Salicornia Bigelovii As an Example with the Association of Nitrogen Fixers Bacterium (Plant Growth Promoting Bacterium- PGPB)
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PROPUSE OF SEAWATER IRRIGATION CROPS Salicornia bigelovii as an Example With the Association of Nitrogen Fixers Bacterium (Plant Growth Promoting Bacterium- PGPB) 1 Instructor: Dr. Edgar Omar Rueda Puente Sonora university Member of the National System of Researchers Sonora, México Tel phone Of. + 01-6625960297 in Agriculture Departament of Sonora University. [email protected] [email protected] [email protected] 1 Picture obtained from: seaphire internacional. OUR JUSTIFICATION WITH HALOPHYTES: WHY WE ARE WORKING WITH Salicornia bigelovii Development of Halophytic Crops Availability of fresh water for agricultural uses continues to decline due to increased demands for urban uses along with shrinking groundwater and surface water reserves. When this is coupled with predicted reductions in rainfall and streamflow that may occur as a consequence of the "greenhouse effect" that will impact major irrigated areas such as Arizona, it is clear that the need for salt tolerant crops will become even greater than at present. In addition to increasing the traditional breeding efforts presently underway to increase salt tolerance within specific crop species, that need should be addressed through the use of as many additional approaches as possible. For example, advances in biotechnology that are making it feasible to consider transfer of genetic information from almost any source into crop plants suggests that large increases in salt tolerance of crops may realistically be expected in the near future. The major constraint to accomplishing that feat is identifying the characteristics and or mechanisms to be transferred into the crop plants. In addition to being potential sources of the required genetic information for the desirable characteristics, halophytes also are ideal experimental model plants to use in the attempt to identify those mechanisms and characteristics. The typical approach to studying salt tolerance is to compare plants (both sensitive and tolerant plants) subjected to excess salinity with plants not subjected to salinity, looking for responses to the added salt. Examples of such responses are production of unique proteins or large amounts of presumed compatible osmotic solutes such as proline and glycinebetaine. The difficulty with such an approach is that it is difficult to distinguish those responses that are truly adaptive from those that are reflections of metabolic lesions. There is an alternative approach that is possible only with extreme halophytes, i.e., those plants are highly adapted to growing in environments with persistently high salinity. In those plants, the adaptation to high salinity has involved giving up the ability to grow as well as at low salinities that still are high enough to inhibit growth of glycophytes. That is, the optimum salinity for growth has shifted from zero in glycophytes and many less tolerant-halophytes to 75-150 mM in many of these highly tolerant halophytes, with decreased growth observed at both higher and lower salinities. Thus, if one compares the responses of those plants to LESS THAN optimum salinity as well as greater than optimum levels with plants grown at optimum salinity, it should be possible to sort out those responses that are truly adaptive from those that are the result of lesions or other forms of damage. A mechanism or process, e.g., that has adapted to now function better at substantial levels of salinity might be expected to function less well at relatively low levels of salinity and result in less growth at those levels of salinity. The challenge is to identify those mechanisms. In addition to contributing a better understanding of salt tolerance per se, this also should be a productive way of identifying those traits that could be transferred to crop plants and contribute to increased salt tolerance. PREVIOUS WORK AND PRESENT OUTLOOK There are two ways in which halophytes can contribute to development of halophytic crops. The first involves domesticating the halophyte by introduction and/or genetic improvement of crop characteristics. The second involves identifying the characteristics, processes, mechanisms, etc. that are responsible for the high salt tolerance in the halophyte and transferring those characteristics to present crop plants. The first approach has been focusing on the considerable attention during the past decade. The potentia1 uses of halophytes as irrigated crop plants have been reviewed by O'Leary (1984), and research during the past decade has validated the concept of obtaining high productivity from halophytes when irrigated with highly saline water (O'Leary et al., 1985; Pasternak et al., 1985; O'Leary, 1988). Most of the emphasis has been on identifying and selecting halophytes that might be valuable as forage/fodder crops (O'Leary, 1986; Watson et al., 1987) however; a potential oilseed crop whose vegetable oil is high in unsaturated fatty acids also has been identified (Glenn et al., 1991). Thus, it is conceivable that, with genetic