Salinity effect on water absorption, germination, growth and its relationship with varietal tolerance
Enviado por L. Argentel
Introduction
Among the adverse conditions of the agricultural systems of the world, soil salinity is the factor that has influenced the most on settlement of human populations. Approximately 43% of the terrestrial surface used for the cultivation around the world is affected by levels of salinity that, in most of the cases, overcome the tolerance of the species of traditional cultivations (1).
The percentage of salinity increases to a half rate of 0.5% annually, mainly due to low rainfalls, high evaporation surface, irrigation with saline waters and because of traditional practices of cultivation that favor the increase of salts concentration in the soil (2). Soil salinization increases at a speed of 3,24 ha.min-1 (3) and nowadays there are around 953 million hectares of lands affected by this stressing factor in different regions of the world.
Cuba, that has an agricultural surface of around 7.08 million hectares, presents near a million hectares affected by salinity and 1.5 millions have already potential salinization problems (4) as a consequence at the eastern region the 55% of the arable soils is classified as salty soils. (5).
A partial solution to these problems is the installation of crops and more tolerant varieties to salinity, that is why, it is necessary to know this tolerance in a precise and consistent way (6, 2). In the recovery and handling policies of these soils, the use of tolerant species and varieties to salt stress is considered very important and it has received special attention by different investigators in Cuba and abroad (7). Concerning this topic, diverse authors (8, 6, 3) state that to maximize the tolerance to salinity in arable species is an important element in the integrated systems of cultivation in areas affected by salinity and that, although this theme has been investigated in several times, particularly in the last 30 years, it do not complete all the expectations and it is necessary to continue working in the genetic improvement for this character.
Wheat, is one of the oldest species cultivated by man and it constitutes, according to some reports (5), the feeding base of more than 96.4% of the world population, it is a rich food in energy and vitamins from which more than 476 nutritious products are obtained, at the same time it is an inigualable food for animals. This specie is considered tolerant to the drought (9) and it supports mean tenors of salinity (10, 4, 1), what transforms it into a sustainable option for its use in affected areas by high percentage of salts where the rehabilitation measures, like the drainage, are both expensive and of difficult execution.
wheat was introduced in Cuba, by the Spaniards, since the first years of the conquest with a successful production. The introduced varieties which were acclimatizing until creating a very well adapted variety that constituted a rarity inside the Spanish wheat flora due to its good growing, development and yield (4). There is already a great quantity of varieties introduced and obtained in Cuba which show a very well genetic -productive potential (4).
In Granma, Cuba, some projects of investigations related to the introduction and validation of salt tolerant varieties of wheat based on phenologic, physiologic, biochemical, molecular and agricultural indicators, are developed. Together whit these projects, an investigation whose results are exposed in the present document, was carried out contributing, this way, to mitigate the problem of the saline soils. That is why the monitory of the response to salt stress in the available germoplasma, based on water absorption, germination, growth and its relationship with varietal tolerance would allow the choice of the existing genetic variability for this character.
MATERIALS AND METHODS
Three experiments were developed at the Nuclear Technics laboratory of the Agricultural Researches Institute "Jorge Dimitrov", Granma, Cuba. The first one with the objective of determining the effect of different levels of salinity that affect the absorption of water by the seeds during the imbibition phase, another one to determine the effect of different levels of salinity that affect the percentage of germination of the seeds and the plants growth and a third one with the purpose of establishing the degree of divergence in the varietal tolerance, based on the indicators studied at the initial phases of the development of wheat plants .
In the first one, seeds of "Cuba-C-204" variety were selected, it was the first Cuban variety obtained by selection at the Fundamental Researches of Tropical Agriculture Institute "Alejandro de Humboldt", starting from the Brazilian floury wheat variety "BH-11", which were put to absorb in petri badges at reason of 25 for badge with 10 ml of a solution of sodium chloride (NaCl) adjusted to electric conductivities (CE) of 12; 15; 22; 25; 28 dS.m-1, as control was used distilled water with an electric conductivity of 0.02 dS.m-1.
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