STAND ESTABLISHMENT TECHNOLOGIES FOR PROCESSING CARROTS

Achieving an optimal crop stand, especially in mineral soils, has been a great challenge in carrot production. Cool soil temperatures, crusting and low moisture availability are some of the factors that contribute to poor germination, slow seedling emergence and reduced vigor. Several anticrustants such as humic acid, orthophosphoric acid and F-68 were applied to soil immediately after sowing. Although soil application of humic acid promoted early seedling emergence there was no significant difference in crop stand among any of the treatments after 41d after sowing. There was no significant yield difference among any of the anticrustant treatments. Primed seeds promoted early emergence with the cv. Indiana but not with cv. Newport. Priming did not alter root length, yield or grades. GA3 promoted germination at 5°C but there was no synergistic effect with any of the salicylates. Optimal soil moisture for early and uniform seedling emergence was 35-40% Field Capacity (FC). Soil moisture above 40% and below 35% FC reduced seedling emergence significantly. Seed preconditioning using natural and synthetic antistress and antioxidant compounds, glycinebetaine (100 mg L) and AMBIOL, a derivative of 5-hydroxybenzimidazole (0.1 mg L) both promoted emergence at 40% FC but at a limiting low moisture content of 25% FC, Ambiol was the most effective. Seed bioconditioning using endophytic beneficial bacteria (EPBBs) obtained from carrot crowns, Pseudomonas fluorescens #37 and P. putida #144 both enhanced seedling growth in vivo. Bacillus magnetarium promoted root length but did not increase biomass of the seedlings. Optimal carrot emergence under low soil temperature and moisture conditions can be achieved through seed preconditioning using GA3 and Ambiol and through bioconditioning using selective EPBBs. INTRODUCTION Sporadic and delayed seedling emergence is a major problem in processing carrot production in cool, dry mineral soils that results in a reduced crop stand, directly lowering root yield and grades. Although germination and vigor are gene controlled, seed size, viability, sowing depth, soil moisture, oxygen concentration and temperature all can influence germination, emergence and vigor (Bewley and Black, 1982; Rajasekaran et al., 1992; Hartman et al., 1997; Rajasekaran et al., 2002). Soil crusts can act as physical barriers limiting emergence, resulting in poor stands (Bewley and Black, 1982). Low soil temperature and moisture affect both germination percentage and vigor value (Kotowski, 1926; Bewley and Black, 1982; Rajasekaran et al., 1992; Rajasekaran et al., 2002). Proc. XXVI IHC – Transplant Production and Stand Establishment Eds. S. Nicola, J. Nowak and C.S. Vavrina Acta Hort. 631, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 106 Temperatures below 20°C limit carrot seed germination (Rajasekaran et al., 2002). Soil moisture deficit can also reduce seed germination through osmotic effects delaying imbibition and/or inhibiting radicle and plumule elongation thereby limiting emergence (Bewley and Black, 1982). Soil drying can eventually lead to soil crusting, especially in mineral soils with low organic matter, obstructing and/or preventing seedling emergence partially or completely (Robbins et al., 1972). Preventing soil crust formation may facilitate seedling emergence. Anticrustants such as phosphoric acid and humic acid have been used to prevent crusting with different degrees of success (Robbins et al., 1972; Hemphill, 1982; Orzolek, 1987). Pregerminated seeds are also used with different degrees of success (M. Upton, Bejo Seeds, New York, personal communication). Pretreating seeds with salicylates such as acetylsalicylic acid, 2,6-dihydroxybenzoic acid and salicylic acid all promote germination at a limiting temperature of 5°C (Rajasekaran et al., 2002). Since salicylates promote seed germination at low temperatures and GA is critical for seed germination and elongation, it is possible that GA could be limiting under low temperature and germination under low temperature can be promoted by seed preconditioning using GA. It is also possible that GA may have synergistic effects in promoting germination when treated with salicylates. Seed treatments using GA3, benzyl adenine (BA), potassium nitrate, phosphate and chloride (Cantliffe et al., 1987), polyethylene glycol (Dearman et al., 1987), ABA (Finch et al., 1989) are all known to promote germination of carrot seeds to different degrees. However, the possibility of using antistress compounds and antioxidants to promote emergence, under limiting moisture conditions, has received relatively little study. Water stressed carrots synthesize a quaternary ammonium compound, glycinebetaine (Caldwell, 2001; Caldwell et al., 2001; Caldwell and Rajasekaran, 2002) which protect carrot plants (Caldwell, 2001). This suggests that that glycinebetaine may be used to enhance emergence, confer osmoprotection and invigorate seedlings under moisture deficit. Ambiol, a derivative of 5-hydroxybenzimidazole enhances drought tolerance of carrot seedlings and confer membrane protection (Rajasekaran and Blake, 2002; Borsos-Matovina and Blake, 2000; Vishnevetskaia and Roy, 1999); however, it is not known whether Ambiol promotes seedling emergence under limiting moisture conditions. Endophytes are known to colonize plant parts including roots and promote plant growth, increase pest and disease resistance and confer protection against various abiotic stresses (Nowak, 1998; Nowak et al., 1995; Conn et al., 1997, Sturz et al., 1998). Although seed bioconditioning with beneficial microorganisms has been known for some time (reviewed in McQuilken et al., 1998), there is no information on utilization of carrot specific endophytes and their roles in invigorating carrot seedlings. Experiments were conducted to determine whether 1) anticrustants promote seedling emergence; 2) seed priming increases emergence in crusty soils; 3) thermogenic compounds and/or GA3 promote germination under limiting low temperature; 4) glycinebetaine and Ambiol promote emergence under low moisture conditions; 5) bioconditioning using carrot endophytes invigorates seedlings. MATERIALS AND METHODS Daucus carota var. Sativus L. cultivar Oranza (Bejo Seed Company, New York, USA) was used in all our studies or as specified in each of the experiments. Field experiments were conducted in Kings County, Nova Scotia, Canada. The soil in the field location was classified as Queens series, a sandy loam texture of moderate to high fertility, with pH of 5.5-6.5 and 1.5-3% organic matter. The fields were generally under a carrot-grain-forage rotation. Seeding was done at a rate of 33 seeds per 30 cm on raised hills spaced at 60 cm using a Stanhay pneumatic seeder. Standard crop production practices were followed.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.