The Correlation between Salinity Resistance Indices and Maize Yield in Stress and Non Stress Conditions

Davar Molazem,

Faculty Member of Islamic Azad University, Astara Branch Astara-Iran.

Abstract

In this research, eight varieties of maize (Zea mays L.)were studied in two separate Randomized Complete Block Design (RCBD) field experiments. Cultivars included K3615/1, S.C704, B73, S.C302, Waxy, K3546/6, K3653/2, and Zaqatala and they were cultivated in two pieces of land in Astara: one with normal soil and the other with salty soil. Five abiotic tolerance indices comprising: stress tolerance index (STI), stress tolerance (TOL), stress susceptibility index (SSI), mean productivity (MP), and geometric mean productivity (GMP) were used. The indices were adjusted based on grain yield under salinity (Ys) and normal (Yp) conditions. This would imply the difficulties of yield improvement in normal conditions for high yield performance in salty condition. Correlation between MP and Ys was significant(r=0.588, p<0.01). Correlation between tolerance and Yp was positive and significant (r=0.821, p<0.01) and relationship between Ys and TOL was negative and significant (r=-0.525, p<0.01) Based on the most of the estimated resistance indices S.C704, S.C302 and Zaqatala were the best cultivars.

Introduction

Earth is a salty planet, with most of its water containing about 30 g of sodium chloride per liter. This salt solution has affected, and continues to affect, the land on which crops are, or might be, grown. Although the amount of salt affected land (about 9003106 ha) is imprecisely known, its extent is sufficient to pose a threat to agriculture [5, 6]. Increased salt tolerance of crops is needed to sustain food production in many regions in the world. In irrigated agriculture, improved salt tolerance of crops can lessen the leaching requirement, and so lessen the costs of an irrigation scheme, both in the need to import fresh water and to dispose of saline water [8]. Salt-tolerant crops have a much lower leaching requirement than salt-sensitive crops. In dry-land agriculture, improved salt tolerance can increase yield on saline soils. In areas where the rainfall is low and the salt remains in the subsoil, increased salt tolerance will allow plants to extract more water. Salt tolerance may have its greatest impact on crops growing on soils with natural salinity as, when all the other agronomic constraints have been overcome (e.g. disease resistance), subsoil salinity remains a major limitation to agriculture in all semi-arid regions. Even where clearing of land in higher rainfall zones has caused water-tables to rise and salt to move, improved salt tolerance of crops will have a place. The introduction of deep-rooted perennial species is necessary to lower the water-table, but salt tolerance will be required not only for the ‘de-watering’ species, but also for the annual crops that follow, as salt will be left in the soil when the water-table is lowered. Only halophytes (plants adapted to saline habitats) will continue to grow at salinities over 250 mM NaCl. Domestication of halophytes as new crops has been reviewed by Colmer et al. [1], who point out that few species have reached the status of crop plant and none has a wide usage. However, some are useful forage species for saline land. Several indices have been utilized to evaluate genotypes for drought resistance based on grain yield. Rosielle and Hamblin [10] defined stress tolerance (TOL) as the differences in yield between the stress (Ys) and non-stress (Yp) environments and mean productivity (MP) as the average yield of Ys and Yp. Fischer and Maurer [4] proposed a stress susceptibility index (SSI) of the cultivar. Fernandez [3] defined a new advanced index (STI= stress tolerance index), which can be used to identify genotypes that produce high yield under both stress and non-stress conditions. Other yield based estimates of drought resistance are geometric mean (GM), mean productivity (MP) and TOL. The geometric mean is often used by breeders interested in relative performance since abiotic stress can vary in severity in field environment over years [9].

Materials and Methods

Considering Iran and Azerbaijan as origin countries, and in order to study the effects of saltiness on growth and yield characteristics of maize plant, its different items were investigated in 2007-2008. Seeds of 8 maize cultivars including K3615/1, S.CDS704, B73, S.C302, Waxy, K3546/6, K3653/2, and Zaqatala were cultivated in two pieces of land in Astara, one with normal soil and the other with salty soil. Experiment was carried out in the form of randomized complete block design in three repetitions. After harvest the grain yield was recorded for every condition. The resistance indices were calculated for every genotype using the corresponding non-stressed and stressed condition in each block. The resulting data were analyzed as obtained from a randomized complete block design. The salty tolerance indices were calculated as follows:

SI is the stress intensity and calculated as:

where Ys and Yp are the yields of genotypes evaluated under stress and non-stress conditions and Ys and Yp are the mean yields over all genotypes evaluated under stress and non-stress conditions. = mean yield in non-stressed environment. = mean yield in salty stressed environment.

