Carrot seed germination and ethylene production at high temperature in response to seed priming

Resumo

ABSTRACT

Carrot (Daucus carota) seed germination can be erratic or reduced under high temperatures above 35ºC.Priming circumvents seed thermoinhibition in several crops, including carrot. The involvement of ethylene in germination at supra-optimal temperatures has been reported in other species, but its role in carrot seed germination has not been examined.  The main objective of this study was to determine whether priming-mediated improvement in carrot seed germination at high temperature was associated with increased ethylene production. Seeds of two tropical carrot genotypes (‘Alvorada’ and ’Brasília’) were incubated over a range of temperatures. ‘Brasilia’ seeds were primed for 72 hours in aerated PEG solutions at 15ºC under light conditions and germination tested at 20 and 35ºC. Seeds of a thermosensitive genotype ‘Arrowhead’ were primed for 0, 4, 8 and 12 days in aerated PEG solutions at 15ºC under light conditions. Seeds were incubated at 20 and 35ºC, and ethylene production was measured immediately before visible radicle protrusion. Temperatures above 30⁰C decreased seed germination percentage  of ‘Alvorada’ and ‘Brasilia’. Priming increased ‘Brasilia’ seed germination at 35ºC. ‘Arrowhead’ germinated 96% at 20ºC,  and 13% at 35ºC.   Seed germination and ethylene production in a ‘Arrowhead’, a thermosensitive genotype increased in response to increased duration of primimng. The results suggest that seed priming circumvents thermoinhibition of carrot seed germination by increasing ethylene production at high temperatures.

Keywords: Daucus carota L., thermotolerance, stand establishment, vigor, cultivars.