DROUGHT EFFECTS ON THE MARKETABLE AND NUTRITIONAL QUALITY OF CARROTS

In two cultivars of carrots (Daucus carota L) drought stress was impos ed at different developmental stages in order to examine how the marke table and nutritional quality was influenced. Experiments were conduct ed on both a sandy loam soil and a coarse sandy soil. Although drought stress during a 3-week period at any growth stage reduced total tap-r oot production, the yield of marketable tap roots increased on the san dy loam soil when drought stress occurred just prior to harvest. This was the result of a decrease in the proportion of split roots when dro ught stress was imposed during this period. An increased risk of infec tion by common scab (Streptomyces scabies) was seen when drought stres s occurred during early growth. Cultivar differences in susceptibility to split roots and common scab were observed. Significant differences in chemical composition between cultivars were seen. However, drought stress imposed at a specific growth stage did not influence the chemi cal composition of tap roots in any consistent manner. When drought st ress occurred during early growth on the coarse sandy soil the concent ration of dry matter was low and that of potassium and nitrate high. H owever, the opposite was found on the same soil when drought stress oc curred just prior to harvest. Averaging the effect of drought periods and cultivars, drought stress was observed to increase the concentrati on of sucrose in tap roots from the sandy loam soil and decrease that of phosphorus in tap roots from the coarse sandy soil. Various effects on magnesium, beta-carotene and vitamin C were detected. Severe droug ht stress increased the storage losses due to the development of disea ses.