Control of Pathogenic Mycorrhizal Fungi in Maintenance of Soil Productivity by Crop Rotation

Abstract

Pathogenic mycorrhizal fungi may be a major reason crops must be rotated to maintain soil productivity. We studied the role such fungi may have in the maintenance of productivity of soil for tobacco (Nicotiana tabacum L.) by rotation with tall fescue (Festuca amndinacea Schreb). Tall fescue ‘Kentucky 31’ and continuous tobacco plots were established on a central Kentucky field previously shown to be infested with the mycorrhizal fungus Glomus macrocarpum Tul and Tul., the cause of a stunt disease of tobacco. Fumigation with 67% methyl bromide‐33% chloropicrin (MBC, trichloronitromethane) covered with plastic was used as a control. Rotation with fescue for 2 yr and fumigation both reduced disease incidence when tobacco was planted on all plots the third year. Effects of rotation and fumigation were not additive, indicating that both control the same disease agent. Only G. macrocarpum, of three mycorrhizal fungi present in high populations, was associated with the disease. Rotation and fumigation controlled mycorrhizal colonization of roots and the build‐up of populations of G. macrocarpum in the root zones of plants. Mycorrhizal fungi should be considered in research on the effects of crop rotation on productivity.

Functioning of mycorrhizal associations along the mutualism–parasitism continuum*

“…An extreme example of a mycorrhizal fungal association that decreases plant performance is observed in an intensively managed agricultural system in Kentucky, USA . A series of field and glasshouse studies has shown that colonization of tobacco by an endemic isolate of Glomus macrocarpum significantly reduces root length, aboveground biomass, and fiowering (Modjo & Hendrix 1986;Jones & Hendrix, 1987;Modjo, Hendrix & Nesmith, 1987;Hendrix, Jones & Nesmith, 1992). Although this isolate of G. macrocarpum is strongly parasitic (pathogenic) on tobacco in field soils with extremely high P, it does not appear to have parasitic effects on other crops.…”

“…Although this isolate of G. macrocarpum is strongly parasitic (pathogenic) on tobacco in field soils with extremely high P, it does not appear to have parasitic effects on other crops. Furthermore, it appears to have some specificity for tobacco because, in field studies, G. macrocarpum populations (and stunt-disease) can be controlled by rotation with Festuca (containing an endophyte that inhibits G. macrocarpum) as effectively as by fumigation (Hendrix et al, 1992;An, Guo & Hendrix, 1993;Hendrix, Guo & An, 1995).…”

Diversity and classification of mycorrhizal associations

“…Mycorrhizal associations have been considered to be parasitic in cases where the costs outweigh the benefits, as occurs in several cropping systems (Hendrix, Jones & Nesmith, 1992;Johnson et al, 1997). However, crops that benefit from mycorrhizas may eventually replace those that do not, because of crop rotation or the implementation of sustainable agricultural systems.…”

The influence of crop rotation and soil fumigation on a mycorrhizal fungal community associated with soybean

“…Fredeen and Terry (1988) observed stunting of soybean roots and shoots by Glomus fasciculatum. In barley (Black and Tinker 1979) and tobacco (Hendrix et al 1992), a negative relationship between colonization and yield has been observed. Other instances of plant stunting by mycorrhizal fungi have been observed (Tinker 1978;Modjo and Hendrix 1986).…”