Robert Habib

Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review

Farmers are facing serious plant protection issues and phytosanitary risks, in particular in the tropics. Such issues are food insecurity, lower income in traditional low-input agroecosystems, adverse effects of pesticide use on human health and on the environment in intensive systems and export restrictions due to strict regulations on quarantine pests and limits on pesticide residues. To provide more and better food to populations in both the southern and northern hemispheres in a sustainable manner, there is a need for a drastic reduction in pesticide use while keeping crop pest and disease damage under control. This can be achieved by breaking with industrial agriculture and using an agroecological approach, whose main pillar is the conservation or introduction of plant diversity in agroecosystems. Earlier literature suggest that increasing vegetational biodiversity in agroecosystems can reduce the impact of pests and diseases by the following mechanisms: (1) resource dilution and stimulo-deterrent diversion, (2) disruption of the spatial cycle, (3) disruption of the temporal cycle, (4) allelopathy effects, (5) general and specific soil suppressiveness, (6) crop physiological resistance, (7) conservation of natural enemies and facilitation of their action against aerial pests and (8) direct and indirect architectural/physical effects. Here we review the reported examples of such effects on a broad range of pathogens and pests, e.g. insects, mites, myriapods, nematodes, parasitic weeds, fungi, bacteria and viruses across different cropping systems. Our review confirms that it is not necessarily true that vegetational diversification reduces the incidence of pests and diseases. The ability of some pests and pathogens to use a wide range of plants as alternative hosts/reservoirs is the main limitation to the suppressive role of this strategy, but all other pathways identified for the control of pests and disease based on plant species diversity (PSD) also have certain limitations. Improving our understanding of the mechanisms involved should enable us to explain how, where and when exceptions to the above principle are likely to occur, with a view to developing sustainable agroecosystems based on enhanced ecological processes of pest and disease control by optimized vegetational diversification.

Architectural analysis and synthesis of the plum tree root system in an orchard using a quantitative modelling approach

A dynamic 3D representation of the root system architecture of plum is proposed by gathering quantitative and morphological observations of the tree root system in a model. The model includes two information levels: (i) a typology of root axes, based on morphological and developmental characteristics; (ii) a set of basic processes (axial and radial growth, ramification and reiteration, decay). The basic processes are qualitatively identical in space and time. An original approach was used to investigate these processes and to formalize them in the model. Concerning the main roots, a mechanism of reiteration is described that has a substantial influence on the structuring of the root system. Root mortality is assessed using the variation in branching density along the root axes. Radial growth is calculated from the ramification of root axes, using root section conservation properties. This model enables a link between static field observations and a dynamic simulation of the root system architecture. The architectural model allows examination of the global consequences of the basic processes at the level of the root system. The simulations provide useful output, from a simple root depth profile to a simulation of the dynamic 3D root system architecture, to investigate plant functioning and especially water and nutrient uptake.

Fruit quality and leaf photosynthesis in response to microenvironment modification around individual fruit by covering the fruit with plastic in nectarine and peach trees

Summary The effects of covering fruit with clear plastic film during the final stage of rapid fruit growth were investigated on ‘Big Top’ nectarine and ‘Opal’ peach over three years. Covering fruit with plastic film modified the microenvironment around the fruit, particularly by increasing relative humidity and temperature during the day. These modifications influenced fruit development, fruit quality and leaf photosynthesis. Covering fruit with plastic film significantly reduced the dry matter content, either for fruit flesh or for total fruit, the content of total soluble solids in fruit fresh, and leaf photosynthesis under high light intensities (photosynthetically active radiation in excess of 1000.m.mol.m–2.s–1) as compared with uncovered control fruit. The relationship between photosynthetic rate and other leaf physiological responses showed that the depression of photosynthetic CO2 assimilation was related to reduced stomatal aperture and increased leaf temperature. It is suggested that the stomatal aperture may be considered as the trigger or promoter and leaf temperature as the regulator of photosynthesis under a lower sink-source ratio.

