5.2.82
BIOCONTROL OF SOILBORNE PATHOGENS OF MAIZE AND POTATO BY INOCULATION WITH VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI (GLOMUS SP.)

RJ HANSFORD, JA RAMOS-ZAPATA, C LEIFERT, I ALEXANDER, and JM DONALD

Department of Plant and Soil Science, University of Aberdeen, Aberdeen, Scotland

Background and objectives
Vesicular-arbuscular mycorrhizal fungi produce associations with many important crop species. They usually result in beneficial effects on the growth of colonised plants. These factors include enhanced nutrient uptake and biocontrol of soilborne pathogens. The aim of this study was to determine if colonisation by commercial preparations of Glomus species would be advantageous to the growth of two important crops, maize (Zea mays) and potato (Solanum tuberosum sp. tuberosum) . In maize it is well established that VAM colonisation causes enhanced growth over uninoculated plants [1], however, relatively little is known about colonisation of potato.

Methods and results
In the first part of this study a greenhouse experiment was done to determine whether Glomus intaradices could prevent or reduce the levels of the maize pathogen Fusarium culmorum. Maize seeds were planted in pots containing G. intaradices-inoculated soil, which were then infected, or not, with F. culmorum. Four weeks after planting there were no significant differences (P<0.05) in root and shoot weights between the pathogen inoculated and uninoculated (control) plants [2]. This indicated that VAM colonisation provides a protective effect during weaning against F. culmorum. Due to the lack of knowledge about colonisation of potato by VAM fungi, especially in peat-based substrates, a second experiment was set up to investigate the optimal VA fungal inoculum ( Glomus sp.) for potato crops. A greenhouse experiment using seven commercially produced Glomus inocula (namely G. intaradices, G. verisforme, G. mosseae, G. etunicatum, G. caledonium, and two mixed commercial Glomus cultures, Vaminoc and Vaminoc T (VA fungal inocula supplied by Microbio Ltd, Hemel Hempstead, UK) was undertaken using micropropagated potato seedlings grown in peat preparations.

After 30 days G. etunicatum and G. verisforme gave the most rapid colonisation of the potato microplants compared to the other inocula used. All VAM fungal inocula, however, resulted in significantly lower shoot weights compared to the non-mycorrhizal control. Root fresh weight was also reduced compared to the control plants. However, regression analysis showed that there was a strong positive correlation between VAM development on both root (R2=60%) and shoot fresh weights (R2=83 %) in inoculated plants. As yet there is no specific biocontrol method for soilborne pathogens of potato crops. Future work will concentrate on the use of VAMs for the control of root pathogens in potato using the above species. In maize the use of VAMs is a definite possibility with future research, as an alternative to pesticides.

References
1. Osnubi O, 1994. Biology and Fertility of Soils 18, 55-59.
2. Ramos-Zapata J A, 1995. MSc dissertation.