The availability of water to the mother plant during seed production is important because it affects seed yield and quality of many species. In general, most of the research on water requirements of different crops has focused on optimizing yield of commodity products and only rarely considered seed yield or quality parameters (George, 1999). Optimal water management for seed production may be different from best management practices for crop production, especially in species for which the final products are not grains (e.g., many vegetables and forages).
Effects of water stress on seed yield depend on the crop and will vary depending on the intensity, duration, and timing of the water deficit (Izzeldin et al., 1980). In general, water stress before and during flowering has been observed to affect seed yield by reducing the number of seeds produced per plant (Bartels and Caesar, 1987; Champolivier and Merrien, 1996; Oliva et al., 1994; Žebrauskienė et al., 2005), whereas individual seed weight has been affected by water deficit after flowering (Castañeda et al., 2006; Champolivier and Merrien, 1996; Fougereux et al., 1997; Ludlow et al., 1990; Ramamoorthy and Basu, 1996). However, there are cases in which moderate water deficits have increased seed yield or seed size. For instance, Shock et al. (2007) reported that moderate deficit irrigation from flowering to seed maturity improved yield and individual weight of alfalfa (Medicago sativa L.) seeds. Santos et al. (2006) observed that seeds of wild bushbean (Macroptilium lathyroides L.) were heavier when produced under restricted water availability (60% to 70% soil field capacity). Less research has examined the effects of water stress on other aspects of seed quality such as germination, germinability, and storability. In general, the consensus is that water deficiency during seed development reduces dormancy and improves germination of wild species (Fenner, 1991; Gutterman, 2000; Hilhorst and Toorop, 1997). Water deficit had no effect on seed germinability and vigor of onion (Allium cepa L.) (Žebrauskienė et al., 2005), peanut (Arachis hypogaea L.) (Ramamoorthy and Basu, 1996), and maize (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench.] (Ghassemi-Golezani et al., 1997). Zhao et al. (1993) observed that seeds from water-stressed cotton (Gossypium hirsutum L.) plants had faster germination and higher vigor. Ramamoorthy and Basu (1996) and Sinniah et al. (1998) reported that water deficit during seed production improved storability of peanut and rapid-cycling brassica [Brassica campestris (rapa) L.] seeds, respectively.
Lettuce (Lactuca sativa L.) is one of the most important vegetables in the world. In the United States, between 2001 and 2006, lettuce was cultivated on over 121,000 ha per year with an annual crop value of ≈2 billion dollars, which makes it the most valuable fresh vegetable in the country (U.S. Department of Agriculture, 2007). Lettuce seed quality is important because it affects establishment of the crop along with final yield and quality (Smith et al., 1973b; Wurr and Fellows, 1985). Working with pot-grown lettuce plants in the greenhouse, Soffer and Smith (1974) observed that withholding water and nutrients during the last half (20 to 25 d) of the seed production period did not affect seed yield per plant, seed weight distribution, or seedling vigor (measured as seedling root length). Izzeldin et al. (1980) studied the effects of water stress on lettuce seed yield and quality by applying three levels of soil moisture deficit (–0.03, –0.08, and –0.5 MPa) at different growth stages of plants grown in a greenhouse. These authors reported that lettuce plants under moderate water deficit produced the highest seed yields; however, the highest quality (size and vigor measured as seedling radicle elongation) occurred for seeds produced under severe water stress treatments.
Because lettuce seeds are mainly produced in arid and semiarid conditions, understanding the effects that restricting water has on seed yield and quality is important to optimize the use of irrigation water. The objective of this study was to determine how water availability during seed development affects lettuce seed production, especially seed yield and quality.
Bartels, M. & Caesar, K. 1987 The influence of drought stress in various growth phases on growth, flower drop and yield of soyabeans Glycine max. (L.) Merr J. Agron. Crop Sci. 158 346 352
Benech-Arnold, R.L., Fenner, M. & Edwards, P.J. 1991 Changes in germinability, ABA content and ABA embryonic sensitivity in developing seeds of Sorghum bicolor (L.) Moench. induced by water stress during grain filling New Phytol. 118 339 347
Castañeda Saucedo, M.C., Córdova Téllez, L., González Hernández, V.A., Delgado Alvarado, A., Santacruz Varela, A. & García de los Santos, G. 2006 Respuestas fisiológicas, rendimiento y calidad de semilla en fríjol sometido a estrés hídrico Interciencia 31 461 466
Champolivier, L. & Merrien, A. 1996 Effects of water stress applied at different growth stages to Brassica napus L. var. oleifera on yield, yield components and seed quality Eur. J. Agron. 5 153 160
Contreras, S. 2007 Effects of maternal plant environment on lettuce (Lactuca sativa L.) seed dormancy, germinability, and storability Ohio State Univ Columbus PhD Diss.