Uptake and allocation of nitrogen in young peach trees as affected by the amount of photosynthates available in roots

Abstract In trees, the regulation of the nitrogen (N) uptake and allocation seems not to be related directly to the photosynthetic activity of the leaves, but more probably to the result of the competition between the sinks which determines the amount of current photosynthates allocated to the roots. We intend here to evaluate the effect of the photosynthate supply to the roots on the (i) N uptake, (ii) N assimilation (i.e., nitrate reduction), and (iii) N allocation (i.e., N export from the roots). Therefore, three‐year‐old peach trees (Prunus persica L. Batsch) were girdled for 2 weeks at three different phenological stages to interrupt the transport of carbohydrates in the phloem from shoot to roots. A 15N labeling of the nutrient solution was included in this treatment. Girdling strongly affected N uptake which decreased, according to the phenological stage to 19% of not‐girdled trees. However, almost all the absorbed nitrate was reduced in the roots soon after its absorption in all the trees. The dis...

THEORETICAL ANALYSIS OF RELATIONSHIPS BETWEEN COMPOSITION, pH, AND TITRATABLE ACIDITY OF PEACH FRUIT

ABSTRACT The chemical reactions that determine pH and titration curve of peach (Prunus persica L. Batsch) fruit flesh tissue have been modeled. Fruit pulp pH is computed as the result of acid/base reactions between organic acids, amino acids, and phosphate derivatives, and their respective salts. Amino acids and phosphate derivatives are taken into account as if they comprised asparagine and phosphoric acid respectively. The computations have been validated by a comparison between measured and predicted pH, titration curves, and titratable acidity on fruits of known chemical composition.

Pollination and fruit growth models for studying the management of kiwifruit orchards. I. Models description

Abstract Two models simulating pollination and fruit growth in kiwifruit orchards are described. They are part of a global biotechnical model which aims at studying the effects of planting scheme, pruning intensity and thinning patterns on fruit number and size. The pollination model calculates the amount of pollen grains deposited on pistillate flowers, according to the position of the female vine and the date of anthesis. On this basis, the number of ovules that develop into seeds, and the success of fruit set given this number, are simulated in a stochastic manner. In the fruit growth model, we assumed that the effects of seed number and crop load act at any time in a multiplicative manner on a reference relative growth rate. These two models make it possible to simulate the between-fruit variation in fruit size.

Development of a simulation model for studying kiwi fruit orchard management

Abstract The paper presents a model designed for studying the effect of orchard management on fruit number and size in kiwi fruit plots. It summarises the submodels (previously published) that take place at different levels of organisation (flower/fruit, cane, plant) and compose the global model (flowering of female and male vines, pollination and fruit growth), explains their relationships and focuses on the way technical operations are incorporated. The characteristics of both planting scheme and choice of pollenisers are inputs of the flowering and pollination submodels. Winter pruning options (plant level) modify the inputs of the female flowering model. Thinning (plant level) influences the overlap of female and male flowering (outputs/inputs of the flowering/pollination models) and vine crop load that acts on fruit growth (individual fruit growth model). Irrigation scheduling participates with the rainfall regime to the calculation of a series of water stress effect at the plot level, which is used to affect individual fruit growth rates. After testing the model against real field data, simulations of the model are presented for sake of illustration. They include the effect of climate and of each technique (comparison of contrasted choices) with the other ones controlled on the performance of a reference plot, and an example with several techniques changed together. The results indicate that the model is sensitive both to climate and to changes in technical operations.

Geostatistical method for independent sampling in kiwifruit vine to estimate yield components

Abstract Classically used in mining problems, the semi-variogram function has been tested for its application to kiwifruit (Actinidia deliciosa (A Chev.) C.F. Liang et AR. Ferguson) sampling. The fruit characteristics studied were: weight, dry matter (%), soluble solid content, acidity, and the distance between fruit was taken as the number of “active” forks to go from one fruit to another. It appeared that there was a dependency between samples taken at short distance (i.e., borne by the same lateral) whatever the fruit characteristic under consideration. The variogram function increased with increasing distances, indicating less and less correlations between samples. Fruits were essentially independent where taken from different canes separated by at least two forks. An anomalous feature in fruit weight correlations at h = 8 appeared to be related to the interactions between morphogenesis and pruning in kiwifruit vines, but has a quite small effect in terms of dependency between samples.

Caractérisation des faibles niveaux de radioactivité d'échantillons végétaux par étude de la décroissance. Application au double marquage 32P/35S

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Caractérisation des faibles niveaux de radioactivité d’échantillons végétaux par étude de la décroissance. Application au double marquage 32P/35S Robert Habib, Franck Aries, Roger Guennelon