Cynodon dactylon (Bermuda grass).

Genetics: The chromosome number reported for C. dactylon varies from 2n = 18 to 2n = 36 with diploid and polyploid populations (Cook et al., 2005). Ramakrishan and Singh (1966) and Sarandon (1991) have found differences in total biomass and biomass partition according to the origin of the population. Sarandon (1991) points out that characters are highly heritable, which means that high genetic variability for biomass production and variable architecture allows an ample base for selection, which in most cases is induced by herbicides, mechanical control or forage production. Reproductive Biology: C. dactylon is wind-pollinated and generally self-incompatible, suffering from inbreeding depression when genotypes are self-pollinated. Quantitative traits such as seed yield and forage yield can be dramatically negatively affected by inbreeding depression (Cook et al., 2005). In diploid populations, caryopses are formed after zygote formation. In polyploids, which are sterile, caryopses may be apomictic. Physiology: This C4 plant (Kissmann, 1991) has high rates of accumulation under adequate irradiance, water and nutrient supply and may consume 75 kg of N, 20 kg of P and more than 1,500,000 litres of water for 5000 kg/ha of biomass dry matter (Fernandez, 1991). In the south of Santa Fe province, Argentina, a maximum biomass of 8000 kg/ha may be generated under a summer crop of maize or sunflower with >75% located in the first 10 cm of the soil profile (Lombardo, 1973), whereas in Balcarce (Argentina) about 5000 kg/ha is commonly found in maize or sunflower stubble. Phenology: A photoperiod of 13 hours induces flowering. Low night temperatures coupled with high diurnal temperatures induces blooming (Nir and Koller, 1976). A reduction in irradiance drastically decreases inflorescence production (Moreira, 1975). In North America, annual plants reproduce during spring and perennial plants reproduce all year long (USDA-NRCS, 2014). Longevity: C. dactylon grows as both an annual and perennial grass. The annual growth-form becomes dormant and turns brown when nighttime temperatures fall below freezing or average daytime temperatures are below 10°C (Cook et al., 2005). Activity Patterns: Seeds may be the route of invasion in weed-free fields through the faeces of cows (Rodriguez, personal communication). Rhizome biomass exhibits an annual cyclic pattern and, as with any perennial weed, low temperatures reduce biomass and viability is lost as a consequence of the consumption of materials due to respiration and maintenance. The digestibility of stocked material is severely decreased, implying a loss in forage quality (Vaz Martins, 1989). This is a character that has largely improved in cultivated varieties. Each node has a physiological self-governing structure in relation to the apex, but is highly dependent on substances from other plant parts. The mother plant determines the runner growth pattern on the soil surface according to the sugar-gibberellin balance (Montaldi 1970). Node disconnection may be caused by natural decay and cultivation and produces damage in the breakdown zone and changes in hormone and nutrient relationships. It is widely demonstrated that rhizome or runner fragmentation induces the activation of buds. The proportion of activated buds increases as the number of buds per segment decreases (Moreira, 1980; Kigel and Koller, 1985; Fernandez and Bedmar, 1992). The cultivation method is mainly responsible for vegetative propagation fragmentation. The higher the cultivation intensity, the smaller the segments produced (Kigel and Koller, 1985). Population Size and Structure This weed produces an enormous number of small seeds (0.25-0.30 mg), the viability and dormancy of which are highly variable according to genotype and the conditions when formed. The seed is important because it confers high genetic variability on the population. Perez et al. (1995) recorded a very low germination rate. Uygur et al. (1985) obtained up to 15% germination at constant temperatures of 35-40°C, and 50% at temperatures alternating between 20 and 30°C. Moreira (1975) obtained up to 80% germination with the help of nitrate, chilling and alternating temperatures, and Elias (1986) recorded up to 96% germination from heavier samples of seed. Seeds remain viable in the soil for at least 2 years (Caixinhas et al., 1988). As a rule, cultivars have relatively high viability. Osmo-conditioning of Bermuda grass seeds with PEG followed by immediate sowing improved seed germination and seedling growth under saline conditions (Al-Humaid 2002). The probability of emergence and successful establishment of C. dactylon decreases with the depth of the fragment, but increases with the weight of the node and internode (Perez et al., 1998). Growth from plants originated from a runner may exhibit a different biomass partition than that from plants originated from a rhizome (Fernandez, 1986). From sprouting onwards, weed growth is controlled mainly by temperature (optimum 25-30°C) and radiation, but also by humidity and soil fertility. The efficiency of carbohydrate reserve usage during sprout growth is highly dependent on temperature and the type of vegetative structure; it is maximum at 20°C and is higher for rhizomes than for stolons (Satorre et al., 1996). Runners and rhizome growth begins 30 days after growth but only if soil temperature is >15°C. Rates of 15 g/g/day have been recorded in Argentina (Lescano de Ríos, 1982).

Reassessing the Role of Potassium in Tomato Grown with Water Shortages

Potassium (K) is closely related to plant water uptake and use and affects key processes in assimilation and growth. The aim of this work was to find out to what extent K supply and enhanced compartmentation might improve water use and productivity when tomato plants suffered from periods of water stress. Yield, water traits, gas exchange, photosynthetic rate and biomass partition were determined. When plants suffered dehydration, increasing K supply was associated with reduction in stomatal conductance and increased water contents, but failed to protect photosynthetic rate. Potassium supplements increased shoot growth, fruit setting and yield under water stress. However, increasing the K supply could not counteract the great yield reduction under drought. A transgenic tomato line with enhanced K uptake into vacuoles and able to reach higher plant K contents, still showed poor yield performance under water stress and had lower K use efficiency than the control plants. With unlimited water supply (hydroponics), plants grown in low-K showed greater root hydraulic conductivity than at higher K availability and stomatal conductance was not associated with leaf K concentration. In conclusion, increasing K supply and tissue content improved some physiological features related to drought tolerance but did not overcome yield restrictions imposed by water stress.

