in the defoliated treatments (14 cf. 6 seedlings/m2). Herbage production was also significantly higher in the defoliated plots (530 cf. 302 kg DM/ha). There was no effect of ground cover. These findings indicate that management strategies that remove excess forage and reduce canopy cover of tropical grass pastures in late summer will maximise regeneration of subterranean clover in autumn.

Biometry and carcass characteristics of lambs supplemented in tropical grass pastures during the dry season

Biometry and carcass characteristics of lambs supplemented in tropical grass pastures during the dry season

Species‐genotypic parameters of the CROPGRO Perennial Forage Model: Implications for comparison of three tropical pasture grasses

AbstractBrachiaria and Cynodon are two of the most important pasture grasses worldwide. Computer model simulations can be used to study pasture species growth and physiological aspects to identify gaps of knowledge for genetic improvement and management strategies. The objective of this research was to compare the performance relative to calibrated parameters of the CROPGRO‐Perennial Forage Model (CROPGRO‐PFM) for simulating three different species (“Marandu” palisadegrass, “Convert HD 364®” brachiariagrass and “Tifton 85” bermudagrass) grown under similar management. The field experiment consisted of two harvest frequencies, 28 and 42 days, under irrigated and rainfed conditions. Data used to calibrate the model included regular forage harvests, plant‐part composition, leaf photosynthesis, leaf area index, light interception and plant nitrogen concentration. The simulation of biomass production of the three grasses presented d‐statistic values higher than 0.80, RMSE ranging from 313 to 619 kg/ha and ratio observed/simulated ranging 0.968 to 1.027. Harvest frequency treatments of 28 and 42 days were well simulated by the model. A sensitivity analysis was conducted to evaluate the most influential parameters needed for model calibration and to contrast the grasses, showing that the differences among the three grasses are mostly driven by plant‐part composition and assimilate partitioning among plant organs.

南西諸島における暖地型マメ科牧草の実用栽培に関する研究 : VIII.暖地型マメ科牧草スタイロ(Stylosanthes spp.)とイネ科牧草との混播栽培における可消化乾物収量

南西諸島における暖地型マメ科牧草の実用栽培に関する研究 : VIII.暖地型マメ科牧草スタイロ(Stylosanthes spp.)とイネ科牧草との混播栽培における可消化乾物収量

南西諸島における暖地型マメ科牧草の実用栽培に関する研究 : XI.国頭および島尻マージにおける暖地型マメ科およびイネ科牧草の燐施与に対する生育反応

南西諸島における暖地型マメ科牧草の実用栽培に関する研究 : XI.国頭および島尻マージにおける暖地型マメ科およびイネ科牧草の燐施与に対する生育反応

Photoperiodic responses in flowering of main tropical pasture grasses.

Photoperiodic responses in flowering of main tropical pasture grasses.

Supplementation strategies for dairy cows kept in tropical grass pastures

This study aimed to evaluate the supplementation strategies on forage intake and nutrient digestibility, feeding behavior, milk production and composition, feed efficiency, nitrogen balance and body weight change of dairy cows kept in Tanzania grass pastures (Panicum maximum Jacq. cv. Tanzania) in the dry season. We used eight crossbred Holstein and Zebu cows in the final third of lactation, with an average weight of 505±44 kg and initial milk production of 9.0±1.44 kg day-1, in a double 4X4 Latin square design. The experiment consisted of four experimental periods of 17 days each, with nine days for initial adaptation and eight days to collect data. Treatments consisted of mineral mix and supplements (energy, protein or multiple) provided in the amount of 2 kg per cow day-1. Supplements promoted increased consumption of dry matter and nutrients (P < 0.05), without changing the forage intake in relation to the mineral mixture. The treatments did not affect the feeding behavior of animals (P > 0.05). There was an increase (P < 0.05) of 19.51% in milk production in the supplemented animals and productive responses approximate marginal 0.64 kg of milk for each kg of supplied supplement, however, the different supplements promoted a drop in the milk fat. There were higher net energy values of animal lactation for protein-energy supplementation and mineral mixture, but no change was observed in feed efficiency and energy efficiency. The performance of dairy cows kept in tropical grass pasture can be improved with the use of a concentrate supplementation of 0.40% of body weight per day-1 without compromising the forage intake of animals.

