Assessment of chromium phytotoxicity, phytoremediation and tolerance potential of Sesbania sesban and Brachiaria mutica grown on chromite mine overburden dumps and garden soil.

The addition of toxic chromium in agrarian soils from mine overburden dump is of serious concern. To combat the toxicity of chromium an experiment was carried out at the Department of Botany, Utkal University, India by taking the chromium rich overburden dump (OBD) from Sukinda chromite mine, India. Different proportions of chromium rich OBD (10%, 20%, 30%, 40%, 50%, 70% and 100% OBD) were supplied to garden soil and plants of legume and non-legume categories (Sesbania sesban L. and Brachiaria mutica L.) were grown for assessment of phytoaccumulation ability of chromium, tolerance index, chlorophyll, protein and proline and the activity of oxidative inhibitors enzymes. After 60 days of experimentation, Cr phytotoxicity on physiological and biochemical parameters were assessed. The outcome of the results showed that the activity of antioxidant enzymes enhanced considerably in roots as compared to shoots with enhancing concentration of chromium. To compare the phytoaccumulation ability, the tolerance index (TI), bio-concentration factor (BCF) and transportation index (Ti) were measured in two different species. The results showed that at 100% OBD the TI, BCF and Ti of S. sesban have 22.30, 0.45 and 71.06 and B. mutica have 20.83, 0.43 and 42.45 respectively. The result showed that S. sesban not only had the highest bioaccumulation capacity of chromium but also have high tolerance index and transportation index as compared to B. mutica. Hence S. sesban can be recommended for phytostabilization programme to alleviate toxic chromium from chromite overburden mining sites.

Aluminum-induced toxicity in Urochloa brizantha genotypes: A first glance into root Al-apoplastic and -symplastic compartmentation, Al-translocation and antioxidant performance.

Previous studies have unraveled contrasting Al genotypic differences between Urochloa brizantha cv. Marandu (moderately tolerant) and Urochloa brizantha cv. Xaraés (more tolerant). Our objective was to evaluate differences in the response to Al-induced stress between these genotypes, focusing on Al compartmentation in the root apoplast and symplast, and antioxidant enzyme activities after Al exposure. Al-accumulation was 25% higher in the roots of cv. Xaraés than cv. Marandu, while in the shoot Al accumulation was 150% higher in cv. Marandu than cv. Xaraés. U. brizantha cv. Marandu accumulated 73% of the Al absorbed in the root symplast and 27% in the root apoplast, while cv. Xaraés accumulated 61% of the Al absorbed in symplast and 39% in apoplast. Furthermore, Al exposure leaded to physiological and developmental changes in root morphology, such as disorganization of vascular system, the collapse of cortical cells and absence of root hairs from the root tip, with more drastic effects detectable in cv. Marandu. Catalase (CAT) and guaiacol peroxidase (GPOX) activities in the roots of cv. Marandu were lower compared to cv. Xaraés. Our results pointed out that higher Al compartmentalization rates in the root apoplast, altogether with up-regulated metabolic activities of CAT and GPOX and also lower long distance transport of Al are seemingly at the base of the Al tolerance in cv. Xaraés. In conclusion, biochemical analysis of roots suggested that understanding of metabolic pathways is one of pressing approach to elucidate stress tolerance mechanisms in this genus.

Do silicon and nitric oxide induce resistance to Mahanarva spectabilis (Hemiptera: Cercopidae) in forage grasses?

BACKGROUND: Great efforts have been made to identify grasses that are resistant to spittlebugs (Hemiptera: Cercopidae). However, the time required to develop and launch new cultivars is relatively long. The employment of resistance inducers is a current strategy that may be useful for the control of insect pests. This analysis evaluates the feasibility of using the chemical inducers silicon and nitric oxide to increase spittlebug resistance based on changes in forage grass vegetative characteristics and the biological traits of Mahanarva spectabilis (Distant, 1909). RESULTS: Mahanarva spectabilis nymphs and adults can cause significant damage to forage grasses. Furthermore, silicon and nitric oxide inducers were not sufficient to lessen this damage by positively influencing the growth and development of forage grasses. These inducers did not negatively alter the biological parameters of M. spectabilis or diminish its population. However, phenolic compound concentrations increased when forage grasses were treated with silicon or attacked by adult insects, but this parameter was not useful to predict spittlebug resistance. This fact suggests that the physiological and biochemical changes caused by silicon should be further studied. CONCLUSION: The current analysis demonstrated that application of the chemical inducers silicon and nitric oxide is currently not a viable strategy for the effective and economic management of M. spectabilis on Brachiaria ruziziensis, Pennisetum purpureum and Digitaria sp. © 2019 Society of Chemical Industry.

