Viability of holm and cork oak seedlings from acorns sown in soils naturally infected with Phytophthora cinnamomi

The emergence and survival of pregerminated holm oak (Quercus ilex) and cork oak (Quercus suber) acorns from two ecologically different dehesas (Mediterranean open woodlands) were studied in two soils from these stands naturally infected with Phytophthora cinnamomi, and in the same soils previously sterilized in the autoclave. Phytophthora cinnamomi was consistently isolated from the radicles of all unemerged and all emerged but dead seedlings from the unsterilized substrates. Seedlings of holm oak were more susceptible to P. cinnamomi than those of cork oak. Mortality of holm oak seedlings was significantly different depending only on soil treatment (sterilized or unsterilized), and it was 100% in unsterilized soils, independent of acorn provenance and soil origin. Mortality of cork oak seedlings was significantly different depending on the acorn origin and soil treatment, and on the interactions acorn origin × soil origin and soil origin × soil treatment. The demonstrated high susceptibility of holm and cork oak young seedlings to P. cinnamomi could be a limiting factor in Mediterranean open woodlands (dehesas) not only in natural regeneration processes but also when reforestation by direct sowing is implemented.     

Acute toxicity in laboratory tests of fresh and aged residues of pesticides used in citrus on the parasitoid Aphytis melinus

California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) is a worldwide citrus key pest. One of the control strategies currently promoted in the Mediterranean basin is the augmentative release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae). A clear understanding of the impact that pesticides commonly used in citrus have on this parasitoid is therefore essential to assure the efficacy of the method. The aims of this study were to evaluate the lethal effects of freshly applied and laboratory-aged residues of eighteen selected pesticides recommended in IPM for citrus on A. melinus adults. According to their toxicity on A. melinus, the pesticides could be divided in four groups. Etofenprox and chlorpyrifos were harmful and persistent; abamectin was moderately harmful and slightly persistent; dimethoate, chlorpyrifos-methyl, and spirodiclofen were slightly harmful and moderately persistent; and azadirachtin, etoxazole, fenbutaestan, hexythiazox, mancozeb, petroleum oil, pirimicarb, propargite, pymetrozine, pyriproxyfen, spirotetramat, and tebufenpyrad were considered harmless. The information presented here will help us to integrate A. melinus release within an IPM for citrus in which pesticides are still used.     

Do vegetative and reproductive phenophases of deciduous tropical spe-cies respond similarly to rainfall pulses?

Deciduous trees with high-density wood that occur in dry seasonal tropical regions respond to rainfall seasonality with synchrony in phenophases. However, they may exhibit interannual differences in sy...     

Intensity and timing of warming and drought differentially affect growth patterns of co-occurring Mediterranean tree species

Climate change involves warmer temperatures, altered precipitation patterns, increased climatic variability and, in Mediterranean regions, increased frequency and severity of droughts. Tree species may show different growth responses to these components of climatic change, which may trigger changes in forest composition and dominance. We assessed the influence of recent climatic changes on secondary growth of mature trees from four species co-occurring in a Mediterranean continental forest: Quercus ilex, Quercus faginea, Pinus nigra and Juniperus thurifera. We used dendrochronology to relate radial-growth variables [earlywood and latewood widths, basal area increment (BAI)] to annual and seasonal climatic variables for the period 1977–2007. Our results showed that Q. faginea BAI has declined, whereas J. thurifera BAI has increased over time while Q. ilex and P. nigra have maintained their growth rates. Growth was mainly favored by higher precipitations and tree size for all species. Reduced growth during extremely dry years was observed for all study species, but all of them except Q. faginea recovered their growth levels 2 years after drought. Our findings illustrate how the effects of climatic changes on growth should include analyses of seasonal climatic trends and extreme events such as severe droughts. We conclude that the seasonal timing of warming and precipitation alterations leading to drought events caused contrasting effects on growth of co-occurring Mediterranean tree species, compromising their future coexistence.     

Quantile regression: prediction of growth and yield for a eucalyptus plantation in northeast Brazil

European Journal of Forest Research - Regression analysis is a traditional technique to fit equations and predict tree and forest attributes. However, problems may occur when the data show high...     

Homegardens of a humid tropical region in Southeast Mexico: an example of an agroforestry cropping system in a recently established community

The major components of the process of production in the homegardens of a tropical Mexican community are described and analyzed. Specifically, management tasks, means of production, and the amount, quality and temporal distribution of the products are discussed. The ecological, technological and productive advantages generally attributed to this kind of agroforestry cropping system in comparison to monocultures were also found in the homegardens of Balzapote. However, the area presently managed under this system is restricted, and its local and regional impact is thus very limited. Based on the detailed analysis of the functional differences in 8 homegardens and the socioeconomic roles they play in the economic organization of peasant families, the possible expansion of homegardens in the Mexican tropics is discussed.     

Soil C and N dynamics, nutrient leaching and fertility in a pine plantation amended with wood ash under Mediterranean climate

Wood ash addition to forest soils can balance exported nutrients by tree harvesting and decrease soil acidity, but its effectiveness in Mediterranean areas has been scarcely evaluated. The aim of the present study was to assess the effects of wood ash application on soil C and N dynamics, nutrient leaching and fertility in a pine stand. Treatments were loose and pelleted ash application (11 Mg ha^?1), alone or combined with N fertilizer, and a control treatment. Nutrient leaching and soil chemical and biological properties were periodically evaluated for a 30-month period. Wood ash increased leaching of base cations (Ca, Mg, Na and K) and P, mainly at the beginning of the study. The effect was more pronounced for the loose formulation. As a consequence, a positive effect on soil nutrient availability (exchangeable base cations and extractable P) and soil acidity reduction was observed for the loose formulation in the 0–10-cm soil layer. Carbon and N dynamics were only affected when ash was applied with N fertilizer, which enhanced CO₂ flux during the study period.     

