Factors affecting Cyperus difformis seed germination and seedling emergence

Specific knowledge about the dormancy, germination, and emergence patterns of weed species aids the development of integrated management strategies. Laboratory studies were conducted to determine the effect of several environmental factors on seed germination and seedling emergence of Cyperus difformis. Germination of freshly harvested seeds was inhibited by darkness; however, when seeds were subsequently transferred to complete light they germinated readily. Our results showed that 2 wk of cold stratification overcome the light requirement for germination. Seeds of C. difformis were able to germinate over a broad range of temperatures (25/15, 30/20, 35/25, and 40/30 ºC day/night). The response of germination rate to temperature was described as a non-linear function. Based on model outputs, the base, the optimum and the ceiling temperatures were estimated as 14.81, 37.72 and 45 ºC, respectively. A temperature of 120 ºC for a 5 min was required to inhibit 50% of maximum germination. The osmotic potential and salinity required for 50% inhibition of maximum germination were -0.47 MPa and 135.57 mM, respectively. High percentage of seed germination (89%) was observed at pH=6 and decreased to 12% at alkaline medium (pH 9) pH. Seeds sown on the soil surface gave the greatest percentage of seedling emergence, and no seedlings emerged from seeds buried in soil at depths of 1 cm.

Reduction of seed production of red rice escapes in clearfield rice

Roguing is a practice used to reduce the seed source of red rice escapes to control in Clearfield-rice areas. However, there is great difficulty in performing it in large and heavily infested rice fields. This objective of this work was to evaluate the effects of the use of imazamox herbicide, applied in different rates and times, on plants of Clearfield-rice and red rice. Four experiments were conducted during the 2007/08 and 2008/09 growing seasons, in completely randomized block design and treatments arranged in factorial design, using three replications per treatment. The treatments had increasing rates of imazamox, application times and rice cultivars. The rice cultivars tested were IRGA 417, IRGA 422 CL, Avaxi CL and Puitá INTA CL. The variables evaluated were the number of panicles m-2, number of grains panicle-1, spikelet sterility in rice and red rice; and, rice grain yield and its components. The imazamox reduced the seed production of red rice escapes in a simulated situation of commercial Clearfield-rice area. The greater percentage reductions were obtained when this herbicide was applied at final formation of the panicle or panicle exertion of the red rice plant escapes to control. The Puitá INTA CL cultivar has high level of resistance to imazamox, independent of rate and application times tested, becoming the only alternative to the use of this practice.

Comparative allelopathic potential of metabolites of two Alternanthera species against germination and seedling growth of rice

A laboratory study was conducted to investigate the allelopathic effect of aqueous extracts of plant parts of Alternanthera philoxeroides and A. sessilis and soil incorporated residues on germination and seedling growth of rice (Oryza sativa). Aqueous extracts prepared from different plant parts of Alternanthera species delayed rice germination. Alternanthera philoxeroides and A. sessilis inhibited rice germination by 9-100% and 4-49%, respectively. Germination of rice seeds was reduced with increasing concentration of aqueous leaf extracts of both weed species. Early seedling growth (root and shoot lengths) and seedling vigor index were significantly reduced by 5% aqueous leaf extract compared with distilled water treated control. Germination, root and shoot lengths, root and shoot dry weights and seedling vigor index of rice were drastically reduced by 3 and 4% in residue infested soil compared with residue free soil. The inhibitory effect of A. philoxeroides in terms of germination and seedling growth of rice was greater than that of A. sessilis. Five percent aqueous leaf extract and 4% residue infested soil of A. philoxeroides caused complete failure of rice seed germination. Alternanthera philoxeroides contained water soluble phenolics, namely 4 hydroxy-3-methoxy benzoic acid (16.19 mg L-1) and m-coumaric acid (1.48 mg L-1), whereas Alternanthera sessilis was rich in chlorogenic acid (17.85 mg L-1), gallic acid (11.03 mg L-1) and vanillic acid (9.88 mg L-1). The study indicates that the allelopathic potential of Alternanthera species may play an important role in enhancing the invasiveness of these species and may suppress rice plants in the vicinity.

