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Appl. Environ. Microbiol., Feb 1995, 456-460, Vol 61, No. 2
JM Ruiz-Lozano, R Azcon and M Gomez
The tolerance of lettuce plants (Lactuca sativa L. cv. Romana) to drought
stress differed with the arbuscular-mycorrhizal fungal isolate with which
the plants were associated. Seven fungal species belonging to the genus
Glomus were studied for their ability to enhance the drought tolerance of
lettuce plants. These fungi had different traits that affected the drought
resistance of host plants. The ranking of arbuscular-mycorrhizal fungal
effects on drought tolerance, based on the relative decreases in shoot dry
weight, was as follows: Glomus deserticola > Glomus fasciculatum >
Glomus mosseae > Glomus etunicatum > Glomus intraradices > Glomus
caledonium > Glomus occultum. In this comparative study specific
mycorrhizal fungi had consistent effects on plant growth, mineral uptake,
the CO(inf2) exchange rate, water use efficiency, transpiration, stomatal
conductance, photosynthetic phosphorus use efficiency, and proline
accumulation under either well-watered or drought-stressed conditions. The
ability of the isolates to maintain plant growth effectively under water
stress conditions was related to higher transpiration rates, levels of leaf
conductance, and proline, N, and P contents. Differences in proline
accumulation in leaves among the fungal symbioses suggested that the fungi
were able to induce different degrees of osmotic adjustment. The
detrimental effects of drought were not related to decreases in
photosynthesis or water use efficiency. Neither of these parameters was
related to P nutrition. The differences in P and K acquisition,
transpiration, and stomatal conductance were related to the mycorrhizal
efficiencies of the different fungi. Our observations revealed the
propensities of different Glomus species to assert their protective effects
during plant water stress. The greater effectiveness of G. deserticola in
improving water deficit tolerance was associated with the lowest level of
growth reduction (9%) under stress conditions. The growth of plants
colonized by G. occultum was reduced by 70% after a progressive drought
stress period. In general, the different protective effects of the
mycorrhizal isolates were not associated with colonizing ability.
Nevertheless, G. deserticola was the most efficient fungus and exhibited
the highest levels of mycorrhizal colonization, as well as the greatest
stimulation of physiological parameters.
Copyright © 1995, American Society for Microbiology
Effects of Arbuscular-Mycorrhizal Glomus Species on Drought Tolerance: Physiological and Nutritional Plant Responses
Departamento de Microbiologia del Suelo and Departamento de Agroecologia, Estacion experimental del Zaidin (CSIC), Apartado 419, 18080 Granada, Spain
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