Some characteristics of Rhizobium leguminosarum isolates from uninoculated field-grown lentil

Abstract

A total of 229 Rhizobium leguminosarum isolates from the lentil-growing region of West Asia-North Africa (WANA) were evaluated for their symbiotic effectiveness and for salt and heat tolerance. These included 65 isolates from the ICARDA culture collection, strains from international collections, and fresh isolates from soils and nodules of lentil (Lens culinaris L.) growing in Turkey, Syria, Jordan and Egypt.

Enumeration of rhizobia populations in lentil fields of Egypt, Jordan and Turkey using most probable number (MPN) technique indicated a range of 3.1 × 101 to 6.9 × 105 viable rhizobia g−1 soil. Only 13% of the 61 soils sampled contained < 103 cells g−1, while 20% of soils had > 105 rhizobia g−1. Lentil fields in Jordan contained higher average population densities than other areas evaluated.

The symbiotic effectiveness of all collected isolates was evaluated on lentil cv. ILL 16 in an aseptic N-free hydroponic gravel culture system. A greater proportion (up to 50%) of highly effective isolates was found in samples from eastern Turkey and Jordan: samples from Syria and Egypt mainly contained rhizobia with moderate to poor N2 fixing capacity. Of the isolates collected from all locations, 44% were of low effectiveness; only 21% were classified as superior fixers.

Distinct variations in salt and heat tolerance were observed for isolates from different regions. A greater proportion of Egyptian isolates and international standard strains grew at 35°C. Only 9 of 229 isolates grew at 40°C; 8 of these came from the southern Nile valley in Egypt. Isolates from Jordan and Turkey were more sensitive to 0.5% NaCl in the growth medium than the others, of which 30–50% were tolerant. Few isolates grew with 1.0% NaCl: most of these came from Syria. None of the heat- or salt-tolerant isolates was among the most effective N2 fixers.