Many publications relate the negative effects of low temperature on carrot stand establishment ( Cantliffe and Elballa, 1994 Corbineau et al., 1994 Nascimento and Pereira, 2007 Pereira et al., 2007 Vieira et al., 2005). thermotolerance stand establishment vigor cultivars germplasmĬarrot crops are established by direct seeding, and poor stands may occur when sowing is done during extremely low or high temperatures. High correlations were observed between first germination count at 35 ☌ and ethylene production, total germination at 35 ☌ and ethylene production, and thermotolerance ratio and ethylene production. Ethylene production during seed germination at high temperature was greater in thermotolerant genotypes than in thermosensitive genotypes. The identified thermotolerant genotypes might be useful for carrot seed germination mechanism studies as well as for breeding programs. Six accessions (Ames 7665, Ames 7698, Ames 25031, PI 167082, PI 294637, and PI 319858) germinated above 80% at 35 ☌ and were also identified as potential sources of thermotolerance. The accession PI 319858 germinated 95% at both temperatures and was considered thermotolerant. A greater number of accessions germinated at 35 ☌ than did the commercial genotypes. ‘XPC-3617’, ‘Alvorada’, ‘Brasilia’, and ‘Esplanada’ had the greatest germination at 35 ☌. Many of the commercial cultivars had reduced germination at 35 ☌. Ethylene production during seed imbibition at high temperature was evaluated in some genotypes. Seeds from 34 commercial cultivars and 125 carrot accessions from the North Central Regional Plant Introduction Station were germinated at 25 ☌ (optimal) and 35 ± 0.5 ☌ (high) in constant light. The objectives of this study were to characterize commercial carrot cultivars and accession lines for their ability to germinate at high temperature and determine the ethylene production during imbibition at high temperature. Even in tropical genotypes (tolerant to high temperatures during crop development), the negative effects of high temperatures on carrot stand establishment have been observed, especially during summer. Carrot ( Daucus carota L.) seed germination may be erratic or reduced under high temperatures (above 35 ☌).
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