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Abstract
Acacia saligna trees and 9 different wild herbaceous legumes grown in El-Ahrash protectorate, North Sinai, were surveyed for nodulation. Sixty five rhizobia were isolated from naturally occurring root-nodules of Acacia saligna trees and the different wild annuals. According to their cultural, morphological and physiological characteristics as well as SDS-PAGE of total cell proteins, the isolates were phenotypically categorized into two distinct groups. The first includes those isolated from Acacia saligna which were differentiated into three distinct clusters. The second group comprises isolates from wild annual legumes; analysis of their phenotypic characters building dendrograms divided them into two distinct clusters. Eight rhizobial isolates representing the various Acacia-rhizobia clusters were examined for inoculation of Acacia saligna seedlings grown in sandy soil plastic bags under sunlight or shade conditions. After 6 months, all seedlings, whether inoculated or not, formed from 4 to 87 nodules seedling-1 with lower number recorded with uninoculated seedlings. In the sunny nursery, Ac22p and Ac18p were the most infective isolates inducing the formation of up to 87 and 75.6 nodules seedlings-1 with maxima nodule biomass, shoot and root length and biomass. Shading severely affected nodulation of Acacia seedlings either with indigenous or introduced rhizobia. Uninoculated seedlings formed 17 nodules seedling-1under sunlight and 4.4 nodules seedling-1under shade conditions. Seedlings grown in the shaded nursery showed a very poor growth after 6 months. A promoting effect on growth of Acacia seedling roots was displayed by the isolates Ac-22p, Ac-23s, Ac-17s and Ac-17f where significantly taller roots were recorded with seedlings drenched with these bacterial inocula. For the first time in Egypt, sugarcane bagasse pith was used as rhizobia inocula carrier. Data recommended pre-sterilization of bagasse pith incorporated in the inocula formula. Survival of rhizobia in pith-based inocula was good or better than that recorded with peat based inocula. Instead of the imported Irish peat moss, the present data recommend sugarcane bagasse pith for rhizobial inoculant formulation.