Juan A. Fernández

Selection and nursery production of ornamental plants for landscaping and xerogardening in semi-arid environments

Summary In landscaping and xerogardening projects, under semi-arid conditions, appropriate plant selection and conditioning techniques used in the nursery during seedling production are crucial for the establishment, survival and subsequent growth of plants after transplanting. Selecting ornamental plants with appropriate morphological and physiological characteristics to improve nursery performance and tolerance of harsh environments is of vital importance. The use of native species of wild flora is of increasing interest because of their capacity to adapt to adverse local environmental conditions. However, the degree of adaptation to abiotic stresses varies considerably within a family, within a genus and even within a species. Morphological and anatomical adaptations in seedlings include reductions in shoot height and/or leaf area, rises in root-collar diameter and root growth potential and, often, a reduction in the shoot:root ratio. These occur as a result of hardening and acclimation processes (pre-conditioning) during the nursery period, and are correlated with the ability to withstand the shock of transplantation and to increase survival and plant growth following transplantation in xerogardens and semi-arid landscapes. In addition, there are physiological characteristics of seedlings related to osmotic adjustment and water-use efficiency, such as low stomatal conductance, leaf water potential, leaf turgor potential and relative water content. These provide seedlings with a considerable capacity to adapt to adverse conditions after transplantation into harsh environments. Suitable environmental conditions and cultivation techniques in the nursery are essential to produce sturdy seedlings, with the above-mentioned morphological and physiological characteristics. Deficit irrigation is the most commonly used pre-conditioning technique to produce high-quality seedlings. In addition, using large-sized containers and appropriate substrates, withholding N nutrition, inoculating arbuscular mycorrhizal fungi, applying plant growth retardants and mechanical conditioning methods (including brushing, and shoot- and/or root-pruning) are common. Varying microclimatic conditions (low temperature, low air humidity, enrichment with CO2, light intensity and photoperiod management) are also used to control growth to produce high-quality seedlings with the ability to withstand transplanting shock and be capable of rapid establishment and resumption of growth under xerogardening and semi-arid landscaping conditions.

Identification of F1 hybrids of artichoke by ISSR markers and morphological analysis

Five different artichoke hybrid populations (crosses between a male sterile artichoke (MS6) and three American accessions (AMA3, AMA7, AMB1) and two Spanish accessions (SP2, SPA2)) plus a commercial hybrid population (Opal F1, Nunhems, Netherlands) were used for molecular and morphological characterisation in order to identify the purity of the F1 populations. Molecular analysis was carried out using the inter-simple sequence repeat (ISSR) technique with twenty primers. Out of these, nine were polymorphic, producing 82 DNA bands per primer on average, 56 of which were polymorphic among the populations. A dendrogram, drawn on the basis of a similarity matrix using the UPGMA algorithm, revealed that the 66 samples (10 plants per F1 populations and their respective progenitors) could be classified into two major clusters at a Nei’s genetic distance of 0.13. The male parents were genetically quite similar to all their respective progenies. In order to confirm hybrid purity, only the primers which amplified bands specific to the male parent of each hybrid were considered and the inheritance of the single locus for each cross-combination was analysed. Three ISSR markers (857c, 857g and 878) were able to confirm the hybrid purity. The morphological trait analysis showed that eight of the 17 morphological characters were significantly different among the six F1 populations. When the Mantel test was applied to the matrix of the Nei’s genetic distances and the matrix of morphological traits, a significant degree of correlation was observed between them. A selection method using ISSR markers based on cluster analysis is suggested to confirm the purity of artichoke hybrids and to predict the characters expected by any F1 hybrid offspring.

Effect of aeration of the nutrient solution on the growth and quality of purslane (Portulaca oleracea)

Summary The aim of this work was to assess the influence of three levels of aeration of the nutrient solution (high, low, or no aeration) on the growth and quality of two cultivars of purslane (Portulaca oleracea L.): the commercial cultivar, ‘Golden Purslane’, and a local Spanish accession, C-215. Both were grown in a floating system over four crop cycles. Our results showed purslane to be a crop that exhibited little sensitivity to oxygen depletion in the rooting medium, since it was able to adapt to a gradual reduction in oxygen content. Under such conditions, purslane plants created an aerenchyma tissue (equivalent to approx. 10% of root sections in the non-aerated treatments in both cultivars) that helped to maintain growth. Under conditions in which no aeration was provided, there was a slight decrease in plant growth. The final quality of the product was improved because leaf nitrate concentrations were reduced (by more than 1,300 mg kg–1 FW) compared with the high aeration treatment, and the content of functional phytochemicals and SPAD values (chlorophyll contents) were increased.