Carrot Seed Germination at High Temperature Conditions

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1 Carrot Seed Germination at High Temperature Conditions W.M. Nascimento a, R.S. Pereira and J.V. Vieira Embrapa Vegetables CP Brasilia-DF Brazil D.J. Cantliffe University of Florida, IFAS Horticultural Sciences Department Gainesville, FL USA Keywords: Daucus carota L., thermoinhibition, seed priming, maturation Abstract Carrot seed germination and consequently stand establishment may be reduced under 35ºC. Studies on carrot germination at high temperature in response to genotype, umbel order, seed maturation and priming were performed to determine some conditions that led to improved germination at 35 C. Seeds from 34 cultivars and 125 accessions were germinated at 25 and 35 C. In other studies, seeds from primary, secondary and tertiary umbels were harvested separately and tested for germination at 20 and 35 C. Seeds harvested at different maturation periods (20, 30 and 40 days after anthesis - DAA) and primed in a PEG solution were also evaluated in both germination temperatures. In all studies, high temperatures decreased germination. Many of the commercial cultivars had reduced germination at 35ºC; XPC-3617, Alvorada, Brasilia and Esplanada had the greatest germination at 35ºC. The accession PI germinated 95% in both temperatures and was considered as thermotolerant. Seeds from primary and secondary umbels had greater vigor and germination at high temperature than seeds from tertiary umbels. At 20ºC, unprimed seeds from umbels harvested after 20, 30 and 40 DAA germinated 88, 95 and 95%, respectively, while at 35ºC, seeds germinated only 4, 13 and 28%, respectively. Seeds from umbels harvested after 40 DAA and primed for 9 days germinated 98 and 89% at 20 and 35ºC, respectively. Selection of superior thermotolerant genotypes, as well as the use of seed priming and/or other cultural practices during seed production may help circumvent carrot thermoinhibition problems. INTRODUCTION Carrot crops are established by direct seeding, and poor stands may occur when sowing is done during extremely warm temperatures. High temperatures (35-40 C) may delay or inhibit carrot seed germination in the field and reduce uniformity and total stand establishment (Cantliffe and Elballa, 1994; Gray et al., 1988; Rubatzky et al., 1999; Nascimento and Pereira, 2007). In tropical areas, carrot production is vulnerable to loss from thermal stress (heat) during stand establishment (Vieira et al., 2005) and most commercial carrot cultivars have reduced seed germination at high temperatures. Seed priming proved to be an effective treatment for the improvement of carrot stand establishment, which corroborate other studies (Cantliffe and Elballa, 1994; Nascimento and Pereira, 2007). Osmotic priming is based on the balance of seed hydration, at a level that allows the occurrence of metabolic activity, but prevents cellular elongation and primary root emergence. Osmotic priming success depends on several factors, including soaking period of seeds in the solution. The objectives of this study were to determine the inhibition effects at high temperatures of carrot seed germination, to characterize commercial carrot genotypes, to screen germplasm with greater tolerance to germinate at high temperatures, as well as to study the effects of seed maturation in response to seed priming and umbel order for seed germination at high temperatures. a wmn@cnph.embrapa.br Proc. XXVIII th IHC IS on Quality-Chain Mgt. of Fresh Veg.: from Fork to Farm Ed.: E. Rosa Acta Hort. 936, ISHS

