Phaseolus vulgaris cultivar and Rhizobium strain variation in acid-pH tolerance and nodulation under acid conditions

Abstract

Acid-soil pH is a major factor limiting nodulation and N 2 fixation in beans. The experiments reported here sought strains of Rhizobium and cultivars of Phaseolus vulgaris L. tolerant of acid pH, and to study the interaction of strains and cultivars differing in pH tolerance. Seventy-eight of 217 isolates of R. leguminosarum bv. phaseoli grew on modified Keyser-Munns medium, pH 4.5. Of these, 33 grew at pH 4.5 in the presence of 100 μM aluminum and 40 tolerated pH 4.5 medium containing 200 μM manganese. Twenty isolates were both highly efficient in nitrogen (N 2) fixation and acid-pH-tolerant. Marked variation was also evident in the growth and nodulation at pH 4.5 of 126 cultivars of Phaseolus vulgaris. Thus ‘Capixaba precoce’, ‘Preto 143’ and ‘Bico de Ouro’ had high nodule number and nodule mass plant −1 when grown at this pH, whereas BAT115 and BAT165 were essentially without nodules. When host cultivars and Rhizobium strains which differed in acid pH tolerance were used in inoculation experiments in soil of pH 4.5, nodulation and plant growth were most affected when both host and Rhizobium were intolerant of low pH. this was associated with reduced multiplication of Rhizobium in the rhizosphere 2 days after planting and with lack of attachment of the Rhizobium to the host root. Competition for nodule sites at acid pH was also affected. When either the Rhizobium strain or the cultivar was acid-tolerant, nodulation and plant development were similar to that achieved when both host cultivars and Rhizobium strain were acid-pH-tolerant.