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

Abstract

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.

Corn Responsiveness to Azospirillum: Accessing the Effect of Root Exudates on the Bacterial Growth and Its Ability to Fix Nitrogen

“…Even though sugars are reported as the main class of root-released compounds by plants [ 13 , 14 ], in the present study, this trend has not been confirmed, as our root exudates contained 60% of amino acids, followed by 30% sugars and 10% organic acids. This contrasting result may be related to the high rates of amino acids released by plant roots at early growth stages, as we sampled the plants at seedling stages [ 15 ].…”

“…Therefore, further researches on the role of root exudates as mediators of the corn- Azospirillum symbiosis need to be carried out, including regarding the amino acids classes, as despite their null chemotaxis, they seemed to be determinant in the degree of the benefits provided by A. brasilense. Additionally, rather than being the cause of the responsiveness, root exudates are more likely to reflect the specificity of transcriptional signaling involved in the mutual recognitions between Azospirillum and its host plant [ 12 , 13 ].…”

“…Part of it has been attributed to genotypic variation of the host genetic background, including the composition of the metabolites it releases toward the rhizosphere [ 12 ]. Crops genotypes, including corn, may differ in the amount and the composition of their exudates, but the implications of this for the rhizosphere colonization by Azospirillum , or for the benefits it provides to plants, remain a poorly-understood subject [ 13 ].…”

Hybrid Breeding for MLN Resistance: Heterosis, Combining Ability, and Hybrid Prediction

“…For the GP of the hybrid's performance, we used a two-stage approach [13], where, in the first stage, the phenotypes were corrected for the experimental design effects, and in the second stage, the prediction models were fitted using the adjusted phenotypes. The details of the model and steps in implementation are explained in our earlier study [51]. In brief, this method is based on the commonly used additive effect model.…”

Diallelic Analysis of Tropical Maize Germplasm Response to Spontaneous Chromosomal Doubling

“…The larger proportion of the mean squares of the GCA compared to SCA for HMF and HF suggests that the additive genetic effect was the main contributor to their inheritance in the F1 hybrids in the two evaluated environments. In a diallel experiment with a fixed-effects model, even though the estimates of additive and dominance variances are less important [ 26 ], the GCA–SCA ratio (GSR) proposed by Baker [ 27 ] (Baker’s ratio) is frequently used in several studies [ 28 , 29 , 30 ] to determine the relative importance of GCA and SCA. If the Baker’s ratio is close to 1, then GCA is predominant for a given trait.…”