Effect of plant density and seed position on mother plant on physiological characteristic of cocklebur (Xanthium strumarium) seeds

Experiments were conducted in 2010 to determine the influence of plant density and seed position on the mother plant on seed physiological characteristics of cocklebur (Xanthium strumarium). Cocklebur burs were collected in fall of 2010 from Research Farm of University of Agricultural Sciences and Natural Resources of Gorgan, Iran. The experiment was established as factorial arrangement using a completely randomized design with three replications. The factors included different densities of cocklebur (0, 2, 4, 6 and 8 plant m-2) and the top and bottom parts of the canopy. Non dormant seeds were used for determining cardinal temperatures and tolerance to salinity and drought stresses. Base, optimum and ceiling germination temperatures were estimated between 7.09 to 12.33, 32 to 35 and 44 to 45 respectively in different treatments. Salinity stress up to 300 Mm and osmotic potential 8 bar inhibited the germination completely. Comparison of base temperatures and sigmoid equation coefficients showed that seeds produced in the top had higher germination than those that produced at the bottom of the mother plant. It seems plant densities through seed position on the mother plant affect seed quality. Likewise changes of light quality and quantity in shade environment increased seed dormancy in matured seeds. Shade environment affect seed germination on mother plant that increased dormancy of seeds maturing under shade be an adaptive response that reduces the probability of germination of offspring under unfavorable (shade, competitive) conditions.

The role of glyphosate in RR soybean production and seed quality

This study aimed to evaluate the production components and quality of RR soybean seeds (Roundup Ready®), after application of increasing rates of gliphosate. Field experiments were conducted in Mandaguari, Paraná, during two seasons. Treatments consisted of five doses of glyphosate. All applications were performed once, between development stages V4 and V5. The experiment was arranged in a completely randomized block design, with four replicates. Data were subjected to analysis of variance, and when significant, t-tests and a regression analysis were applied to verify the behavior of the treatments. The physiological and sanitary quality, yield and mass of one thousand seeds were evaluated. The results indicated that seed quality can be adversely affected by glyphosate, and also showed a probable reduction in yield components with increasing rates of application.

Evolution of Ryegrass Seed Banks Depending on Soil Tillage and Crops

The seed bank is characterized by the amount of seeds and other viable reproductive structures in the soil and it is changed by the input and output of seeds, being classified by its permanence in the soil as transient or permanent. The tillage and crops used decisively influence this dynamic and more disturbed areas tend to have richer seed banks. The purpose of this study was to test different soil tillage and crop systems, aiming to reduce or eliminate the ryegrass in the area. The experiment was conducted from 2010 to 2012. In the first year, the effect of chemical tillage was assessed, compared to the area without tillage. From the second year on, in the area that received chemical tillage, the second experiment was installed, where it was assessed the effect of soil tillage and crop rotation in the ryegrass seed yield. The soil tillage treatment was chisel plow and non-chisel plow. The crop rotation was: fallow/soybean; wheat/soybean; black oat/maize. The samples of soil were taken three times a year and split in 0-5, 5-10, 10-15 and 15-20 cm. After sampling, the seeds were separated from the soil and sterilized. Afterwards, germination and tetrazolium test were conducted. In the same plots used for soil sampling, the emergence flow of ryegrass was assessed in the winter 2011 and 2012. In the first year it was observed that chemical tillage had considerably reduced the amount of ryegrass in the soil. The crop rotations used were more effective than soil tillage in reducing the seed banks in the soil. The rotation oat/maize and wheat/soybean, in only two years, practically zeroed the ryegrass seed banks in the area.

PHYSIOLOGICAL QUALITY OF SOYBEAN SEEDS DEPENDING ON THE PREHARVEST DESICCATION

ABSTRACTDepending on the cultivar, the use of desiccants in the preharvest can favor maintenance of physiological quality. The objective of the study was to assess the physiological quality of soybean seeds as due to the use of apreharvest desiccant and desiccation time in two harvests (2011/12 and 2012/13). The treatments were five soybean cultivars, two growth stages of application, a control (without desiccant application), and three desiccants (glufosinate-ammonium, carfentrazone-ethyl and paraquat) (2011/12 harvest). In the 2012/13 harvest the carfentrazone-ethyl desiccant was replaced by diquat. The physiological quality of seeds was assessed by the percentage of viability and vigor (cold test, tetrazolium test and accelerated aging test). In 2011/12 harvest, there was an early harvest in six days with the use of glufosinate-ammonium and paraquat desiccants, when desiccation was done in stage R7.1, with maintenance of seed quality; however it was dependent on the cultivar. In the 2012/13 harvest there was no early harvesting due to the presence of rain in the preharvest and the use of desiccation did not affect the physiological quality of the seeds either. Cultivar NA5909 RG was more tolerant to remaining in the cultivation environment and maintained higher viability than 90% and greater vigor of 71% by the cold test compared to cultivar BMX Turbo (2011/12 harvest). It is concluded that desiccation can be a viable alternative to the soybean early harvesting, but it depends on the cultivar, the time of desiccation, the active principle of the desiccant and the absence of rain in preharvest.

