Raúl Cárdenas-Navarro

Root colonisation by the arbuscular mycorrhizal fungus Glomus intraradices alters the quality of strawberry fruits (Fragaria × ananassa Duch.) at different nitrogen levels

BACKGROUND Arbuscular mycorrhizal fungi (AMF) increase the uptake of minerals from the soil, thus improving the growth of the host plant. Nitrogen (N) is a main mineral element for plant growth, as it is an essential component of numerous plant compounds affecting fruit quality. The availability of N to plants also affects the AMF-plant interaction, which suggests that the quality of fruits could be affected by both factors. The objective of this study was to evaluate the influence of three N treatments (3, 6 and 18 mmol L(-1)) in combination with inoculation with the AMF Glomus intraradices on the quality of strawberry fruits. The effects of each factor and their interaction were analysed. RESULTS Nitrogen treatment significantly modified the concentrations of minerals and some phenolic compounds, while mycorrhization significantly affected some colour parameters and the concentrations of most phenolic compounds. Significant differences between fruits of mycorrhizal and non-mycorrhizal plants were found for the majority of phenolic compounds and for some minerals in plants treated with 6 mmol L(-1) N. The respective values of fruits of mycorrhizal plants were higher. CONCLUSION Nitrogen application modified the effect of mycorrhization on strawberry fruit quality.

Effect of Co-Inoculation with Mycorrhiza and Rhizobia on the Nodule Trehalose Content of Different Bean Genotypes

Studies on Rhizobium-legume symbiosis show that trehalose content in nodules under drought stress correlates positively with an increase in plant tolerance to this stress. Fewer reports describe trehalose accumulation in mycorrhiza where, in contrast with rhizobia, there is no flux of carbohydrates from the microsymbiont to the plant. However, the trehalose dynamics in the Mycorrhiza-Rhizobium-Legume tripartite symbiosis is unknown. The present study explores the role of this tripartite symbiosis in the trehalose content of nodules grown under contrasting moisture conditions. Three wild genotypes (P. filiformis, P. acutifolis and P. vulgaris) and two commercial genotypes of Phaseolus vulgaris (Pinto villa and Flor de Mayo) were used. Co-inoculation treatments were conducted with Glomus intraradices and a mixture of seven native rhizobial strains, and trehalose content was determined by GC/MS. The results showed a negative effect of mycorrhizal inoculation on nodule development, as mycorrhized plants showed fewer nodules and lower nodule dry weight compared to plants inoculated only with Rhizobium. Mycorrhizal colonization was also higher in plants inoculated only with Glomus as compared to plants co-inoculated with both microsymbionts. In regard to trehalose, co-inoculation negatively affects its accumulation in the nodules of each genotype tested. However, the correlation analysis showed a significantly positive correlation between mycorrhizal colonization and nodule trehalose content.

Effects of Nitrogen Source on Growth and Development of Strawberry Plants

ABSTRACT An experiment was conducted to study the effects of nitrate (NO3 −) and ammonium (NH4 +) ratios in nutrient solutions on the growth and production of fruits, runners, and daughter plants of strawberry Fragaria x ananassa Duch., grown in a hydroponic system. Five treatments were applied, consisting of different proportions of NH4 + and NO3 − in the nutrient solution. The NH4 +:NO3 − ratios were: T0 = 0:4, T1 = 1:3, T2 = 2:2, T3 = 3:1, and T4 = 4:0, at a constant nitrogen (N) concentration of 4 mol m−3. Growth and morphogenesis were characterized by monitoring leaf-area increase, number of flowers and fruits per plant, and number of daughter plants of first and second generations. Nitrogen and carbon (C) content were measured at the end of the experiment in the organs of both mother and daughter plants. None of the variables related to the growth of the mother plant was affected by the treatments. However, the number of fruits increased with the proportion of NH4 + in the nutrient solution. The number of daughter plants produced was affected only at high NH4 + proportions, and their size (dry matter per daughter plant) and fertility (number of second-generation plants per first-generation plants) were reduced. The N or C content of the plants was not significantly affected by the treatments, but the C/N ratio in the crowns of mother plants was higher in treatments with 25% and 50% NH4 + in the nutrient solution.

