Corn (Zea mays) is the main cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the corn kernels. This paper reports on the identification of internal and external mycoflora of corn kernels harvested in the main production area in Argentina in 1990. A mycological survey was carried out on 178 corn samples, from five locations in that area and the isolation frequency and relative density of the prevalent fungal genera compared. Genus Fusarium was the most prevalent component of the internal seedborne mycoflora in the five locations. Penicillium was prevalent in all locations, taking into account the frequency. However, this genus was predominant only in two locations, when the relative density was considered. The predominant Fusarium was F. moniliforme and the most frequently isolated species of Alternaria, Aspergillus and Penicillium were A. alternata, A flavus and P. decumbens, respectively. Diplodia species were not isolated from any of the samples.
RESUMENEl presente trabajo se desarrolló en el oeste de la provincia de Buenos Aires, Argentina con el objetivo de ajustar funciones de biomasa de árboles individuales y determinar la biomasa en diferentes compartimientos de la planta y el sotobosque. Se identificaron rodales de Eucalyptus viminalis Labill. cuyas edades oscilaron entre 4 y 14 años. Se apearon 21 árboles con diámetros entre 9,2 y 32,5 cm. Se desarrollaron regresiones simples y múltiples y se estimó el volumen, la biomasa en ramas, hojas y fuste. Las ecuaciones de volumen de mejor comportamiento son basadas en modelos lineales en su forma normal, y el modelo más adecuado fue el que incorporó al d 2 (R 2 = 0,92). Para la estimación de la biomasa en hojas, ramas, copa y fuste se recomienda los modelos ln-ln que consideran el d y h o solo el d. El componente de la biomasa en hojas presentó una estimación más débil. La distribución de la biomasa en los individuos sigue el patrón de desarrollo que se encuentra en la bibliografía. La proporción de la biomasa en la copa disminuye con la edad, contrariamente a lo sucedido con el fuste. Palabras claves: modelos de biomasa; modelos de volumen; Eucalyptus; región semiárida. ABSTRACTThe present work was developed in the West of Buenos Aires Province (Argentina) with the objective of adjusting functions of biomass of individual trees, in their different compartments and in the understorey. Stands of Eucalyptus viminalis Labill. were identified, with ages between 4 and 14 years-old. Twenty-one individuals were felled with diameters ranging from 9,2 to 32,5 cm. Simple and multiple regression models were developed and volume, branch leaf and stem biomass were estimated. The best volume equations were based on lineal models and the most adequate behavior was obtained with d 2 . To estimate leaf, branch and stem, ln-ln models have been suggested, with diameter and h or only diameter. The leaf biomass presented the weakest adjustment. The distribution of trees biomass agrees with the bibliography. The proportion of crown biomass decreases with age; on the other hand, the proportion of stem biomass increases with age.
Argentina is the first popcorn exporting country worldwide. In 1997-1998 harvest season, 40,000 ha were sown with a production of 125,000 tons; 120,000 tons of this production were exported to more than 40 countries. The objectives of this study were to isolate and to identify the fungi present in this cereal and to assess the occurrence of mycotoxins in freshly harvested popcorn in Buenos Aires province, Argentina, in 1999. All popcorn samples showed fungal contamination. A total of 4,211 isolates were recovered from popcorn kernel samples. The prevalent species isolated wasFusarium verticillioides followed byPenicillium funiculosum, F. graminearum andAlternaria alternata. No aflatoxins, zearalenone, deoxynivalenol or ochratoxin A were detected in the 42 popcorn simples. All samples but one were contaminated with fumonisins (FB) in a range in ug/kg of (not detected-529) for FB1; (not detected-216) for FB2 and (not detected-103) for FB3. Fumonisin contamination levels in Argentinean popcorn were lower than observed in flint corn. No significant differences in fungal and fumonisins contamination levels were observed in the different tested hybrids.
The effect of initial planting density on the growth and wood density of Eucalyptus globulus was examined in a trial established in the southeast of Buenos Aires Province, Argentina. A modified Nelder design was used to generate 9 planting densities ranging from 582 to 2.083 trees/ha. The effect of planting density on diameter at breast height, total tree height, basal area, relative bark thickness and wood density was studied over a 10-year period. By reducing the initial density of planting to 761 trees/ha, an increase on individual tree growth was observed, principally on diameter and to a lesser extent on tree height. However, basal area (m2/ha) was greatest at intermediate densities. Initial planting density affected wood basic density at 6 years of age but not relative bark thickness. In conclusion, 1,095 trees/ha was found to be the best initial density to optimize individual and stand growth.
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