Tolerance to nymphs and adults of Mahanarva spectabilis (Hemiptera: Cercopidae) by forage plants in fertilized soils.

BACKGROUND: Several factors may degrade pastures, in particular, inadequate nutrient application and spittlebug attacks. Mahanarva spectabilis (Distant, 1909) (Hemiptera: Cercopidae), one of the species that occur in Brazil, is a limiting pest in forage production. This study analyzes the influence of fertilization with the macronutrients nitrogen, phosphorus and potassium (NPK) on the survival of M. spectabilis nymphs, and the effects of damage by nymphs and adults on the production, quality and regrowth capacity of the forages Brachiaria ruziziensis, Pennisetum purpureum and Digitaria sp. RESULTS: Fertilization of the forages differentially affected damage due to spittlebug herbivory. Attacks by nymphs and adults decreased chlorophyll content, plant regrowth and forage quality, and increased injury, regardless of fertilization. The availability of nutrients in the soil not only decreased fiber content, but also increased crude protein, chlorophyll content and regrowth, even when pest infested. Soil fertilization increased the capacity of forage plants to lessen, albeit not eliminate, the effects of injury by M. spectabilis. CONCLUSION: Forages in fertilized soil are more tolerant to attacks by M. spectabilis nymphs and adults. © 2019 Society of Chemical Industry.

Influence of water limitation on the competitive interaction between two Cerrado species and the invasive grass Brachiaria brizantha cv. Piatã.

Invasive grasses inhibit the growth of other plant species, and water deficit is one of the major competition problems for native vegetation. We evaluated whether the presence of Brachiaria brizantha cv. Piatã has a negative influence on the competition for water and nutrients between Anadenanthera macrocarpa and Anadenanthera colubrina (Angico species). The interspecific competition was evaluated using a randomized experimental design with the following treatments: 1) free competition (FC), in which the native species were cultivated without the grass presence and 2) under competition (UC), in which the native species grew together with the invasive grass for 120 days. We analysed the water relationships in the two species, the effect of water limitation on the antioxidant stress, the nutritional content of shoots and roots, the relative competition intensity (RCI) and growth. The presence of Piatã grass reduced the soil moisture causing a decrease of 21.9% and 29.5% in the relative water content (RWC) of leaves for A. macrocarpa and A. colubrina, respectively. For the two Angico species, the quantum efficiency of Photosystem II (ΦPSII) decreased with reduction of RWC leaf, resulting in the H2O2 increase (57.5% at day 30 for A. colubrina and 38.8% at day 120 for A. macrocarpa). The oxidative stress was evidenced by the increase in the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities in leaves and roots of both young native trees. In the UC treatment, reductions in water uptake also led to a decrease in root absorption of N, P, K, a Mg and low transport of these nutrients to the leaves of both Angico species. A. macrocarpa and A. colubrina showed less growth caused by limitation of water uptake, but the joint activity of the physiological and biochemical adjustments provided competitive ability.

How Do Collaria oleosa and Brachiaria spp. Respond to Increase in Carbon Dioxide Levels?