2 MATERIALS AND METHODS Germination at High Temperature of Carrot Cultivars from Various Commercial Sources Seeds of 34 commercial carrot genotypes from different seed companies were used in this study (Table 1). Three replications of 25 seeds were placed in a 5.5 cm Petri dish with two layers of 4.5 cm diameter #3 filter paper (Anchor Paper, Hudson, WI) moistened with 4 ml of distilled water. Seeds were incubated under constant light (30 μmol m -2 s -1 ) in Precision Scientific (Winchester, VA, USA) incubators at 25ºC (optimal) and 35±0.5ºC (adverse). Germination was defined as visible radicle protrusion through the seed coat and was evaluated after 5 (first counting) and 10 (final) days of incubation. Screening Carrot Germplasm for Seed Germination at High Temperature Seeds of 125 carrot accessions from the North Central Regional Plant Introduction Station (NCRPIS), located in Ames, IA, part of the United States National Plant Germplasm System were used in this study. Three replications of twenty seeds were incubated using the same procedures as described in the previous study. Distances were performed with the Genes Program (Cruz, 2001), where the dissimilarity matrix was transferred to the NTSYSpc Program (Rohlf, 2000) for the creation of a dendogram based on the unweighted pair group method using arithmetic averages (UPGMA) clustering algorithm and determination of a cophenetic correlation coefficient between the matrix and the clusters (Rohlf and Sokal, 1981). An estimation of hypothetical ideal (Ideotype) was performed, where the values for each character were considered as the highest among the accessions. For the accessions of each group a means analysis was performed following the procedures of Scott and Knott (1974). Seed Maturation and Priming Study Seeds from a thermosensitive population ( 07 EC-403, Nunhems) were produced under Florida, USA, field conditions from March to July using vernalized roots. Secondary umbels were labeled at anthesis. At 20, 30 and 40 days after anthesis (DAA), umbels were harvested, dried and manually processed. Part of the seed batch was primed in an aerated polyethylene glycol (PEG) (30%) solution at 15ºC for 0, 3, 6 and 9 days, under light conditions. Seeds were incubated using the same procedures as described in the previous study. Umbel Orders Study In a Brasilia carrot basic seed production field in Brasilia, DF, Brazil, primary, secondary and tertiary umbels were harvested separately. After threshing, seeds were tested for germination at 20 C (optimal) and 35 C (adverse) using the same procedures as described in the previous study. RESULTS AND DISCUSSION Germination at High Temperature of Carrot Seeds from Different Commercial Cultivars At 25ºC, seed germination of most of cultivars was above 80% (Table 1). The three subtropical cultivars ( Alvorada, Brasilia and Esplanada ) and XCR-3617 had the greatest germination under high temperature. Most other cultivars had reduced germination at 35ºC. Screening Carrot Germplasm for Seed Germination at High Temperature Two different groups, according to the germination at high temperatures were formed (data not shown). In the first group, the ideal accession was PI from Japan, which germinated 95% in both temperatures and was considered as thermotolerant. For the second group, no significant differences occurred among the means at 25ºC, as 134

