The physiological properties of samples at different stages during conditioning of shrivelled soybean seedlots were analyzed and correlated with physical properties. Conditioning improved seed viability and vigor. Operation capacities needed to be reduced to obtain optimal separation of shrivelled seeds with minimal loss of good seeds. Correlations of shrivelled seeds with germination, cold, stress, oil and yield tests presented a negative trend.

Oospores were produced by crossing two isolates of opposite mating type of Phytophthora capsici obtained from pepper on clarified V8 agar. Cultures were incubated in the dark at 24 C for 2 mo. Germination of oospores produced in the dark at 24 C was reduced by 78 or 90% when cultures were exposed to light (cool-white fluorescent, 40 micromole m(-2)s(-1) or incubated at 30 C for 1 wk before oospore collection and germination. Exposure of oospores to light during germination did not significantly affect the percentage of oospores that germinated, regardless of pregermination conditions. Germination of oospores in the dark was reduced by exposure to continuous light during oospore formation. Germination of oospores in sterile distilled water or soil extract showed a quadratic response to temperature, with maximum germination at 24 C. The mode and rate of germination of oospores was affected by incubation media. The predominant mode of oospore germination was via formation of sporangia. After 5 days, sporangia developed on germ tubes from approximately 94% of the oospores that germinated in soil extract, whereas sporangia developed on 33 or 8% of the oospores that germinated in root extract or sterile distilled water, respectively. Oospores incubated in root extract and distilled water formed germ tubes that continued to elongate for several days before sporangia were formed. However, after 12 days, sporangia had formed on germ tubes from 82, 78, or 94% of the oospores that germinated in distilled water, root extract, or soil extract, respectively. The total percentage of oospores that germinated after 12 days was 29, 39, or 36% in distilled water, root extract, or soil extract, respectively. Treatment of oospores with Novozym effectively removed sporangia and mycelial fragments from suspensions, but it either increased or did not affect germination in two experiments, and decreased germination in two additional experiments. The total percentage of oospores that germinated differed among experiments using oospores of similar age produced under identical conditions. Germination was greatest (51%) when oospores were produced in the dark and germinated in soil extract at 24 C in the dark for 12 days. Oospores germinated predominantly by production of sporangia in all experiments.

Suitability of different methods of seed stratification in grapevine and of physical and chemical methods of germination increase in the breeding process was tested in 1981-1987. The application of H2O2 and GA-3 did not have any significant effects, moreover, morphological changes were observed in seedlings. Germination is strongly influenced by the year and genetic differences. A simple procedure, suitable for breeding practice, was prepared pursuant to the results of experiments. Dry seeds, harvested from ripe grapes, are kept in winter at a dry place at the temperature of 5-20 degrees C. Before sowing the seeds are soaked in water for 30-40 day; water must be changed at the beginning. For another 15-30 days the seeds were kept in cold at a temperature of 2-5 degrees C; this regime can be combined with alternating temperatures (5-10 days the temperatures of 5 and 20 degrees C for 16 and 8 hours). After the seeds are planted in substrate, alternating temperatures of 20 and 30 degrees C are maintained in the intervals of 16 and 8 hours. After 10-20 days the seeds begin to germinate in a spontaneous and regular manner and high germination is achieved. The results of seed stratification in sand were worse than the outcome of stratification in water and cold; moreover, the former method requires greater labour input.

Loblolly pine (Pinus taeda) is the initial successful woody invader of abandoned old fields in the Piedmont region of North Carolina, but hardwood tree species also invade old fields and develop an understory community beneath young pine stands. The composition of this early hardwood community will be regulated by factors affecting the relative establishment success of these species in old—field habitats. Mechanisms influencing differential seedling emergence of such early successional tree species were studied in multifactor field experiments. Seeds of six wind—dispersed species (Acer rubrum, Fraxinus americana, Liquidambar styraciflua, Liriodendron tulipifera, Ulmus alata, and Pinus taeda) were sown into old fields at equal densities, and their relative germination (emergence) in two successive years was evaluated with respect to: (1) presence of old—field vegetation (tested with a weeding treatment), (2) vertebrate seed predation (tested with exclosures), (3) variation in life history traits (seed size and germination phenology), and (4) variation in physical factors (spring drought). Emergence of one species (Liriodendron) was limited by intrinsically low seed viability. In 1984, a wet spring, emergence of Pinus exceeded that of all hardwood species, and the smaller—seeded Liquidambar and Ulmus had higher emergence than the larger—seeded Acer and Fraxinus. Seed predators reduced emergence proportionately more in larger—seeded species than in smaller—seeded species. Herbaceous cover facilitated emergence of larger—seeded species by providing a moister germination microenvironment, and perhaps also by reducing visibility of seeds to predators. In 1985 an early spring drought reduced emergence of fall—dispersed species (Pinus, Liquidambar, and Fraxinus), whose earlier germination phenology coincided with the drought. Later—germinating, spring—dispersed species (Ulmus and Acer) avoided this drought period and displayed similar germination responses in both years. The prominence of drought effects in 1985 reduced the apparent impact of other experimental factors upon emergence rates. The emergence stage is an important filter on relative establishment success of tree species colonizing old—field habitats, and multiple "mechanisms" interact in complex ways to influence emergence rates.