The current study determines the indirect effect of CO2 level increase on Collaria oleosa (Distant, 1863) (Hemiptera: Miridae) fed on Brachiaria spp. (Poaceae), at two trophic levels, and evaluates resistance to these forages against the insect pest. Mirid bug nymphs and host plant were maintained under four climate environments: (1) nymphs and plants kept at 400 ppm CO2 level; (2) nymphs kept at 400 ppm CO2 level and fed on plants grown at 700 ppm CO2 level; (3) nymphs kept at 700 ppm CO2 level and fed on plants grown at 400 ppm CO2 level; (4) nymphs and plants kept at 700 ppm CO2 level. A totally randomized design was employed with 50 replications. Mean duration and survival of each instar and nymphal phase of insect, subjected to different climate scenarios and food sources, were evaluated. High CO2 levels promote changes in the plant, which trigger changes in the biology of C. oleosa, especially when the insects are kept at the current CO2 level. Moreover, since longer developmental period and shorter survival rates will induce the reduction of the number of generations and number of specimens, it may be underscored that B. brizantha species resistance will be maintained in future climate scenarios. Similarly, genotypes of B. ruziziensis demonstrated that they will be resistant at current and future CO2 levels.

Meiotic behavior of Brachiaria decumbens hybrids.

Brachiaria decumbens is a forage grass of inestimable value for livestock in Brazil due to its production of good quality forage even when planted on acid and poor soils, although it is susceptible to pasture spittlebugs. Only one cultivar, cv. Basilisk, has been used as the pollen donor in crosses with Brachiaria ruziziensis since 1988 at Embrapa Gado de Corte Research Center. Breeding within the species only became possible from 2009 when sexual accessions were successfully tetraploidized using colchicine. Three sexual genotypes were obtained and hybridization within B. decumbens was finally achieved. Here, we evaluated microspore tetrads using conventional cytology and found meiotic indexes above 78% for all three female genitors (cD24-2, cD24-27, cD24-45), but a low meiotic index (<22%) in the natural apomictic genitor D62 (cv. Basilisk) and in 49 hybrids. Analysis of the relationship between abnormal tetrad frequency and non-viable pollen grains yielded a highly significant Pearson correlation coefficient. The t-test proved significant for the progeny of cD24-45 x D62, with lower abnormalities and pollen sterility when compared to the other two progenies resulting from cD24-2 and cD24-27 crossed to D62, but these two did not differ. Apomictic hybrids such as S036 and X030 with low pollen sterility have the potential for use in cultivar development, whereas the sexual hybrids T012, X072, and X078 might be of use as female genitors in polycross blocks if they display good agronomic traits.

How many adults of Mahanarva spectabilis (Hemiptera: Cercopidae) should be used for screening Brachiaria ruziziensis (Poales: Poaceae) resistance?

This study determined the number of spittlebug adults, Mahanarva spectabilis Distant (Hemiptera: Cercopidae), that should be used in selection tests of the forage grass, Brachiaria ruziziensis (Germain and Evrard). In this study, 0, 1, 2, 4, or 8 M. spectabilis adults were kept in plants for 4 or 8 d per experimental plot. After these periods, the insects were removed from the plants and chlorophyll content, damage score, dry weight, fresh weight, and percent dry matter of shoots were evaluated. Chlorophyll content decreased significantly with higher density of M. spectabilis in plants exposed to the pest for 4 or 8 d. Plants that were exposed to eight spittlebugs for 8 d showed a approximately 60% loss of chlorophyll content. When the forage was infested with eight adults for 4 d, the average damage score was 3 (50% of the leaf area was affected). The damage score and fresh and dry weights of the forage did not change depending on the exposure time of the plants to the spittlebugs. The percentage of dry matter of the plants infested was higher with the increase insect density and exposure time for all densities. Thus, the minimum recommended number is eight M. spectabilis adults for 4 d in resistance tests of B. ruziziensis to this pest species.

Desempenho de bovinos Tabapuã e seus cruzados em pastagens de braquiária no estado da Bahia / Performance of straightbred and crossbred Tabapuã cattle on brachiaria pasture in Bahia state

