Gustavo A. Orioli

Germination parameterization and development of an after-ripening thermal-time model for primary dormancy release of Lithospermum arvense seeds.

BACKGROUND AND AIMS Models based on thermal-time approaches have been a useful tool for characterizing and predicting seed germination and dormancy release in relation to time and temperature. The aims of the present work were to evaluate the relative accuracy of different thermal-time approaches for the description of germination in Lithospermum arvense and to develop an after-ripening thermal-time model for predicting seed dormancy release. METHODS Seeds were dry-stored at constant temperatures of 5, 15 or 24 degrees C for up to 210 d. After different storage periods, batches of 50 seeds were incubated at eight constant temperature regimes of 5, 8, 10, 13, 15, 17, 20 or 25 degrees C. Experimentally obtained cumulative-germination curves were analysed using a non-linear regression procedure to obtain optimal population thermal parameters for L. arvense. Changes in these parameters were described as a function of after-ripening thermal-time and storage temperature. KEY RESULTS The most accurate approach for simulating the thermal-germination response of L. arvense was achieved by assuming a normal distribution of both base and maximum germination temperatures. The results contradict the widely accepted assumption of a single T(b) value for the entire seed population. The after-ripening process was characterized by a progressive increase in the mean maximum germination temperature and a reduction in the thermal-time requirements for germination at sub-optimal temperatures. CONCLUSIONS The after-ripening thermal-time model developed here gave an acceptable description of the observed field emergence patterns, thus indicating its usefulness as a predictive tool to enhance weed management tactics.

Spurred Anoda (Anoda cristata) Competition in Narrow- and Wide-Row Soybean (Glycine max) 1

The effect of spurred anoda competition in narrow- (35 cm) and wide-row (70 cm) soybean was studied in field experiments for 2 yr. Vigorous early soybean growth in narrow- compared with wide-row soybean resulted in lower radiation transmitted through the canopy, which can partially account for greater competitiveness of narrow-row than wide-row soybean. Soybean plant height was not significantly influenced by the row spacing. Relative yield total (RYT), which is the relationship between yield in mixtures and in monocultures of the crop or the weed and indicates resource complementarity, was equal to 1 with 12 spurred anoda/m2 in the year with less precipitation. Regardless of the row spacing, spurred anoda gave resource use complementarity with the crop (RYT > 1) in all other treatments; therefore, partial avoidance of competition in mixed species was evident. Soybean aggressivity, which takes into account the effect of competition on both the crop and the weed and indicates competitive ability, decreased with weed density in both row spacings. Soybean yield loss at harvest was linearly related to relative dry weight 40 d after planting. Weed-free narrow- and wide-row soybean produced similar yields. In the presence of the spurred anoda, soybean yield was greater in narrow-row compared with wide-row soybean only in the most humid year. A management system that uses quick canopy closure with narrow-row soybean can provide excellent soybean yield and suppression of low spurred anoda densities. Nomenclature: Soybean, Glycine max (L.) Merr.; spurred anoda, Anoda cristata (L.) Schlecht. #3 ANVCR. Additional index words: Aggressivity, competition, crop and weed biomass, row spacing, weed density. Abbreviations: DAP, days after planting; PPF, photosynthetic photon flux; RDW, relative dry weights; RYT, relative yield total.

Absorption of iron Fe-humate in nutrient solutions by plants

Humic substances have significant practical implications regarding the transport and availability of micronutrients to plants. Nutrient solution studies were conducted to evaluate Fe-humate complexes as a iron source to plants. A short term Fe-humate absorption study was conducted using excised barley roots, while long term absorption studies were conducted using sunflower andSpirodella intermedia. Humic acid was extracted with 0.5N NaOH from a Typic Argiudol, A horizon, and purified with exhange resins and EDTA. The Fe-humate was obtained by passing purified humic acid through a cation exhange resin saturated with iron using59Fe as a tracer. In the short term, absorption studies, the absorption of iron by barley roots was insensitive to metabolic inhibitors, low temperature and anaerobiosis. This may be due to a strong adsorption or precipitation of Fe-humate in the root free spaces masking the absorption. However, long term studies indicated that Fe-humate was a good source of iron which was readily absorbed and transported to the shoot.

Changes in peroxidases associated with radiation-induced sprout inhibition in garlic (Allium sativum L.)

