Salinity effect on water absorption, germination, growth and its relationship with varietal tolerance (página 2)

A totally randomized experimental arrangement was used with three repetitions for each experimental variant. The duration of the first rehearsal was  24 hours. The variables evaluated were the content of absorbed water (AW) by means of the gravimeter method and it was expressed in fresh base (6): 

AW= (FW-IW)/FW

Where PI and PF, represent  the initial and final weight of the seeds, respectively. 

 This experiment was  repeated twice in the time and due to  the similarity of the data    they were analyzed in a combined way. 

A similar experiment was mounted but using filter paper in the badges to evaluate, 7 days  after  the germination, the growth variables: plants height  (HP), root length (RL) and    fresh (FM) and dry matters (DM) accumulation, all data were expressed in relative values to the control. 

In the third experiment  12 varieties of wheat of the species Triticum aestivum and Triticum durum were selected, coming from Cuba and Mexico, which  are described in the following chart. 

   Studied wheat varieties . Species and origin. 

A simple of 100 seeds was taken, distributed at reason of 25 by badge, placed on 10 ml of a saline solution of sodium chloride  (NaCl), adjusted to an electric conductivity (CE) of 16 and 25 dS.m-1, as  a control  was used distilled water to an electric conductivity (CE) of 0.02 dS.m-1. The badges were distributed  in a totally randomized experimental arrangement and for each variant  4 repetitions were carried out. 

24 hours after the beginning of the experiment, the content of water absorbed was determined by the  gravimeter method expressed in fresh base and 7  days after the germination, the growth variables: plants height (PH), root length (RL) and  fresh (FM)  and dry (DM) matters accumulation, were evaluated. Starting from these data the relative tolerance (RTI) to  salinity was calculated, following  formula: 

RTI (%)= 100 (TSI/TCI),

where TSI and TCI, are the indicators evaluated in the saline and control solutions, respectively. 

After checking that the obtained data fulfilled the theoretical suppositions of normality and variance homogeneity,  an  analysis of variance of simple classification was carried out and  the  differences among the treatments  were  detected and compared by  Duncan"s multiple test of comparison   for p <0.01.  

An analysis of linear regression among the values of growth expressed in relative values to the control and the salinity levels  was also carried out. Starting  from these equations  the theorical values of electric conductivity (CE) that diminish the growth and the biomass accumulation  in 50% were determined.

With the purpose of establishing the most appropriate indicators for the differentiation of the varieties an analysis of principal components was carried out. After that a cluster analysis of  complete binding based on a euclidian distance matrix , was carried out, whit the objective of  clustering the variables according to its behavior, using for these analyses the  professional statistical package STATISTICA, version 6.0 for Windows´2000. 

RESULTS AND DISCUSSION

Although the content of absorbed water by  the seeds diminished as well as  the saline concentration increased, the differences were only significant for the levels of 25 and 28 dS.m-1 ( Figure 1), this result  confirms what have been  outlined by different authors about the tolerance of  this process to salinity and that it is only inhibited at  high salt concentrations (10). It has been pointed out that during this stage take place mainly  physique – chemical processes in the seed, such as the epiblast imbibition that is resistant to salinity (7).  

About  the influence of  salinity in the absorption of water by  the seeds of different crops several  researchers have worked (11; 9) and they have arrived to similar conclusions. These authors point out, that such affectations are attributed to the high osmotic potential that is created around the seeds, causing  a  lengthening in the beginning of the germination, slowing the speed and the final percentage of the process. 

Figure 1. Seeds water absorption at different saline concentrations.

However, in this experiment, certain delay was observed during  germination, but the final percentage didn't show significant affectations which could be motivated due to  wheat seeds have a very soft and permeable seminal cover that facilitates the entrance of water and oxygen, as well as the root emerging  (12), moreover wheat seeds are also characterized by having  none or residual endosperm and mature embryos that facilitates the germination (13). Similar results with  wheat mutants BHP-15 AND BHP-31 (14) and with  WL – 711 variety, (15) working with saline concentrations from 4 up to 16 dS.m-1   were observed. 

