Productivity of potato seed-tubers from different latitudes
Wahab, Mohamed Noorul Jazeem
Potato (Solanum tuberosum L.) seed-tubers from northern latitudes are usually more vigorous and higher yielding than seed from more southern latitudes. It is not clear whether the superiority of northern seed is due to physiological and/or disease related causes. This study was conducted to examine the relative growth and yield potential of Norland and Russet Burbank seed from different latitudes with the objective of relating seed-tuber vigour to physiological or pathological factors associated with seed production environment. In a five year study, comparisons were made for seed sources from Saskatchewan, Colorado, Minnesota, Nebraska and Wisconsisn that provided a range of environmental conditions. Norland and Russet Burbank seed from Saskatchewan usually outyielded seed from Minnesota or Nebraska but was rarely better than Colorado seed. Tuber yields for the various Saskatchewan seed sources were similar. Lower yields for Russet Burbank from the southern sources was associated with reduced seed piece vigour and greater hill-to- hill variability. However, with Norland, yield increases for northern seed was mainly due to increased seed piece vigour. Northern seed lots produced more vigorous and persistent haulms than southern seed. Premature senescence of plants from southern seed was caused by reduced allocation of dry matter to shoots in favour of tubers. This differential allocation was, in turn, triggered by high levels of tuberizing stimulus present in the southern seed. Differences in shoot vigour, mainstem number, tuber initiation, tuber yield, and tuber dry matter concentration did not indicate that seed-tubers from cooler (northern) sites were physiologically younger than seed from relatively warmer (southern) sites. Rather, seed-tuber vigour appeared to be more closely related to the extent of diurnal temperature fluctuations at each seed production site. Seed potatoes from Saskatchewan retained their productive vigour over Minnesota source for at least two generations. Cycling low yielding Minnesota seed through Saskatoon increased its productive capacity. However, cycling superior Saskatchewan seed through Minnesota reduced its yield potential but it was still superior to seed grown continuously in Minnesota. This is further evidence that the site related variability of seed stocks is due to physiological factors rather than disease conditions.