Description et modélisation de la croissance et du développement du pommier (Malus x domestica Borkh.) I. Structure la plus probable de l'arbre jeune

Description and modelisation of growth and development of appletree (Malus x domestica Borkh.). I. Most probable structure of young tree. Based on the observation of all or, at least, a large number of shoots growing on unpruned apple trees, cv. Cox's Orange Pippin and Jonagold grafted on EM9, an original codification system has been conceived. It allows to locate and identify quickly and unequivocally any shoot or growth. From a comprehensive collection of such codified observations, the most probable structure of young one to five year old trees has been established, with the amount and characters of the different observed shoot types. Both varieties display very similar gross structures, despite minor differences in form, flowering mode and productivity. The development of the trees occurs in two phases. The first one builds up a frame composed by the trunk and several storied sets of branches. Flowering is rather strictly alternate during this phase. The second one consists in the reinforcement of the branches by axillary growth, but even more by sympodial branching due to increasing and repeated terminal flowering. This basic structure provides a reference to appreciate changes in tree development brought about by rootstock, fruit load or training practices

Qualité de validation des modèles de régression logisitique binaire

peer reviewedIn this paper, we summarize a study of the quality of validation given by binary logistic regression models. We have studied the effect of the proportion of events (ie proportion of individuals having the code 1) and the way of using data for selecting variables and fitting a model. In particular, we show the interest of leading those two steps separately or not. Artificial data were used to carry out this study. We show that proportion of events influences the quality of the models. Especially, this effect is great when the proportion is very low (5% in our study). We also meet problems like non-convergence of the algorithm when trying to fit a model. However, quality is much better when a proportion equal to 25% or 50% is used. For the latter one, precision of the estimations is even a little bit better and the others studied factors have no effect. The simulations also show that separating selection and fitting is not an interesting strategy because we never obtain a good quality. Difference of quality is however close to 10 per cent.Dans cet article, on étudie la qualité de validation des modèles de régression logistique binaire. En particulier, on s’intéresse à l’effet de la proportion d’individus ayant le caractère étudié (c’est-à-dire le code 1) sur cette qualité. De même, on évalue l’intérêt qu’il peut y avoir à séparer ou non les étapes de sélection et d’ajustement sur deux échantillons indépendants. L’ensemble de l’étude est basée sur des données simulées. La proportion d’individus codés 1 a une influence sur la qualité des modèles. Cet effet est d’autant plus important que la proportion est très faible. Des situations de non-convergence ont d’ailleurs été rencontrées. Par contre, la qualité des modèles est assez constante pour les proportions 25% et 50%. Pour cette seconde modalité, la précision des estimations est un peu meilleure et surtout l’effet des autres facteurs étudiés s’estompe. Par ailleurs, les simulations ont montré que la séparation des étapes de sélection et d’ajustement ne conduisent jamais à une meilleure qualité de validation des modèles. Au contraire, cette qualité est généralement moins bonne mais l’écart n’est que de l’ordre de 10%

Guide diagram for the computerizing of an agricultural exploitation

peer reviewe