Comparou-se o desempenho de bovinos de diferentes grupos genéticos quanto a algumas características produtivas da desmama até o abate. Os dados são referentes a 827 bovinos machos oriundos do cruzamento de vacas Tabapuã com touros Tabapuã (TAB), Red Angus (REDTAB), Santa Gertrudis (STATAB), e das fêmeas TabapuãxRed Angus com touros Santa Gertrudis (STAREDTAB) (nascidos entre 1999 e 2001 e criados em pastagens de braquiária, no Estado da Bahia). Foram analisados o peso à desmama ajustado aos 205 dias (PD205), o peso ao abate (PA), o ganho médio diário da desmama ao abate (GMD) e a idade ao abate (IA). O grupo contemporâneo (GC), o grupo genético (GG) e a interação entre GC e GG influenciaram as características avaliadas (P<0,05). O REDTAB apresentou superioridade entre os GG para GMD no primeiro ano do GC (1GC), com média de 0,552kg (P<0,05). Os cruzados STATAB e STAREDTAB não apresentaram diferenças significativas para as médias de GMD (P>0,05); entretanto, apresentaram médias inferiores às do grupo REDTAB e TAB. Em condição de ambiente mais favorável, o REDTAB pode ser mais precoce, obtendo maior GMD e PA com menor IA, sendo superior ao Tabapuã e aos cruzados da segunda geração (F2). Os cruzados F2 não demonstraram vantagem em relação ao cruzado F1 e à raça pura.

The aim of this study was to compare the different genetic groups performances from weaning to slaughter. The d ata are referred to 827 male calves of Tabapuã c ows crossed with Red Angus (REDTAB) and Santa Gertrudis sires and from Tabapuã x Red Angus cows crossed with Santa Gertrudis sires , born from 1999 to 2001 and raised in Brachiaria pastures, in Bahia state , Brazil. The w eaning weight was adjusted to 205 day s (WW205), slaughter weight (SW ), average daily gain from weaning to slaughter (ADG) and age slaughter (AG), were analyzed. The contemporary group (CG), genetic group (GG) and the interaction between CG and GG influenced the parameters (P<0.05). The REDTAB showed superiority between GG for ADG in 1CG, with an average of 0.522 kg (P<0.05). The cro s sbreed STATAB and STAREDTAB weren 't different to ADG (P>0.05), however, ha d lower averages than REDTAB and TAB. In more favorable environment al conditions, REDTAB s hould get higher ADG and SW and lower AG , being superior than Tabapuã and to the second generation's crossbr ed (F2). The crossbr ed F2 show ed no advantage over F1crossbr ed and straightbred.

Why is it so difficult to identify a single indicator of water stress in plants? A proposal for a multivariate analysis to assess emergent properties.

Because of the complexity of plant responses to water deficit, researchers have attempted to identify simplified models to understand critical aspects of the problem by searching for single indicators that would enable evaluations of the effects of environmental changes on the entire plant. However, this reductionist approach, which is often used in plant sciences, makes it difficult to distinguish systemic emergent behaviours. Currently, a new class of models and epistemology have called attention to the fundamental properties of complex systems. These properties, termed 'emergent', are observed at a large scale of the system (top hierarchical level) but cannot be observed or inferred from smaller scales of observation in the same system. We propose that multivariate statistical analysis can provide a suitable tool to quantify global responses to water deficit, allowing a specific and partially quantitative assessment of emergent properties. Based on an experimental study, our results showed that the classical approach of the individual analysis of different data sets might provide different interpretations for the observed effects of water deficit. These results support the hypothesis that a cross-scale multivariate analysis is an appropriate method to establish models for systemic understanding of the interactions between plants and their changing environment.

Characterization of resistance to adult spittlebugs (Hemiptera: Cercopidae) in Brachiaria spp.

Nymphs and adults of several spittlebug (Hemiptera: Cercopidae) species are key pests of forage brachiariagrasses (Brachiaria spp.) in tropical America. To support current breeding programs, a series of experiments aimed at characterizing the mechanisms of resistance to adult feeding damage were carried out. Five genotypes were used: two susceptible checks (CIAT 0606 and CIAT 0654) and three nymph-resistant genotypes (CIAT 36087, CIAT 6294, and SX01NO/0102). Test insects were Aeneolamia varia (F.), A. reducta (Lallemand), and Zulia carbonaria (Lallemand). The nymph-resistant genotypes showed tolerance to all spittlebug species tested. Tolerance in these genotypes can be classified as only moderate given the extent of losses (60-80%) caused by both female and male adults. None of the nymph-resistant genotypes had antibiotic effects on adults feeding on foliage. The results also indicated that antixenosis for feeding is not a plausible explanation for lower damage scores and less biomass losses in resistant genotypes. The fact that adult longevity (usually 8 d) was not affected when the adults were forced to feed on roots of a genotype with strong antibiotic resistance to nymphs is regarded as additional evidence that resistances to nymphs and to adults in Brachiaria are largely independent.

