Plant Volatiles Inhibit Pollen Germination of Apple and Other Species

Abstract

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.