Contreras, S. & Barros, M. 2005 Pruebas de vigor en semillas de lechuga y su correlación con emergencia Cienc. Invest. Agraria 32 3 11
Fougereux, J.A., Doré, T., Ladonne, F. & Fleury, A. 1997 Water stress during reproductive stages affects seed quality and yield of pea (Pisum sativum L.) Crop Sci. 37 1247 1252
Ghassemi-Golezani, K., Soltani, A. & Atashi, A. 1997 The effect of water limitation in the field on seed quality of maize and sorghum Seed Sci. Technol. 25 321 323
Gutterman, Y. 2000 Maternal effects on seeds during development 59 84 Fenner M. Seeds: The ecology of regeneration in plant communities 2nd ed CABI Publishing Wallingford, UK
Hayes, R.G. & Klein, W.H. 1974 Spectral quality influence of light during development of Arabidopsis thaliana plants in regulating seed germination Plant Cell Physiol. 15 643 653
Ikuma, H. & Thimann, K.V. 1964 Analysis of germination processes of lettuce seed by means of temperature and anaerobiosis Plant Physiol. 39 756 767
Izzeldin, H., Lippert, L.F. & Takatori, F.H. 1980 An influence of water stress at different growth stages on yield and quality of lettuce seed J. Amer. Soc. Hort. Sci. 105 68 71
Ludlow, M.M., Santamaria, J.M. & Fukai, S. 1990 Contribution of osmotic adjustment to grain yield in Sorghum bicolor (L.) Moench under water-limited conditions: II. Water stress after anthesis Aust. J. Agr. Res. 41 67 78
Michel, B.E. 1983 Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes Plant Physiol. 72 66 70
Ni, B.R. & Bradford, K.J. 1993 Germination and dormancy of abscisic acid- and gibberellin-deficient mutant tomato (Lycopersicon esculentum) seeds: Sensitivity of germination to abscisic acid, gibberellin, and water potential Plant Physiol. 101 607 617
Oliva, R.N., Steiner, J.J. & Young W.C. III 1994 Red clover seed production: II. Plant water status on yield and yield components Crop Sci. 34 184 192
Oweis, T. & Hachum, A. 2006 Water harvesting and supplemental irrigation for improved water productivity of dry farming systems in West Asia and North Africa Agr. Water Manage. 80 57 73
Pieta-Filho, C. & Ellis, R.H. 1991 The development of seed quality in spring barley in four environments: I. Germination and longevity Seed Sci. Res. 1 163 177
Ramamoorthy, K. & Basu, R.N. 1996 Studies on the effect of moisture stress at different growth phases on seed vigour, viability and storability in peanut (Arachis hypogaea L.) J. Agron. Crop Sci. 177 33 37
Sako, Y., McDonald, M.B., Fujimura, K., Evans, A.F. & Bennett, M.A. 2001 A system for automated seed vigour assessment Seed Sci. Technol. 29 625 636
Santos, A.M.D., Rosa, L.M.G., Franke, L.B. & Nabinger, C. 2006 Heliotropism and water availability effects on flowering dynamics and seed production in Macroptilium lathyroides Rev. Bras. Sementes 28 45 52
Shock, C.C., Feibert, E.B.G., Saunder, L.D. & Klauzer, J. 2007 Deficit irrigation for optimum alfalfa seed yield and quality Agron. J. 99 992 998
Sinniah, U.R., Ellis, R.H. & John, P. 1998 Irrigation and seed quality development in rapid-cycling brassica: Seed germination and longevity Ann. Bot. (Lond.) 82 309 314
Smith, O.E., Welch, N.C. & Little, T.M. 1973a Studies on lettuce seed quality, I. Effect of seed size and weight on vigor J. Amer. Soc. Hort. Sci. 98 529 533
Smith, O.E., Welch, N.C. & McCoy, O.D. 1973b Studies on lettuce seed quality: II. Relationship of seed vigor to emergence, seedling weight, and yield J. Amer. Soc. Hort. Sci. 98 552 556
Soffer, H. & Smith, O.E. 1974 Studies on lettuce seed quality: III. Relationships between flowering pattern, seed yield, and seed quality J. Amer. Soc. Hort. Sci. 99 114 117
Toyomasu, T., Kawaide, H., Mitsuhashi, W., Inoue, Y. & Kamiya, Y. 1998 Phytochrome regulates gibberellin biosynthesis during germination of photoblastic lettuce seeds Plant Physiol. 118 1517 1523
U.S. Department of Agriculture 2007 Vegetables and Melons Outlook/VGS-321/21 June 2007. Economic Research Service 18 July 2007 <http://www.ers.usda.gov/publications/vgs/tables/fresh.pdf>.
van der Woude, W.J. & Toole, V.K. 1980 Studies of the mechanism of enhancement of phytochrome-dependent lettuce seed germination by prechilling Plant Physiol. 66 220 224
Wery, J. 2005 Differential effects of soil water deficit on the basic plant functions and their significance to analyze crop responses to water deficit in indeterminate plants Aust. J. Agr. Res. 56 1201 1209
Wurr, D.C.E. & Fellows, J.R. 1985 A determination of the seed vigour and field performance of crisp lettuce seedstocks Seed Sci. Technol. 13 11 17
Yogeesha, H.S., Upreti, K.K., Padmini, K., Bhanuprakash, K. & Murti, G.S.R. 2006 Mechanism of seed dormancy in eggplant (Solanum melongena L.) Seed Sci. Technol. 34 319 325
Žebrauskienė, A., Kmitienė, L., Bobinas, Č., Duchovskis, P. & Kmitas, A. 2005 Influence of soil moisture deficit in various phases of edible onion development on seed yield and quality Sodininkystė Ir Daržininkystė 24 261 272
Zhao, D.L., Xu, Y.Z., Huang, Y.F. & Xu, X. 1993 The effects of water deficiency on the development of cotton seeds during flowering and fruiting stages Acta Agron. Sinica 19 546 552