improvement of the crop characteristics of these highly productive halophytes, some useful halophytic crops can be developed. There has been a reasonable amount of information published on the physiology of halophytes in the past. A considerable amount of attention has be en devoted to documentation and analysis of growth reductions due to excess salinity in halophytes as well as glycophytes, including crop plants. However, no attention has been given to determining the causes for the growth reduction at low salinity in those halophytes that have growth optima at salinity levels such as 75-150 mM.. In the few instances where anyone has speculated about the cause of the reduced growth at less than optimum salinity, it is attributed to lack of sufficient solutes in the leaves to generate turgor (Jennings, 1976; Flowers et al.,1977; Munns et al.,1983; Flowers and Yeo, 1986), even though that hypothesis is not well supported with data. Since growth depends on substrate availability as well as sufficient turgor, it is reasonable to question the effect of the less than optimum salinity on photosynthesis. The effect of salinity on photosynthesis in halophytes has been investigated, and in spite of the fact that the focus usually was on comparing optimum versus excess salinity, in some cases data were obtained for a range of salinity levels that enable one to compare photosynthesis rates at less than optimum salinities with those at optimum levels. In Salicornia, arguably the most salt tolerant C3 vascular plant, photosynthesis was higher at -32 bars osmotic potential (Tiku, 1976) or 342 mM salinity (AbdulRahman and Williams, 1981) when measurements were made at several salinity levels, however, Pearcy and Ustin (1984) found no differences from O to 450 mM. In Atriplex nummularia, photosynthesis was higher at leaf water potentials of -1.5 to -2.0 MPa than at either higher or lower water potentials (Pham Thi, 1982). In Leptochloa fusca, grown in the absence of NaCl or with NaCl at 250 mM, photosynthesis was higher in the presence of added NaCl than when it was absent at 32°C or 39°C, but the reverse was true when the temperature was 19° C (Gorham, 1987). In all cases there was insufficient information to determine whether the lower photosynthetic rates at the lower salinities (or higher water potentials) were due to stomatal or non-stomatal effects. In fact, even in the cases where investigators have demonstrated the reduced photosynthetic rates at excessive salinity levels in halophytes, the picture is unclear. Some have attributed the reduced photosynthesis to reduced leaf conductance (Farquhar et al., 1982; Guy et al., 1986a, 1986b) while others have concluded that photosynthesis was reduced independent1y of changes in stomatal conductance (Ball & Farquhar, 1984; Longstreth et al., 1984; Pearcy & Ustin, 1984). Furthermore, in some cases it has been concluded that growth was reduced by some factors other than photosynthesis, and the net effect was due to reduced photosynthetic surface rather than reduced photosynthetic rate per unit leaf surface (De Jong, 1978; Gale & Poljakoff-Mayber, 1970; Winter, 1979). Some of the differences may be due to real differences among species, but some are also the result of differences in experimental conditions and differences in the manner in which the data are expressed. It depends on whether the photosynthetic rate is expresses on a leaf area, leaf weight, or chlorophyll basis. Depending on which is used, the photosynthetic rate may be shown to be longer or higher (Winter, 1979). Salicornia bigelovii as an Example With the Association of Nitrogen Fixers Bacterium (Plant Growth Promoting Bacterium- PGPB) I. Introduction One of the scarcest and most finite resources in the world is fresh water. Specifically, fresh-water for agriculture. On this planet, only one half of one percent of the water is fresh water, the other 99.5 % being locked up on polar ice caps or the sea. The sea covers 2/3 of the Earth’s surface. The remaining 1/3 of the Earth’s surface is land, with 1/3 of that being desert. That desert has 22.000 miles of coastline. To the Agricultural laboratory “Dr. Félix Ayala Chairez” into the Sonora University, this presents an essentially untapped resource for the benefit of the environment and the Earth’s people -the challenge of providing food crops grown on seawater, and realizing research and experimentation with halophytes -salt tolerant plants – to developed the technologies to contribute to the world’s food supply, make the deserts bloom and be beneficial to the planet as a whole. This critical research and development must continue into the next century. II. Social, ecological and economic potential The cultivation of Halophyte crops, Salicornia bigelovii in particular, has utilized marginal and which has little or no value for conventional agricultural crops. Its natural habitat is sandy soil close to the ocean -where the only irrigation source is seawater. There are genotypes, the first Halophyte selected for agricultural development has been grown and harvested on demonstration plots and farms in México, Egypt, The United Arab Emirates, Kuwait and Saudi Arabia.