1.4.21
SYSTEMIC ACTIVITY OF BABA (-AMINOBUTYRIC ACID) AGAINST DOWNY MILDEW IN GRAPES

Y COHEN1, M REUVENI2 and A BAIDER1

1Department of Life Sciences, Bar-Ilan University, Ramat-Gan 52900; Israel; 2The Golan Heights Research lnstitute, Katzrin, Israel

Background and objectives
BABA was reported to induce local and systemic resistance against late blight (Phytophthora infestans) in tomato [1], blue mold in tobacco [2] and a series of other foliar and root fungal pathogens [3]. Pathogenesis-related (PR) protein accumulation was reported to occur in tomato 141. BABA had no effect on fungal germination or growth in vitro. The present study was conducted to learn the potential of BABA in controlling downy mildew (Plasmopara viticola) in grapes with the hope of introducing it to the market as an environmentally safe SAR product.

Materials and methods
Various aminobutyric acids were dissolved in water and supplied to grape leaf discs by floating (lower surface uppermost), or to intact grape plants either as foliar spray (to lower leaf surfaces) or via the root system. Inoculation with sporangia of P. viticola was done either by inoculum droplets (on leaf discs), or a foliar spray (on intact plants, to lower leaf surfaces). Disease and fungal development were followed visually or microscopically. Calcofluor, phlorglucinol and basic aniline blue were used to detect callose or lignin deposits. 14C-BABA (supplied by Novartis) was used to follow the translocation of the compound in intact plants.

Results and conclusions
Leaf discs of susceptible cultivars placed on BABA solutions and inoculated with P. viticola on the counter surface produced brownish local lesions below the inoculation site which failed to support fungal sporulation. As low as 25 g/ml of BABA sufficed to prevent tissue colonization with the fungus. Five other isomers of BABA, including DL-2-aminobutanoic acid (AABA) and 4-aminobutanoic acid (GABA) gave no protection against the downy mildew. Of the two (R and S) enantiomers of BABA, only the R form was active, suggesting a specific stereostructure requirement for activity. BABA could stop fungal colonization even when applied post-infection to leaf discs. BABA provided systemic activity against the disease when applied via the root system or bottom leaves of grape plants. Application of 14C- BABA to a single leaf of intact plants showed the accumulation of the 14C label in upper leaves (and root tips) in a similar manner to that reported for tomato [5]. The mode of action of BABA is not known. Hypersensitive response and lignification were observed in treated leaf discs following inoculation.

References
1. Cohen Y, 1994. Phytopathology 84, 55-59.
2. Cohen Y, Niderman T, Mosinger E, Fluhr R, 1994. Plant Physiology 104, 59-66.
3. Cohen Y, 1994. Physiological and Molecular Plant Pathology 44, 273-288.
4. Cohen Y, 1995. In Lyr H, Russell PE, Sisier HD, eds. Intercept, Andover, pp. 461-466.
5. Cohen Y, Gisi U, 1994. Physiological and Molecular Plant Pathology 45, 441-456.