Consequences of Mesocriconema xenoplax Parasitism on Pinot noir Grapevines Grafted on Rootstocks of Varying Susceptibility

Abstract

Pinot noir grapevines grafted to five rootstocks (Vitis vinifera) and a self-rooted control known to vary in resistance to ring nematode (Mesocriconema xenoplax) were studied over four years to evaluate durability of resistance to ring nematode and to better understand how ring nematode parasitism affects below- and aboveground vine growth and physiology. Ring nematode populations in infested microplots of all three susceptible vines (self-rooted, 3309C, 1103P) increased rapidly during the second year and remained high throughout the study, while nematodes increased in two of the previously resistant rootstocks (110R, 101-14) during the third year. Only 420A remained resistant through the entire 4-year period. The impact of ring nematode parasitism on vines was most apparent in the susceptible rootstocks and self-rooted vines with reductions in fine root growth and colonization by arbuscular mycorrhizal fungi (AMF) occurring as early as the second year. Reductions in both fine root production and AMF colonization due to ring nematode were greater in subsequent years in the susceptible vines. The frequency of fine roots containing vesicles of AMF was reduced in all five rootstocks that supported a population increase of ring nematode (only 420A was unaffected). Ring nematode did not alter aboveground vine performance until the third or fourth growing season, when shoot lengths and pruning weights were reduced in the three susceptible vines. Ring nematode did not alter shoot growth in any of the three resistant rootstocks, nor did it affect leaf gas exchange or leaf water potential in any vines in any year. However, by year four ring nematode reduced fruit yield as a main effect across all rootstock treatments.