The importance of the period immediately preceding anthesis for grain weight determination in wheat

Although individual grain weight is an important source of variation for gr ain yield, there is still poor understanding of the causes determining fina l grain weight. Almost all studies conducted for understanding the determin ants of grain weight have been focused on the post-anthesis period. However , there is important evidence that pre-anthesis conditions could also modif y final grain weight. Three experiments including different sowing dates, g enotypes and temperature regimes between booting and anthesis, were carried out in Argentina and Mexico to analyse the effect of temperature and assoc iated traits during the pre- and post-anthesis periods on grain weight unde r field conditions. In these experiments final grain weight could not be ex plained by average or maximum temperature during the post-anthesis period. However, average temperature between booting and anthesis was closely relat ed to the observed grain weight differences, probably as a consequence of t he effects of this factor on carpel growth. Differences in grain weight bet ween genotypes and grain position were successfully explained by difference s in carpel weight at anthesis. These results suggest that our knowledge to determine grain weight could improve if the immediately pre-anthesis perio d conditions were taken into account.