Effects of liming on dry biomass, lead concentration and accumulated amounts in roots and shoots of three tropical pasture grasses from lead contaminated acidic soils

AbstractLiming the contaminated soil is the most widely used remediation treatment to reduce the bioavailability of heavy metals. The objective of this study was to evaluate the effect of liming on the change of dry matter and lead uptake by three tropical pasture grasses from lead contaminated acidic soil. Lime at five rates of 0, 1, 2, 3 and 4 g kg−1 soil was amended to the Neubauer's pots filled with 500 g Kunigami‐maji soils and then the limed soil was contaminated with 150 mg kg−1 lead after it was maintained for 1 week. Addition of lime increased soil pH significantly from 4.43 to 5.40. The root and shoot dry matter of all three tropical pasture grasses increased with the increasing doses of lime. An elevation of soil pH induced by liming resulted in a significant reduction of lead concentrations in both roots and shoots of all experimental grasses. The effectiveness of liming on lead concentration and accumulation varied with the pH values of limed soil and grass species. The results of this study imply that napiergrass was the most effective tropical pasture grass in reducing lead concentration and accumulation of roots and shoots as a consequence of liming, and could be used for lead stabilization in moderately lead contaminated acidic soil. The shoot lead concentration of napiergrass in limed soils was within the critical level of lead tolerable to feeding domestic animals, and may act as low level lead toxicity in fodder for grazing livestock. However, lime application or soil pH had a little influence on the lead accumulated amount in roots and shoots of atratum and signalgrass. The high amounts of lead accumulated in shoots of atratum and signalgrass were found to be useful for lead phytoextraction.

Efficiency of rumen microbial protein synthesis in cattle grazing tropical pastures as estimated by a novel technique

The efficiency of microbial protein synthesis (EMPS) in cattle grazing a range of tropical pasture types was examined using a new method of intra-jugular infusion of chromium–EDTA to estimate urinary excretion of purine derivatives. Seven pasture types were studied in south-eastern Queensland, Australia, over a 13-month period. These included native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii) studied in the early wet, the wet–dry transition and the dry season; introduced tropical grass (C4) pasture (Bothriochloa insculpta) in the mid-wet season; two introduced tropical legume species (C3; Lablab purpureus and Clitoria ternatea); and the temperate-grass (C3) pasture, ryegrass (Lolium multiflorum). There was a large range in EMPS across pasture types, with a range of 26–209 g microbial crude protein per kilogram digestible organic matter intake (DOMI). Estimated rumen-degradable protein (RDP) supply (42–525 g/kg DOMI) was the major factor associated with EMPS across the range of pasture types studied. EMPS in steers grazing all tropical grass pastures was low (<130 g/kg DOMI) and limited by RDP supply. Negative linear relationships (P < 0.05) between EMPS and concentrations of both neutral detergent fibre and acid detergent fibre in extrusa were evident. However, non-fibre carbohydrate in extrusa, total non-structural carbohydrate concentration in plucked pasture leaf, rumen fluid and particle dilution rate, protozoal concentration in rumen fluid and rumen fluid pH were not correlated with EMPS. It was concluded that EMPS was well below 130 g microbial crude protein per kilogram DOMI when cattle grazed unfertilised, tropical grass pastures in south-eastern Queensland and that RDP was the primary limiting nutrient. High EMPS was associated with a very high RDP, vastly in excess of RDP requirements by microbes.

Effects of lead contamination in soils on dry biomass, concentration and amounts of lead accumulated in three tropical pasture grasses

AbstractA greenhouse pot‐experiment was conducted to evaluate the phytoremediation abilities of three tropical pasture grasses (signalgrass, napiergrass and atratum) in response to two types of soils (Kunigami‐maji and Shimajiri‐maji) contaminated with three levels of lead (0, 150 and 300 mg kg–1). The results demonstrated that the dry biomass, lead concentration and the accumulated amounts were different among the plant species and between the soil types. The amounts of dry matter in three tropical pasture grasses grown on Kunigami‐maji soil were higher than that on Shimajiri‐maji soil. On both soils, lead concentration of roots was higher than that of shoots, and it was suggested that transportation of lead from roots to shoots was restricted in these plants. The lead accumulated amounts per plant grown on Kunigami‐maji soil were higher than that on Shimajiri‐maji soil. And, on Kunigami‐maji soil, accumulation of lead was relatively high in both shoots and roots of signalgrass and atratum, while, in napiergrass, the high level of lead was found only in roots. Amounts of lead extracted from the shoots of signalgrass, napiergrass and atratum grown on Kunigami‐maji soil contaminated with the highest lead level of 300 mg kg–1 were 1.64, 0.17 and 0.92 mg plant–1, respectively. As Kunigami‐maji had lower soil pH than Shimajiri‐maji, it can be suggested that lower soil pH may enhance lead bioavailability and uptake by the tropical pasture grasses. In conclusion, signalgrass and atratum could be useful for phytoremediation of lead contaminated soil, especially on Kunigami‐maji soil.

