Determination of the Critical Level of Saline Stress in Yellow Passion Fruit Seedlings with Two Phenological Phases
摘要
Salinity is a serious environmental problem affecting yellow passion fruit (Passiflora edulis Sims) among other crops. The knowledge of the phenological stage, level and time of exposure of plants to stress is essential to identify tolerant genotypes. The morphophysiological responses of five P. edulis accessions to saline stress were evaluated with seedlings at two stages of development (1–2 and 4–5 leaves) and six electrical conductivities (ECw: 2 dS m−1 of the nutrient solution; 3, 6, 9, 12 and 15 dS m−1 of the nutrient solution + NaCl) to select the seedling stage, dose and discriminatory characteristics to identify tolerant Passiflora spp. The experiment was carried out in a semi-hydroponic setting, with a completely randomized design and a 6 × 2 factorial scheme. The data were subjected to descriptive and multivariate analysis. No significant differences were observed in relation to the stages of development, but seedlings with 4–5 leaves showed less variation in aerial and root growth. Salinity had a negative influence on morphophysiological characteristics from 3 dS m−1 onwards, with more marked decreases in growth and dry matter accumulation at 9 dS m−1 compared to the control (2 dS m−1 of nutrient solution). The threshold level of 9 dS m−1 also caused an increase in internal carbon and reductions of transpiration, stomatal conductance, photosynthesis, chlorophyll and stomatal functionality. Principal component analysis revealed no differences between the P. edulis accessions under 9 dS m−1. Ten characteristics were selected for the evaluation and discrimination of salinity tolerance in Passiflora spp. and the use of 30-day-old plants (4–5 leaves) under 9 dS m−1 and 21 days of exposure is recommended for the rapid selection of genotypes.