The two cultivars of Cajanus cajan were studied for their growth and physical parameters in order to screen the better one. The study showed that the percentage of germination was significantly higher in white cultivar. Besides, the fresh weight of aboveground and total biomass were found higher in this cultivar. The height of plant and chlorophyll a and b content were found significantly superior in white cultivar. Besides, the fresh weight of aboveground and total biomass were found higher in this cultivar. On the other hand, the tensile strength of the stems of the red cultivar were found to be significantly higher.

Brachiaria dictyoneura CIAT 6133 es un pasto adaptado a condiciones de suelos ácidos e infértiles, altamente promisorio en las evaluaciones realizadas en Centro América. Desde 1988, el comportamiento reproductivo ha sido estudiado en tres diferentes ecosistemas de Costa Rica, donde la accesión muestra dos picos de floración bien definidos, en junio y octubre, y fluctuaciones cíclicas de rendimiento de semilla pura (RSP). El efecto de tres niveles de nitrógeno (0, 75, 150 kg/ha), aplicado una semana antes de la floración y el efecto de tres épocas de cosecha (0, +4, +8 días) sobre RSP y la calidad de la semilla se estudiaron en Atenas en 1990. Los resultados indican que la fertilización nitrogenada tardía no tiene efecto sobre la densidad de inflorescencias y RSP, mientras que la época de cosecha afecta marcadamente RSP, reflejando una floración y una maduración de la semilla altamente sincronizada. Altos niveles de nitrógeno aplicado poco antes de la floración incrementan el peso unitario y el vigor de la semilla en términos de velocidad de germinación. La calidad fisiológica de la semilla se caracterizó a través de pruebas de viabilidad en tetrazolio, germinación y emergencia hasta los 34 meses post-cosecha. Dos formas de latencia han sido detectadas, una fisiológica, la otra física, impuesta por la lemma y la palea. La latencia embrional (fisiológica) representa el principal factor limitante de la germinación de esta especie cultivada en Costa Rica. Esta puede ser superada en espiguillas intactas por medio de un período de almacenaje de casi dos años. En semilla recién cosechada, el KNO3 puede reducir sólo en forma parcial dicha latencia en un regimen de luz y temperatura variables. En contraste, la latencia impuesta por las glumas parece operar reduciendo los intercambios gaseosos, pero, también como barrera impermeable a los iones NO3-. La presencia de inhibidores de la germinación a nivel de las glumas no puede ser excluida, mientras que restricciones de caracter mecánico a la emergencia radicular no parecen jugar ningún papel en esta especie. Durante los dos primeros años de almacenamiento a 20°C, la latencia física puede ser eliminada completamente por medio de la escarificación con H2SO4, sin afectar en forma significativa la viabilidad de la semilla. La edad de la semilla, la escarificación y la imbibición con nitrato son factores que interactúan positivamente en eliminar la latencia. Por lo menos se necesitan tres meses de post-maduración antes que la escarificación con ácido, combinada al tratamiento con nitrato, sea efectiva en reducir parcialmente la latencia de la semilla. El máximo efecto de ambos químicos se alcanza seis meses post-cosecha, si se aplican combinados, u 8-10 meses post-cosecha, aplicando uno sólo de estos. El calor seco puede incrementar la germinación reduciendo la latencia física, de acuerdo a la temperatura, el tiempo de exposición a ésta y, posiblemente, al estado de post-maduración de la semilla. La germinación relativa (GR) es el parámetro de más relevancia para comparar valores de germinación entre diferentes lotes. Su uso permite describir la dinámica de la germinación de semilla intacta y escarificada, imbibidas con y sin KNO3. La evolución en el tiempo de GR en los cuatro tratamientos presentó una distribución sigmoide. El modelo logístico es apropiado para interpretar tal distribución en espiguillas intactas, mientras que el de Gompertz se ajusta mejor a las distribuciones de los otros tratamientos. Ambas latencias, física y embrional, siguen un patrón sigmoide, siendo eliminadas completamente después de dos años de post-maduración en un ambiente controlado (20°C y 40 por ciento de humedad relativa). La latencia embrional alcanza valores del 50 por ciento aproximadamente al 9° mes post-cosecha, y la física al 16° mes. | Tesis (Mag Sc) | Brachiaria dictyoneura CIAT 6133 is a