Nitrogen use of Panicum and Brachiaria cultivars vary with nitrogen supply: I. Differences in plant growth

Tropical grass pastures are broadly split between those that use high N fertilizer rates and those that use little or none. Maximizing the efficiency of N application in pastures requires understanding which features and adaptations species utilize to take advantage. This study was designed to determine the variation in growth of Brachiaria cultivars (Basilisk, Marandu, Piata and Xaraes) and Panicum cultivars (Aruana, Massai, Mombaca and Tanzania) under two N supply rates (low and high) in order to understanding forage-grass species adaptive mechanisms for high and low N supply. Changes in growth were determined based on the following characteristics: number of leaves and tillers, leaf area (LA), shoot dry matter (SDM) production, root surface area (RSA), root length (RL) and root dry matter(RDM) production. The experimental design consisted of 8 forage-grass cultivars x 2 N rates (30 and 300 mg dm -3 ) in a randomized block design with four replications. At low N supply, Marandu, Xaraes, Piata, Basilisk and Mombaca cultivars maintained a constant number of tillers but showed a decrease in the number of leaves and LA compared to high N. Tanzania cultivar maintained a constant number of tillers and LA but showed a decrease in the number of leaves under low N. In contrast, cultivars Aruana and Massai showed an increased number of tillers and a reduced LA. At low N rate, Brachiaria cultivars prioritized roots growth but with high N supply increased leaf and tiller growth. Brachiaria cultivars demonstrated high plasticity of reserve allocation, suggesting that these cultivars may better withstand N stress, ensuring their persistence. Panicum cultivars exhibited vigorous roots growth which may improve the capture of soil N and reduce losses from leaching and volatilization, and also can contribute to reduce environment contamination.

Value of copper, zinc, and oxidized charcoal for increasing forage efficiency of urea N uptake

Volatilization losses reduce the efficiency of surface-applied urea for crop N uptake, and can be controlled using urease inhibitors to retard hydrolysis or by the presence of other amendments that enhance retention of NH4+ formed by urea hydrolysis. A greenhouse study was conducted to evaluate the effectiveness of oxidized charcoal (OCh; 150gkg−1 fertilizer) applied with or without Cu and/or Zn (∼0.5–2gkg−1 fertilizer), and of Cu and/or Zn applied without OCh, for increasing uptake of urea 15N by a common tropical pasture grass, capim-Mombaça (Panicum maximum Jacq. Cv. Mombaça), grown on a coarse-textured Oxisol. Cuttings were collected 5, 14, 28, 42, and 56days after surface placement of amended or unamended urea pellets to estimate dry matter production, total N uptake, and 15N recovery. Soil sampling was carried out in conjunction with the first and fourth cuts to evaluate exchangeable NH4+ and NO3− concentrations. At the concentrations studied, OCh was more effective than Cu and/or Zn for prolonging NH4+-N availability in urea-treated soil; however, OCh alone or in combination with Zn and Cu had no effect on biomass production or N recovery and can safely be eliminated as a useful option for pasture improvement. The most promising amendment was Zn, which significantly increased total N uptake and the efficiency of urea N fertilization. The use of Zn in conjunction with urea has practical potential to improve forage production on tropical soils.

