Charles A. Farrar

Cross protection of cantaloupe with a mild strain of zucchini yellow mosaic virus: effectiveness and application

Abstract Plants infected with a severe strain of zucchini yellow mosaic virus (ZYMV-CA) produced fewer marketable fruit than non-infected control plants or plants infected with a mild strain of ZYMV (ZYMV-WK); cross protection conserved marketable yield by nearly 75%. Cantaloupe plants in the non-infected control treatment and plants infected solely with ZYMV-WK produced similar numbers of marketable fruit. In another study, ZYMV-WK was introduced successfully into cantaloupe plants using standard agricultural spray equipment at 2.1 kg cm −2 pressure. Infection with the mild strain was related directly to the concentration of virus in our sprays. The highest infection rate (77%) was achieved with a 10% solution of fresh tissue in buffer. Lower percentage solutions, 2 and 1%, resulted in 27.5 and 25% infection, respectively. A 10% spray solution made from frozen infected tissue resulted in 56% infection. Our studies demonstrate the effectiveness of cross protection in cantaloupe and offer a method to growers for applying this technology to large-scale, direct-seeded agriculture.

Intraplant Sampling of Grapevines for Pierce's Disease Diagnosis

The bacterium Xylella fastidiosa Wells et al. induces Pierces disease (PD) of grapevine. This study was initiated to improve sampling protocols to identify X. fastidiosa-infected grapevines (Vitis vinifera L.) in California vineyards. Several potential PD symptoms, including leaf necrosis and chlorosis, internodal distance, petiole length and weight, and extent of cane branching, were not reliable indicators of X. fastidiosa infection. The matchstick symptom (i.e., abscised leaf blades leaving behind a dried, burnt-appearing petiole tip) was the only consistent indicator of infection in X. fastidiosa-positive grapevines. Further study revealed that leaves selected from the most basal nodes of positive canes had the highest probability of X. fastidiosa detection, with enzyme-linked immunosorbent assay. A symptom reliability index (SRI) was created to assess visual PD diagnosis by node location. The SRI values were the highest at basal node locations, but symptoms at any single node were not consistently reliable for PD diagnosis. Our results showed that PD diagnosis based on foliar symptoms was unreliable. However, taking samples from the basal portion of a cane increased the probability of X. fastidiosa detection.