Seed aging during storage results in loss of vigor and germination ability due to
the accumulation of damage by oxidation reactions. Experimental aging tests,
for instance to study genetic variation, aim to mimic natural aging in a shorter
timeframe. As the oxidation rate is increased by elevating the temperature,
moisture, and oxygen levels, this study aimed to (1) investigate the effect of
experimental rice seed aging by an elevated partial pressure of oxygen (EPPO),
(2) elucidate the mechanism of dry-EPPO aging and (3) compare aging under
dry-EPPO conditions to aging under traditional moist-controlled deterioration
(CD) conditions and to long-term ambient storage. Dry seeds from 20 diverse
rice accessions were experimentally aged under EPPO (200 times higher
oxygen levels), at 50% relative humidity (RH), along with storage under highpressure nitrogen gas and ambient conditions as controls. While no decline in
germination was observed with ambient storage, there was significant aging of
the rice seeds under EPPO storage, with considerable variation in the aging rate
among the accessions, with an average decline toward 50% survival obtained
after around 21 days in EPPO storage and total loss of germination after 56
days. Storage under high-pressure nitrogen gas resulted in a small but
significant decline, by an average of 5% germination after 56 days. In a
second experiment, seven rice seed lots were stored under EPPO as
compared to a moist-CD test and two different long-term ambient storage
conditions, i.e., conditioned warehouse seed storage (CWSS) and traditional
rice seed storage (TRSS). Untargeted metabolomics (with identification of lipid
and volatile compounds profiles) showed a relatively high increase in levels of
oxidized lipids and related volatiles under all four storage conditions. These
compounds had a high negative correlation with seed viability, indicating
oxidation as a main deteriorating process during seed aging. Correlation
analysis indicated that EPPO storage at 50% RH is more related to aging under TRSS at 60% and CD-aging at 75% ERH rather than CWSS at 40% ERH. In
conclusion, aging rice seeds under EPPO conditions is a suitable experimental
aging method for analyzing variation among seed lots or genotypes for
longevity under storage.