Relationship between temperature and the early growth of Triticum aestivumand three weed species

Experiments were conducted in controlled environments and in the field on w inter-hardy Triticum aestivum and three weed species commonly found in cere al fields in the United Kingdom to examine whether overwinter shoot growth of individual plants could be described by accumulated thermal time calcula ted using base temperatures derived from growth cabinets. Individuals of ea ch species were grown in a controlled environment at constant temperatures ranging from 5 to 20 C and harvested sequentially Base temperatures for the increase of dry weight and green area were estimated by fitting a simple l inear model describing growth in response to the thermal sum. The estimated base temperatures for shoot dry matter accumulation of Alopecurus myosuroi des, Stellaria media, Galium aparine, and T. aestivum were -0.8, -3.3, -1.4 , and 0.2 C, respectively and estimated base temperatures for increase in g reen area were 0.4, -1.7, 1.9, and 2.2 C, respectively. Each species also w as grown in monoculture in the field over 2 yr at a range of sites to exami ne whether the base temperatures estimated from the controlled environment studies could be used to model weed and crop growth in response to thermal time in the field. The field data were described well when an expolinear fu nction was fitted to accumulated thermal time calculated using the base tem peratures derived from the controlled environment studies.