SEED DORMANCY BREAKING TREATMENTS FORAFRICAN PURSLANE (Zaleya pentandra)

ABSTRACT Understanding the mechanisms involved in releasing seed dormancy is crucial for effective plant management and renewal of species in the arid zone. Zaleya pentandra is an emerging invasive weed of the arid areas of Pakistan. We investigated the effects of different dormancy breaking treatments on the germination of Z. pentandra seeds. Seeds were treated with hot water (by placing them in boiling water for 5, 15, 30, 60, 90, 120, and 150 min), dry heat (by placing them in a preheated oven at 70 oC for 1, 2, and 4 hours; at 70 oC for 1, 2, 3, and 4 days, and at 200 oC for 5, 10, 15, 30, and 45 min) and stratification (by placing them at 2-5 ºC in a refrigerator for 5, 10, 30, and 60 min; for 3, 6, and 12 hours, and for 1, 2, 4, 8, 15, and 30 days). Seeds also were soaked in thiourea ([(NH2)2CS] (0, 2,500, 5,000, 7,500, and 10,000 mg L-1 for 24 h at 30 oC) and in KNO3 (0, 10,000, 20,000, 30,000, 40,000, 50,000, and 60,000 mg L-1 for 24 h at 30 oC). Additionally, seeds were scarified with HCl (for 3, 6, 9, 12, 15, 18, and 21 h), HNO3 (for 3, 6, 9, 12, 15, 18, and 21 h), and H2SO4 (for 20, 40, 60, 80, 100, and 120 min at 30 oC) and also mechanically scarified with sandpaper. Zaleya pentandra seeds showed typical signs of hard seed coat dormancy. Mechanical scarification and acid treatments promoted seed germination to a varying degree. Seed scarification with HNO3 for 12 to 18 h as well as with HCl for 12 h and 15 h was efficient in breaking dormancy of Z. pentandra seeds, providing germination up to 92.5%. Seed scarification with H2SO4 from 20 to 120 min showed little effect, whereas hot water, dry heat, stratification and various concentrations of thiourea and KNO3 were ineffective in breaking Z. pentandra seed dormancy.

SEED MORPHOLOGY IN OnobrychisMILLERSECTION HYMENOBRYCHIS DC. FROM TURKEY

ABSTRACT The seed (nutlet) morphology of four Onobrychis Miller (Fabaceae: subfamily Papilionoideae, Section Hymenobrychis DC.) taxa from Turkey, including three endemic taxa, was examined using scanning electron microscopy. Onobrychis tournefortii, O. galegifolia, O. cappadocica, O. albiflora. The seed examined exhibited variation in size, shape, colour, and surface sculpturing. Seed size ranged between 4.0-5.2 mm length and 2.0-3.6 mm width. Observed shapes included; ellipticus anguste asymmtricus reniformis, Ovatus anguste asymmetricus reniformis and ellipticus reniformis. Seed surface sculpturing revealed two distinct types: reticulate and rugulate. Species of Onobrychisare generally similar and confused with those of Hedysarumduring the identification process. Seed surface micromorphology can suggest taxonomical diagnostic characters for distinguishing species. Many of these characteristics are diagnostic at both the generic and specific levels.

Exploring Herbicidal Potential of Aqueous Extracts of Some Herbaceous Plants Against Parthenium Weed

To assess the phytotoxic potential of Achyranthes aspera, Alternanthera philoxeroides, Datura metel and Rumex dentatus against Parthenium hysterophorus, 5% (w/v on dry weight basis) aqueous extracts from root, stem, leaf, flower and whole plant were tested through a Petri plate-based germination and pot-cultured seedling bioassays. Achyranthes aspera and A. philoxeroides inhibited parthenium weed germination more than extracts from other species. Whole plant, leaf and fruit extracts of A. aspera reduced the germination percentage (5%); leaf extract from A. philoxeroides caused lower germination index (0.4), higher mean germination time (14 d) and longer time to 50% germination (13.5 d) of parthenium weed. In the foliar spray bioassay, A. aspera reduced parthenium weed shoot growth more than the other species whereas R. dentatus caused more reduction in root growth. Whole plant extract from A. aspera caused maximum reduction in parthenium weed seedling vigor index (98%) and seedling biomass (96%). The aqueous extracts of A. aspera and A. philoxeroides contained higher concentrations of phenolics viz. gallic (16.9 mg L-1), caffeic (7.4 mg L-1), chromatotropic (63.8 mg L-1), p-coumaric (10.5 mg L-1), m-coumaric (3.1 mg L-1), syringic (9.21 mg L-1) and 4 hydroxy-3-methoxy benzoic (118.6 mg L-1) acids compared with extracts of the other two species tested.

