Eighty-two strains of rhizobia were isolated from soils taken from several sites in Mauritania and Senegal. These soil samples were collected from natural stands of Acacia nilotica and Acacia senegal. The soils from Mauritania were less rich in native rhizobia than the soils from Senegal. The strains were characterized using polymerase chain reaction-restriction fragment length polymorphism and by sequencing the rDNA 16S-23S intergenic spacer region (IGS). They were sorted into seven IGS groups. These groups were not associated with the geographical origin of the strains or with the host-plant species at the site where the soils were collected. Most of the strains were in three of the IGS groups (I, IV, and V). One representative strain from each IGS group was sequenced and showed that the strains were from the genus Mesorhizobium. IGS groups I, IV, and VI were close to the species M. plurifarium (AF34563), IGS groups IIand III were close to the species Mesorhizobium sp. (AF510360), IGS group V was close to the species Mesorhizobium sp. (AF510366), and IGS group VII was close to Mesorhizobium sp. (AF510346).
The effect of urea, sulfate ammonium, nitrate potassium and horse manure on S. rolfsii was tested in vitro, alone and in combination with T. harzianum. Tests on liquid culture media showed that Sclerotium rolfsii did not utilize urea as a source of nitrogen while sulfate ammonium and nitrate potassium allowed the growth of the fungus. On a solid medium, the fertilizers at rates of 12 g N•m-2 and 18 g N•m-2 had an inhibitory effect on the growth of Sclerotium rolfsii mycelium. The highest effect was observed for urea. In contrast, Trichoderma harzianum assimilated all fertilizers but had a preference for sulfate ammonium. The antagonistic activity of Trichoderma harzianum on Sclerotium rolfsii on solid culture media was stimulated in the presence of the three nitrogen sources. The horse manure at high rates inhibited the growth of S. rolfsii, favored the development of T. harzianum and enhanced its antagonistic effect on S. rolfsii. The confrontation of Trichoderma harzianum with sclerotia of Sclerotium rolfsii in soil fertilized separately with urea, sulfate ammonium, nitrate potassium or manure showed an increase in the antagonistic activity. Particularly, the manure in combination with T. harzianum induced high mortality of sclerotia of the fungus. In the agronomic context of the region of Doukkala, it seems adequate to add these nitrogen sources to contribute to the biological control of Sclerotium rolfsii.
. Rôle des champignons mycorhiziens à arbuscules de zones arides dans la résistance du trèfle (Trifolium alexandrinum L.) au déficit hydrique. Agronomie, EDP Sciences, 2000, 20 (3) Résumé -La tolérance du trèfle mycorhizé (Trifolium alexandrinum L.) à la sécheresse diffère selon les isolats de champignons mycorhiziens associés à la plante hôte. Cinq isolats fongiques ont été isolés à partir des sols de palmeraies marocaines et étudiés pour leur aptitude à améliorer la tolérance du trèfle au stress hydrique. L'application d'une contrainte hydrique de 30 % de la capacité au champ réduit sévèrement la progression des champignons mycorhiziens dans le cortex racinaire du trèfle. Les isolats provenant de la palmeraie d'Aoufous sont moins affectés par le dessèche-ment du sol que les Glomus et Sclerocystis d'Agdz. L'effet de la mycorhization quant à l'amélioration de la production de biomasse du trèfle est bien apparu dans le cas d'infection par les isolats fongiques d'Aoufous et le Glomus mosseae (souche de référence provenant de l'INRA de Dijon, France). Ces mêmes champignons mycorhiziens ont permis au trèfle de maintenir sa teneur en eau, son potentiel hydrique et sa transpiration foliaire à des valeurs élevées par rapport au témoin non inoculé. Les valeurs de la résistance des stomates et du déficit de saturation en eau sont restées plus faibles chez les plantes mycorhizées que chez les plantes non mycorhizées. On note également, que les isolats du complexe d'Aoufous et le Glomus mosseae se sont montrés les plus agressifs dans la colonisation des racines du trèfle et ce quel que soit le niveau du traitement hydrique imposé au sol. Les isolats fongiques provenant des sols de la palmeraie d'Aoufous se sont montrés aussi efficaces que Glomus mosseae. mycorhize / croissance / relation hydrique / sécheresse / zone aride Abstract -Effect of arbuscular mycorrhizal fungi on drought resistance of clover. Tolerance of mycorrhized clover (Trifolium alexandrinum L.) to drought depends on the arbuscular mycorrhizal fungi associated to the host plant. Five arbuscular mycorrhizal fungi isolates were collected from five Moroccan date palm grove's soils and were investigated for their ability to improve the plant tolerance to water deficit stress. Applying a constraint of 30% field capacity reduces severely the mycorrhizal rate in the root cortex of most of the tested isolates. Fungi collected from Aoufous
Effects of salt stress in hydroponic media on clover plants inoculated with Rhizobium. The application of salt stress in hydroponic conditions on clover seedlings (Trifolium alexandrinum L.) inoculated with Rhizobium affected the nodulation starting from 2 g NaCl•l -1 , whereas the growth began to be reduced only from 4 g•l -1 . The growth of shoots was reduced by about 20% at 4 g•l -1 and 44% at 6 g•l -1 . The development of the root system was less sensitive. This depressive effect on the growth was accompanied by biochemical and ultrastructural modifications. The soluble protein content of the leaves fell by about 75% at 6 g•l -1 of NaCl. Proline and soluble sugars accumulated mainly in leaves, where they probably contributed to the osmotic adjustment phenomena. The transport and/or the utilization of starch was affected, so it accumulated in the chloroplasts. Salt stress also caused disorganization of the thylakoid membranes and an accumulation of lipidic globules inside the chloroplasts. clover / Rhizobium / salt stress / nodulation / growth Résumé -L'application d'un stress salin en milieu hydroponique à des plantules de trèfle (Trifolium alexandrinum L.) inoculées par le Rhizobium affecte la nodulation à partir de 2 g•l -1 NaCl alors que la croissance ne l'a été qu'à partir 4 g•l -1 . La croissance pondérale de la partie aérienne a été réduite de 20 % à 4 g•l -1 et de 44 % à 6 g•l -1 . Le développement du système racinaire a été moins sensible. Cet effet dépressif sur la croissance s'est accompagné de modifications biochimiques et ultrastructurales. La teneur en protéines foliaires solubles a chuté d'environ 75 % à 6 g•l -1 de NaCl. La proline et les sucres solubles se sont significativement accumulés dans les feuilles sous l'effet du sel. Ils participeraient aux phénomènes d'ajustement osmotique. Le transport ou/et l'utilisation de l'amidon ont été perturbés causant son accumulation dans les chloroplastes. Le stress salin a provoqué aussi une désorganisation des membranes thylakoïdiennes et une accumulation de globules lipidiques au niveau du stroma.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.