Deep planting with shelters improves performance of different stocktype sizes under arid Mediterranean conditions

New Forests - Increasing plant size has been considered a way to improve survival and growth of planted containerized stock under dry conditions. Additionally, deep planting provides advantages to...     

Spatial genetic structure and dispersal of the cacao pathogen Moniliophthora perniciosa in the Brazilian Amazon

Moniliophthora perniciosa is the causal agent of witches’ broom in Theobroma cacao (cacao). Three biotypes of M. perniciosa are recognized, differing in host specificity, with two causing symptoms on cacao or Solanaceae species (C‐ and S‐biotypes), and the third found growing endophytically on lianas (L‐biotype). The objectives of this study were to clarify the genetic relationship between the three biotypes, and to identify those regions in the Brazilian Amazon with the greatest genetic diversity for the C‐biotype. Phylogenetic reconstruction based on the rRNA ITS regions showed that the C‐ and S‐biotypes formed a well‐supported clade separated from the L‐biotype. Analysis of 131 isolates genotyped at 11 microsatellite loci found that S‐ and especially L‐biotypes showed a higher genetic diversity. A significant spatial genetic structure was detected for the C‐biotype populations in Amazonia for up to 137 km, suggesting ‘isolation by distance’ mode of dispersal. However, in regions containing extensive cacao plantings, C‐biotype populations were essentially ‘clonal’, as evidenced by high frequency of repeated multilocus genotypes. Among the Amazonian C‐biotype populations, Acre and West Amazon displayed the largest genotypic diversity and might be part of the centre of diversity of the fungus. The pathogen dispersal may have followed the direction of river flow downstream from Acre, Rondônia and West Amazon eastward to the rest of the Amazon valley, where cacao is not endemic. The Bahia population exhibited the lowest genotypic diversity, but high allele richness, suggesting multiple invasions, with origin assigned to Rondônia and West Amazon, possibly through isolates from the Lower Amazon population.     

Soil water content and water relations in planted and naturally regenerated Pinus halepensis Mill. seedlings during the first year in semiarid conditions

The capacity of Aleppo pine (Pinus halpensis Mill.) seedlings to overcome the planting shock in dry conditions was assessed by firstly studying the survival and water status during the first year after planting in relation to soil water content. In spite of receiving only 177 mm rainfall during the year studied, survival of planted Aleppo pine was very high (88.5%). Soil water during summer months (after receiving 67 mm rainfall in winter and spring) was only available at 30–60 cm depth, with tension values of –1.1 and –1.3 MPa in July and August respectively; in these conditions, July predawn xylem water potential measured was –2.5 MPa, and midday potential was –3.6 MPa. According to different authors, these values don't jeopardize the survival of Aleppo pine. In addition, acclimation of outplanted seedlings to environmental conditions was followed by comparing their water relations with those of naturally regenerated seedlings on the site. Predawn and midday xylem water potential showed differences in favour of outplanted seedlings since June, indicating an adjustment to this dry site. Compared to naturally regenerated trees, nursery grown stock of the same age before field planting had much more biomass and higher N and P concentrations and contents; although shoot:root balance and Dickson quality index were not significantly different. Finally, planted seedlings acclimation level during first year was also evaluated by Transplant Stress Index, which value (–0.1278) indicated a slight planting impact.     

Field performance of <Emphasis Type="Italic">Pinus halepensis</Emphasis> planted in Mediterranean arid conditions: relative influence of seedling morphology and mineral nutrition

In Mediterranean arid regions, relatively small planting stock has traditionally been used in an attempt to reduce drought susceptibility, though few studies have examined influences of initial seedling morphology and nutrition on long-term plantation establishment. We fertilized Pinus halepensis Mill. seedlings in the nursery with controlled release fertilizer (CRF) varying in formulations and rates; 9-13-18 and 17-10-10 (N-P-K) formulations at 3, 5 and 7 g l⁻¹ substrate plus an unfertilized control and we evaluated growth and survival 7 years after planting in arid conditions in Almería province, southeast Spain. Interactions between initial height and fertilizer treatments occurred during the first 3 years; initial size advantages of specific fertilizer treatments (7 g l⁻¹ of 9-13-18 and 17-10-10 at 3 g l⁻¹) persisted after 7 years. The largest and most nutrient-rich seedlings from 9-13-18 at 7 g l⁻¹ (41.0 cm tall, 4.4 mg of P per g of root tissue at time of planting) exhibited the highest survival after 7 years (79%), while survival declined to 42% for non-fertilized plants (12.9 cm tall and 0.6 mg of P per g of root tissue). Initial seedling morphological parameters were most consistently correlated with field performance. Root P concentration was the nutrient variable most closely related to survival. Our data emphasizes importance of longer-term experiments to accurately assess influences of nursery treatments on field responses, particularly in arid areas. We suggest that larger seedlings with greater nutrient reserves than are currently being used should be incorporated into Mediterranean plantations.