Endomycorrhizal Fungal Survival in Continuous Corn, Soybean, and Fallow

Abstract

of propagules, and grow rapidly (Menge, 1985). Arbuscular mycorrhizal fungal species that adapt to a wide Survival of arbuscular mycorrhizal (AM) fungi in soil may be afrange of hosts and edaphic contingencies presumably fected by the presence or absence of crops and by the crop being grown. Field studies were conducted in central Iowa during three have a better chance of long-term survival. One means growing seasons with cropping to continuous corn (Zea mays L.) by which AM fungi survive is the production of spores (two cultivars), continuous soybean [Glycine max (L.) Merr.] (two although the length of survival of spores in field soils cultivars), or fallow in three soils to determine AM selection and under varying conditions is not well documented. Presurvival. The initial numbers of spores (all following soybean) in May sumably, when conditions are favorable, these spores 1996 averaged 0.9 g Ϫ1 soil in Clarion (well drained), 1.1 in Nicollet germinate, grow, and produce other fungal structures. (somewhat poorly drained), and 3.6 in Webster (poorly drained) soils. Many cornfields, especially in low-lying areas, exhib-In May 1998, the highest spore count average was 11.2 g Ϫ1 soil in Webster under corn and 3.0 spores g Ϫ1 under soybean. Nicollet soil ited stunting and purple coloration characteristic of seaveraged 6.8 spores g Ϫ1 for corn and 0.9 for soybean in May 1998, vere P deficiency in the fall following the central U.S. whereas Clarion soil had 6.3 for corn and 2.0 for soybean. The fallow floods of summer 1993 (Fixen et al., 1994). Plants treatments consistently had low spore counts, ranging from 0.7 to 1.0 seemed not to be absorbing sufficient P for fast early spores g Ϫ1 for all three soils. After 3 yr under the same cropping growth even though soil tests indicated adequate P. regime, spore numbers in soil were corn Ͼ soybean Ͼ fallow; no Farmers were advised to use 35 to 40 kg P ha Ϫ1 as starter significant differences were found between cultivars of the same crop. fertilizer in areas that had been flooded the previous Most probable number counts were correlated with spore counts and averaged 11% of spore counts, suggesting that only a portion of the year. Ellis (1998) conducted a survey to determine the spores were viable (or culturable in our determination). By the end status of AM fungal populations in areas that were of the study, Glomus albidum and G. etunicatum dominated under flooded in 1993 and reported a decline in AM fungal corn, whereas G. constrictum dominated under soybean.

Distribution of Arbuscular Mycorrhizal Fungi in Upland Field Soil of Japan: 2. Spore Density of Arbuscular Mycorrhizal Fungi and Infection Ratio in Soybean and Maize Fields

“…One way to achieve an increased spore density would be to shorten the period of bare ground (Isoi, 1997;Isobe and Tsuboki, 1999;Usuki and Yamamoto, 2003). However, because the density of AM fungi spores greatly varies with the species and cultivar of the crop, the crop type and the crop system (Troeh and Loynachan, 2003;Usuki and Yamamoto, 2003), it is necessary to understand the correlation between spore production and the type of crop. It is anticipated that the composition of the species of the AM fungi differs with the sampling site.…”

“…We need to determine whether this negative relationship between available phosphorus content of soil and the density of AM fungal spores or the infection ratio holds true in various soil types and environmental conditions. In addition, because the density of AM fungal spores varies with the crop under cultivation (Isobe and Tsuboki, 1999;Troeh and Loynachan, 2003;Usuki and Yamamoto, 2003), soil samples from upland fi elds of various crops need to be examined. The density of AM fungal spore varied with the kind of cultivated crop in the sampling field (Isobe et al, 2007).…”

Advances in Molecular Diversity of Arbuscular Mycorrhizal Fungi (Phylum Glomeromycota) in Forest Ecosystems

“…According to Rosendahl (2008), quantitative studies of arbuscular mycorrhizal fungal communities based on the presence of spore numbers are complicated as some species produce few spores on the mycelium, whereas species such as G. intraradices, G. versiforme or G. fasciculatum produce hundreds of spores on the same hypha. Another technique, the Most Probable Number (MPN) method is a microbiological approach that allows the detection of AMF species which do not produce www.intechopen.com spores (Troeh & Loynachan, 2003) by soil dilution. However, there are several experimental variables which may influence the final estimations.…”

Farming System and Management

“…With soybean, plant growth promoting rhizobacteria (PGPR) such as rhizobia and Bacillus form symbiosis (Bai et al, 2003;Cattelan et al, 1999;Gray & Smith 2005), and arbuscular mycorrhizal (AM) fungi form symbiosis, too (Troeh & Loynachan, 2003). The AM fungi increase N2 fixation (Antunes et al, 2006).…”

“…Soybean is influenced by a biologic factor. Soybean forms symbiosis not only rhizobia but also arbuscular mycorrhizal (AM) fungi (Antunes et al, 2006;Troeh & Loynachan, 2003). The biologic factors such as nematodes, soil-borne diseases become the problem in soybean.…”