Field symptoms of grapevine redleaf disease in two red-berried wine grape cultivars.

<p>(A) Merlot grapevine with symptoms on the left and non-symptomatic grapevine on the right. (B) and (C) Leaves of Merlot showing red veins and irregular blotches in the initial and advanced stages of symptom development, respectively, are on the left and leaves from non-symptomatic grapevines on the right. (D) Cabernet Franc grapevine with symptoms on the right and non-symptomatic grapevine on the left. (E) and (F) Leaves of Cabernet Franc showing discolorations between veins in the early and advanced stages of symptom development, respectively, are on the right and leaves from non-symptomatic grapevines on the left. Symptomatic leaves of GRD-affected grapevines are smaller in size compared to leaves from neighboring non-symptomatic grapevines. Note differences in color of symptomatic leaves between the two cultivars and red veins in Merlot (B–C) and presence of a narrow strip of green tissue on either side of the major veins (green veins) in Cabernet Franc (E–F).