J. Ordovás

Predictive factors for the suppression of Fusarium wilt of tomato in plant growth media

ABSTRACT Fusarium wilts are economically important diseases for which there are no effective chemical control measures. However, biological control and fertility management are becoming efficient alternatives for controlling this disease. Growth media formulated with composts that are able to suppress Fusarium wilt of tomato provide a control system that integrates both strategies. The aim of this study was to predict Fusarium wilt suppression of growth media using abiotic and biotic variables. Grape marc compost was the most effective medium used to suppress Fusarium wilt. Cork compost was intermediate, and light peat and expanded vermiculite were the most conducive growth media. The growth media evaluated were in a pH range of 6.26 to 7.97. Both composts had high beta-glucosidase activity. When pH and beta-glucosidase activity were taken into account as predictive variables, more than 91% of the variation in severity of Fusarium wilt was explained. This relationship illustrates the effect of nutrient availability and the degree of microbiostasis, two key factors in this pathosystem. Microbial populations involved in suppressiveness were cellulolytic and oligotrophic actinomycetes, fungi, and the ratios cellulolytic actinomycetes/cellulolytic bacteria, oligotrophic bacteria/copiotrophic bacteria, and oligotrophic actinomycetes/oligotrophic bacteria. Based on community level physiological profiles, different community structures were evident among growth media evaluated.

Behaviour of different horticultural species in phytotoxicity bioassays of bark substrates

Abstract The use of forestry wastes (barks, sawdust, wood chips) as potting media components can involve serious problems of toxicity that must be evaluated. Evaluation methods may consist of analytic techniques to detect and quantify phytotoxic molecules, or rapid bioassays, with low technical requirements, using species sensitive to the toxic elements. These bioassays should be able to predict plant behaviour in real growing conditions. In this study we used as substrate cork oak bark ( Quercus suber L.). This material, like other forestry wastes, contains phytotoxic phenolic compounds which can be washed out with hot water. The phenolic content of cork (C) and washed cork (WC) was measured, and two germination bioassays were carried out with eight horticultural species. In the first, aqueous extracts of cork (C) and washed cork (WC) obtained with water at 15 °C and 70 °C were used, and the second was done directly on the substrates. In addition, a seedling growing test was carried out with the same species. We concluded that tomato and lettuce are the most sensitive species, and the direct test on the substrate is recommended owing to its simplicity and close correspondence to growing conditions.

Possible early selection of short juvenile period olive plants based on seedling traits

The relationship between the length of the juvenile period and nine olive seedling parameters (plant height, diameter, number of nodes, lateral shoots, internode length, leaf length, width, area, and shape index) was explored in 287 plants belonging to four different progeny. The traits were measured at two timepoints: after the plants had completed a forced growth cycle in the greenhouse/shadehouse (15 months after sowing) and after one growing season in the field (27 months after sowing). Strong linear tendencies of most vigour traits (mainly plant height and diameter) with the time of first flowering were observed. Leaf traits measured after one year in the field were also related to the length of the juvenile period, but not the same traits that were measured the previous year. Strong positive correlations were observed between the parameters studied. All results are discussed in terms of selecting the best seedling traits to be used as pre-selection criteria for short juvenile period during early stages.

Iron chlorosis in gerber as related to properties of various types of compost used as growing media

Abstract Nutrient deficiencies in crop plants may be influenced by a number of properties of the growing media. Some peat‐substitute substrates can promote iron (Fe) chlorosis in sensitive plants, which has traditionally been ascribed to the elevated pH of growing media. To identify the origin of this problem in various types of composted organic residues used as growing media and possible corrections, a complete randomized experiment on gerber (Gerbera jamesonii Adlam) as an Fe‐chlorosis sensitive crop involving three factors (growing medium, medium acidification, and the medium treatment with Fe) was performed. Although the Fe content in plants decreased with increasing pH in the growing medium, the chlorophyll content as measured using a chlorophyll meter (Minolta Soil Plant Analysis Development, SPAD) was not significantly related to pH. The SPAD readings and Fe concentrations in plants, dry matter, and flower production were not significantly related to diethylenetriaminepentaacetic acid (DTPA)–extractable Fe in the growing media. The addition of Fe‐chelate significantly increased yield (P<0.01), and SPAD at 65 and 96 days after planting (P<0.001 and P<0.01, respectively). However, the effect of the acid treatment was, different depending on the growing media. When the acidification promoted a positive effect on SPAD readings, this was nonsignificantly different than that obtained with the application of Fe‐chelate. The estimated amount of available Fe in the growing media was not relevant, which explains the incidence of chlorosis as physiological factors related to pH.