Temperature-stress tolerance of asparagus seedlings through symbiosis with arbuscular mycorrhizal fungus

Abstract

Temperature-stress tolerance through symbiosis with arbuscular mycorrhizal (AM) fungi [Gigaspora margarita (GM) and Glomus sp. R10 (GR)] in seedlings of asparagus (Asparagus officinalis L., cv. Mary Washington 500W) was investigated. Seven weeks after inoculation under a bed soil kept at 25 °C/20 °C (clay/night) under a 16-hr photoperiod, AM fungus-infection levels in a root system reached 63.0% in GM and 20.0% in GR. AM fungus-infected plants were taller, produced more shoots, accumulated more dry matter and attained higher P concentration in both shoots and roots than the noninoculated plants. Under a constant 15 °C bed soil for 4 weeks followed by an elevation to 25 °C/20 °C, shoot elongation was promoted in AM fungus-infected plants, especially after the third emergence; the effect was more pronounced in GR than in GM plots. Eleven weeks after inoculation, AM fungus infection levels reached 48.9% in GM and 58.9% in GR. Plant height, no. of shoots, no. of crowns, dry weight, and phosphorus concentration in shoots and roots became greater in AM fungus-infected plants than in noninoculated ones. When bed soil was heated to 30 °C, shoot growth after the fourth emergence became restricted in noninoculated plants, whereas shoot emergence and elongation were promoted, especially after the fifth and fourth emergences in GM and in GR plots, respectively. Eleven weeks after inoculation, AM fungus infection levels reached 66.3% in GM and 36.7% in GR. All measured parameters in AM fungus-infected plants were larger than in the noninoculated plants; the effect appeared significantly greater in GM than in GR plots. These results reveal that the asparagus seedlings infected with AM fungus tolerated greater temperature stress through symbiosis and that the degree of tolerance differed with the fungal species.