EFFECTS OF CLIMATE ON DIFFERENT POTATO GENOTYPES .2. DRY-MATTER ALLOCATION AND DURATION OF THE GROWTH-CYCLE

The total growth and tuber dry matter production of a potato crop are determined mainly by the duration of its growth cycle. This in turn de pends on climate, cultivar and crop management. The influence of clima te factors defining crop growth and its timing were analysed by dividi ng the growth cycle into three phases and relating the duration of the se phases to temperature, daylength and radiation. The variation in th e length of all three phases contributed to the variation in the durat ion of the growth cycle and thus to the variation in tuber dry matter production. The variation in the length of the first phase (between em ergence and tuber initiation) was best explained by the meteorological variables observed. Both higher temperatures and shorter daylengths h astened development in this phase. The magnitude of their effects depe nded on cultivar. In the second phase, from tuber initiation to end of leaf growth, temperature and daylength had similar effects but they w ere less clear and the variation in duration of phase 2 could not be e xplained as well as variation in the duration of phase 1. The last pha se, from the end of leaf growth to the end of crop growth, was shorten ed by high temperatures and high radiation. A small part of the variat ion in the duration of this phase was explained by these variables, At this level of crop analysis, the effect of climate on crop developmen t was explained best for the first phase, which is the most important one in explaining the variation in ground cover duration and tuber dry matter production, Quantitative understanding of the processes involv ed is required to be able to explain the effect of climate during the various phases of the growth cycle.