In vitro mycorrhization of micropropagated plants: studies on Castanea sativa Mill.

In vitro mycorrhization can be made by several axenic and nonaxenic techniques but criticism exists about their artificiality and inability to reproduce under natural conditions. However, artificial mycorrhization under controlled conditions can provide important information about the physiology of symbiosis. Micropropagated Castanea sativa plants were inoculated with the mycorrhizal fungus Pisolithus tinctorius after in vitro rooting. The mycorrhizal process was monitored at regular intervals in order to evaluate the mantle and hartig net formation, and the growth rates of mycorrhizal and nonmycorrhizal plants. Plant roots show fungal hyphae adhesion at the surface after 24 hours of mycorrhizal induction. After 20 days a mantle can be observed and a hartig net is forming although the morphology of the epidermal cells remains unaltered. At 30 days of root–fungus contact the hartig net is well developed and the epidermal cells are already enlarged. After 50 days of mycorrhizal induction, growth was higher for mycorrhizal plants than for nonmycorrhizal ones. The length of the major roots was lower in mycorrhizal plants after 40 days. Fresh and dry weights were higher in mycorrhizal plants after 30 days. The growth rates of chestnut mycorrhizal plants are in agreement with the morphological development of the mycorrhizal structures observed at each mycorrhizal time. The assessment of symbiotic establishment takes into account the formation of a mantle and a hartig net that were already developed at 30 days, when differences between fresh and dry weights of mycorrhizal and nonmycorrhizal plants can be quantified. In vitro conditions, mycorrhization influences plant physiology after 20 days of root–fungus contact, namely in terms of growth rates. Fresh and dry weights, heights, stem diameter and growth rates increased while major root growth rate decreased in mycorrhizal plants.Springe

Agroclimatologie appliquée à la canne à sucre sur l'Ile de la Réunion. : Approches méthodologique et expérimentale en vue de déterminer la contribution des composantes climatiques et de l'apport d'eau à l'élaboration du rendement

L'étude réalisée a pour principal objectif de faire le point sur la valeur et la précision du support de travail dont dispose la recherche sur "agropédoclimat" de la canne à sucre, afin de déterminer une stratégie de recherche efficace. Cette stratégie s'appuiera sur la pratique de l'irrigation qui crée un "agropédoclimat" nouveau dans lequel les besoins en eau de la canne peuvent être entièrement satisfaits

Évaluation en jeune plantation de 2 types de plants de douglas mycorhizés artificiellement par Laccaria laccata S 238 N

Pour évaluer l'intérêt respectif de 2 types de plants de douglas vert mycorhizés artificiellement par Laccaria laccata S 238 N, 4 dispositifs de plantation ont été installés par le CEMAGREF en 1990 et 1991. Des plants naturellement mycorhizés en pépinière et répondant aux normes du Fonds forestier national constituent une modalité témoin (témoin FFN) commune à tous les essais. Un bilan des performances est dressé 3 ans après plantation sur la mortalité, la hauteur et la croissance des plants. Les résultats montrent que les plants artificiellement mycorhizés et de type 1+1 (élevés en 2 ans mais repiqués à 1 an) présentent le meilleur niveau de performance globale. Sur les 4 sites de référence, ils sont 2 fois significativement supérieurs aux plants témoins FFN et 2 fois égaux. Les améliorations constatées portent dans 1 cas sur la survie (+26%) et dans l'autre cas sur la croissance (+20%). Ce dernier résultat est obtenu avec un taux de mycorhization par L laccata S 238 N de seulement 10% en sortie de pépinière. À l'inverse des plants repiqués, les plants de type 2+0, mycorhizés artificiellement mais de moindre qualité extérieure (allure filiforme), présentent un mauvais niveau de performance globale.Early assessment of 2 plant types of Laccaria laccata S 238 N mycorrhizal Douglas fir seedlings in field trials. To assess the respective abilities of 2 plant types of Douglas fir inoculated in nursery seedbeds with Laccaria laccata S 238 N, 4 field trials were established by CEMAGREF in 1990 and 1991. For each experiment, naturally mycorrhizal seedlings matching the "Fonds Forestier National" (FFN) standards were used as controls. Three years after planting, the performance was reviewed on mortality rate, seedling height and height increment, according to the nursery treatment. The results showed that the 2-year-old which had been inoculated in seedbeds transplants performed very well. Indeed, the performance level was significantly improved, compared to the FFN control, in 2 of 4 trials. On the 1st site, survival rate was increased by 26%. On the 2nd site, overall height increment was increased by 20%. The latter result was obtained with a percentage of Laccaria laccata S 238N mycorrhizal short roots of only 10% at lifting. On the 2 other planting sites, there were no significant differences between the 2 nursery treatments. Contrary to the transplants, the 2+0 seedlings, inoculated in seedbeds but lacking sturdiness, revealed a poor overall performance