The floating gardens of Chan Cahal: Soils, water, and human interactions

Ancient Maya wetland agriculture has been studied since the 1960s, but there are still too few multiproxy excavations to adequately portray this phenomenon. This paper builds on multidisciplinary and multiproxy research near the ancient Maya site of Chan Cahal, near Blue Creek, Belize, with two new excavations, four new cores, 22 new AMS dates, and a new review of the site's water chemistry and archeology. A long-term study of the site's water chemistry has shown its pervasive impacts on wetland formation and limits to agricultural uses. We argue that a reservoir in the midst of the wetlands became inundated above a paleosol during the earliest Maya occupation in the Middle Preclassic, was dredged out during a time of population expansion sometime in the Late Preclassic to Early Classic, and was filled again with ‘Maya clay’ during and after the Classic period. Vibracores through two wetland fields and one canal corroborated our earlier model of Preclassic through Classic inundation of a paleosol by peat formation, flood sands, clay deposition, and gypsum precipitation. These cores produced new evidence for field and canal construction starting in the Late Preclassic. A later addition was a platform added at the very end or after the main occupation ended in the Terminal Classic. A new excavation at Sayap Ha on the Coastal Plain wetlands 7m lower than Chan Cahal experienced a similar history of inundation and aggradation. Here, Maya farmers reclaimed these wetlands with canals and raised fields late in the Late or Terminal Classic and abandoned them soon thereafter. The Sayap Hah fields thus parallel the BOP fields 9km south since both were built and abandoned at a late stage. As a comparison with other wetland field studies, the stable C isotopes of soil humin through soil profiles showed a strong Classic period to present influence of C4 species at Sayap Hah and an increase in C4 inputs in the upper 25cm at both Sayap Hah and the Chan Cahal platform, perhaps due to tropical pasture grasses prevalent here for the last 50years.

Seasonal and interannual variations in feeding station behavior of cattle: effects of sward and meteorological conditions

A feeding station is the area of forage a grazing animal can reach without moving its forefeet. Grazing behavior can be divided into residence within feeding stations (with bites as benefits) and movement between feeding stations (with steps as costs). However, relatively little information has been reported on how grazing animals modify their feeding station behavior seasonally and interannually in response to varying environmental conditions. The feeding station behavior of beef cows (Japanese Black) stocked on a tropical grass pasture (bahiagrass dominant) was monitored for 4 years (2010 to 2013) in order to investigate the association of feeding station behavior with meteorological and sward conditions across the seasons and years. Mean air temperature during stocking often exceeded 30°C during summer months. A severe summer drought in 2013 decreased herbage mass and sward height of the pasture and increased nitrogen concentration of herbage from summer to autumn. A markedly high feeding station number per unit foraging time, low bite numbers per feeding station and a low bite rate were observed in summer 2013 compared with the other seasons and years. Bite number per feeding station was explained by a multiple regression equation, where sward height and dry matter digestibility of herbage had a positive effect, whereas air temperature during stocking had a negative effect (R2=0.658, P<0.01). Feeding station number per minute was negatively correlated with bite number per feeding station (r=–0.838, P<0.001). It was interpreted that cows modified bite number per feeding station in response to the sward and meteorological conditions, and this largely determined the number of feeding stations the animals visited per minute. The results indicate potential value of bite number per feeding station as an indicator of daily intake in grazing animals, and an opportunity for livestock and pasture managers to control feeding station behavior of animals through managements (e.g. fertilizer application, manipulation of stocking intensity and stocking time within the day).

An evaluation of the performance and efficiency of nitrogen utilization in cattle fed tropical grass pastures with supplementation

The objective of this study was to evaluate the efficiency of nitrogen utilisation (ENU) and animal performance in cattle fed tropical grass pastures and receiving nitrogen supplementation, using a meta-analytical approach. The dataset used to evaluate the ENU was compiled from 10 experiments carried out in Brazil, which were published between 2009 and 2012, totalling 47 treatment means. To compose the dataset for animal performance evaluation, mean treatment values were collected from 44 experiments involving grazing beef cattle, which were published in Brazil from 2001 to 2012, totalling 182 treatment means. The relationships between variables were evaluated using linear or non-linear mixed models, taking into account the random variations among experiments. There was no association between ENU and the balance of nitrogen in the rumen and the efficiency of microbial synthesis in the rumen (P>0.05). The ENU was linearly associated with the dietary content of digestible organic matter in the diet (DOM) and relative production of microbial nitrogen in the rumen (NMICR), which was positive with DOM (P<0.04) and negative with NMICR (P<0.03). The relationships between ENU and dietary crude protein (CP) and the concentration of rumen ammonia nitrogen (RAN) were described using hyperbolic models (P<0.05). The estimated values that correspond to the apparent equilibrium point (i.e., ENU=0) were 108g CP/kg of dry matter and 6.30mg RAN/dL of rumen fluid. There was a positive response on weight gain as the amount of supplement increased (P<0.01). However, this relationship was interactively affected by CP content in the supplement (P<0.02) and in the forage (P<0.01). Through this way, the response of weight gain to supplement is improved by increasing the CP content of the supplement, but decreased as the CP in the forage increases. From this it can be conclude that there is a positive response to nitrogen supplementation with regards to ENU and animal performance. The main benefit of supplementation is the improvement of the nitrogen status in the animal׳s metabolism.