Nitrogen availability drives the effect of Glomus intraradices on the growth of strawberry (Fragaria x ananassa Duch.) plants.

BACKGROUND On the one hand, the critical nitrogen (N) content curve allows the minimal N content necessary for maximum growth rate at any stage of crop development to be predicted. On the other hand, arbuscular mycorrhizal fungi (AMF) transfer N from the soil to the plants and its growth and activity depends on the availability of soil N. Our objective was to investigate how the availability of N in the soil affects growth and the accumulation of N in inoculated strawberry plants. Root colonisation, dry matter accumulation and the critical N% curve were studied during growth of inoculated and non-inoculated strawberry plants grown at several N levels. RESULTS (1) The increase in the availability of N augmented root colonisation by AMF. (2) The effect of AMF on plant growth depended on N availability and the plant developmental status. (3) The critical %N curves were fitted by the following equations: %N = 2.81× (DM)(-0.21) (r² = 0.81) and %N = 2.89× (DM)(-0.32) (r² = 0.80) for inoculated and non-inoculated plants, respectively (where DM is the weight of leaf dry matter, in g plant⁻¹). CONCLUSION N availability was a key factor for root colonisation by AMF and for its contribution to plant growth. The patterns of the critical %N curves suggest that AMF modified the photosynthetic N use efficiency.

Estimating the Nitrogen Concentration of Strawberry Plants from Its Spectral Response

Abstract Estimating the nitrogen (N) status of plants as a function of their spectral response is a promising technique to diagnose and optimize N fertilization. An experiment was conducted in Jiquilpan (Michoacán, México) in which three N levels (0.3, 3, and 20 mM of NO3 − in the irrigation water) were applied to strawberry (Fragaria vesca) in a randomized complete block design with three replicates. The spectral response of strawberry was measured at both the canopy and leaf level using individual wavebands as well as vegetation indices. Individual leaves were separated into three strata (young, mature, and old) and leaf dry matter, leaf area, and N content (% dry matter) were measured in each stratum. Leaf area, biomass, and N content differed significantly between strata. Leaf area, biomass, and N content in all strata were affected by N fertilization. At the canopy level, N content was highly correlated with green reflectance (R550) (r2=0.50) and red reflectance (R680) (r2=0.60) as well as the vegetation indices simple ratio (SR) (r2=0.56), normalized difference vegetation index (NDVI) (r2=0.56), and hyperspectral NDVI (HNDVI) (r2=0.56). For individual leaves, significant differences between strata were found with normalized total pigment to chlorophyll a ratio index (NPCI) and MERIS terrestrial chlorophyll index (MTCI) (p<0.001) as well as R550, photochemical reflectance index (PRI), red edge position (REP), and REP calculated using the MERIS satelite wavelengths (p<0.01). Relationships between spectral indices and N content at the leaf level were found with the youngest leaves only, with NPCI (p<0.01) and MTCI (p<0.05), whereas only R550 responded to N fertilization (p<0.05).

Nitrate Influx in Rose Plants during Day-Night Cycle

ABSTRACT In herbaceous plants grown in controlled environmental conditions nitrate (NO3−) uptake increases during the day and decreases in the night. The aim of this work was to measure NO3− uptake rates along the day-night cycle, in rose (Rosa hybrida L.) plants grown under controlled environmental conditions. Two independent experiments were conducted inside a growth chamber at 20 ºC and 25 ºC, using rose mini-plants cv. Texas, grown in a hydroponic nutrient film technique (NFT) set-up with at 3.0 mol m−3 NO3− concentration. Dry matter and nitrogen (N) accumulation were registered during growth and NO3− uptake rates were measured during a day-night cycle, using 15N as 15NO3−. In both experiments the hourly estimated N-NO3− accumulation rates are near to the measured uptake rates of 15NO3− and nitrate uptake decrease during the day and increase in the night, in contrast with the herbaceous plants. Results are discussed on the basis of N plant demand and carbohydrates availability.