Root system characteristics of Marandu palisadegrass supplied with nitrogen and magnesium rates

The development of root system of forage grasses is influenced by the supply of mineral nutrients. The experiment was carried out in a greenhouse in Piracicaba, São Paulo State, with the objective of evaluating the effect of nitrogen and magnesium rates on dry mass yield, total length and surface, specific length and surface, and concentrations of nitrogen, magnesium, calcium and potassium in the root system of Brachiaria brizantha Stapf. cv. Marandu. It was studied five rates of nitrogen (2, 9, 16, 23 and 30 mmol L-1) and five rates of magnesium (0.05, 0.70, 1.35, 2.00 and 2.65 mmol L-1) in nutrient solutions in an incomplete 5² factorial arrangement, which resulted in the following combinations: 2/0.05; 2/1.35; 2/2.65; 9/0.70; 9/2.00; 16/0.05; 16/1.35; 16/2.65; 23/0.70; 23/2.00; 30/0.05; 30/1.35 and 30/2.65. The experimental design was a randomized block with four replications. Plants had two growth periods, and after the second harvest the roots were separated from the plant tops. Combination of the high rates of nitrogen and magnesium resulted in expressive increases in rooty dry matter yield, in the length and in the root surface of marandu palisadegrass. High rates of nitrogen and magnesium resulted in short root specific length and surface. Combinations of high rates of nitrogen and magnesium increased nitrogen concentration or decreased potassium concentration in the roots. Calcium concentration in the roots was increased by nitrogen rates and decreased by magnesium rates. Magnesium rates resulted in increase in magnesium concentration in the roots of marandu palisadegrass

Impact of antifungals producing rhizobacteria on the performance of Vigna radiata in the presence of arbuscular mycorrhizal fungi

Plant growth-promoting rhizobacteria (PGPR) that produce antifungal metabolites are potential threats for the arbuscular mycorrhizal (AM) fungi known for their beneficial symbiosis with plants that is crucially important for low-input sustainable agriculture. To address this issue, we used a compartmented container system where test plants, Vigna radiata, could only reach a separate nutrient-rich compartment indirectly via the hyphae of AM fungi associated with their roots. In this system, where plants depended on nutrient uptake via AM symbiosis, we explored the impact of various PGPR. Plants were inoculated with or without a consortium of four species of AM fungi (Glomus coronatum, Glomus etunicatum, Glomus constrictum, and Glomus intraradices), and one or more of the following PGPR strains: phenazine producing (P+) and phenazine-less mutant (P-), diacetylphloroglucinol (DAPG) producing (G(+)) and DAPG-less mutant (G(-)) strains of Pseudomonas fluorescens, and an unknown antifungal metabolite-producing Alcaligenes faecalis strain, SLHRE425 (D). PGPR exerted only a small if any effect on the performance of AM symbiosis. G(+) enhanced AM root colonization and had positive effects on shoot growth and nitrogen content when added alone, but not in combination with P+. D negatively influenced AM root colonization, but did not affect nutrient acquisition. Principal component analysis of all treatments indicated correlation between root weight, shoot weight, and nutrient uptake by AM fungus. The results indicate that antifungal metabolites producing PGPR do not necessarily interfere with AM symbiosis and may even promote it thus carefully chosen combinations of such bioinoculants could lead to better plant growth