In  relation  to plants growth (Figure 2) a significant increment in the inhibition of height (HP) and  root length (RL) was observed as the concentrations of salts increased, affectations were found  in relation to the control of  33 and 35% respectively for levels of 25 and 28 dS.m-1. In some other experiments, when evaluating  plants height of the in different cultivars of hard wheat (T. durum) affectations from 30% to 23 dS.m-1 were found (16)similar to this variety for 22dS.m-1.  

Figure 2. Wheat plants growth  inhibition under saline conditions.

On the other hand  (15) in the variety WL – 711 a reduction of 50% of   plants height (AP) was found  after  7 days of  germination and affectations  of 20% in the root length (LR) in  a solution of 28 dS.m-1 were also found. The affectations observed in plants growth at the early stages of the development could be explained by a reduction of water absorption by the endosperm, in the embryonic axles and a decrease of carbohydrates translocation toward these axles or because of  the inhibition of cellular division processes, lengthening and cellular differentiation associated to the lack of water or to the toxic effect of  saline ions.  

The inhibition of  total fresh and dry matter accumulation increased significantly ( Figure 3) as the saline concentrations increased, affectations of 41 and 43% respectively in a  solution of 28 dS.m-1 were seen. Affectations of  43 and 48% during  the accumulation of fresh and dry matters in  WL – 711 have been found (15) in saline solution with a electric conductivity of 16 dS.m-1,  measured 7 days after  germination.  Such authors  have also pointed out that the adverse effect of the salinity in plants growth and biomass accumulation  can be  attenuated with the exogenous  hormones application. 

Figure 3. Inhibition of   total fresh and dry matter  accumulation under salt conditions

Starting from  the linear regression analysis between the evaluated indicators and the levels of salinity studied  (Table 1) the correlation coefficient in all cases was negative and highly significant  what corroborates that as well as  saline concentrations increase, plants  growth and fresh and dry matter accumulation diminishes. 

Table  1. Regression equation, correlation coefficient and levels of salinity that diminish  plants growth  in a 50%.

 HP: plants height    RL: root length    FM: Fresh matter  DM: Dry matter.

 ** high significative differences.

Starting from the regression  equations between the evaluated indicators and the levels of salinity (Table 2), the theoretical levels of electric conductivity that diminish the growth and biomass  accumulation  in 30% were determined being a bigger sensibility in  dry and fresh biomass accumulation and  plants height in  relation to root length, agreeing  with the results obtained by several authors (15, 17, 18) which have recommended such  indicators for the efficient selection of tolerant wheat varieties to salinity.

By observing  the Principal Component Analysis, in the two first  components obtained  a greater  percentage of the total variability with  55.98% and that: absorbed  water at 16 dS.m-1, plants  height  at 16 dS.m-1, root length at 25 dS.m-1  at the first component and dry matter accumulation at 16dS.m-1  at the  second component  resulted the variables of  higher correlation with the principal axis (Table 2) showing the practicality of such indicators for an  efficient selection of  tolerant varieties to salinity at the early stages of growing  in wheat. 

        Some authors have arrived to similar conclusions about the use of such indicators for discriminating   tolerant genotypes to salt stress in several crops  including wheat  (8, 9, 10).

Table  2: Principal Compounds Variables.

       Starting from  these variables of more correlation with principal  axes, a cluster analysis, of Complete ligkange  based on  Euclidian distance matrix, was  carried out,  in order to group   the varieties, what allowed to gather the genotypes in three groups, showing  the existence of genetic variability for the response to salt stress (Figures 1). This is an  important aspect since the tolerance to  salinity is considered a finite magnitude character  and its improvement presupposes the existence of usable levels in the germoplasm conserved in  banks (8). Some differences in salt stress tolerance in  wheat have been informed by several authors (9, 10). In this  respect 1300 wheat varieties  during the germination phenophase were evaluated and a high genetic diversity was found, what allowed to select varieties with high tolerance to salinity (9,10). These authors also pointed out that the hexaploid varieties (AABBDD) showed higher tolerance index than tetrapliod  (AABB) and diploid (AA) varieties, concluding   that the genetic factor that control  salt stress tolerance should be localized at "DD genome"

Chart 4. Dendrogram obtained from the cluster analysis.