The potential for sown tropical perennial grass pastures to improve soil organic carbon in the North-West Slopes and Plains of New South Wales

Sown tropical perennial grass pastures may be a means to restore soil organic carbon (C) lost by cropping with conventional tillage to the levels originally present in native grass pastures. To assess this, total organic carbon and related soil properties were measured under sown tropical pastures, conventionally cultivated cropping, and native pastures on 75 Chromosols and 70 Vertosols to 0.3 m depth in the New South Wales North-West Slopes and Plains region of Australia. The impact of several perennial pasture species on soil organic carbon was also assessed in a 6-year-old, sown pasture experiment on a previously cropped Chromosol. Soil cores in 0.1-m segments to 0.3 m were analysed for total organic carbon, total nitrogen (N), pH, and phosphorus (Colwell-P). Mid-infrared scans were used to predict the particulate, humus, and resistant fractions of the total organic carbon. Bulk density was used to calculate stocks of C, N, and C fractions. In Chromosols, total organic carbon in the surface 0–0.1 m was greater under sown tropical pastures (23.1 Mg ha–1) than conventional tillage cropping (17.7 Mg ha–1), but still less than under native pastures (26.3 Mg ha–1). Similar land-use differences were seen for particulate and resistant organic C, and total N. The proportional differences between land uses were much greater for particulate organic C than other measures, and were also significant at 0.1–0.2 and 0.2–0.3 m. Subsurface bulk density (0.1–0.2 m) was lower under sown tropical pastures (1.42 Mg m–3) than conventionally tilled cropping (1.52 Mg m–3). For Vertosols, total organic carbon in the surface 0–0.1 m was greater under sown tropical pastures (19.0 Mg ha–1) and native pastures (20.5 Mg ha–1) than conventional tillage cropping (14.0 Mg ha–1). Similar land-use effects were seen for the particulate and humus organic C fractions, and total N. In the sown pasture species experiment, there was no significant difference in total N, total organic carbon, or any C fraction between soils under a native-grass species mixture, two improved tropical grass species, or a perennial pasture legume. Regular monitoring is required to better discern whether gradual changes are being masked by spatial and temporal variation. The survey results support previous research on Vertosols within the New South Wales North-West Slopes and Plains that show sown tropical grass pastures can improve total organic carbon. Improvements in total organic carbon on Chromosols have not previously been documented, so further targeted soil monitoring and experimentation is warranted for the region.

Potential for biological nitrification inhibition to reduce nitrification and N2O emissions in pasture crop–livestock systems

Agriculture and livestock production systems are two major emitters of greenhouse gases. Methane with a GWP (global warming potential) of 21, and nitrous oxide (N2O) with a GWP of 300, are largely emitted from animal production agriculture, where livestock production is based on pasture and feed grains. The principal biological processes involved in N2O emissions are nitrification and denitrification. Biological nitrification inhibition (BNI) is the natural ability of certain plant species to release nitrification inhibitors from their roots that suppress nitrifier activity, thus reducing soil nitrification and N2O emission. Recent methodological developments (e.g. bioluminescence assay to detect BNIs in plant root systems) have led to significant advances in our ability to quantify and characterize the BNI function. Synthesis and release of BNIs from plants is a highly regulated process triggered by the presence of NH4+ in the rhizosphere, which results in the inhibitor being released precisely where the majority of the soil-nitrifier population resides. Among the tropical pasture grasses, the BNI function is strongest (i.e. BNI capacity) in Brachiaria sp. Some feed-grain crops such as sorghum also have significant BNI capacity present in their root systems. The chemical identity of some of these BNIs has now been established, and their mode of inhibitory action on Nitrosomonas has been characterized. The ability of the BNI function in Brachiaria pastures to suppress N2O emissions and soil nitrification potential has been demonstrated; however, its potential role in controlling N2O emissions in agro-pastoral systems is under investigation. Here we present the current status of our understanding on how the BNI functions in Brachiaria pastures and feed-grain crops such as sorghum can be exploited both genetically and, from a production system's perspective, to develop low-nitrifying and low N2O-emitting production systems that would be economically profitable and ecologically sustainable.

