Abstract
In vitro-propagated potato plantlets are commonly used in potato seed tuber production. Four experiments were carried out to identify how the duration of the last in vitro phase (‘age’) before planting of in vitro-produced plantlets affects the early growth and development ex vitro, assessed 10–14 days after planting. Experiments included varying ranges in age of the in vitro plantlets at planting (10–40, 15–45, 14–28 and 14–56 days old at the moment of planting in the respective experiments) and different cultivars. Because in vitro plantlet size increases with age, the first experiment studied interactions between age and planting method. Planting ‘deep’ (the upper four visible leaves above the ground) seemed more robust than planting ‘shallow’ (all nodes/leaves above ground except the lowest two), and in later experiments, only deep planting was applied. Across experiments, plants grown from younger in vitro plantlets had smaller leaf areas 10–14 days after planting than those from older in vitro plantlets. The increase in leaf area levelled off with increasing age of the in vitro plantlets used, especially when plantlets were older than c. 28 days. Larger leaf areas 10–14 days after planting were related to the older in vitro plantlets having higher absolute growth rates after planting and a larger above-ground leaf area at planting, even though four leaves were kept above ground in all treatments. Below ground, plants from older in vitro plantlets had more stem nodes, initiated stolons earlier after planting and initiated more stolons per plant. Tuber initiation rarely occurred within 14 days after planting, but was observed in some plants from 42- and especially 56-day-old in vitro plantlets of the very early cultivar Gloria and a single plant from 56-day-old in vitro plantlets of the mid-early cultivar Bintje. The data show that planting older in vitro plantlets can enhance early leaf area growth. Plants from older in vitro plantlets also more readily initiate stolons below ground and may be more advanced in the tuber formation process, especially when from early cultivars.
