Research Article: Maize responsiveness to Azospirillum brasilense: Insights into genetic control, heterosis and genomic prediction

Date Published: June 7, 2019

Publisher: Public Library of Science

Author(s): Miriam Suzane Vidotti, Filipe Inácio Matias, Filipe Couto Alves, Paulino Pérez-Rodríguez, Gregório Alvarado Beltran, Juan Burgueño, José Crossa, Roberto Fritsche-Neto, Kandasamy Ulaganathan.


Several studies have shown differences in the abilities of maize genotypes to facilitate or impede Azospirillum brasilense colonization and to receive benefits from this association. Hence, our aim was to study the genetic control, heterosis effect and the prediction accuracy of the shoot and root traits of maize in response to A. brasilense. For that, we evaluated 118 hybrids under two contrasting scenarios: i) N stress (control) and ii) N stress plus A. brasilense inoculation. The diallel analyses were performed using mixed model equations, and the genomic prediction models accounted for the general and specific combining ability (GCA and SCA, respectively) and the presence or not of G×E effects. In addition, the genomic models were fitted considering parametric (G-BLUP) and semi-parametric (RKHS) kernels. The genotypes showed significant inoculation effect for five root traits, and the GCA and SCA were significant for both. The GCA in the inoculated treatment presented a greater magnitude than the control, whereas the opposite was observed for SCA. Heterosis was weakly influenced by the inoculation, and the heterozygosity and N status in the plant can have a role in the benefits that can be obtained from this Plant Growth-Promoting Bacteria (PGPB). Prediction accuracies for N stress plus A. brasilense ranged from 0.42 to 0.78, depending on the scenario and trait, and were higher, in most cases, than the non-inoculated treatment. Finally, our findings provide an understanding of the quantitative variation of maize responsiveness to A. brasilense and important insights to be applied in maize breeding aiming the development of superior hybrids for this association.

Partial Text

In recent years, several Plant Growth-Promoting Bacteria (PGPB) have been isolated, and their beneficial effects on the production of phytohormones and biological nitrogen fixation (N) have been identified [1,2]. The presence of these mechanisms permits certain strains to be used commercially as inoculants, which is a sustainable alternative to the use of chemical fertilizers and to mitigate biotic and abiotic stress. In this context, the species belonging to the genus is Azospirillum sp. have been extensively studied for agricultural purposes due to the excellent potential for response in association with cereal crops, such as maize [3]. The use of Azospirillum sp. in cropping areas increase up to 30% the grain yield and reduce up to 25% in N fertilizer needs [4,5]. Other beneficial effects of its use include the ability to modulate the root architecture, leading to a greater exploration of the soil and root expansion to deeper soil layers improving the access to water and nutrients [6,7].

We verified a quantitative inheritance of the maize responsiveness to A. brasilense, and that both additive and dominance genetic effects are involved the genetic control of this association. Furthermore, the heterozygosity and N status in the plant could influence the regulation of A. brasilense benefits to the plant. Prediction accuracies showed moderate to high values indicating an opportunity for genomic selection of traits related to the maize- A. brasilense partnership in the early stages of the plant development. Finally, our results may support possible plant breeding strategies to explore the genetic variability among maize genotypes relative to their differential ability to allow the colonization by A. brasilense and take advantage of this beneficial interaction.




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