Impact of the spittlebug Mahanarva spectabilis on signal grass.

The aim of this study was to determine the damage in Brachiaria ruziziensis (Germain & Edvard) according to the density of and exposure time to adults of Mahanarva spectabilis (Distant, 1909) (Hemiptera:Cercopidae). Each plant was kept with 0, 12, 18, or 24 adults of M. spectabilis for five or ten days. Then, the insects were removed from the plant, and the following parameters were evaluated: content and loss of chlorophyll, visual damage score, shoot dry mass, and the capability for regrowth. In fact, plants exposed to the highest level of infestation for 10 days showed an 80.97% loss of chlorophyll, which is 25% higher than that shown by the plants exposed for five days. The damage score also increased with infestation levels. In the levels of 12 and 18 adults per plant, the damage score increased with increasing time of exposure. The dry mass content was higher in plants exposed to 24 insects for 10 days, suggesting that the attack of spittlebugs caused premature drying of the plant. These effects caused significant reduction in the number of tillers of infested plants. Our results indicate that exposure to adults of M. spectabilis causes significant damage and affects the development and persistence of B. ruziziensis plants.

Microsporogenesis in Brachiaria brizantha (Poaceae) as a selection tool for breeding.

The genus Brachiaria comprises more than 100 species and is the single most important genus of forage grass in the tropics. Brachiaria brizantha, widely used in Brazilian pastures for beef and dairy production, is native to tropical Africa. As a subsidy to the breeding program underway in Brazil, cytological studies were employed to determine the chromosome number and to evaluate microsporogenesis in 46 accessions of this species available at Embrapa Beef Cattle (Brazil). Thirty-four accessions presented 2n = 36; seven had 2n = 45, and five had 2n = 54 chromosomes. Based on the higher level of chromosome association observed in diakinesis, in tetra-, penta-, and hexavalents, respectively, it was concluded that they are derived from x = 9; consequently, these accessions are tetra- (2n = 4x = 36), penta- (2n = 5x = 45), and hexaploids (2n = 6x = 54). The most common meiotic abnormalities were irregular chromosome segregation due to polyploidy. Chromosome stickiness, abnormal cytokinesis, non-congressed bivalents in metaphase I and chromosomes in metaphase II, and chromosome elimination were recorded at varying frequencies in several accessions. The mean percentage of meiotic abnormalities ranged from 0.36 to 95.76%. All the abnormalities had the potential to affect pollen viability by generating unbalanced gametes. Among the accessions, only the tetraploid ones with less than 40% of abnormalities are suitable as pollen donors in intra- and interspecific crosses. Currently, accessions with a high level of ploidy (5 and 6n) cannot be used as male genitors in crosses because of the lack of sexual female genitors with the same levels of ploidy.

Physiological and bromatological aspects of Brachiariahumidicola / Aspectos fisiológicos y bromatológicos de Brachiaria humidicola / Aspectos fisiológicos e bromatológicos de Brachiaria humidicola

Brachiaria humidicola was brought to Colombia in order to improve forage production and poor acid soils wherethere was no fodder adapted to these conditions in which this species could be an excellent alternative. However,work to compile aspects and qualitative physiological characteristics are scarce, for this reason, a brief review botanyand morphophysiological of this species also present results of various studies that show the values of quality foragesuch as content protein, neutral detergent fiber (NDF) and acid detergent fiber (FDA), in vitro digestibility of dry matter and lignin content among others. The review took into account the behavior of Brachiaria in environments of special interest such as: soil, nutrients and water.