A qPCR method for distinguishing biomass from non-axenic terrestrial cyanobacteria cultures in hetero- or mixotrophic cultivations

The cultivation of cyanobacteria with the addition of an organic carbon source (meaning as heterotrophic or mixotrophic cultivation) is a promising technique to increase their slow growth rate. However, most cyanobacteria cultures are infected by non-separable heterotrophic bacteria. While their contribution to the biomass is rather insignificant in a phototrophic cultivation, problems may arise in heterotrophic and mixotrophic mode. Heterotrophic bacteria can potentially utilize carbohydrates quickly, thus preventing any benefit for the cyanobacteria. In order to estimate the advantage of the supplementation of a carbon source, it is essential to quantify the proportion of cyanobacteria and heterotrophic bacteria in the resulting biomass. In this work, the use of quantitative polymerase chain reaction (qPCR) is proposed. To prepare the samples, a DNA extraction method for cyanobacteria was improved to provide reproducible and robust results for the group of terrestrial cyanobacteria. Two pairs of primers were used, which bind either to the 16S rRNA gene of all cyanobacteria or all bacteria including cyanobacteria. This allows a determination of the proportion of cyanobacteria in the biomass. The method was established with the two terrestrial cyanobacteria Trichocoleus sociatus SAG 26.92 and Nostoc muscorum SAG B-1453-12a. As proof of concept, a heterotrophic cultivation with T. sociatus with glucose was performed. After 2 days of cultivation, a reduction of the biomass partition of the cyanobacterium to 90% was detected. Afterwards, the proportion increased again.

Growth of cut roses under application of products with physiological effects

The cultivation of cut roses can be compromised when cultivated in regions where climatic conditions are limiting for their adequate growth and development, so it is necessary to use appropriate technologies and inputs for their production. The application of products that promote physiological changes in the plant, such as fungicides or plant regulators might be viable technologies for rose production. The objective of this study was to evaluate the growth of cv. Carola under application of products with physiological effects cultivated in the Valley of the submedium São Francisco. The experimental design was a randomized complete block design in a 6 x 6 factorial design, with 6 products with physiological action (control - application of water, boscalid, pyraclostrobin, boscalid + pyraclostrobin, fluxapyroxad + pyraclostrobin and plant growth regulator) and 6 periods of analysis (40, 68, 124, 180, 236 and 292 days after transplantation, DAT) with four replicas of 12 plants each. Throughout the dates were evaluated the number of leaves, leaf area, total leaf chlorophyll, dry mass of leaves, stems, flowering branches, total dry mass, production of stems per plant and the biomass partition. There were significant differences for all variables studied except for the production of stems per plant. Regarding the biomass partition, a variation of values among applied products was observed over time, however, fluxapyroxad + pyraclostrobin and the growth regulator presented a balance among the dry mass of leaves, stem and flowering branches. The application of products belonging to the group of strobilurins as well as growth regulators is promising for the cultivation of cut roses in the semiarid.

Accumulation and biomass partition and nutrients per tropical ornamental plants grown in Ribeira Valley region

For many ornamental plants there are no fertilization tables in Brazil and growers use, inappropriately, the same fertilizing for different species of ornamental plants. A first step is to know the nutrient uptake by these plants. The objective of this study was to determine the concentration and to characterize the accumulation of nutrients of the main tropical ornamental plants grown in the Ribeira Valley region, São Paulo state, Brazil: Clusia fluminensis, Dracaena marginata, Dypsis lutescens, Gardenia jasminoides, Ixora coccinea, Ligustrum sinense, Murraya paniculata, Podocarpus macrophyllus, Rhapis excelsa e Viburnum prunifolium. The plants were donated by local farmers and after sorting, these were divided into roots, stems and leaves, and, subsequently, washed, dried and was determined their concentration of nutrients. The experimental design was randomized using four repetitions and the species of ornamental plants were considered as treatments. The results were submitted to analysis of variance and compared by Scott-Knott test (5%). For the macronutrient, the greater accumulation of N was in Podocarpus macrophyllus. The Clusia fluminensis tree had the highest calcium and magnesium accumulations. The largest amounts of P and S were accumulated in Rhapis excelsa and Podocarpus macrophyllus. The greatest accumulation of K was in Rhapis excelsa, Dracaena marginata, Podocarpus macrophyllus, Murraya paniculata and Ixora coccinea. Smaller amounts of macronutrients were accumulated in Dypsis lutescens and Viburnum prunifolium. As for the macronutrients, the largest accumulation of Cu was observed in broad leaf Rhapis excelsa. Clusia fluminensis tree and Dracaena marginata accumulated the largest amounts of Mn. Regarding the Zn, Rhapis excelsa, Dracaena marginata and Ligustrum sinense were plants with higher accumulation. Smaller amounts of B were accumulated in Viburnum prunifolium, Dracaena marginata and Dypsis lutescens. Ligustrum sinense, Dypsis lutescens and Ixora coccinea accumulated lower amounts of Fe in relation to others. The accumulation of nutrients by ornamental plants is very different between species and this information should be used to adjust fertilizer recommendations. Ornamental plants were grouped as demand and NPK ratio, to assist in the management of fertilizer.