The effects of an acute dose of gamma-rays (10 Gy) to post-dormant garlic cloves on inner sprout growth and changes in peroxidases and soluble proteins were evaluated up to 100 days of storage in darkness at 19 +/- 1 degree C and 42 +/- 2% relative humidity. Radiation-induced inhibition of sprout growth became evident after 25 days of treatment and was synchronous with a marked increase in peroxidase activity. Thin-layer isoelectric focusing revealed that radiation induced an increase in the number of anodic peroxidase isoenzymes at 100 days, suggesting modifications in the vascularization process. Neither the soluble protein content nor the protein pattern were affected by irradiation. These results are discussed in terms of a possible mediating effect of peroxidase on radiation-induced sprout inhibition in garlic.

Electrophoretic subfractionation of low and high molecular weight humic acids fractions

SummarySoil humic acid was fractionated on a molecular weight basis either using Sephadex gel filtration or electrophoresis on a discontinuous polyacrylamide gel. Low and high molecular weight fractions obtained by these two methods were choosen for subsequent subfractionation using electrophoretic methods. The high and low molecular weight fractions yielded several subfractions after separation by isotachophoresis or isoelectric focusing. Components of the high molecular weight fractions occupied the upper portion of the mobility train; components of the low molecular weight fractions lead the mobility train. Adsorption by Sephadex was avoided by using 4M urea as an eluent. The elution of the humic substances adsorbed to the polyacrylamide gel matrix was achieved by using a 0.1M Tris −0.025M EDTA solution.

Edaphic mobility of complete humic acid and fractions of high and medium molecular weight

Soil mobility of a complete humic acid and high and medium molecular weight fractions was determined by a soil TLC method. High and medium molecular weight fractions were obtained by ultrafiltration and then labeled with radioiodine. Infrared, visible- and UV spectra, as well as isotachophoretic studies, showed marked differences among the three humic fractions. The results obtained made evident the presence of soil mobile humic fractions of medium molecular weight. Alkalinization increased the soil mobility of humic acid.

THE EFFECT OF FIRE ON SOIL HUMIC SUBSTANCES

SummaryHigh temperature effects on soil humic substances were investigated both in natural and laboratory conditions. Differential Thermal Analysis and pyrolysis show that only temperatures above 250°C produce changes in the humic acid fraction. The mean change is a loss of weight due to decarboxylation. Isotachophoretic studies also show that temperatures higher than 250°C produce alteration in the separation pattern of the different subfractions due to changes in the ‘core’ or/and in the amount of carboxyl and hydroxyl groups. Isotachophoregrams done on soil samples extracted from an area before and after fire show no differences. This result is taken as an indication that there was no direct effect of the temperature on the soil humic substances.

Effect of gamma rays on seed cloves of garlic (Allium sativum L.) at post-harvest: Reversion by exogenous growth regulators

Abstract The aims of this work were to analyze the effect of (1) acute doses of gamma rays (1.0–10.0 Gy) on dormant and post-dormant garlic seed cloves, and (2) exogenous applications of growth regulators in reversing the effect produced by irradiation. The results indicated that a 10.0-Gy dose applied in post-dormancy significantly decreased sprouting; sprouts were modified in size (length), color and peroxidase activity. No changes were observed for the dormancy period treatments. The storage leaf showed no modifications. Application of some growth regulators was effective in modifying the effectiveness of the gammarays exposure. Indole acetic acid was the most effective, followed by gibberellic acid; benzyl-adenine gave no evidence of reversal of sprout growth inhibition in in vitro conditions.

Imbibition and germination rates of sunflower (Helianthus annuus L.) seeds according to fruit size

Abstract The influence of size and pericarp structure of sunflower ( Helianthus annuus L.) fruits on imhibition and germination rates of the seed was investigated. The results show a positive correlation between fruit width, pericarp thickness and fruit weight. Germination rate was not affected by fruit size. Nevertheless, although large fruits (more than 4.5 mm width) have a rapid imbibition rate there was a significant lag in the start of their germination in relation to that of the smaller fruits (less than 2.5 mm width).

Morphological changes induced by different doses of gamma irradiation in garlic sprouts

Abstract The objective of this work was to evaluate the effects of different doses of gamma rays applied in dormancy and post-dormancy on garlic bulbs in relation with some morphophysiological parameters. High (commercial) doses cause the complete inhibition of sprouting and mitosis (due to nuclear aberrations). Relatively low doses show no effects on bulbs but doses of 10 Gy applied in post-dormancy reduce sprouting and stop mitosis. This inhibition becomes noticeable from 150 days post-harvest onwards. Exogenous growth regulators can reverse these effects. Results may reinforce the good practice of radioinhibition processes in garlic.