3 only three clusters were formed. At 35ºC however, many accessions did not germinate or had low germination values. The accessions Ames from Turkey, PI from Pakistan and Ames from Bulgaria had the highest germination at 35ºC, although their values were lower than those from the first group. The best genotypes for all characters in each group, according to the selection index based upon Desirable Gains of Pesek and Baker (1969), were: Group 1 (Ideotype, PI from Turkey, PI and PI from Japan and PI from Jordan); and Group 2 (Ames from Greece, PI from Pakistan, Ames and Ames from Greece and Ames from Syria). Seed Maturation and Priming Study Germination of unprimed seeds was 96% at 20ºC (data not shown), whereas at 35ºC, germination was 13% (Fig. 1). Priming increased germination rate and total germination at both temperatures, and the better response was observed especially in longer soaking periods. For example, priming for 4 days increased germination at 35ºC to 66%, whereas priming for 8 and 12 days increased to 96 and 97%, respectively. Unprimed seeds from umbels harvested at 20, 30 and 40 DAA germinated at 20ºC, 88, 95 and 95%, respectively (data not shown), while at 35ºC, seeds germinated only 4, 13 and 28%, respectively (Fig. 1). Seed germination increased in response to seed maturation (corroborating Nascimento et al., 2003) and soak duration. For example, seeds from umbels harvested at 40 DAA and primed for 9 days germinated 98 and 89% at 20 and 35ºC, respectively. To improve stand establishment, especially during periods of high temperatures, carrot seeds must be well developed in order to optimize the response from priming. Umbel Orders Study High temperatures decreased carrot seed germination. Seeds germinated better at 20 C (data not shown) than 35ºC. Seeds from primary and secondary umbels had higher vigor and germination at high temperature than seeds from tertiary umbels (Fig. 2). Carrot seeds from superior umbels generally have better seed quality than those from inferior umbel orders. High quality seeds may have a better performance in adverse conditions. Selection of superior thermotolerant genotypes, as well as the use of seed priming and/or other cultural practices during seed production may help circumvent carrot thermoinhibition problems. Literature Cited Cantliffe, D.J. and Elballa, M Improved germination of carrot at stressful high temperature by seed priming. Proc. Flo. Sta. Hort. Soc. 107: Gray, D., Steckel, J.R.A., Dearman, J. and Brocklehurst, P.A Some effects of temperature during seed development on carrot (Daucus carota L.) Ann. Appl. Bio. 112: Nascimento, W.M. and Pereira, R.S Preventing thermo-inhibition in carrot by seed priming. Seed Sci. Tech. 35: Nascimento, W.M., Vieira, J.V. and Alvares, M.C Physiological maturity of carrot seeds cv. Alvorada under tropical conditions. Acta Hort. 607: Pesek, J. and Baker, R.J Desired improvement in relation to selected indices. Can. J. Plant Sci. 49: Rubatzky, V.E., Quiros, C.F. and Simon, P.W Carrot and related vegetable Umbelliferae. CABI Publishing, New York, NY. 294p. Vieira, J.V., Cruz, C.D., Nascimento, W.M. and Miranda, J.E.C Seleção de progênies de meio-irmãos de cenoura baseada em características de sementes. Horticultura Brasileira 23:

4 Tables Table 1. Germination at 25ºC (TG25) and 35ºC (TG35) from 34 commercial carrot cultivars. Genotype TG25 TG35 TG25 TG35 Genotype (%) (%) (%) (%) Arrowhead 100 a 7 b Sugarsnax xx 96 a 17 b Copperhead 100 a 15 b Sugarsnax xc 97 a 15 b Trinity 84 b 1 b Esplanada 89 b 53 a Columbia 91 a 1 b Brasília EH 71 c 47 a Spearhead 96 a 20 a Alvorada EH 73 c 45 a XCR a 68 a Alvorada IL 79 c 35 a Maverick 100 a 11 b Brasília IL 80 c 12 b Nantindo 89 b 23 a Kuronan 84 b 28 a R. Chantenay 83 b 9 b Tropical 88 b 43 a Magnum 87 b 35 a Burpee A1 88 b 15 b Scarlet Nantes 85 b 1 b Imperator a 13 b Topcut 93 a 20 a Danvers b 25 b Navajo 97 a 5 b Chantenay 79 c 9 b Primecut xx 96 a 28 a Nantes C. 96 a 35 a Primecut xc 97 a 24 a Senator 79 c 17 b Topcut a 35 a Major 99 a 15 b Topcut xx 88 b 19 a Osiris 88 b 53 a 136

5 Figurese 100 Germination (%) Unprimed 3 days 6 days 9 days Days after anthesis (DAA) Fig. 1. Germination at 35 C of carrot seeds harvested after different maturation time and primed for different soaking periods. A a A ab b A Fig. 2. Means within each column (germination at 7 ( ) and 14 ( ) days at 35ºC of Brasilia carrot seeds from different umbel orders), followed by different letters are significantly different at P 0.05 according to Duncan test. 137

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

NASCIMENTO WM; HUBER DJ; CANTLIFFE DJ. 2013. Carrot seed germination and ethylene production at high temperature in response to seed osmopriming. Horticultura Brasileira 31: 554-558. Carrot seed germination