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

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 inves tigated. Seven weeks after inoculation under a bed soil kept at 25 degrees C/20 degr ees C (day/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 plant s were taller, produced more shoots, accumulated more dry matter and attain ed higher P concentration in both shoots and roots than the noninoculated p lants. Under a constant 15 degrees C bed soil for 4 weeks followed by an elevation to 25 degrees C/20 degrees C, shoot elongation was promoted in AM fungus-i nfected plants, especially after the third emergence; the effect was more p ronounced 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 degrees C, shoot growth after the fou rth emergence became restricted in noninoculated plants, whereas shoot emer gence and elongation were promoted, especially after the fifth and fourth e mergences in GM and in GR plots, respectively. Eleven weeks after inoculati on, AM fungus infection levels reached 66.3% in GM and 36.7% in GR. All mea sured parameters in AM fungus-infected plants were larger than in the nonin oculated plants; the effect appeared significantly greater in GM than in GR plots. These results reveal that the asparagus seedlings infected with AM fungus t olerated greater temperature stress through symbiosis and that the degree o f tolerance differed with the fungal species.