2019 ASHS Annual Conference

Fruit set of some apple cultivars is low despite abundant flowering. This could be due to high ethylene production of the flowers, poor receptivity of the stigmas and or short ovule longevity. The ethylene synthesis inhibitor aminoethoxyvinylglicine (AVG) is known to reversibly inhibit the activity of the enzyme 1-aminocyclopropane-l-carboxylic acid (ACC) synthase. ACC is a directly precursor of ethylene. The objective of this study was to investigate ethylene evolution of different apple varieties during early flowering and fruit set under the climatic conditions of New York state and, furthermore, understand the effect of AVG on ethylene evolution and consequently, fruit set. We harvested flowers/fruitlets every three days from 2 days before full bloom until 18 days after full bloom of 4 apple cultivars (Gala, Fuji, Honeycrisp and Minneiska). The flowers/fruitlets were placed into a sealed container for 4 hours and a gas sample of the headspace was analyzed by gas chromatography for ethylene production. ‘Gala’, ‘Fuji’ and ‘Honeycrisp’ had low levels of ethylene production over the measurement period, but each had a distinct peak of production of about 3.5 µL L^-1h^-1. ‘Gala’ had the earliest peak at 2 days after full bloom while ‘Fuji’s’ peak was about 4 days after bloom and ‘Honeycrisp’s’ peak was about 7 days after bloom. For each cultivar the ethylene peak was short lived and dropped to low levels within 4 days of the peak. In contrast Minneiska had a much greater level of ethylene production than the other cultivars reaching 8 µL L^-1h^-1 at its peak. The level of flower produced ethylene rose above the level of other cultivars by day 4 after full bloom and reached a peak at 8-9 days after full bloom then dropping to the level of the other cultivars by day 12 after full bloom. This high and sustained level of ethylene may be the cause of the lower set of Minneiska compared to the other 3 cultivars. In a related study we applied AVG, at bloom, petal fall and 12mm fruit size to Minneiska flowers/fruitlets. At the bloom and petal fall timing AVG reduced flower ethylene evolution in a rate dependent manner. At 12mm fruit size there was no effect of AVG since fruitlet ethylene level was very low at that time. Due to the higher ethylene level in Minneiska flowers/fruitlets compared to the other cultivars we studied and its typically low fruit set, our results suggest that AVG could be a potential tool to overcome high ethylene production and low fruit set issues in Minneiska apples in order to help apple growers achieve greater yields and profits.