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Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/17/2002 Publication Date: 4/1/2003 Citation: MYCORRHIZAL COLONIZATION OF GRAPEVINE ROOTSTOCKS UNDER FIELD CONDITIONS. Schreiner, R.P. Interpretive Summary: Phyollexera-resistant grapevine rootstocks were studied over 3 years in a red-hill soil to examine potential differences in root growth and colonization by beneficial mycorrhizal fungi. The quantity of fine (feeder) roots within a given volume of soil increased over time or was similar for all rooststocks, except for Riparia Gloire. Fine roots decreased in Riparia Gloire in the fourth year of growth when vines carried the first normal crop of grapes. Colonization of roots by mycorrhizal fungi was generally high in all rootstocks. However, some rootstocks had consistently greater levels of root colonization. Fine roots and mycorrhizal colonization were both correlated to scion fruit yield and pruning weights. In other words, those rootstocks conferring greater vigor to the scion had greater quantities of fine roots and greater colonization of those roots by mycorrhizal fungi. The activity of mycorrhizal fungi within roots was assessed by examining the proportion of roots containing arbuscules. Arbuscules are believed to be the site of nutrient transfer between host plants and mycorrhizal fungi. The activity of the mycorrhizal fungi decreased in the fourth year in proportion to the amount of fruit carried on different rootstocks. Therefore, mycorrhizal activity was depressed by higher crop loads, suggesting that nutrient or water uptake was impaired in vines carrying larger crop loads. Soil moisture content also influenced the colonization of roots by mycorrhizal fungi. This study showed that different grapevine rootstocks affect colonization by mycorrhizal fungi, but crop load and soil moisture contents also affect mycorrhizal fungi in roots. Technical Abstract: Mycorrhizal colonization of grafted grapevines was studied during the establishment years in an experimental rootstock block to determine whether different rootstocks varied in their ability to form functional mycorrhizas. Roots of 10 different rootstocks were examined for presence of arbuscular mycorrhizal (AM) fungi at the end of the second growing season (1998), and at the time of veraison of the third (1999) and fourth (2000) growing seasons. The root length density of fine roots (primary roots with intact cortex) increased in most rootstocks over time or remained similar, except for Riparia Gloire which decreased markedly in the 4th year when vines carried their first significant fruit crop. Mycorrhizal colonization was generally above 60% of fine root length for all rootstocks, although significant differences due to rootstock and time of sampling were evident. Higher vigor rootstocks at this site, particularly Ruggeri 140, Kober 5BB and SO4, had consistently higher levels of root colonization by AM fungi. The proportion of roots containing arbuscules at veraison declined from the third to fourth year in those rootstocks carrying the highest crop loads. While mycorrhizal colonization of different rootstocks was positively correlated yield in 2000, the proportion of roots with arbuscules was negatively correlated to yield. Block effects on mycorrhizal colonization were significant because of different levels of irrigation water applied in 1999 and 2000. The proportion of roots that were colonized by AM fungi and the presence of arbuscules were negatively correlated to soil moisture contents irrespective of rootstock. We conclude from our study that small but significant differences in the ability to form mycorrhizas occurs among rootstocks, but other factors including soil moisture and crop load have a large influence on root colonization by mycorrhizal fungi. |
