Abstract
Arbuscular mycorrhizal fungi (AMF) enhance the growth of numerous plants, including grapevines, by increasing the absorptive surface area between roots and soil. A survey of commercial vineyards in Oregon was conducted to assess the levels of root colonization by AMF at two times during the growing season. Grapevines sampled, ranged in age from 2 to 29 years old and were growing in 10 different soil types from 3 soil orders. AMF colonization of fine (feeder) roots of vines was generally high, averaging 73% and 69% of root length colonized at bloom and veraison, respectively. Vine age, soil type, cultivar, trellis type and vine row aspect did not influence colonization of roots by AMF. In-row cultivation reduced AMF colonization at bloom, and foliar application of soluble phosphorus fertilizers reduced arbuscules (the site of nutrient transfer in mycorrhizas) in roots at veraison. The proportion of roots colonized by AMF at bloom was negatively correlated to leaf N concentrations and positively correlated to soil and leaf K concentrations. The proportion of roots containing arbuscules at bloom was positively correlated to soil pH and leaf K concentrations, but negatively correlated to leaf P and N concentrations. AMF colonization of roots was negatively correlated to soil moisture at veraison. Root colonization by AMF in Oregon's dryland vineyards appears to be reduced by cultivation and foliar P application, but may be enhanced by increasing soil pH.
