What are the implications of changes in the heterogeneity of a seed population upon accelerated aging?

Pea (Pisum sativum L.) seeds were subjected to accelerated aging for 16 days at 40 degrees C and 80% relative humidity. After 5-7 days, seed germination decreased from 82 to 72%. After 8-10 days, the germination unexpectedly increased to 92% but then decreased on further aging. The aging-dependent changes in room-temperature phosphorescence (an indicator of moisture content in seeds) and electrolyte leakage (an indicator of seed intactness) were opposite to the changes in the germination. Changes in germination capacity during the initial 10-day period of aging were due to an altered proportion between normal and abnormal seedlings. It was found that the increase in seed heterogeneity upon aging was caused by the appearance of a new fraction in an initially uniform seed lot. The air-dry seeds of this fraction had a lower moisture content and differed from other seeds by twofold phosphorescence intensity and a twofold extent of electrolyte leakage. These seeds germinated earlier but grew slower and gave rise to many abnormal seedlings. This new fraction contained seeds of low vigor. It is supposed that the vigor of an individual seed, i.e., the ability of the seed to produce a normal seedling, declines in a step-wise manner. The gradual vigor reduction in the total seed population upon aging seems to result from step-wise transitions of individual seeds to a subpopulation with low vigor but not from continuous vigor decline in all seeds.