Microtubers vs Other Propagules for Field
Tuber Production
Yield comparisons between microtubers, plantlets, mini-
tubers, and conventional seed tuber pieces in the field did not
always agree. Yields from plantlets were less (Haverkort and
van der Zaag 1989) or similar (Wattimena et al. 1983; McCown
and Wattimena 1987; Leclerc and DonneUy 1990) to yields
from 40- to 60-g whole seed tubers. Disagreement exists
110 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 80
regarding the practicality of directly field-planting microtu-
bers. Some have found it easy to adapt them to large-scale
mechanized field-planting (reviewed by Naik et al. 1998). In
other cases, directly field-planted microtubers were not found
to be practical; crop development was too slow. However,
when pre-planted in a greenhouse and transferred to plastic
mulch in the field, larger micr0tubers (>0.5 g) significantly out-
yielded plantlets and gave comparable yields to seed tubers for
late, but not early maturing cultivars (Haverkort et al. 1991).
For later-maturing cultivars, plants from microtubers formed
greater amounts of foliage before tuber induction, resulting in
greater yields than the early cultivars. Physiologically older
microtubers also performed better in the field than younger
ones. This was apparent for late but not early cultivars (Ranalli
et al. 1994a). Small microtubers (0.090-0.120 g) yielded far less
tuber fresh weight than minitubers or seed tubers (Ranalli et
al. 1994b). However, total tuber number per m 2 was quite high
(160) at close row spacing (60 cm). There have been distm'b-
ing reports of increased sensitivity in transplants or minitubers
to potato viruses S and Y transmission or spread compared
with plants from field grown tubers (McDonald 1987). Boiteau
et al. (2000) suggested that these concerns have been partly
responsible for the limited use of ex v/tro transplants. How-
ever, their research demonstrated that plant origin has very lit-
fie to do with aphid colonization, which is more influenced by
factors such as relative plant height, surface features and matu-
rity. This report should lead to renewed interest in the use of ex
v/tro propagules and minitubers in the seed tuber industry.