Laurent Gomez

HPLC Assay of Tomato Carotenoids: Validation of a Rapid Microextraction Technique

Carotenoids are studied for their role as pigments and as precursors of aromas, vitamin A, abscisic acid, and antioxidant compounds in different plant tissues. A novel, rapid, and inexpensive analytical protocol is proposed to enable the simultaneous analysis of four major tomato carotenoids: lutein, lycopene, beta-carotene, and phytoene. Microextraction is performed in the presence of sodium chloride, n-hexane, dichloromethane, and ethyl acetate on fresh tomato powder that has been finely ground in liquid nitrogen. The carotenoids are extracted by agitation and centrifugation and then analyzed by HPLC using a diode array detector. The principal advantage of this extraction resides in the absence of an evaporation step, often necessary to assay tomato carotenoids other than lycopene. Whatever the carotenoid, tests for accuracy, reproducibility, and linearity were satisfactory and indicative of the methods reliability. The stability of extracts over time (several days at -20 degrees C) as the satisfactory sensitivity of the assay whatever the fruit ripeness had a part in the robustness of the method. Reliable, rapid, simple, and inexpensive, this extraction technique is appropriate for the routine analysis of carotenoids in small samples.

Sugar and acid concentrations associated with several qualitative traits in unselected Prunus persica P. davidiana progenies

Summary Five qualitative traits, peach/nectarine, white/yellow flesh, freestone/clingstone, speckled/non-speckled skin and red flesh/non-red flesh colour were studied in terms of their relationships to sugar and acid concentrations in an unselected Prunus persica P. davidiana population in 2001 and 2002. Mean sucrose, sorbitol, total sugar, quinate and total acid concentrations and soluble solids content of nectarine genotypes were significantly higher than those of peach genotypes in both years. Mean sucrose, sorbitol, total sugar concentrations and soluble solids content in genotypes with skin speckles were significantly higher than those in genotypes without skin speckles. Skin speckle had no obvious effect on mean acid concentrations in both years. There were few significant differences in mean sugar and acid concentrations between yellow- and white-fleshed, freestone and clingstone, or red flesh and non-red flesh coloured genotypes in both years. The five qualitative traits are discussed from a breeding point of view.

Influence of neighbouring companion plants on the performance of aphid populations on sweet pepper plants under greenhouse conditions

Companion plants (CPs) may affect the performance of pests on their hosts because of their potential to emit volatile organic compounds (VOCs) and their effectiveness depends not only on the species, but also on their arrangement in the crop system. The present study aimed to evaluate the effect of intercropping rosemary, lavender or basil on the performance of Myzus persicae populations on sweet pepper plants (Capsicum annum) under greenhouse conditions. In a first set of experiments, sweet pepper plants were neighboured by either one or two CPs. In another set of experiments, rosemary was tested at three distances (0.5, 1.5 and 2.5 m) from the host plant. The first set of experiments showed similar patterns of aphid performance (i.e. number of females and nymphs) when a sweet pepper plant was surrounded by one or two companion plants. However, aphid performance was affected more when sweet pepper plants were intercropped with rosemary compared with lavender or basil. The effect of the companion plant decreased significantly with distance. Rosemary was most effective at 0.5 m, although its effectiveness decreased at 1.5 m, becoming insignificant at 2.5 m. The results suggest that a CP may be effective under greenhouse conditions provided that it is located near the target plant.

Which companion plants affect the performance of green peach aphid on host plants? Testing of 12 candidate plants under laboratory conditions

Intercropping of companion plants (CPs) that release distinct volatile compounds with horticultural crops has been proposed to improve pest management. Although CP extracts or essential oils have been reported to be efficient in disturbing the settling of insects such as aphids, the effect of using actual CPs remains relatively unknown. Our aim was to screen odorous CP species for their effect on the performance of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae), when released on adjacent pepper plants. Intercropping was tested in growth chambers using potted plants to avoid root interactions and homogenise the abiotic environment of CPs. Our results indicated that eight CP species—rosemary, African marigold, French marigold, geranium, lavender, basil, chives, and pot marigold—affected aphid performance by reducing the reproductive performance and/or settlement of females. Rosemary followed by African and French marigold was associated with the largest reduction in adult female and nymph number. Chemical analyses indicated that rosemary and French marigold emit specific volatiles. In contrast, four CP species (false yellowhead, thyme, savoury, and peppermint) were not associated with a significant change in aphid performance and emitted a lower diversity of volatiles. This screening of CPs under controlled conditions may be considered as a first step towards the identification of volatiles emitted by actual plants that can affect aphid performance and help the choice of CPs to optimise intercropping strategies.

Companion Plants for Aphid Pest Management

A potential strategy for controlling pests is through the use of “companion plants” within a crop system. This strategy has been used in several trials to fight against a major crop insect pest: the aphid. We reviewed the literature to highlight the major mechanisms by which a companion plant may act. Trials carried out under laboratory or field conditions revealed that companion plants operate through several mechanisms. A companion plant may be associated with a target crop for various reasons. Firstly, it can attract aphids and draw them away from their host plants. Secondly, it can alter the recognition of the host plant. This effect is mostly attributed to companion plant volatiles since they disturb the aphid host plant location, and additionally they may react chemically and physiologically with the host plant, making it an unsuitable host for aphids. Thirdly, it can attract natural enemies by providing shelter and food resources. In this review, the feasibility of using companion plants is discussed. We conclude that many factors need to be taken into account for a successful companion plant strategy. For the best long-term results, companion plant strategies have to be combined with other alternative approaches against aphids.