Thermal-biological aspects on the seed germination of Cucumis anguria L.: influence of the seed coat

The seed coat influences the early stages of germination of many seeds and sometimes maintains seed dormancy. Early reports have shown that the testa influences the germination response of Cucumis anguria seeds to light although the response to temperature as influenced by the tegument is not well understood. The main purpose of this study was to observe the influence of the testa on the germination of Cucumis anguria by using parameters as germinability and isothermal germination rate. The assays were carried out in a thermal-gradient block with water imbibed seeds kept in darkness. Estimates of the activation enthalpies (deltaH) show |deltaH| < 50 kJ.mol-1 between 26.1 °C and 35.2 °C (intact seeds) and between 25.4 °C and 35.2 °C (scarified seeds), whereas at temperatures greater than 35.2 °C the germination may be limited by processes with |deltaH| > 125 kJ.mol-1. It is suggested that the testa limits embryo expansion rather than interfering with diffusion processes.

Morphology and anatomy of the fruit and seed in development of Chorisia speciosa A. St.-Hil. - Bombacaceae

The structure of the fruit and seed in development of Chorisia speciosa are described with the main purpose of clarifying the origin and nature of the hairs that cover the seeds and aiding future taxonomical and ecological studies of the group. The fruit is an ellipsoid loculicide capsule and presents the exocarp formed by 7-10 cells layers, with very thick walls and evident simple pits. A great number of mucilage secretory cavities and ramified vascular bundles, accompanied by fibers, occur in the parenchymatic mesocarp. The endocarp derives from the ventral epidermis of the ovary wall, whose cells undergo a gradual elongation, become lignified, and constitute the trichomes which cover the mature seeds. The fruit aperture occurs by means of a suture evident in the ovarian wall in the middle region of the carpel leaf. Anatropous and bitegmic ovules, provided by a hypostase, give rise to campilotropous and bitegmic seeds. The testa is uniseriate, the exotegmen is completely formed by macrosclereids, and mucilage secretory cavities occur in the mesotegmen. The endotegmen, which is differentiated in the endothelium, is crushed in the mature seed. The plicate embryo, which occupies practically the entire seminal cavity, is found between endosperm layers, both being rich in lipids.

Flowering phenology, seed set and arthropod guilds in Trichogoniopsis adenantha (DC) (Asteraceae) in south-east Brazil

and glades. This species blooms throughout the year, attracting arthropods of various guilds, including herbivores, pollinators and predators. In this study, done over a two year period, we described the phenology of T. adenantha and assessed the seasonal variation in arthropod numbers of different guilds. We also determined the periods of lowest and highest seed set. T. adenantha population showed a peak in flowering in March-April (rainy season) with greater production of achenes in December-April. April and October had respectively highest and lowest number of fertilized, undamaged ovules, and this pattern is possibly related with population dynamics of pollinators and herbivores. In August, which was the period of greatest damage to the stigma (by geometrid larvae), there was a positive relationship between the proportion of unfertilized ovules and flowers with damaged stigma, suggesting that floral herbivory may affect reproduction in T. adenantha. We discuss the complex dynamics of the beneficial and harmful interactions between arthropods and the host plant.

Seed predation of Virola bicuhyba (Schott) Warb. (Myristicaceae) in the Atlantic forest of south-eastern Brazil

Seed predation of Virola bicuhyba (Myristicaceae) was studied in an area of Atlantic forest in south-eastern Brazil, with the objective of testing the Janzen-Connell model. The predation of seeds was evaluated at three different distances from the parent tree for two classes of predators: invertebrates and vertebrates. The method of exclosure plots (closed plots) and open control plots was used, distributed at 5, 15 and 25 m from the trunk of each adult fruiting tree of V. bicuhyba. In Experiment 1, 1,200 seeds were used and, in Experiment 2, 1,440 seeds. Both experiments did not agree with Janzen-Connell model, as seed predation by invertebrates and vertebrates was independent of the distance from the parent tree. Seed predation rate was high, however the impact of predation by vertebrates was higher than by invertebrates, indicating that it is the main cause of seed mortality.

Seed characteristics and dispersal of dimorphic fruit segments of Cakile maritima Scopoli (Brassicaceae) population of southern Brazilian coastal dunes

Cakile maritima occurs sporadically along the southern Brazilian coast, where it is restricted to more protected sites at the base of foredunes. Somatic dimorphism in C. maritima is manifested as morphologically distinct upper and lower fruit segments (silicules). The two morphs were tested for differences in size, number of seeds, dispersal ability and natural establishment. In the C. maritima population of southern Brazil, the lower silicule has more seeds than upper silicule, and lower seeds are more likely to abort than the upper ones. Seeds from upper segments were significantly larger than those from lower ones; however, their mass ranges overlap. The mean silicule mass was not significantly different from both segments, but the silicule/seed mass ratio from upper and lower segments was significantly different. Both segments had high ability to float in sea water, more than 50% were still afloat after 70 days. Nevertheless, dispersal occurs mainly to landward due to dominant wind action. Most of the seedlings were restricted to within a one-metre radius of the mother plant, and were principally derived from lower fruit segments.