Abstract
Background and AimsUnderstanding variation in seed longevity, especially within closely related germplasm, will lead to better understanding of the molecular basis of this trait, which is particularly important for seed genebanks, but is also relevant to anyone handling seeds. We therefore set out to determine the relative seed longevity of diverse Indica rice accessions through storage experiments. Since antioxidants are purported to play a role in seed storability, the antioxidant activity and phenolic content of caryopses were determined.MethodsSeeds of 299 Indica rice accessions harvested at 31, 38 and 45 d after heading (DAH) between March and May 2015 and differing in harvest moisture content (MC) were subsequently stored at 10.9 % MC and 45 °C. Samples were taken at regular intervals and sown for germination. Germination data were subjected to probit analysis and the resulting parameters that describe the loss of viability during storage were used for genome-wide association (GWA) analysis.Key ResultsThe seed longevity parameters, Ki [initial viability in normal equivalent deviates (NED)], −σ−1 (σ is the time for viability to fall by 1 NED in experimental storage) and p50 [time for viability to fall to 50 % (0 NED)], varied considerably across the 299 Indica accessions. Seed longevity tended to increase as harvest MC decreased and to decrease as harvest MC increased. Eight major loci associated with seed longevity parameters were identified through GWA analysis. The favourable haplotypes on chromosomes 1, 3, 4, 9 and 11 enhanced p50 by ratios of 0.22–1.86.ConclusionsThis is the first study to describe the extent of variation in σ within a species’ variety group. A priori candidate genes selected based on rice genome annotation and gene network ontology databases suggested that the mechanisms conferring high seed longevity might be related to DNA repair and transcription, sugar metabolism, reactive oxygen species scavenging and embryonic/root development.
Highlights
Orthodox seeds can remain viable for many years if stored at low moisture content (MC) and low temperature (Bewley and Black, 1994)
The aims of this study were to: (1) characterize the survival curves of seeds of diverse Indica rice accessions; and (2) identify loci/candidate genes associated with seed longevity in Indica rice through genome-wide association (GWA) analysis, taking into account the effects of seed maturity and harvest moisture content
The seeds did not consistently lose or gain moisture during the seed storage experiment, or differ in MC within an accession depending on maturity
Summary
Orthodox seeds can remain viable for many years if stored at low moisture content (MC) and low temperature (Bewley and Black, 1994). This ‘storability’ or ‘longevity’ is exploited as a means of ex situ conservation of biodiversity in seed-/ genebanks. The length of time that seeds can survive varies among species (Justice and Bass, 1978; Walters et al, 2005; Probert et al, 2009; Merritt et al, 2014). It varies among seed lots within a species and among the individual seeds within a seed lot. Seed lots with high viability are likely to have high vigour; reduced vigour is an early symptom of seed ageing
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