This present thesis contains five sections about the effects of mineral nutrients, water regimes and seed characteristics on seed production in lettuce (Lactuca sativa L.) cultivar 'Avon Defiance'. The vegetative growth during the last seed harvest was also evaluated, A further section deals with the influence of light and different temperatures during the early imbibition on the germination. Three levels each of nitrogen (N0 0 g N, N1 0.291gN, N2 0.416 g N per container), phosphorus (P0 0 g P2O5, P1 0.312 g P2O5, P2 0.468 g P2O5 per container) and potassium (K0 0 g K2O, K1 0.312 g K2O, K2 0.468 g K2O per container) combined factorially were examined in relation to the yield and quality of seed produced in addition to vegetative growth. The highest and the lowest seed yield were recorded in the N2 K2, K2 P1, N2 P2 and N0 K0, K0 P0 and N1 P0 respectively. The heaviest thousand grain weight was found in N1 P1 K0 and the lightest in N0 P2 K0. The N1 P1 K2 produced the highest numbers of compound fruits and N0 P1 K0 the lowest. Neither the percentage germination nor the seedling evaluation were significantly influenced by the nutrients. The highest number of primary and secondary shoots occurred in the N2 K0 treatment and the lowest in N2 K1. In an experiment evaluating effects of cotyledon size on subsequent seed yield, number of compound fruits and primary and secondary shoots, plant height, seedling evaluation, germination percentage and the thousand grain weight there was no significant difference. Two experiments were made to investigate the effect of the seed weight on plant growth and the subsequent seed yield and it was found that the seed weight did not significantly effect the plant height, number of primary and secondary shoots, compound fruits, seed yield, thousand grain weight or germination percentage. But the progeny of the heavy seed in one of these experiments produced a significantly lower percentage of normal seedlings than those of the medium and light seeds. Two further experiments were performed to examine effects of the mother plant's nitrogen nutrition on the performance of the progeny and it was noted in both of them that the seed yield, number of compound fruits and primary and secondary shoots, plant height, percentage germination or seedling evaluation was not significantly influenced by any treatments. In an experiment investigating the interaction between the moisture regime and nutrients, mineral nutrient treatments significantly increased the seed yield but the moisture and combined moisture and nutrients did not. The moisture, the nutrients and their interactions significantly increased the percentage germination of the seed produced. The seedling evaluation was significantly increased only by the nutrients where the high level of potassium increased the percentage of seedlings. The interaction of light and temperatures in the beginning of the seed imbibition had a significant effect on the percentage germination at 5%. Light at constant temperature during the remainder of this experiment significantly increased (at 1%) the percentage germination in comparison with the dark at the same temperature.
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