EFFECTS OF SEED CROP HUSBANDRY, SEED SOURCE, SEED TUBER WEIGHT AND SEED RATE ON THE GROWTH OF WARE POTATO CROPS

The results of 20 experiments which compared seed from July-planted crops with seed from earlier planted (April-May) crops either grown locally or from certified seed-producing areas are reported. The effects of dates of planting and harvesting of late-planted seed crops and seed storage temperature were examined in eight experiments. In five experiments, the effect of seed rate was studied on two weights of seed-tubers in the July-planted crops. Tubers of several cultivars from the July-planted crops ended their dormancy close to the normal planting time of ware crops, 2-4 months later than tubers from spring-planted crops grown either locally or in areas certified for seed production. Tubers from seed crops planted in July produced fewer mainstems in ware crops than tubers from spring-planted crops, but effects on stem density were usually too small to have any significant effect on foliar ground cover and consequently on tuber yield. Date of planting the seed crops in July and date of harvest of the seed-tubers had no effect on sprout or ware crop growth in Record or Wilja. Ware tuber yields were similar for the different seed sources in 12 out of 15 experiments, suggesting little difference in the performance of tubers from seed crops planted early and late in the season. At equivalent seed rates, small seed-tubers (12.5+/-2.5 g) from July-planted seed crops usually produced more stems and tubers and greater ware yields than larger tubers (37.5+/-2.5 g). For the smaller seed, the results suggested optimum seed rates for ware tuber yields of c. 0.88, 0.88 and 0.59 t/ha for Wilja, Record and Saturna, respectively. These are substantially lower than those currently used in the UK. For the larger seed, rates of c. 2.64, 2.64 and 1.76 t/ha were adequate for Wilja, Record and Saturna, respectively.