Germinação de sementes de cenoura e produção de etileno em alta temperatura em resposta ao osmocondicionamento

Carrot (Daucus carota) seed germination can be erratic or reduced under temperatures above 35 degrees C. 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 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 Bras lia) were incubated over a range of temperatures. 'Brasilia' seeds were primed for 72 hours in aerated PEG solution at 15 degrees C under light conditions and germination tested at 20 and 35 degrees C. Seeds of a thermosensitive genotype 'Arrowhead' were primed for 0, 4, 8 and 12 days in aerated PEG 6000 solutions at 15 degrees C under light conditions. Seeds were incubated at 20 and 35 degrees C, and ethylene production was measured immediately before visible primary root protrusion. Temperatures above 30 degrees C decreased seed germination percentage of 'Alvorada' and 'Brasilia'. Priming increased 'Brasilia' seed germination at 35 degrees C. 'Arrowhead' germinated 96% at 20 degrees C, and 13% at 35 degrees C. Seed germination and ethylene production of 'Arrowhead', a thermosensitive genotype, increased in response to increased duration of priming. The results suggest that seed priming circumvents thermoinhibition of carrot seed germination by increasing ethylene production at high temperatures.