IMPACT OF POLLINATION TIME, SEED SIZE, POSITION AND MATURITY ON QUANTITATIVE VARIATION IN NICOTIANA-RUSTICA

Many biological experiments and almost all quantitative genetic studie s draw conclusions from differences between families. Such differences are caused as much by heritable as by non-heritable sources. This pap er investigates the impact of seed quality on the expression of quanti tative variability among 20 highly inbred lines of Nicotiana rustica u sing ten seed categories representing different pollination times, see d sizes, seed positions in the capsule and seed maturity. Analysis of variance revealed that while the mean performance of the inbred lines remained more or less the same across all the seed categories, their i ndividual performances differed widely, showing a highly significant i nteraction between lines and seed categories. This interaction account ed for up to 12% of the total variation and was largely attributable t o late pollinations and immature seed. Seed categories were also the m ain source of heterogeneity among the within-line variances, but only immature seed lowered the correlation between the inbred means. In gen eral, seed quality affected the developmental characters much less tha n the traits measured at or after flowering, and the expression of gen etic variation was not critically affected by seed size or position. I mmature seed, on the other hand, generated the highest level of unreli ability in the comparative performance of lines and such seeds should therefore not be used in quantitative genetic experiments under any ci rcumstances. Further implications of seed quality effects on the inter pretation of genetic components are discussed in detail.