Genomic DNA methylation-demethylation during aging and reinvigoration of Pinus radiata

In animals, DNA methylation is related to gene silencing during ontogenic development. Little is known about DNA methylation in plants, although occasional changes in the DNA methylation state of specific gene promoters have been reported in angiosperms during some developmental processes. We found large differences in the extent of DNA methylation between meristematic areas of juvenile and mature Pinus radiata D. Don. trees, whereas differences in the extent of DNA methylation between differentiated tissues of juvenile and mature trees were small. In meristematic areas, there was a gradual decrease in extent of DNA methylation as the degree of reinvigoration increased. The observed changes in extent of DNA methylation during aging and reinvigoration indicate that reinvigoration could be a consequence of epigenetic modifications opposite in direction to those that occur during aging.     

Within-tree density gradients in Gmelina arborea in Venezuela

Abstract. Variation of wood specific gravity from the base to the top of tree and from pith to bark was investigated for Gmelina arborea Roxb. plantations in western Venezuela. Increment cores were taken from thirty trees at five different sections up the stem: 0.1?m; 1.3?m, half total height, 3/4 total height and at the top. These trees were chosen from commercial plantations located at three different sites. Specific gravity was obtained using an X-ray densitometer. The results show that there is an increase in specific gravity from pith to bark. It was also evident that specific gravity decreased from stump to half of the total height, then increased towards the top of the stem. No correlation between specific gravity and height of the tree was found. Correlations in specific gravity with height categories were generally small, and non-significant at level α=0.05.

Palabras clave: Gmelina arborea, Propiedades de la madera, Gravedad específica

Resumen. En la Gmelina arborea Roxb se estudió la variación de la gravedad específica desde la base hasta el tope del árbol y desde la médula hasta la corteza. Se tomaron muestras de madera provenientes de treinta árboles a cinco alturas diferentes a lo largo del fuste a 0.1?m; 1.3?m, mitad de la altura total, 3/4 de la altura total, y del tope, las cuales fueron seleccionadas de plantaciones comerciales localizadas en tres sitios distintos al occidente de Venezuela. La gravedad específica fue determinada con la ayuda de un densitómetro de rayos-x. Los resultados muestran un incremento de la gravedad especifica desde la médula hacia la corteza. También se encontró que la gravedad específica disminuye de la base a la mitad del fuste y luego aumenta hacia el tope del fuste. No se encontró correlación entre la gravedad específica y la altura del árbol. La correlación entre la gravedad específica y las categorías de altura donde las muestras fueron tomadas son generalmente pequeñas y poco significativas a un nivel de probabilidad α=0.05.

     

Intra and interlocus interactions between alcobaça (alc), crimson (og c ), and high pigment (hp) loci in tomato Lycopersicon esculentum Mill.

The ripening mutant allele alcobaça (alc/alc) may be deployed to extend shelf life in tomatoes, but has reportedly negative effects on fruit colour development. Colour enhancing mutants crimson (og ^c /og ^c) and high pigment (hp/hp) could potentially overcome this limitation, but a detailed account of their interactions with alc is not available. In this paper, we report on intra-allelic (additive and dominant) interactions within these 3 loci, and on their possible interallelic (epistatic) interactions. Eight near-isogenic (NIL) tomato lines in background Flora-Dade were obtained, representing all possible 2ⁿhomozygous combinations in the n = 3 loci. The 8 NIL were crossed in all possible combinations (reciprocals excluded), to obtain 28 hybrids that were heterozygous in at least one locus. The 36 treatments (= 8NIL + 28 hybrids) were grown in a randomized complete block design with 4replications, and the following traits were evaluated: total yield, average fruit mass, fruit firmness at harvest (= breakerstage) and 6 days after harvest (d.a.h)., % coloured fruit surface, fruit lycopene and beta-carotene contents, fruit % soluble solids and solids/acidity ratio, internal and external fruit colour. The loci alcobaça, crimson and high pigment or their epistatic interactions had significant influence on the expression of all traits measured. Epistatic effects were responsible for most of the variation among genotypes (with a minimum of 48.1%of the total sum of squares for % coloured fruit surface and a maximum of 82.8% for total yield). External fruit colour was defficient in all alc/alc genotypes, and their commercial use is impaired, in spite of improvements in fruit internal and external colour brought about by deployment of specific genotypic constitutions in lociog ^c and hp. Some but not all alc ⁺ /alc genotypes were firmer and showed improved fruit quality over the normal Flora-Dade (alc ⁺ /alc ⁺ og ^c+ /og ^c+ hp ⁺ /hp ⁺) background. The following genotypic combinations represented good compromises between yield, long shelf life and fruit quality traits: alc ⁺ /alc og ^c+ /og ^c hp ⁺ /hp, alc ⁺ /alc og ^c /og ^c hp ⁺ /hp ⁺ and alc ⁺/alc og ^c+/og ^c+ hp ⁺ /hp