Patterns of mitochondrial DNA fragmentation in bread wheat (Triticum aestivum L.) seeds under ex situ genebank storage and artificial aging

Monitoring viability loss of seeds conserved ex situ for timely germplasm regeneration is a challenging task in germplasm management and conservation as the process of seed deterioration under long-term storage remains poorly understood and effective tools for assessing seed deterioration are lacking. This paper reports findings from four experiments that were aimed to study the fragmentation of mitochondrial DNA (mtDNA) due to degradation in naturally or artificially aged (NA or AA) wheat seeds. Together, it was found that mtDNA fragmentation occurred in aged wheat seeds. More mtDNA fragmentation was observed in AA than NA seeds and degradation was more prominent in abnormal seedling tissues than in normal seedling tissues. Fragmentation of mtDNA was linearly associated with sample germination; more in less viable seed samples. Mitochondria (mt) in aged seeds were found to break throughout the mitochondrial genome with the observed loss of PCR amplification of atp1-5, nad4.2, atp4, and nad9 gene loci and at the roughly 80 kb repetitive region. These findings are useful for understanding the process and involvement of mtDNA degradation in NA or AA wheat seeds and for further exploration to develop aging biomarkers for monitoring seed viability.