Constant advances in studies on the behavior of maize genotypes and their interactions with the environment are of great importance for the best performance of the plant. This study verifies effects and causes of agronomic variables of maize hybrids on grain yields and performs the indirect selection of superior genotypes by principal component analysis (PCA). Two hundred and thirty maize genotypes were used, with two hundred and twenty--nine topcross hybrids (consisting of crossings of two hundred and twenty-nine partially inbred genotypes with a tester) and one check in a randomized block design with two repetitions. The genotypes were evaluated during the 2016 and 2016/2017 crops considering the agronomic variables plant height, ear insertion height, ear position, lodging, breakage, and grain yield. Data were submitted to analysis of variance and means were compared by the Scott-Knott test (p<0.05) with subsequent multivariate exploratory analysis by PCA. In the principal component analysis, components explained 52.07% and 55.69% of the variance contained in the original variables for the 2016 and 2016/2017 crops, respectively. The variable that was most significant in both crops was ear insertion height, allowing the indirect selection of more productive genotypes. Indirect selection of the most productive genotypes was also conducted through variables that contributed significantly in the principal component analysis. Thus, the use of multivariate exploratory analysis is efficient in the characterization and selection of maize genotypes evaluated in different crop seasons.

Maize has a high nitrogen demand; as a result, more sustainable alternatives are needed to reduce demand for mineral fertilizers. This study aimed to evaluate and characterize the agronomic performance of maize genotypes submitted to topdressing nitrogen fertilization and inoculation with Azospirillum brasilense. An experiment was conducted in the second season of 2017, in Jaboticabal-SP (Brazil), using 48 maize genotypes in a randomized block design. Treatments consisted of: 1) application of 140 kg ha-1 nitrogen, using urea as mineral fertilizer; 2) A. brasilense inoculation via soil, at a rate of 600 mL ha-1, as biological fertilization. Grain yield and agronomic traits were evaluated. The data were subjected to analysis of variance (F-Test), means were compared by Scott-Knott test at 5% probability, and multivariate statistical analysis was performed by principal component analysis. A. brasilense inoculation via soil has a significant effect on female flowering, on the interaction between genotype versus N supply for Fusarium spp., and increases the maize grain yield; however, the responses of agronomic attributes vary with genotype. Highlights The inoculation with Azospirillum brasilense via soil increases maize grain yield, becoming viable and more sustainable alternative in the supply of nitrogen. The choice of the genotypes is an essential fator for the sucessful use of Azospirillum brasilense application or mineral fertilization, because the responses of agronomic attributes vary with the genotype. The most contrasting genotypes can be recombined in new stages of crossbreeding and selection, aiming at obtaining genotypes with greater yield potential in the use of Azospirillum brasilense inoculation. Further studies are needed to better understand this technology under conditions with different genotypes, soils and production systems.

Sugarcane yellow leaf virus (ScYLV), Polerovirus, Luteoviridae, is one of the main viruses that infect sugarcane worldwide. The virus is transmitted by the aphid Melanaphis sacchari in a persistent, circulative manner. To better understand the interactions between ScYLV, sugarcane genotypes and M. sacchari, we explored the effect of sugarcane cultivars on the feeding behavior and biological performance of the vector. The number of nymphs, adults, winged, total number of aphids and dead aphids was assayed, and an electrical penetration graph (EPG) was used to monitor the stylet activities. Multivariate analysis showed changes in the vector’s behavior and biology on cultivars, identifying specific groups of resistance. In the cultivar 7569, only 5.5% of the insects were able to stay longer on sustained phloem ingestion, while in the other seven cultivars these values varied from 20% to 60%. M. sacchari showed low phloem activities in cultivars 7569 and Bio266. Overall, cultivar 7569 showed the worst biological performance of aphids, with the insects presenting mechanical difficulties for feeding and a shorter duration of the phloem period, and thus being considered the most resistant. We conclude that ScYLV virus infection in different sugarcane cultivars induced specific changes in the host plant, modifying the behavior of its main vector, which may favor or impair virus transmission.

Objetivou-se avaliar e caracterizar o desempenho agronômico de genótipos de milho submetidos a dois fornecimentos de nitrogênio (químico e biológico). O experimento foi conduzido na em segunda safra 2017 e primeira safra 2017/2018, utilizando-se 48 genótipos de milho. Foram adotados dois manejos de fornecimento de nitrogênio em cobertura, sendo eles (1) aplicação de 140 kg ha-1 de nitrogênio mineral em cobertura e (2) inoculação com Azospirillum brasilense (600 mL ha-1 via solo). Os dados foram submetidos a análises exploratórias multivariadas de agrupamento, por método hierárquico, e de componentes principais. Foram identificados quatro grupos, associando as maiores produtividades de grãos com plantas com maior altura e as menores produtividades com período de florescimento curto, plantas com menor altura a com maiores taxas de quebramento e acamamento. Os dois primeiros componentes principais explicaram 70,67% e 66,54% da variabilidade total dos dados para a inoculação com A. brasilense e adubação nitrogenada em cobertura, respectivamente. As análises exploratórias de dados são ferramentas eficientes na caracterização, seleção e agrupamento de genótipos superiores e contrastantes de milho aos manejos de fornecimento de nitrogênio.