Energy and Protein Supplementation Can Improve Liveweight Gain of Steers Grazing Good Quality Tropical Pasture in the Wet Season

This experiment aimed at maximising wet season liveweight gain (LWG) of cattle grazing good quality tropical pasture. Twenty-five Brahman crossbred steers (203 ± 4.2 kg) were allocated into 5 treatments, namely control (Con; grazing only), grazing + molasses/urea mixture (MU) at 0.5% liveweight (LW) (5MU) or 1% W (10MU), and grazing + mixture of molasses/urea (55%), fish meal (25%) and whole cottonseed (WCS; 20%) at 0.5% W (5MWF) or 1% W (10MWF). Steers grazed fertilized pangola grass pasture (Digitaria eriantha cv. Steudal) for 84 days. Pasture DM availability was maintained at > 1.5 t/ha. The Mean green leaf yield was 1.9 t DM/ha, in vitro DM digestibility was 64%, and crude protein content was 15%. The LWG of Con steers was 960 g/d. Providing MU did not increase LWG, but inclusion of fishmeal and whole cottonseed markedly improved LWG above control by 34% and 39% for 5MWF and 10MWF, respectively. Levels of supplement had no affected on LWG. It is concluded that supplementing rumen fermentable energy and protein alone did not increase LWG of steers grazing good quality tropical grass pasture, but the inclusion of rumen bypass protein and energy in supplement significantly increased LWG, as a result of the higher bypass protein and energy intake.

Molecular Diversity and Genetic Structure of Guineagrass (Panicum maximum Jacq.), a Tropical Pasture Grass

Guineagrass (Panicum maximum Jacq.) is a forage grass found in tropical and subtropical regions. It is an apomictic and tetraploid species from Africa. The objective of this study was to evaluate the genetic diversity of guineagrass accessions sampled from its regions of origin, which is in Tanzania and Kenya. In this study, a total of 396 accessions were analyzed, and a collection of reproducible and informative microsatellites was developed. Thirty microsatellites were employed to characterize these accessions. A total of 576 clones were sequenced from microsatellite-enriched libraries. Flanking primers were designed for 116 microsatellite loci and screened using a sample of 25 guineagrass accessions. The thirty selected polymorphic microsatellites employed in this study produced a total of 192 bands when evaluated in the 396 P. maximum accessions, with an average of 6.4 bands per microsatellite. Four genetic clusters were identified in the collection using STRUCTURE analysis, and these results were confirmed using AMOVA. The largest genetic variation was found within clusters (65.38%). This study revealed that the collection of accessions from the P. maximum region of origin was a rich source of genetic variability. The geographical distances and genetic similarities among accessions did not indicate a significant association between genetic and geographical variation, supporting the natural interspecific crossing between P. maximum, P. infestum and P. trichocladum as the origin of the high genetic variability and the existence of an agamic complex formed by these three species.

Genetic diversity and population structure analysis of the tropical pasture grassBrachiaria humidicolabased on microsatellites, cytogenetics, morphological traits, and geographical origin

Brachiaria humidicola (Rendle) Schweick. is a warm-season grass commonly used as forage in the tropics. Accessions of this species were collected in eastern Africa and massively introduced into South America in the 1980s. Several of these accessions form a germplasm collection at the Brazilian Agricultural Research Corporation. However, apomixis, ploidy, and limited knowledge of the genetic basis of this germplasm collection have constrained breeding activities. The objectives of this work were to identify genetic variability in the Brazilian B. humidicola germplasm collection using microsatellite markers and to compare the results with information on the following: (1) collection sites of the accessions; (2) reproductive mode and ploidy levels; and (3) genetic diversity revealed by morphological traits. The evaluated germplasm population is highly structured into four major groups. The sole sexual accession did not group with any of the clusters. Genetic dissimilarities did not correlate with either geographic distances or genetic distances inferred from morphological descriptors. Additionally, the genetic structure identified in this collection did not correspond to differences in ploidy level. Alleles exclusive to either sexual or apomictic accessions were identified, suggesting that further evaluation of the association of these loci with apospory should be carried out.