       The group I formed by IRM-26 IRM-29 IRM-31, RM-36,  IRM-37 Cuba-C-204 floury wheat varieties (Triticum aestivum) was the one of  better response to salt stress, with the  highest tolerance  index (more than 80% in all cases) for the four variables that more contributed to the total variability, classifying as a tolerant (Chart III), however, the  absorbed  water index at 25 dS.m-1  was smaller than the remaining variables  of this group, which will be studied based on advanced indicators like  seeds water potential, better  than quantity of absorbed water by the gravimeter method, due to  the Importance of  this process for correct germination. In such sense, it has  been concluded  that there is not  a direct relationship among the response to salinity evaluated based on the water absorption of  seeds and the plants growth (11) and since during the water absorption take place mostly physical phenomena (4) it is accepted that the evaluation of varietal response to salinity, according to the quantity of absorbed water by the seeds in saline solutions related to  control, is not a highly precise indicator and it can only be used as a reference indicator, to simplify the work in the initial evaluation of big groups of varieties and/or lines to discriminate susceptible varieties.

Chart III: Means values of tolerance  index based on  water absorption  and  growing indicators. 

AA. Absorbed water; HP. plants height;  RL. root length.  DM; dry matter accumulation.

 The second group formed by Mexicana24, 10 TH29   IRM-30, IRM-37,   IRM-32 Idyn18 floury wheat varieties (Triticum aestivum) and a hard wheat variety (Triticum durum) (Idyn18),  was classified as moderately tolerant. This cluster of floury wheat varieties  in first and second groups indicates the superiority of this species in the response to  salt stress (10), aspect that is necessary  to check based on biochemical and molecular indicators with the purpose of isolating tolerance genes  that can be transferred to commercial varieties of high productivity (9).

The variety of hard wheat Eduyt 16 formed the third group classifying as susceptible, for that, in futures implementation programs in affected areas by salt stress or in genetics improvement programs for this character could be discriminated against.

        In some  experiments with T. Aestivum, T. Durum Desf, T. turanicum Jakubz and T. ispahanicum Heslot and the endemic T. dicoccoides Aarans, T. timofheevi Zhuk, T. spelta and T. turgidum L., there was a higher salt stress  tolerance  in T. aestivum and this behavior  was  attributed due  to the  great distribution all over the world and/ or   to  this specie is conformed by a great quantity of varieties of different ecologist-geographical origins affected by  soil salinity (12).

       The varieties with name (INIFAT)  of the group I were obtained, in Cuba at  the of fundamental Investigations of Tropical Agriculture Institute (INIFAT), by   mutation induction, starting from the Cuban variety CubaC – 204 the one which, in previous experiences, showed a good response in high  saline concentrations for  evaluating seeds germination and  plants growth (4). In this respect the possibility of  generating heritable variation for the tolerance to salinity in wheat has been indicated (13, 18) which has an important practical significance, because the natural variability for this character  it is considered low in the cultivated plants in general and in particular in  wheat.   

       Something significant in all groups was  that at 28 dS.m-1 the tolerance indexes  for root length variable (RL) were high, agreeing  with results obtained by several authors (17,15) recommending this variable as an efficient indicator for the selection of tolerant  varieties to salinity. It has been concluded that the gramineous ones that, placed in high saline concentrations, and they reach a good root  system development they have big possibilities to be tolerant to this kind of stress (15,16 ).  

The evaluating methodology  used  in this experiment  means to be  simple and economic since it allows to discriminate, under laboratory conditions, the varieties with more susceptibility grade  (17,18) and to incorporate to the field those that show a good behavior, which, constitutes its biggest utilitarian value in a first phase, to isolate the initial material with less perspectives inside a genetic improvement program for  salinity tolerance.

REFERENCES

1.        Royo. A y  R. Aragues . Establecimiento   de   nuevos  índices  de tolerancia   de los cultivos a la salinidad: la cebada como caso  de estudio. Investigación  Agraria. Producción y Producción Vegetal, 2002. 17 (3): 410- 421.