grass adapted to acid and infertile soil conditions, highly promising in evaluations in Central America. Since 1988, reproductive behavior has been studied in three different ecosystems in Costa Rica, where the accession shows two well-defined flowering peaks, in June and October, and cyclic fluctuations in pure seed yield (PSY). The effect of three nitrogen levels (0, 75, 150 kg/ha), applied one week before flowering and the effect of three harvest times (0, +4, +8 days) on PSY and seed quality were studied in Atenas in 1990. Results indicate that late nitrogen fertilization has no effect on inflorescence density and PSR, while harvest time markedly affects PSR, reflecting highly synchronized flowering and seed maturation. High levels of nitrogen applied shortly before flowering increase unit weight and seed vigor in terms of germination speed. Seed physiological quality was characterized through tetrazolium viability, germination and emergence tests up to 34 months post-harvest. Two forms of dormancy have been detected, one physiological, the other physical, imposed by lemma and palea. Embryonic (physiological) dormancy represents the main factor limiting germination of this species cultivated in Costa Rica. This can be overcome in intact spikelets by means of a storage period of almost two years. In freshly harvested seed, KNO3 can only partially reduce dormancy in a variable light and temperature regime. In contrast, dormancy imposed by glumes seems to operate by reducing gas exchanges, but also as an impermeable barrier to NO3- ions. The presence of germination inhibitors at the glume level cannot be excluded, while mechanical constraints to root emergence do not seem to play a role in this species. During the first two years of storage at 20°C, physical dormancy can be completely eliminated by scarification with H2SO4 without significantly affecting seed viability. Seed age, scarification and nitrate imbibition are factors that interact positively in eliminating dormancy. At least three months of post-ripening are needed before acid scarification, combined with nitrate treatment, is effective in partially reducing seed dormancy. The maximum effect of both chemicals is reached six months post-harvest, if applied in combination, or 8-10 months post-harvest, if applied alone. Dry heat can increase germination by reducing physical dormancy, depending on the temperature, the time of exposure and, possibly, the post-maturation state of the seed. Relative germination (GR) is the most relevant parameter to compare germination values between different lots. Its use allows describing the germination dynamics of intact and scarified seed, imbibed with and without KNO3. The evolution over time of GR in the four treatments showed a sigmoid distribution. The logistic model is appropriate to interpret such a distribution in intact spikelets, while the Gompertz model fits better the distributions of the other treatments. Both physical and embryonic dormancy follow a sigmoid pattern, being completely eliminated after two years of post-ripening in a controlled environment (20°C and 40 percent relative humidity). Embryonic dormancy reached values of 50 percent at approximately 9 months post-harvest, and physical dormancy at 16 months.

Abandoned coal waste exhibits adverse physical and chemical properties which preclude vegetation establishment. Coal waste from a site in Montana was acidic (pH 2.8), black, 85% coarse fragments and had a low water holding capacity. Incorporation of cement kiln dust (CaO) and limestone (CaCO3) to 35 cm at rates recommended by a weathering procedure neutralized coal waste acidity in the surface 10 cm. Incorporating CaO to 100 cm neutralized coal waste to the 30-cm depth. Seeded vegetation was healthy and vigorous where lime was applied, though percent canopy cover and aboveground production were low after 2 yr. Application of kiln dust five times the recommended rate significantly reduced plant performance. Application of coversoil significantly increased plant performance compared to sites without coversoil by providing a more suitable germination medium. Increasing coversoil application from 15 to 30 cm did not significantly increase plant performance. Depth of root penetration was a function of depth of lime incorporation and coversoil thickness. Root distribution was neither confined to nor concentrated in the coversoil. Root proliferation into limed coal waste was similar to that present in overlying coversoil.

