Maturity at harvest influenced storage life of guava (Psidium guajava L.) fruit kept at 3.5, 7, or 11C and 80% or 88% RH. Quality characteristics considered were firmness, pH, titratable acidity, ascorbic acid and soluble solids concentrations, and weight loss. Chilling injury was observed only in guavas harvested at the mature-green stage and kept at 3.5 or 7C. The storage life of fruit kept at 11C was reduced due to fungal attack. The best results were obtained with guavas harvested at the color-turning stage followed by storage at 7C and 80% RH for 3 weeks. These fruits had good appearance 5 days after removal from storage.
Roberto I. Vazquez-Ochoa and Maria T. Colinas-Leon
Elvia Hernández-Gómez, Luis A. Valdez-Aguilar, Ana M. Castillo-González, María T. Colinas-León, Donita L. Cartmill, Andrew D. Cartmill and R. Hugo Lira-Saldívar
The uptake of nitrogen (N) in nitrate or ammonium (NH4 +) form affects physiological and metabolic processes and toxicity may develop in plants receiving high concentrations of NH4 +. The objective of the present study was to delineate the response of bell pepper plants to varying proportions of NH4 + combined with increasing concentrations of potassium (K) in the nutrient solution. Bell pepper plants were tolerant to moderate proportions of NH4 + (25% or less or 50% or less); however, higher proportions resulted in growth reduction. The application of higher K concentrations in the nutrient solution did not ameliorate the growth on vegetative plant parts; however, when K was increased to 9 mm, the yield was sustained even when 50% of total N was in the NH4 + form. Decreased shoot:root ratio and harvest index indicated that biomass accumulation was affected more in the shoot than in the root and in the fruit than in the shoot, respectively. There was a lower concentration of NH4 + in the roots compared with leaves, suggesting that the higher K concentration that resulted from the increased K in the nutrient solution was associated with NH4 + translocation through the xylem. A decrease in calcium and magnesium detected in leaves suggests an antagonistic relationship with NH4 + and K in the nutrient solution, which was correlated with the acidification of the growing medium. Higher yields when K was at 9 mm may be the result of the high photosynthetic rate and stomatal conductance (g S) detected in plants fertigated with 25% of total N as NH4 + and the higher leaf water potential when the proportion of NH4 + was 50%. The biochemical composition of fruits was affected because both high NH4 + and increased K resulted in higher ethylene production, lipid peroxidation, superoxide dismutase activity, and carotenoids.
Nadia Jiménez-Peña, Luis A. Valdez-Aguilar, Ana M. Castillo-González, María T. Colinas-León, Andrew D. Cartmill and Donita L. Cartmill
The domestication of wild orchids for commercial production is a new endeavor, which may represent a sustainable alternative to the collection/harvest from natural populations of threatened or endangered orchid species. In the present study, the growth and nutrition of vegetative plants of Laelia anceps Lindl. as affected by three components of the growing medium (peat, volcanic rock, and/or horticultural grade charcoal) and the nutrient solution concentration, measured as osmotic potential (ψS), were assessed using mixture experiments methodology. Leaf dry mass (DM) was the highest when plants were irrigated with nutrient solutions of –0.076 MPa. The lower leaf DM at lower or higher ψS was influenced by the medium because plants grown in 100% volcanic rock exhibited no effect, whereas plants grown in either 100% charcoal or 100% peat had a marked reduction. Regardless of the ψS of the nutrient solution, the highest leaf DM was observed in mixtures of two components containing charcoal and peat at high proportions. Dry mass of pseudobulbs and roots was highest in plants irrigated with solutions of –0.051 MPa, especially in mixtures with charcoal or 100% peat. Decreasing the ψS of the nutrient solution resulted in increased shoot nitrogen (N) and potassium (K) concentrations and decreased concentration of phosphorus (P), calcium (Ca), magnesium (Mg), boron (B), manganese (Mn), zinc (Zn), and copper (Cu). Increasing charcoal proportion in the growing media resulted in increased plant iron (Fe) and Cu concentration. However, increasing volcanic rock reduced plant P and K and increased Mn concentration. A higher proportion of peat was correlated with a decrease in plant Fe concentration. Leaf DM fit models on which macronutrient:micronutrient or micronutrient:micronutrient ratios were calculated, suggesting that nutrient imbalance may be responsible for a plant’s responses. The coefficients with the higher values included a micronutrient:micronutrient ratio, suggesting that an extremely fine balance in the uptake of a given micronutrient in relation to other micro- or macronutrient is of major importance for adequate growth of Laelia.