No abstract

Fenpropimorph and fenhexamid are sterol biosynthesis inhibitor (SBI) molecules widely used to control diseases in agriculture. Both molecules, at increasing concentrations, have been shown to impact on the non-target arbuscular mycorrhizal (AM) fungi. Root colonization, spore production and mycelium architecture, including the branched absorbing structures which are thought to be involved in phosphorus (P) uptake, were affected. In the present study, we investigated the capacity of Glomus sp. MUCL 43204 to take up, transfer and translocate labelled P to Medicago truncatula in the presence of these SBI molecules. We used a strict in vitro cultivation system associating an autotrophic plant of M. truncatula with the AM fungus. In addition, the effects of both SBI molecules on the proportion of hyphae with alkaline phosphatases (ALP), succinate dehydrogenase (SDH) activity and on the expression of the mycorrhiza-specific plant phosphate transporter MtPT4 gene were examined. We demonstrated that the two SBI molecules impacted the AM fungus. This was particularly evidenced for fenpropimorph. A decrease in P transport and ALP and SDH activities associated with the extraradical mycelium and MtPT4 expression level was noted. These three factors were closely related to the development of the AM fungus, suggesting a direct impact not only on the AM fungal growth but also on the physiology and metabolic activities of the AM fungus. These results further emphasized the interest on the autotrophic in vitro culture system as an alternative to pot experiments to investigate the mechanisms behind the impact of disease control molecules on the non-target AM fungal symbionts.

Special liming materials have the potential to control soil acidity and constitute a source of nutrients for plant development. In this study, the efficiency of special liming materials was evaluated. Their effects in soil exchangeable cations and available P concentrations were compared with the ones of dolomitic limestone (DL). Samples of Typic Distrudept and Rhodic Hapludox were collected from 0 to 20 cm layer. Two experiments were conducted in a completely randomized block of 4x4x8 factorial design. Four liming materials were studied: DL, granulated micronized calcite (GMC), granulated micronized dolomite (GMD) and carbonated suspension (CS). The liming materials were added to the soils doses that increase the soil bases saturation (V) to 50, 70 and 90%; and a control treatment. The treated soil samples were incubated at 23 ± 2°C and 60% of soil water retention capacity for eight periods (0, 7, 15, 30, 45, 60, 75 and 90 days). Exchangeable Ca, Mg and K, and available P were determined. All liming materials increase exchangeable Ca and Mg, and available P. However, the most efficient source that increased exchangeable Ca in the studied soils were CS followed by GMC.

Soil acidity has been the major limiting factor to farming activities in the tropics and subtropics. The objective of this study was to verify the efficacy of special liming materials, when compared with the dolomitic limestone, regarding the correction of soil acidity with variable charge in controlled conditions. Samples of a Typic Dystrudept and Rhodic Hapludox were collected from a of layer 0-20 cm, and used to carry out two experiments in a completely randomized design of 4 x 4 x 8 factorial design. Four liming materials were studied: dolomitic limestone (DL), granulated micronized calcite (GMC), granulated micronized dolomite (GMD) and carbonated suspension (CS). After they have been characterized, each liming material was added to the soils using doses that aimed to increase the base saturation (V) to 50, 70 and 90% and a control treatment was included. The treated soil samples were incubated at 23 ± 2°C and 60% soil water retention capacity for eight periods (0, 7, 15, 30, 45, 60, 75 and 90 days). The attributes active (pH), potential (H+Al) and exchangeable (Al 3+) acidity and V were evaluated. The special liming materials GMC and CS were efficient enough to reduce the active potential and exchangeable acidity, and increase V in soils with variable charge.