ABSTRACT
In 1998, several 10-year-old 'Marquis' and 'Vanessa' (Vitis sp.) table grapevines at the Southwest Michigan Research and Extension Center in Benton Harbor started showing decline symptoms such as stunted shoots with small leaves and berries. Vines eventually stopped producing fruit and died. In 1999, symptomatic vines were indexed on cucumber (Cucumis sativus L. 'National Pickling') cotyledons, which developed chlorotic local lesions. Symptomatic cucumber tissue was tested using Ouchterlony double diffusion with polyclonal antibodies for Tomato ringspot virus (ToRSV) and Tobacco ringspot virus (TRSV) provided by D. Ramsdell. Samples tested positive for TRSV. 'Marquis' vines (9 of 45) in the affected area also tested positive in double-antibody sandwich enzyme-linked immunosorbent assay with polyclonal antibodies for TRSV (Agdia, Inc., Elkhart, IN). Analysis of soil samples from the site in 1989 yielded five dagger nematodes (Xiphinema americanum Cobb) per g of soil, confirming the potential for virus spread by nematodes (1). TRSV reportedly infects Vitis vinifera L. but not V. labrusca L. (1). 'Marquis' and 'Vanessa' have V. vinifera heritage. The detection of TRSV has led to the establishment of a program for the production of virus-tested table grape planting stock, as well as research on the utility of nematode-resistant rootstocks for growing table grapes at the infested site. Reference: (1) R. C. Pearson and A. C. Goheen, eds. Compendium of Grape Diseases, The American Phytopathological Society, St. Paul, MN, 1995.
ABSTRACT
A relationship between abscisic acid concentration and leaf water status is reported. Water potentials were measured in leaves of Ambrosia artemisiifolia L. and Ambrosia trifida L. throughout a period of dehydration of intact plants. Tissues from the same leaves were analyzed for abscisic acid. For both species, abscisic acid began to increase in a critical water potential range (-10 to -12 atmospheres). These data suggest a threshold water potential that stimulates abscisic acid synthesis. The data support the hypothesis that a small change in water potential could affect stomatal resistance to water loss by means of a very sensitive chemical feedback control mechanism.