Brachiaria humidicola, fue traída a Colombia con el propósito de mejorar la producción de forraje en suelos ácidos y pobres donde no se contaba con forrajes adaptados a estas condiciones, en las cuales esta especie pudiera ser una excelente alternativa. Sin embargo, trabajos que compilen aspectos relacionados con sus características fisiológicas y bromatológicas son escasos; por tal motivo se realizó una breve revisión botánica y morfofisiologíca de estaespecie, además se presentan resultados de diversas investigaciones que muestran valores de calidad de este forraje tales como contenido proteico, fibra en detergente neutra (FDN) y fibra en detergente acida (FDA), digestibilidad in vitro de la materia seca y contenido de lignina entre otros. En la revisión se tuvo en cuenta el comportamiento de Brachiaria en ambientes de especial interés como son: suelos, nutrientes y agua.

Brachiaria humidicola, foi trazida para a Colômbia com um propósito de melhorar a produção de forragem emsolos ácidos e pobres onde não se contava com forragens adaptadas a estas condições, nas quais esta espécie pudesse ser uma excelente alternativa. Contudo, trabalhos que juntem aspectos relacionados com as suas característicasfisiológicas e bromatológicas são escassos; por tal motivo foi realizada uma breve revisão botânica e morfofisiológicadesta espécie, ademais são dados resultados de diversas pesquisas que mostram valores de qualidade desta forragem tais como conteúdo proteico, fibra em detergente neutra (FDN) e fibra em detergente acida (FDA), digestibilidade in vitro da matéria seca e conteúdo de lignina entre outros. Na revisão foi tido em conta o comportamento de Brachiariaem ambientes de interesse especial como: solos, nutrientes e água.

Fertile transgenic Brachiaria ruziziensis (ruzigrass) plants by particle bombardment of tetraploidized callus.

We have produced transgenic plants of the tropical forage crop Brachiaria ruziziensis (ruzigrass) by particle bombardment-mediated transformation of multiple-shoot clumps and embryogenic calli. Cultures of multiple-shoot clumps and embryogenic calli were induced on solidified MS medium supplemented with 0.5mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) and 2mg/L 6-benzylaminopurine (BAP) or 4mg/L 2,4-D and 0.2mg/L BAP, respectively. Both cultures were bombarded with a vector containing an herbicide resistance gene (bar) as a selectable marker and the ß-glucuronidase (GUS) reporter gene. Sixteen hours after bombardment, embryogenic calli showed a significantly higher number of transient GUS expression spots per plate and callus than multiple-shoot clumps, suggesting that embryogenic callus is the more suitable target tissue. Following bombardment and selection with 10mg/L bialaphos, herbicide-resistant embryogenic calli regenerated shoots and roots in vitro, and mature transgenic plants have been raised in the greenhouse. Polymerase chain reaction (PCR) and DNA gel blot analysis verified that the GUS gene was integrated into the genome of the two regenerated lines. In SacI digests, the two transgenic lines showed two or five copies of GUS gene fragments, respectively, and integration at different sites. Histochemical analysis revealed stable expression in roots, shoots and inflorescences. Transgenic plants derived from diploid target callus turned out to be sterile, while transgenics from colchicine-tetraploidized callus were fertile.

Genetic diversity and population structure analysis of the tropical pasture grass Brachiaria humidicola based 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.

Toward in vitro fertilization in Brachiaria spp.

Brachiaria are forage grasses widely cultivated in tropical areas. In vitro pollination was applied to accessions of Brachiaria spp. by placing pollen of non-dehiscent anthers on a solid medium near isolated ovaries. Viability and in vitro germination were tested in order to establish good conditions for pollen development. Comparing sexual to apomictic plants, apomictic pollen has more abortion after meiosis during the microspore stage and a lower viability and, of both types, only some plants have sufficient germination in a high sugar concentration. Using in vitro pollination with the sexual plant, the pollen tube penetrates into the nucellus and micropyle, but the embryo sac degenerates and collapses. In the apomictic B. decumbens, in vitro pollination leads to the transfer of the sperm nuclei into the egg cell and the central cell. The results are discussed according to normal fertilization and barriers in sexual and apomictic plants.

