Modifications in root morphology are important strategies to maximize soil exploitation under phosphorus starvation in plants. Here, we used two multiple interval models to map QTLs related to root traits, biomass accumulation and P content in a maize RIL population cultivated in nutrient solution. In addition, we searched for putative maize homologs to PSTOL1, a gene responsible to enhance early root growth, P uptake and grain yield in rice and sorghum. Based on path analysis, root surface area was the root morphology component that most strongly contributed to total dry weight and to P content in maize seedling under low-P availability. Multiple interval mapping models for single (MIM) and multiple traits (MT-MIM) were combined and revealed 13 genomic regions significantly associated with the target traits in a complementary way. The phenotypic variances explained by all QTLs and their epistatic interactions using MT-MIM (23.4 to 35.5 %) were higher than in previous studies, and presented superior statistical power. Some of these QTLs were coincident with QTLs for root morphology traits and grain yield previously mapped, whereas others harbored ZmPSTOL candidate genes, which shared more than 55 % of amino acid sequence identity and a conserved serine/threonine kinase domain with OsPSTOL1. Additionally, four ZmPSTOL candidate genes co-localized with QTLs for root morphology, biomass accumulation and/or P content were preferentially expressed in roots of the parental lines that contributed the alleles enhancing the respective phenotypes. QTL mapping strategies adopted in this study revealed complementary results for single and multiple traits with high accuracy. Some QTLs, mainly the ones that were also associated with yield performance in other studies, can be good targets for marker-assisted selection to improve P-use efficiency in maize. Based on the co-localization with QTLs, the protein domain conservation and the coincidence of gene expression, we selected novel maize genes as putative homologs to PSTOL1 that will require further validation studies.

Maximizing soil exploration through modifications of the root system is a strategy for plants to overcome phosphorus (P) deficiency. Genome-wide association with 561 tropical maize inbred lines from Embrapa and DTMA panels was undertaken for root morphology and P acquisition traits under low- and high-P concentrations, with 353,540 SNPs. P supply modified root morphology traits, biomass and P content in the global maize panel, but root length and root surface area changed differentially in Embrapa and DTMA panels. This suggests that different root plasticity mechanisms exist for maize adaptation to low-P conditions. A total of 87 SNPs were associated to phenotypic traits in both P conditions at −log₁₀(p-value) ≥ 5, whereas only seven SNPs reached the Bonferroni significance. Among these SNPs, S9_137746077, which is located upstream of the gene GRMZM2G378852 that encodes a MAPKKK protein kinase, was significantly associated with total seedling dry weight, with the same allele increasing root length and root surface area under P deficiency. The C allele of S8_88600375, mapped within GRMZM2G044531 that encodes an AGC kinase, significantly enhanced root length under low P, positively affecting root surface area and seedling weight. The broad genetic diversity evaluated in this panel suggests that candidate genes and favorable alleles could be exploited to improve P efficiency in maize breeding programs of Africa and Latin America.

The beetle Anthonomus grandis Boheman, 1843, is the main cotton pest, causing enormous losses in cotton. The breeding of genetically modified plants with A. grandis resistance is seen as an important control strategy. However, the identification of molecules with high toxicity to this insect remains a challenge. The susceptibility of A. grandis larvae to proteins (Cry1Ba, Cry7Ab, and Mpp23Aa/Xpp37Aa) from Bacillus thuringiensis Berliner, 1915, with toxicity reported against Coleopteran, has been evaluated. The ingestion of different protein concentrations (which were incorporated into an artificial diet) by the larvae was tested in the laboratory, and mortality was evaluated after one week. All Cry proteins tested exhibited higher toxicity than that the untreated artificial diet. These Cry proteins showed similar results to the control Cry1Ac, with low toxicity to A. grandis, since it killed less than 50% of larvae, even at the highest concentration applied (100 μg·g⁻¹). Mpp/Xpp proteins provided the highest toxicity with a 0.18 μg·g⁻¹ value for the 50% lethal concentration. Importantly, this parameter is the lowest ever reported for this insect species tested with B. thuringiensis proteins. This result highlights the potential of Mpp23Aa/Xpp37Aa for the development of a biotechnological tool aiming at the field control of A. grandis.

Plant growth-promoting rhizobacteria (PGPR) can ensure the sustainability of agricultural growth. The objectives of this study were to characterize and determine the effects of Bacillus subtilis, isolate IMA Bs/170005, applied as co-inoculant in the soybean planting furrow. In all treatments, the seeds had been pre-inoculated with Bradyrhizobium japonicum. The experiments were carried out in a greenhouse, and in the field. Different doses of formulated (8.10⁸ spores mL^-1) product with B. subtilis (0; 0.2; 0.4; 0.8; 1.2; 1.6 and 2.0 L ha^-1) were tested. The isolate proved efficient for in vitro auxin production. Under greenhouse conditions, the response to B. subtilis co-inoculation consisted of an increase of up to 26% in length of the root system. In the field, co-inoculation in the furrow proved beneficial for crop growth and yield and can be recommended. The best response rate was 0.4 L ha^-1. At this dose, averaged over 20 and 40 days after sowing and compared to the control with Bradyrhizobium inoculation alone, increases of 5.3% were observed for plant height, 14.8% for shoot fresh weight, 14.1% for shoot dry weight, 8.5% for root dry weight and 6.5% for soybean yield, demonstrating the efficiency of this B. subtilis isolate as a PGPR.

The main objective of this study was to characterize the toxicity and genetic divergence of 18 Bacillus thuringiensis strains in the biological control of Spodoptera eridania. Bacterial suspensions were added to the S. eridania diet. Half of the selected B. thuringiensis strains caused high mortality seven days after infection. The genetic divergence of B. thuringiensis strains was assessed based on Enterobacterial Repetitive Intergenic Consensus (ERIC) and Repetitive Extragenic Palindromic (REP) sequences, and five phylogenetic groups were formed. Despite their genetic diversity B. thuringiensis strains did not show any correlation between the collection sites and toxicity to larvae. Some B. thuringiensis strains are highly toxic to S. eridania, thus highlighting the potential of their endotoxins as biopesticides.

O Complexo Quarentenário IAC tem como atribuição, efetuar a quarentena de materiais vegetais que serão introduzidos no Brasil por empresas privadas ou instituições públicas, com objetivo de pesquisa científica. Os materiais são analisados quanto a agentes patogênicos, bem como semeados em casa de vegetação para análise do crescimento e verificar possíveis sintomas de patógenos. Alguns vírus, bactérias e fungos, presentes em materiais importados, requerem técnicas de diagnóstico e rastreabilidade cada vez mais aprimoradas. A partir de novembro de 2012 foram iniciadas as implementações para promover o desenvolvimento desse trabalho dentro de uma moderna estrutura, baseada em modelos quarentenários internacionais. Incluindo adaptações das casas de vegetação, câmaras frias, organização e montagem de novos laboratórios para as análises dos materiais, dessa forma, novas metodologias foram estudadas e aplicadas, como as técnicas envolvendo biologia molecular (PCR). Para complementar a eficiência das análises realizadas em quarentena vegetal, foram elaborados testes mais específicos e precisos. Para um melhor resultado e maior segurança, as análises são feitas dentro do complexo do Quarentenário IAC.