How Age of Transplants from In Vitro Derived Potato Plantlets Affects Crop Growth and Seed Tuber Yield After Field Transplanting

In vitro produced plantlets are used in potato seed systems for production of minitubers under protected conditions or for production of transplants to be transplanted to the field. Three field experiments were carried out to analyse how transplant age (Age) affected the field performance. In the main experiments, 2-, 3- and 4-week-old transplants of the very early cultivar Gloria (Exp. 1) and the mid-early cultivar Bintje (Exp. 2) were produced in a glasshouse. Exp. 3 was a check experiment in which 2- and 3-week-old transplants of cv. Gloria were produced in growth chambers under conditions that were non-inductive for tuberization (24-h photoperiod, high temperature). Ground cover (GC) was assessed weekly and weights of the tuber and canopy fractions were assessed at 0, 14, 28, 42, 56, 70 and 84 days after transplanting (DAT). Yield analysis [accumulated intercepted radiation (AIR), radiation use efficiency (RUE), total dry weight (TDW), harvest index (HI) and tuber dry matter concentration] was carried out; the fraction dry matter (DM) allocated to the tubers and the canopy was calculated for three 2-week intervals after field transplanting. When raised in the glasshouse, older transplants were more advanced in tuber formation and canopy growth than younger transplants and had a higher GC at transplanting. However, crops from younger transplants produced significantly higher fresh tuber yields than crops from older transplants in the later part of the growing period in Exp. 1; the same trend was observed in Exp. 2. AIR was the most important yield component affected by transplant age; RUE, HI and tuber dry matter concentration were not or not meaningfully affected by transplant age. In the first 2 weeks after field transplanting, a very high percentage of the DM produced (>85%) was allocated to tuber growth in crops from the oldest transplants. This reduced AIR severely. The results show clearly that seed crops from younger transplants will perform better than crops from older transplants or at least perform at par. Implications for transplant production management are discussed.