Rapid seed germination and stand establishment are critical factors to crop production under salt‐stress conditions. In many crop species, seed germination and early seedling growth are the most sensitive stages to salinity stress. Salinity may delay the onset, reduce the rate, and increase the dispersion of germination events, leading to reductions in plant growth and final crop yield. The adverse effects of salt‐stress can be alleviated by various measures, including seed priming (a.k.a. pre‐sowing seed treatment). The general purpose of seed priming is to partially hydrate the seed to a point where germination processes are begun but not completed. Most priming treatments involve imbibing seed with restricted amounts of water to allow sufficient hydration and advancement of metabolic processes but preventing germination or loss of desiccation tolerance. Treated seeds are usually redried before use, but they would exhibit rapid germination when re‐imbibed under normal or stress conditions. Various seed priming techniques have been developed, including hydropriming (soaking in water), halopriming (soaking in inorganic salt solutions), osmopriming (soaking in solutions of different organic osmotica), thermopriming (treatment of seed with low or high temperatures), solid matrix priming (treatment of seed with solid matrices), and biopriming (hydration using biological compounds). Each treatment has advantages and disadvantages and may have varying effects depending upon plant species, stage of plant development, concentration/dose of priming agent, and incubation period. In this article, we review, evaluate, and compare effects of various methods of seed priming in improving germination of different plant species under saline and non‐saline conditions. We also discuss the known metabolic and ultra‐structural changes that occur during seed priming and subsequent germination. To maximize the utility of various seed priming techniques, factors affecting their efficiency must be examined and potential benefits and drawbacks determined. For example, quality of the seed before treatment, concentration/dose of priming agent, time period for priming, and storage quality of the seed following priming treatment must be carefully determined. Furthermore, such assessments must be based on large‐scale experiments if seed priming is to be used for large‐scale field planting. A better understanding of the metabolic events that take place in the seed during priming and subsequent germination will improve the effective application of this technology. The incorporation of advanced molecular biology techniques in seed research is vital to the understanding and integration of multiple metabolic processes that can lead to enhanced seed germination, and consequently to improved stand establishment and crop yield under saline and non‐saline conditions.

Pre‐Sowing Seed Treatment—A Shotgun Approach to Improve Germination, Plant Growth, and Crop Yield Under Saline and Non‐Saline Conditions

Preplant Physiological Seed Conditioning

Presowing Seed Priming

A matricondition ing procedure based on the matric properties of Micro-Cel E and expanded vermiculite #5 has proved effective in improving seedling emergence in growth chambers. The major objectives of this study were to examine some physical characteristics of the carriers and their effectiveness as preplant conditioning media in improving stand establishment of vegetable seeds in field plantings. Carrier characteristics included no detectable solute or osmotic potential, low electrical conductivity (0.48-0.04 mmho/cm), high water-retaining capacity (450% to 600%), a pH range of 7.0 to 8.4, and ability to effectively control seed hydration (conditioning) at low matric potential. The seed : carrier : water ratio for seed conditioning ranged from 1:0.3-0.5:1-2 (by weight). In a field trial, condi- tioning of 'Long Imperator' and 'Nantes' carrot (Daucus carota var. sativus Hoffm.) seeds reduced the time to 10% of final emergence (T1O) by 2.6 to 2.8 days and to 50% of final emergence (T 50) by 2.1 to 3.0 days. Conditioning increased the final emergence percentage by 39% in 1-year-old 'Long Imperator' compared to 150% in 4-year-old 'Nantes' seeds. In another field trial, the effect of conditioning on stand establishment was evaluated in 'Jackpot' tomato (Lycopersicon esculentum Mill.), 'California Wonder' pepper (Capsicum annuum L.), and 'BBL 47' snap bean (Phaseolus vulgaris) seeds. In tomato, conditioning reduced the T 10 by 0.9 day, had no effect on T 50, and increased the emergence percentage by 86%. In pepper, conditioning reduced the T 10 and T50 by 1.5 days and increased the percentage emergence by 30%. In snap bean seeds, conditioning in Micro-Ccl E reduced the T 1O and T50 by 0.8 day but adversely affected the percentage emergence. Further reductions in T 10 and T50 (1.2 and 1.6 days, respectively) and restoration of percentage emergence to control level occurred upon addition of 0.001 mM GA 3 during conditioning. Fungicides added to carrot, tomato, and pepper seeds, with or without conditioning, showed no additional improve- ments and, in a few cases, adversely affected emergence. A preplant conditioning in Micro-Ccl E, alone or in combination with GA3, smears to be a viable alternative to conditioning! seeds in liquid carriers. Chemical name used: gibberellic acid (GA3 ) Osmoconditioning or priming of seeds in solutions of low water potential, e.g., polyethylene glycol (PEG) and salts, has been used extensively as a preplant seed treatment to reduce germination or seedling emergence time, synchronize emer- gence, and improve stand establishment and yield (Bradford, 1986; Heydecker and Coolbear, 1977; Khan, 1991; Khan et al., 1978). A preplant seed conditioning has also been achieved by mixing seeds with moist solid or semisolid carriers (e.g., ver- miculite, expanded calcined clay, Agro-Lig, sodium polypro- pionate gel, synthetic calcium silicates) (Bennett and Waters, 1987; Callan et al., 1990; Khan et al., 1990; Kubik et al., 1988; Parera and Cantliffe, 1990; Peterson, 1976; Taylor et al., 1988; Zuo et al., 1988). Postplant conditioning of beet seeds in moist soil microenvironment in the field has been achieved by incor- porating PEG into solid material used for seed pelleting, as indicated by improved emergence and yield (Khan and Taylor, 1986). Hydration or conditioning of seeds can be regulated by os- motic and/or matric components of the carrier matrix water po- tential. The water potential component(s) of the carrier can be

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Matriconditioning of Vegetable Seeds to Improve Stand Establishment in Early Field Plantings

Enhancement of seed vigour following insecticide and phenolic elicitor treatment.

Cold soil interferes with early establishment of uniform, vigorous seedlings in vegetables and other crops. The aim of this work was to determine if the changes induced in carrot (Daucus carota L.) seeds during partial hydration by low osmotic potential polyethylene glycol 6000 (PEG) solution would allow early planting in cold soil and thereby improve germination, growth, and yield. Seeds of two carrot cultivars, ‘Nantes’ and ‘Perfekcja’, were treated in —8.6 bars PEG solution for 6 days at 15 C. The effects of the seed treatment were evaluated by germinating the seeds on filter paper at 10 C, in Cornell Soil Mix (peat-lite Mix A) in a growth chamber at an alternating temperature regime of 5 and 10 C and in the field (Glossoboric Hapludalf, fine loamy, mixed mesic soil) where the average soil temperature during the first 2 weeks after field planting was 10.5 C and during the first 5 weeks 12.6 C. Seed osmoconditioning unproved the emergence time, stand size, and uniformity of stand in the field and increased the total yield. The increase in fresh weight of roots in Nantes and Perfekcja from PEG treated seeds were 32 and 93% and in number of roots 37 and 100%, respectively, compared to the untreated seeds

Anna Szafirowska

Papers

Osmoconditioning of Carrot Seeds to Improve Seedling Establishment and Yield in Cold Soil1

Presowing seed conditioning to improve stand establishment and yield of vegetables