Control of the development of mummified fruit of ‘Elstar’ apple

Abstract

SummaryThe apple cultivar ‘Elstar’ (Malus domestica Borkh.) is characterized by a high incidence of mummified fruit that remain firmly attached to spurs far into the next growing season. The percentage of mummified fruit was highest in ‘Elstar’ (22.1%) followed by ‘Regine’ (8.7%), but very low (<1.0%) in ‘Gala’, ‘Golden Delicious’, ‘Idared’ and ‘Jonagold’. With a single exception, the percentage of mummified fruit did not differ significantly among ‘Elstar’ and a range of ‘Elstar’ mutants or with four dwarfing rootstocks. In ‘Elstar’, the weight and diameter of mummified fruit after drying at 1058C had log normal distributions with medians of 0.21 g and 6.8 mm, respectively. The number of mummified fruit per tree was linearly related to fruit number at harvest. Mummified fruit had maximum diameters and growth rates that matched fruit abscising during “June” drop. The number of seeds did not differ among mummified fruit, abscising fruit and normal fruit (9.2, 9.9 and 9.9 seeds per fruit respectively), but more underdeveloped seeds were found in mummified fruit and abscising fruit. The amounts of polar indoleacetic acid (IAA) exported from fruit that developed into mummified fruit was less than from normal, non-abscising control fruit (1.9 vs. 4.5 ng fruit–1 in 20 h respectively) but similar to that from fruit abscising during “June” drop (2.3 ng fruit–1 in 20 h). De-fruiting pedicels 20 d after full bloom did not stimulate abscission in ‘Elstar’ (14% and 6% abscission for de-fruited pedicels and control fruit, respectively), but did so in ‘Gala’ (94% of de-fruited pedicels abscised within 18 d after de-fruiting cf 20% of control fruit). The data suggest that the formation of mummified fruit in ‘Elstar’ is the result of early inactivation of the abscission layer, resulting in delayed and reduced abscission.