No abstract

Phosphorus (P) deficiency is a major constraint in highly weathered tropical soils. Although phosphorous rock reserves may last for several hundred years, there exists an urgent need to research efficient P management for sustainable agriculture. Plant hormones play an important role in regulating plant growth, development, and reproduction. Humic substances (HS) are not only considered an essential component of soil organic carbon (SOC), but also well known as a biostimulant which can perform phytohormone-like activities to induce nutrient uptake. This review paper presents an overview of the scientific outputs in the relationship between HS and plant hormones. Special attention will be paid to the interaction between HS and plant hormones for nutrient uptake under P-deficient conditions.

Seed germination events modulate microbial community composition, which ultimately influences seed to seedling growth performance. Here we evaluate the germinated maize (variety SHS 5050) root bacterial community of disinfected seed (DS) and non-disinfected seed (NDS). Using a gnotobiotic system, sodium hypochlorite (1.25%, 30 min) treated seeds showed a reduction of bacterial population size and an apparent increase of bacterial community diversity associated with a significant selective reduction of Burkholderia related sequences. The shift in the bacterial community composition in DS negatively affects germination speed, seedling growth, and reserve mobilization rates compared with NDS. A synthetic bacterial community (syncom) formed by twelve isolates (9 Burkholderia spp.; 2 Bacillus spp. and 1 Staphylococcus sp.) obtained from natural microbiota maize seeds herein were capable of recovering germination and seedling growth when reintroduced in DS. Overall results showed that changes in bacterial community composition and selective reduction of Burkholderia related members dominance interfere with germination events and initial growth of the maize plantlets. By cultivation-dependent and independent approaches, we deciphered seed-maize microbiome structure, bacterial niches location, and bacterial taxa with relevant roles in seedlings growth performance. A causal relationship between seed microbial community succession and germination performance open opportunities in seed technologies to build-up microbial communities to boost plant growth and health.

Effective microorganisms (EM) are inoculants formed by fungi and bacteria isolated from soil. EM are commonly used by farmers on agronomic crops to stimulate plant growth, but their composition and their benefi ts has been controverted. This study aimed to analyze the diversity of microorganisms growing in three EM inoculants, as well as to evaluate their effi ciency in the germination of palisade grass seeds. The total DNA of the three EM inoculants was extracted, the 16S rRNA and ITS genes were amplifi ed by PCR and sequenced on the Illumina MiSeq platform. Germination tests were conducted with three type of the EM, in three concentration and two times of the immersion. The bacterial group was the most abundant in EM, followed by fungi. Bacterial operational taxonomic units OTUs were shared by all EMs. Pre-treatments of palisade grass seeds with EMs resulted in a higher germination percentage (% G) and germination speed index (IVG) when EM was used at concentration of 1 or 2% in water. Seed immersion for 5 min was more effi cient than immersion for 24 h. We can conclude that EM of different origin can share microbial groups and diversity of microorganisms, besides being an alternative to increase palisade grass seeds germination.

Seeds are reservoirs of beneficial and harmful microorganism that modulates plant growth and health. Here, we access seed to seedling bacteriome assembly modified by seed-disinfection and the underlined effect over maize germination performance and root-seedlings microbial colonization. Seed-disinfection was performed with sodium hypochlorite (1.25%, 30 min), resulting in a reduction of the cultivable-dependent fraction of seed-borne bacteria population, but not significantly detected by real-time PCR, microscopy, and biochemical analysis of the roots on germinated seeds. 16S rRNA sequencing revealed that the seed and root bacteriome exhibited similar diversity and did not differ in the structure concerning seed-disinfection. On the other hand, the abundance reduction of the genera f_Enterobacteriaceae_922761 (unassigned genus), Azospirillum, and Acinetobacter in disinfected-seed prior germination seems to display changes in prominence of several new taxa in the roots of germinated seeds. Interestingly, this reduction in the bacteriome negatively affected the germination speed and growth of maize plantlets. Additionally, bacteriome re-shape increased the maize var DKB 177 susceptible to the seed-borne plant pathogen Penicillium sp. Such changes in the natural seed-borne composition removed the natural barrier, increasing susceptibility to pathogens, impairing disinfected seeds to germinate, and develop. We conclude that bacteria borne in seeds modulate the relative abundance of taxa in the root, promote germination, seedling growth, and protect the maize against fungal pathogens.