Some cultivars of prune (i.e. `Brooks') consistently set good crops while others (i.e. `Italian') are erratic bearers. Fall-applied ethephon increases fruit set. Ovule longevity has been hypothesized to be an important factor in fruit retention. The effects of the cultivar and fall ethephon application on ovule longevity were determined.
Ethephon (0 and 500 mg·l-1) was applied to `Italian' and `Brooks' prune trees at the 50% leaf drop stage. The following spring, flower buds were emasculated and covered to prevent pollination. Ten flowers were sampled every two days from anthesis until 20 days after anthesis (DAA). Flowers were fixed in FAP and ovule longevity determined using fluorescence microscopy. Ovule longevity was longer in `Brooks' than `Italian'. At 20 DAA, all of the `Brooks' flowers still had viable ovules. Only 40% of the `Italian' flowers had viable ovules. The `Italian' flowers excised from ethephon-treated trees had at least one non-senescent ovule at 17 DAA. Ethephon prolonged ovule longevity in `Italian' prune flowers. No effect of ethephon was observed on the ovule longevity of the `Brooks' prune.