Effect of constant and diurnally fluctuating temperatures on arbuscular mycorrhizal fungus infection and the growth of infected asparagus (Asparagus officinalis L.) seedlings

Abstract

Effect of constant and diurnally fluctuating temperatures on arbuscular nycorrhizal (AM) fungi [Glomus elunicatum (GE) and Gigaspora margarita (GM)] infection and the promotion of infected seedling growth through asparagus AM fungus symbiosis were investigated. 1. At constant temperatures spore germination rate became maximum at 25 °C in GE, and at 25 °and 30 °C in GM. Hyphal growth was enhanced at 20 °, 25 °and 30 °C in GE, and at 25 °, 30 °and 35 °C in GM. 2. Under constant bed soil of 20 °, 25 °and 30 °C for 8 weeks after inoculation, there was no growth enhancement at 20 °C regardless of the AM fungus species, whereas at 25 °and 30 °C, the GE- and GM-inoculated plants were taller than the noninoculated plants. At 30 °C, the GM-inoculated plants were taller than those inoculated with GE. At 25 °C, the GE or GM-inoculated plants had the most shoots and storage roots than did those at other temperatures. The rate of AM fungus-infected portions in a whole root system (as percentage of the total portions infected with AM fungus is a whole root system) was maximum at 25 °C in GE-inoculated plants but at 25 °and 30 °C in GM-inoculated ones. 3. Under the bed soil temperature conditions diurnally fluctuating in the range of 25 °C to 15 °C and 30 °C to 18 °C, 8 weeks after inoculation, the plants were taller and had more numerous shoots and storage roots in GE-inoculated plants than in GM-inoculated ones in a regime between 25 °C and 15 °C, the reverse was noted in a regime between 30 °C and 18 °C. Little difference in the rate of AM fungus-infected portions in a whole root system was recognized between the two temperature regimes in GE-inoculated plants, whereas in GM-inoculated ones, the rate became higher at the temperature fluctuated between 30 °C and 18 °C than it did at the temperature fluctuated between 25 °C and 15 °C. Consequently, it seems that in asparagus, the optimum temperature range for infection and the plant growth enhancement through symbiosis differed between Glomus etunicatum and Gigaspora margarita.