Irradiation with radiofrequency energy (RF), which includes microwaves, brings about dielectric heating of moist materials. Some agricultural applications of dielectric heating by RF have included insects control in stored grains and improved germination of seed stocks. The objective of the present research was to evaluate microwave heating of soils as a technique for weed control. Approximately 800-g masses of soil of variable wetness (10-280 g H₂O/kg soil) containing seeds of oat (Arena sativa L.) and indigenous weeds were heated in a microwave (2.45 GHz) oven for IS to 240 s. Soil masses were 5 cm deep in flats. Oat seeds were placed 2 cm deep into the soil. Hearing of soils to 80 °C or higher inhibited emergence of oats and weed species. About 120 s of heating were needed to reach 80 °C. Maintaining this temperature for 30 s was needed for strong inhibition. Moisture content in this experiment had little effect on dielectric heating. Time required to heat soil to killing temperatures appears to be a factor limiting application of this technique. The procedure may be applicable to soil sterilization in cases in which other physical processes or chemical means are inconvenient or undesirable. Contribution of Massachusetts Agric. Exp. Stn., Journal Series no. 2964.

Se utilizaron semillas de col inoculadas artificial y naturalmente infectadas; en la primera variante se usaron diferentes métodos de contaminación de la misma para determinar el más adecuado. Con posterioridad se ensayaron tratamientos físicos y químicos y la combinación de éstos para demostrar su eficacia en la erradicación del patógeno. El mejor método de infectación resultó tres horas con Tween con el que se obtuvo una alta concentración de la bacteria sobre medio de cultivo y un elevado porcentaje de plántulas con síntomas. El tratamiento que ejerció el mejor control fue la acción conjunta de estreptomicina 500 ppm durante una hora con hipoclorito de sodio 0,5 %, 30 minutos. Otras variantes como el antibiótico solo por una hora y el agua caliente a 52°C, aunque tuvieron un buen efecto desinfectante, produjeron fitotoxicidad e influyeron notablemente sobre la germinación de las semillas. | Cabbage seeds artificially inoculated and others naturally infected were used and, in the first case, the best of various methods of contamination was determined. Physical and chemical treatments were then tested as well as combinations of both in order to demonstrate their efficiency in eradicating the pathogen. The best method of infection was found to be that of three hours with Tween which gave a high bacterium concentration on the culture medium and a high percentage of seedlings with symptoms. The best control was obtained with the joint action of streptomycin at 500 ppm during one hour and 0,5 % sodium hypochlorite during 30 minutes. Other variants such as the antibiotic alone during Ane hour and hot water at 50°C had a good desinfecting effect but they produced phytotoxicity and influenced considerably the seed germination.

(1) Modes of recruitment of herbs and shrubs, and the extent to which availability of propagules affected distribution of the various species after disturbance were examined in a field experiment of canopy removal at the Hubbard Brook Experimental Forest, New Hampshire, U.S.A. (2) The most common shrubs after canopy removal were Rubus idaeus and Viburnum alnifolium; the most common herbs were Aster acuminatus, Dennstaedtia punctilobula and Dryopteris spinulosa. All of the first-year recruitment of Rubus occurred through germination of buried seeds. In contrast, first-year recruitment of the other four species occurred through survival of pre-existing stems or expansion of pre-existing patches, or both. Recruitment of Viburnum, Dennstaedtia and Dryopteris during the second and third years of regrowth continued to be strictly vegetative, whilst recruitment of Aster occurred through newly dispersed seeds as well as rhizomatous growth. (3) The spatial distribution of herbs and shrubs after overstorey removal was strongly related to the location of predecessors before removal. During the first year of regrowth, the locations of almost all stems of all species except Rubus were associated with presence of pre-disturbance individuals on that site. (4) Collections from seed traps indicate that seed production in the site with overstorey removal was higher than in the surrounding, intact forest for most species. Some unoccupied sites were colonized by these seeds during the second and third years of regrowth. (5) The overall distribution of woodland species such as Viburnum alnifolium, Dryopteris spinulosa and Lycopodium lucidulum was unaffected by overstorey removal. After three years of regrowth, the spatial distribution of these species was entirely restricted to locations where predecessors grew in the pre-disturbance forest. (6) Life-history traits of herbs and shrubs at the Hubbard Brook Experimental Forest closely corresponded to Grime's c̀ompetitive', s̀tress-tolerant' and r̀uderal' strategies. It appears that ruderals obscured but did not affect spatial patterns of stress-tolerators and competitors that were present in the forest before overstorey removal. This suggests that, in the absence of physical destruction to existing herbs and shrubs in the forest, d̀isturbance' has, in the short term at least, little effect on spatial patterns of some understorey species.