The ifluence of seed size on seed vigour and field performance of sorghum (S.bicolor) [Sudan]

Seven laboratory, and a field experiments were conducted in 1994 and 1995 during the course of this study. The laboratory experiments determined the effect of size on seed vigour via measuring the 1000-seed weight, standard germination, coefficient of rate of germination (CRG) and response to the accelerated ageing (AA), cold, warm and seedling growth tests. The field experiment investigated the influence of seed size on seedling emergence, plant growth, flowering, yield components and final seed yield of sorghum. Seed lots of four sorghum varieties viz, Dabar 1/1/1/1, Dwarf white Milo, Gadam El Hamam and Um-benein 22 were used in these experiments. The seed classes used were: large, small and ungraded seed. Generally, all vigour attributes studied in the laboratory were affected by the size of the seed, variety and their interaction, except in seedling growth, where no significant effect was found for either the seed size on seedling shoot length, or the variety on seedling dry weight. Large seed markedly excelled small seed in 1000-seed weight, standard germination and rapidity of germination - as determined by CRG. Also large seed had significantly higher AA, cold and warm germination than small seed, which indicated higher tolerance level and consequently, higher vigour potential for large seed fraction. The ungraded seed resembled the large seed in standard germination, CRG and cold test, but was outstripped by the large seed in the remaining tests. Regarding 1000-seed weight, varieties were ranked as: Dwarf white Milo Dabar 1/1/1/1 Gadam El Hamam Un-benein 22, whereas in standard germination and CRG Um-benein 22 excelled other varieties, but Dabar 1/1/1/1 was similar to it in CRG. Both seed size and variety affected seedling emergence in the field. Small seed fraction showed lower emergence percentage as compared with both large and ungraded seed classes which were similar. The superiority of large and ungraded seed plants over those of small seed in plant height and dry weight/plant was manifest during the first 2 weeks and first month of the growing period, respectively, but it was maintained, with respect to plant height in the second season, throughout the crop life. The varietal effects on plant growth were generally, more apparent in the progressive growing period. Seed size affected the time to 50 flowering in the second season, but not in the first season; and to 100 flowering in both seasons. Large seed plants attained 50 (in the second season); and 100 flowering earlier than those of small seed. Dwarf white Milo was the earliest variety in flowering. Large seed plants had the highest number of heads/m to power two. , but no significant differences were found between large and small seed plants in number of seeds/head. Seed size did not affect the final seed yield, and differences among varieties were obvious in the second season. It was concluded that sorghum seed grading is not feasible whenever the seed bulk was consisted of higher proportion of large seeds, but in conditions of high percentages of small seeds in the bulk grading is beneficial to ensure high-vigour seed stock