Enhancement of Apiaceae pre-germination embryo growth, mericarp ageing resilience and germination differs between hormone, gas plasma, and hydropriming technologies

Different seed priming technologies are used to improve germination performance and seedling vigour of vegetable crops. Daucus carota (carrot), Pastinaca sativa (parsnip), and other Apiaceae produce morphologically dormant single-seeded fruit halves (mericarps) as dispersal units. In mature mericarps the underdeveloped (small) embryo is embedded in abundant endosperm tissue and pre-germination embryo growth to a critical embryo:seed (E:S) length ratio is a requirement for the completion of germination by radicle emergence. We investigated how hydropriming and additive priming with gibberellins (GA), abscisic acid (ABA), and gas plasma-activated water (GPAW) affected carrot and parsnip mericarp germination and ageing sensitivity accessed using a wet ageing assay (80% RH, 42ºC). Carrot and parsnip mericarp priming enhanced germination speed (germination rate GR50%), maximal germination percentage (Gmax), and germination vigour. This was associated with enhanced pre-emergence embryo growth inside hydroprimed, hormone-primed and GPAW-primed mericarps. Hydropriming affected the hormone contents and ABA sensitivity of parsnip mericarps. It reduced the contents of bioactive GAs and indole-3-acetic acid ~2.1 and ~7.7-fold, and of the germination inhibitors ABA and cis-(+)-12-oxo-phytodienoic acid ~9.2 and ~6.0-fold, respectivily. Hydroprimed carrot and parsnip mericarps were more sensitive in the wet ageing assay. GPAW-priming increased carrot salinity tolerance, but did not increase its wet ageing resilience to a Controlled Deterioration Treatment (CDT). In contrast, GPAW-priming increased the wet ageing resilience of many other vegetable seeds and cereal grains. ABA-priming not only enhanced embryo growth and germination performance, it also increased the wet ageing resilience of carrot and parsnip mericarps. We conclude that ABA-priming and GPAW-priming are promising technologies to improve vigour and wet ageing resilience of primed seeds.