Seleção de genótipos mesoamericanos e andinos de feijoeiro em resposta à inoculação com rizóbio

Abstract

The use of the diversity of common bean (Phaseolus vulgaris L.) germplasm collections can provide materials with higher contribution of biological nitrogen fixation. The aim of this study was to identify, in germplasm bank of Embrapa Rice and Beans, common bean genotypes of Mesoamerican and Andean origin with potential for obtaining N2 by rhizobia inoculation. The evaluation consisted of two screenings of 879 genotypes in greenhouse. Further, 15 of these genotypes and two commercial cultivars were evaluated under field conditions. Greenhouse experiments were conducted in randomized block design with three replications in which 879 genotypes were evaluated in response to inoculation with commercial Rhizobium strains (SEMIA 4077, SEMIA 4080, SEMIA 4088). The cultivar Ouro Negro was used as reference. Pre-germinated seeds were seeded in 3 L pots with sterile sand and vermiculite. Plants were inoculated seven days after emergence (DAE), and sterile Norris solution without N was added weekly. The number of nodules, nodule dry weight and one nodule dry weight were determined 35 DAE. The percentage of genotypes that exceeded the reference was established, as 21% for number of nodules, 46% for nodule dry weight and 32% for one nodule dry weight. We selected 116 genotypes, which were evaluated in other experiment. A joint analysis of the data obtained in the first and second phases for these 116 genotypes was performed, and 15 genotypes were selected. These 15 genotypes and the commercial cultivars Pérola and Ouro Negro were evaluated at field conditions under two N sources, inoculation with rhizobia or fertilization with 80 kg N ha-1. Five experiments were carried out in Santo Antônio de Goiás – GO, Ponta Grossa – PR and Seropédica – RJ. A split plot design in randomized complete block was used with N sources as main plots and genotypes as sub-plots. The nodulation, plant biomass, and grain yield were evaluated, and in some experiments the BNF contribution by 15N natural abundance technique and ureides sap content were also assessed. There were differences between genotypes and regions. All genotypes had nodules even under mineral N. The most efficient genotypes in nodulation and in obtaining N by biological fixation were CNF 0011234, CNF 0011028, CNF 0011559 and PI 387865, Andean genotypes, and CNF 0011075, CNF 0011137, CNF 0011240, PI 325750, Mesoamerican genotypes. The natural abundance of 15N technique showed that the Mesoamerican genotypes had higher contribution of N2 fixation. Most genotypes showed similar grain yields to commercial cultivars. The most pronounced differences between the genotypes and cultivars were detected in the experiment in GO in 2013 winter and the greatest similarities in 2014 winter. Most of the genotypes did not have grain yield differences between the two N sources. The fertilized genotypes had grain yields ranging from 167 to 3567 kg ha-1 and inoculated genotypes ranging from 180 to 3307 kg ha-1. In both cases, the lowest values of grain yield were found in PR, and the highest values in the winter of 2014 in GO, reflecting the average yield obtained in each location.