Abstract
ABSTRACT The common bean has been considered to have low biological nitrogen fixation capacity; however, this process can be made more effective with molybdenum (Mo) supplementation. The objective of this study was to evaluate the influence of Mo rates on the growth and biological nitrogen fixation by two Brazilian common bean cultivars using the 15N isotope dilution technique. The experiment was performed in 2014 in a completely randomized design arranged in a 5 x 3 factorial scheme, corresponding to 5 rates of Mo (control, 40, 80, 120 and 240 g ha-1), the common bean cultivars Aporé, Ouro Negro and NORH-54 (a non-nodulating common bean cultivar), and three replicates. The application of Mo and the inoculation with rhizobia strains contributed to improving nitrogen fixation and grain weight. The cultivar Ouro Negro showed a higher number and weight of nodules and a higher amount of nitrogen derived from the atmosphere than the cultivar Aporé. The biological nitrogen fixation of Aporé was more dependent on the application of Mo. These results indicated that inoculation with Rhizobium strains and Mo supply effectively contributed to biological nitrogen fixation and improving grain production.
Highlights
The common bean (Phaseolus vulgaris L.) is a staple food in many Latin American and African countries, regarded as a primary source of daily proteins and minerals
The cultivars Aporé and Ouro Negro presented hundreds of nodules, while the non-nodulating cultivar formed an insignificant number (Table 1), indicating that inoculation with the selected Rhizobium strain was effective for producing nodules in the common bean, contributing to N supply and helpful in improving grain production
Some studies indicate that indigenous rhizobia strains are not efficient in common bean biological N2 fixation (BNF), and these strains could hinder the introduction of more efficient strains (Vieira, 1998a), which is usually attributed to the lack of competitiveness against indigenous rhizobia, environmental conditions and plant genetic factors (Piha & Munns, 1987; Hardarson et al, 1993)
Summary
The common bean (Phaseolus vulgaris L.) is a staple food in many Latin American and African countries, regarded as a primary source of daily proteins and minerals. The carioca and black common bean group are the two most consumed types in Brazil (Vogt et al, 2013), cultivated mainly by small holder farmers. The common bean has been considered to have low biological N2 fixation (BNF) capacity compared to other legumes, such as soybean (Piha & Munns, 1987). The common bean can form symbiosis with a wide range of indigenous rhizobia, these rhizobia have been considered low efficiency for BNF, in addition to having a short vegetative fixation period (Piha & Munns, 1987). Inoculating the common bean with selected rhizobia strains could increase the N2 fixation, as expressed by higher N content in plant tissues, demonstrated by Hungria et al (2003) and Kimura et al (2004)
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