Optimizing Tuber Set and Size Distribution for Potato Seed (Solanumtuberosum L.) Expressing Varying Degrees of Apical Dominance

Plant emergence, apical dominance, tuber set, and size are affected by the physiological age of seed tubers, which can substantially impact overall crop value. This study investigated the efficacy of seed spacing (15, 25, and 35 cm) and 1-naphthaleneacetic acid (NAA) seed treatments in altering these variables in cv. Ranger Russet to improve yield and tuber size distribution of seed expressing low (2.8 stems/seed piece) and high (4.8–5.4 stems/seed piece) apical dominance. Age primed, high-stem seed produced more tubers per plant and per ha than non-aged seed; however, tuber number per ha from both seed lots fell to the same extent with decreasing plant density. Importantly, tuber set per plant increased substantially more for the physiologically older, high-stem seed as plant spacing increased. Average tuber weight also increased with decreasing plant density but the response was greatest for the physiologically younger, low-stem seed. Regardless of seed age, marketable yields were comparable at 25- and 35-cm spacing. Tuber size distributions from the 2.8-stem seed shifted from oversize (>340-g) tubers to higher percentage 113–284-g tubers as spacing decreased from 35 to 15 cm. The 5.4-stem seed produced less undersize (<113 g) tubers and a greater proportion of >284-g tubers when planted at 35-cm spacing. Adjusting in-row spacing relative to seed age and expected stem numbers improved tuber size distribution and value. However, because plants from older seed set more tubers in response to decreasing plant density than younger seed, average tuber weight and size distribution never matched the younger seed at any spacing. Restoration of apical dominance by treatment of seed with NAA was more effective in this regard. Depending on seed age, NAA delayed plant emergence (22–74 %) and decreased stem (24–38 %) and tuber numbers per plant (8–13 %). Stem numbers from age-primed seed fell from 4.8 to 3.0 as NAA concentration increased. Marketable yields were not affected by seed age but decreased slightly (7.3 %, P < 0.01) with increasing NAA concentration. NAA effectively shifted the tuber size distribution from age-primed seed toward larger (>284-g) tubers, resulting in a yield profile approaching that of the non-treated younger seed. Although seed spacing and NAA treatments are effective techniques for altering tuber size distribution to maximize crop value in relation to seed age and expected stem numbers, tuber age had a small but residual effect on productivity beyond that attributable to apical dominance.