Abstract

AGUIRRE-MEDINA, Juan F.; MINA-BRIONES, Francisco O.; CADENA-INIGUEZ, Jorge  and  SOTO-HERNANDEZ, Ramón M.. Effectiveness of biofertilizers and brassinosteroids in Stevia rebaudiana Bert. Agrociencia [online]. 2018, vol.52, n.4, pp.609-621. ISSN 2521-9766.

The demand for low-calorie products has increased. One of them is a natural product extracted from stevia (Stevia rebaudiana Bert.) whose diterpene glucosides generate outstanding sweetening power. The organic cultivation of this species is increasing in the southern region of Chiapas, México, but its asexual establishment through cuttings presents agronomic limitations. This can be improved with the incorporation of biofertilizers. It is the case of the efficiency in N fixation by Azospirillum brasilense and the endomycorrhizae Rhizophagus intraradices, which improve the transport of nutrients and water to the host plant. These microorganisms have been used in biofertilizer induction programs in annual and perennial crops in México. The objective of this study was to evaluate the effect of R. intraradices (Schenck & Sm.) Walker & Schüßler and A. brasilense Tarrand, Krieg & Döbereiner in interaction with brassinosteroids in S. rebaudiana Bert. plants through morphological, physiological and biochemical changes. The cv Morita 2 was established in a greenhouse, in plastic bags with 6 kg of fluvisol-euthric soil plus washed river sand (1:1) and 4 g of each inoculant at the moment of transplant. The concentration of A. brasilense was 9X106 bacteria g-1 and that of R. intraradices 40 spores g-1 of soil with 95 % colonization of the root system. The brassinosteroid (CIDEF-4, Natura del Desierto, S. A. de C.V., steroid content 80 % with 10 % i.a.) (2 mg L-1 of water) was sprayed on the foliage after 28 d of sowing, plus three later applications with frequency of 14 d. The experimental design was completely random with seven repetitions; the treatments were the microorganisms and the brassinosteroid applied individually and combined, and the control without application or with inoculum. The experimental unit was one pot. The variables recorded were yield, percentage of mycorrhizae root colonization, content of sweetener in leaves, and of N and P in shoots 90 d after sowing. The inoculated plants and treated with brassinosteroid in different modality increased the leaf area (1728 cm2 per plant), content of stevioside (35.8 mg g-1), rebaudioside (29.5 mg g-1) and steviol (5 mg g-1) compared to the control (p≤0.05). The content of N and P increased with the application of R. intraradices alone and combined with brassinoesteroid.

Keywords : Rhizophagus intraradices; Azospirillum brasilense; brassinosteroid; steviosides; nitrogen and phosphorus.

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