الفهرس 
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Abstract
Il\YfRODUCTION
Iron deficiency in calcareous or alkaline soils, is a
worldwide problem in limiting production of crops including
annual and perennial legumes. In Egypt, a high proportion of
soil have a pH superior to 7.5 . In agroforestry, nitrogen fixing
trees (NFT) are usually utilized for improving the mtrogen
content of tropical soils and production of forage for animal
feeds. (Galiana et al., 1990 and Sutherland & Sprent, 1993).
Recent observation showed that some species ofleguminous
trees seemed to have good growth in iron limited soils (Dr.
Didier Lesueur, personal communication). Studies on
siderophore - mediated iron uptake by rhizobia to improve
nodulation and N2- fixing activity in legume - rhizobium
symbiosis have attracted an increased number of investigators
(Guerinot, 1991; Crowley et al., 1991; Barton et al., 1996).
The establishing of a large collection of Rhizobium strains
from NFT, isolated from calcareous or alkaline soils, is very
important for increasing the N2- fixing potential of this
symbiosis. The effect of siderophore production by rhizobia
and other root associated microorganisms on growth,
nodulation and iron uptake by leguminous hosts should also be
evaluated. Therefore, this study was planned to examine the
following aspects:
1- Possible relationship between adaptability ofN2-fixing tree
species to Fe stress and siderophore production by root
associated microorganisms
2- Qualitative and quantitative examination of siderophore
production ability amongst rhizosphere microorganisms
with special reference to rhizobia and fluorescent
pseudo monads.
3- Evaluation of possible improvement of N2-fixing tree
legume, sensitive to Fe stress, by using rhizobia effective in
siderophore production.