Thesis (M. Sc.(Plant Pathology))--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 48-51).

In N. Uruguay two potato (Solanum tuberosum L.) crops are grown per year, one in the fall and the other in spring. In each season physiologically young seed tubers are planted, resulting in relatively slow crop emergence and low yields. The aim of the current research was to determine the effects of physiological ageing of seed tubers on the dynamics of canopy growth, radiation interception and radiation use efficiency (RUE) of crops in the short seasons of Uruguay and to identify opportunities for increasing yield. Experiments were conducted on cv Chieftain over three years from 2000 to 2002. Prior to planting seed was stored at different controlled temperatures to generate physiological ages (measured in thermal time) ranging from 0 (the youngest) to 1200 oC days (the oldest). Ageing led to earlier crop emergence (3-9 days depending on the year), but its potential benefits on radiation interception, dry matter production and yield were negated by an earlier canopy senescence and often smaller canopy size. There was no consistent effect of ageing on RUE although the harvest index was increased. Leaf tagging showed that leaf appearance and senescence was advanced by ageing and the lifespan of individual leaves was reduced. Leaf lifespan did not appear to be related to the sink demand by tubers for assimilate, because removal of tubers at the start of bulking had no effect on lifespan. Maintaining canopy structure during senescence led to a small increase in yield. Although physiological ageing did not result in a consistent increase in yield in either season, use of older seed may provide an insurance against the risk of adverse weather conditions late in the season terminating tuber bulking prematurely.