Is quality more important than quantity? Insect behavioural responses to changes in a volatile blend after stemborer oviposition on an African grass.

Plants subjected to insect attack usually increase volatile emission which attracts natural enemies and repels further herbivore colonization. Less is known about the capacity of herbivores to suppress volatiles and the multitrophic consequences thereof. In our study, the African forage grass, Brachiaria brizantha, was exposed to ovipositing spotted stemborer, Chilo partellus, moths. A marked reduction in emission of the main volatile, (Z)-3-hexenyl acetate (Z3HA), occurred following oviposition but the ratio of certain other minor component volatiles to Z3HA was increased. While further herbivore colonization was reduced on plants after oviposition, the new volatile profile caused increased attraction of an adapted parasitoid, Cotesia sesamiae. Our results show that insect responses are dependent on the quality of volatile emission rather than merely the quantity in this multitrophic interaction.

Evidence for biological nitrification inhibition in Brachiaria pastures.

Nitrification, a key process in the global nitrogen cycle that generates nitrate through microbial activity, may enhance losses of fertilizer nitrogen by leaching and denitrification. Certain plants can suppress soil-nitrification by releasing inhibitors from roots, a phenomenon termed biological nitrification inhibition (BNI). Here, we report the discovery of an effective nitrification inhibitor in the root-exudates of the tropical forage grass Brachiaria humidicola (Rendle) Schweick. Named "brachialactone," this inhibitor is a recently discovered cyclic diterpene with a unique 5-8-5-membered ring system and a gamma-lactone ring. It contributed 60-90% of the inhibitory activity released from the roots of this tropical grass. Unlike nitrapyrin (a synthetic nitrification inhibitor), which affects only the ammonia monooxygenase (AMO) pathway, brachialactone appears to block both AMO and hydroxylamine oxidoreductase enzymatic pathways in Nitrosomonas. Release of this inhibitor is a regulated plant function, triggered and sustained by the availability of ammonium (NH(4)(+)) in the root environment. Brachialactone release is restricted to those roots that are directly exposed to NH(4)(+). Within 3 years of establishment, Brachiaria pastures have suppressed soil nitrifier populations (determined as amoA genes; ammonia-oxidizing bacteria and ammonia-oxidizing archaea), along with nitrification and nitrous oxide emissions. These findings provide direct evidence for the existence and active regulation of a nitrification inhibitor (or inhibitors) release from tropical pasture root systems. Exploiting the BNI function could become a powerful strategy toward the development of low-nitrifying agronomic systems, benefiting both agriculture and the environment.

Effects of biostimulation and nutritional supplementation on pubertal age and pregnancy rates of Nelore heifers (Bos indicus) in a tropical environment.

To determine effects of biostimulation (BIO) and dietary supplementation (BIO+S) on pubertal age and pregnancy rates, Nelore heifers (n=392) were randomly assigned to one of four treatment groups (n=98/group). All animals were in tropical environmental conditions, in the middle-west region of Brazil, grazing in pastures of Brachiaria brizantha, cv. Marandu; Panicum Maximum, cv. Tanzânia and Brachiaria humidícula. The heifers of the BIO group were kept in the presence of bulls while being maintained on pasture; the animals in the BIO+S group were kept in the presence of bulls while being managed on pasture and were fed a diet with greater energy and protein content to produce 0.49 kg of BW gain/day; the animals in control group (the NBIO) were kept away from bulls and under pasture conditions; and the animals in the NBIO+S group were kept away from bulls, were maintained on pasture, and were fed the same diet as the BIO+S group. Heifers were bred at 22-23 months of age, and pregnancy diagnosis was made 45 days after the end of the breeding season. There were differences (P<0.05) between groups regarding pubertal heifers up to 19 months (NPH), final body weight (FBW) and pregnancy rates (P<0.01), with an advantage for the animals in the BIO and BIO+S groups. Although the effect of a diet with greater protein and energy content was not clear in this experiment, the exposure of heifers to a male during the prepubertal period decreased age at the first breeding season, resulting in a significant reduction in age of first pregnancy in Nelore heifers kept under extensive management systems in a tropical environment.