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Positional effects on retention potential within the spur of apple (Malus × domestica) with and without competition with other fruit on the spur

Goffinet, M. C., Lakso, A. N.
Acta horticulturae 2017 no.1177 pp. 169-176
Malus domestica, apples, cultivars, fruit drop, fruits, leaves, phyllotaxy, plant ovary, trees, New York
Some apple cultivars in New York (e.g., 'Gala' and 'Red Delicious') appear “king dominant” while others (e.g., 'Empire' and 'McIntosh') appear “non king dominant”, especially in unthinned trees. Floral position in the spur is tied to the phyllotaxy of spur leaves. In 'Empire', 'McIntosh', and 'Gala' spurs thinned at bloom to include the king and the largest three lateral flowers, ovary weight of kings at bloom in 'Gala' was greater in relation to the three largest lateral fruits than it was for 'Empire' and 'McIntosh'. We compared fruit abscission patterns within 6-flowered spurs in unthinned trees of 'Empire' and 'Gala' and patterns on spurs thinned to individual fruits within the spur phyllotaxy. This was done to see whether lack of nearby competition affects retention by position or fruit size or weight at harvest. In 6-flowered clusters of 'Empire', fruit abscission of laterals was significantly greater than that of kings, and laterals had smaller fruits at harvest. In contrast, any lateral fruit on single-flowered clusters had the potential to reach king size, except for the most distal lateral. 'Gala' spurs thinned to single fruit showed laterals were still inherently inferior to kings in both fruit retention and in harvest size. Thus, 'Gala' is indeed king-dominant and 'Empire' and 'McIntosh' are non king-dominant. We have shown previously that fruit drop is a function of reduced fruit growth rate, but have found that king fruit have much less drop at the same reduction in growth than lateral fruit.