H ORT SCIENCE 27(3):267. 1992. Plant Volatiles Inhibit Pollen Germination of Apple and Other Species Douglas D. Archbold, Thomas R. Hamilton-Kemp, and John H. Loughrin Department of Horticulture and Landscape Architecture, University of Kentucky, Lexington, KY 40546-0091 Additional index words. Malus domestica. Prunus avium, P. domestica, plum, sweet cherry, bioassay French et al. (1979) reported that volatile compounds similar to those known to affect fungal spore germination in vitro affected germination of Pinus spp. pollen. Our ob- jectives in this preliminary work were to screen plant-derived volatile compound mix- tures, floral and vegetative, to determine if they influenced germination of pollen from several fruit species. Apple (Malus domestica Borkh. ‘Red De- licious’ and ‘Golden Delicious’), sweet cherry (Prunus avium L. ‘Van’), and plum (P. do- mestica L. ‘Friar’) pollen (Antles Pollen Supplies, Wenatchee, Wash.) were stored at -20C over anhydrous CaCl 2 . Aliquots of stamen were rehydrated in 13 × 100-mm test tubes at room temperature and 100% rel- ative humidity for 30 min. The tubes were shaken to facilitate pollen release; pollen grains were captured on a camel hair brush and dispersed across the surface of a l-cm 3 block of 3% agar (Sigma, St. Louis) by gently moving the brush across a fine mesh screen. The agar block was placed in an uncovered 5-cm glass petri dish contained within a 9- cm glass petri dish. Selected tissues were then placed around the perimeter of the 5- cm dish, and the cover was placed on the 9- cm dish and sealed with parafilm. The sealed dishes were maintained in the laboratory in darkness at ambient temperature. Each treat- ment was replicated three times and experi- ments were repeated at least twice. in March and April, and the apple flowers were collected from field-grown trees ‘at full bloom. With the exception of the rose petals, all tissues were tested either intact or ma- cerated by light grinding in a mortar and pes- tle. In addition, to determine if ethylene released upon maceration had an effect, in- tact tomato leaves were dipped in 1000 ppm 2-chloroethyl phosphonic acid (ethephon) before bioassay. After 2 h, microphotographs ( × 40) of the pollen were taken. Four fields from each agar block were photographed. Total and germi- nated pollen grains were counted from the photographs, recording only single grains on the agar surface. Grains were classified as germinated when the pollen tube length ex- ceeded the diameter of the grain. Percent germination values were derived for each treatment and tested by analysis of variance. After determining that data transformation was not necessary, treatments means were compared by Dunnett’s test. Pollen germination was assessed in the presence of the following tissues (number used): tomato (Lycopersicon esculentum Mill.) leaflets (five), cucumber (Cucumis sa- tivus L.) leaves (one), chrysanthemum [Den- dranthema × grandiflorum (Ramat.) Kit- amura] leaves (five), strawberry (Fragaria × ananassa Duch.) leaflets (five), rose (Rosa spp.) petals (10), and ‘Red Delicious’ apple flowers (five). The leaves and rose petals were collected from greenhouse-grown plants Intact leaves from the tested species did not affect apple pollen germination (Table 1). However, with the exception of chrysan- themum leaves, macerated leaves inhibited ‘Red Delicious’ apple pollen germination. Neither apple flowers, macerated or intact, nor rose petals influenced apple pollen ger- mination (data not shown). The pollen of ‘Golden Delicious’ apple, ‘Van’ sweet cherry, and ‘Friar’ plum were also inhibited by the volatiles produced by macerated tomato leaves (Table 2). Thus, the response was not spe- cies-specific. may have influenced the responses, subse- quent bioassay work with pure volatile com- pounds (i.e., no leaf tissue) revealed that the macerated tomato leaf volatiles Z-3-hexenal and E-2-hexenal were inhibitory (Hamilton- Kemp et al., 1991). Thus, altered ethylene, CO 2 , and O 2 levels in the dishes were not solely responsible for the observed inhibition of pollen germination. Stimulatory effects similar to those described by French et al. (1979) were not observed. Our work did not separate inhibitory effects on germination from effects on tube elongation. Literature Cited Buchanan, D.W. and R.H. Biggs. 1969. Peach fruit abscission and pollen germination as influ- enced by ethylene and 2-chloroethane phos- phonic acid. J. Amer. Soc. Hort. Sci. 94:327- 329. French, R.C., C.L. Graham, R.A. Long, and A.W. Gale. 1979. Effect of nonanal and related fun- gal spore stimulators on germination of pollen of several Pinus species. J. Agr. Food Chem. 27:184-187. Received for publication 28 May 1991. Accepted for publication 9 Oct. 1991. Paper no. 91-10-84, Kentucky Agricultural Experiment Station. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regu- lations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Exposure to elevated levels of ethylene failed to affect pollen germination (data not shown); thus, the response to volatiles pro- duced by macerated leaves was not due to ethylene. Ethylene generation by the ethe- phon-treated leaves at levels three times that of the macerated tissues was confirmed by GC-FID analysis (data not shown). Ethylene has been reported to have no effect or to promote germination in other species (Buch- anan and Biggs, 1969; Sfakiotakis et al., 1972). High CO, levels, which may have developed in the enclosed dishes containing macerated leaf tissues, have been reported to stimulate tulip pollen germination (Sfaki- otakis et al., 1972), although stimulation was absent in this study. Although low O 2 levels Hamilton-Kemp, T.R., J.H. Loughrin, D.D. Archbold, R.A. Andersen, and D.F. Hilde- brand. 1991. Inhibition of pollen germination by volatile compounds including 2-hexenal and 3-hexenal. J. Agr. Food Chem. 32:952-956. Sfakiotakis, E.M., D.H. Simon, and D.R. Dilley. 1972. Pollen germination and tube growth de- pendent on carbon dioxide and independent of ethylene. Plant Physiol. 49:963-967. HORTSCIENCE, VOL. 27(3), MARCH 1992 267