2.        CUBA. MINAGRI. Informe anual  sobre  la Agricultura. Avances y pérdidas. P.P Granma, Jueves, 25 Diciembre.2003.

3.        González, L.M  y R.  Ramírez. Los suelos salinos y su utilización en la producción agrícola. Alimentaria. 2002, Dic. 339: 103-107.

4.        Mesa, D.  Obtención de plantas resistentes a la salinidad para los suelos salinos cubanos. Revista Cubana de Ciencia Agrícola. 2003, 37 (3): 217-226.  

5.        FAO.  Fooding distribution along the wold, 2003. Paper  23, Roma, 186 pp.

6.        Isla y Royo. Tolerancia a la salinidad en la tribu triticeae. Investigación    Agraria, Producción y Protección vegetal, 1997, 12 (1, 2 y 3): 133-145.

7.        González, L. M.  Reflexiones sobre los mecanismos generales de adaptación de las plantas a la salinidad y a otros tipos de estrés, Alimentaria, 2002. Dic. 339: 99-102..

8.        Chávez, L;  LM. González y R. Ramírez.  Efecto de la salinidad sobre a absorción de agua por las semillas de Vigna unguiculata (L) y su relación con la tolerancia varietal. Alimentaria, 2002, 339: 99-102.

9.        González, L.M  y R. Ramírez.  La absorción de agua  por las semillas de arroz a  altas concentraciones salinas, como posible indicador de la tolerancia varietal. Cultivos Tropicales, 1999, 20 (1): 31-34.

10.   Prazak, R.  Salt-tolerance of triticum monococum L. , Triticum dicocum (s   chank) Schubl., Triticum durum  Desf and Triticum eastivum L. Seedlgings. Journal of Aplied Genetic,   2000, vol. 42, no. 3  p. 289-292.

11.   Maya, P; A. Monzón y M. Ponce. Datos sobre la germinación de especies endémicas Canarias.  Bot. 1988, M, 16: 677-680.

12.   Scott, S. J; Jones, R.A; Wiliams.  Review of data analysis. Methods for seed germination. Crop  Science. 1984, 24: 1192-1199.

13.   Kumar, D y J.S.P. Yadav. Salt tolerance of mutants from wheat veriety HD 1553. Indian Journal of Agricultural Science, 1983,53 (12) 1009- 1015.

14.   Singh, G; P. Kaur y R. Sharma.   effect of  CCC on seed germination and  early seedling growth in wheat under saline conditions. Indian Journal of Agricultural Science. Plant Physiology, 1985, 28 (4): 310-317.

15.   Royo, A. Y D Abió.   Sal tolerance in durum wheat cultivars. Spanich Journal of  Agricultural  Research, 2003,1 (3):  27-35.

16.   Argentel, L., L.M. González. Comportamiento de la tolerancia interespecífica a la salinidad en dos especies del género Triticum. Cultivos Tropicales, 2006, vol. 27 no. 2, p. 51-52

17.   González, L.M,  L. Argentel. Efecto de la sequía simulada con PEG-6000 sobre la germinación y el crecimiento de dos variedades de trigo.  Cultivos Tropicales, 2005, vol. 26 no. 4, p. 49-54

18. Mano, Y & K Takeda. Genetic resourses of salt- tolerance at germination and  the seedling stage  in wheat. Japanese Journal  of Crop Science 2001, vol. 70, no. 2, p.  215-220. 

Autor:

M Sc. L. Argentel

leandris[arroba]udg.co.cu

Dr. C. L. M. Gonzalez

Ing. I.  Fonseca

R. Samsom

Dr. C. R. Lopez

Lic. R.Girón

M Sc. L. Argentel, Ing. I. Fonseca . Dr. C. R. Lopez  Asistant  teachers of Granma University. Bayamo. Cuba. Dr. C. L. M. Gonzalez, Titular Researcher of ARI J. Dimitrov, Bayamo. Cuba. .  R. Samsom .Lic. R.Girón