The optimal selection criterion should distinguish genotypes express uniform superiority in both tress and nonstress environments from the genotypes that are favorable only in one environment E1 or E2). Among the stress tolerance indicators, a larger value of TOL and SSI represent relatively more sensitivity to stress, thus a smaller value of TOL and SSI are favored. Selection based on these two criteria favors genotypes with low yield potentional under non-stress onditions and high yield under stress conditions. On the other hand, selection based on STI and MP will be resulted in genotypes with higher stress tolerance and yield potential will be selected [3].

Correlation between yield and salinity tolerance indices was evaluated by MSTATC and SPSS computer programs.

Results and Discussion

Stress Intensity (SI) was higher in this experiment (SI=0.55). SI ranges between 0and1 and the larger the value of SI, the more sever is the stress intensity.

To determine the most desirable salty tolerance criteria, the correlation coefficient between Yp, Ys and other quantitative indices of salty tolerance were calculated (Table1). Correlation between Yp and Ys was non significant(r=0.054).So, yield selection in non stress conditions increased yield only in non stress environment and yield selection in stress conditions caused higher yield in this conditions(Table 1).Mean Productivity(MP) favors higher yield potential and lower stress tolerance. Correlation between MP and Yp was significant(r=0.84, p<0.01). Correlation between MP and Ys was significant (r=0.588, p<0.01) (Table 1). Thus, selection based on Mp can be increased yield in stress environments. S.C704, Zaqatala and S.C302 were the best maize cultivar based on this index (Table 2). positive and significant correlations among Yp and (MP,GMP and STI) and Ys and (MP, GMP and STI) and they hence were better predictors of Yp and Ys than TOL and SSI. The observed relationship between Yp and (MP and STI) and Ys and (MP and STI) are in consistent with those reported by Fernandez [3] in mungbean and Farshadfar [2] in maize. Ramirez and Kelly [9] observed positive and significant correlation of some yield components with geometric mean yield (GMP) in common bean. Nasir ud-Din et al [7] showed significant and positive correlation between Ys and TOL, and Ys and Mp as well as between Yp and MP, while TOL was negatively correlated with Yp and MP.

Table 1.

Correlation coefficients among salty resistance indices and grain yield in stressed and no stressed environments.

* significant difference in probability level of 5%

** significant difference in probability level of 1%

A larger value of TOl show more sensitivity to stress, thus a smaller value of TOL is favored. Selection based on TOL favors cultivars with low yield potential and high yield under stress conditions. Correlation between tolerance and Yp was positive and significant (r=0.821, p<0.01) and relationship between Ys and TOL was negative and significant(r=-0.525, p<0.01)(Table 1).Waxy, S.C302, B73K3653/2 and Zaqatala were the smallest TOL, so were the best cultivars based on this index (Table 2).

Mp is based on the arithmetic means and therefore it has an upward bias due to a relatively large difference between Yp and Ys, whereas the geometric mean is less sensitive to large extreme value [3]. Relationship between GMP and Yp was significant and positive (r=0.558, p<0.01) (Table 1). S.C704, Zaqatala and S.C302 were the best cultivars based on this index (Table 2). The smaller SSI caused the greater stress tolerance.ToL and SSI were positively correlated(r=0.867, p<0.01). Correlation between SSI and Yp was significant and positive(r=0.495, p<0.05).But correlation between Ys and SSI was negative and significant(r=-0.779, p<0.01). (Table 1). Waxy, S.C302, B73 and Zaqatala were the best cultivars based on this index (Table 2). The higher STI values caused higher stress tolerance and yield potential [3]. This index selected S.C704, Zaqatala and S.C302 (Table 2).

Table 2.

Ys, Yp and salinity tolerance indices in maize genotypes.

STI= stress tolerance index, TOL= stress tolerance, SSI= stress susceptibility index, MP= mean productivity, GMP= geometric mean productivity, Ys= grain yield under salt conditions and Yp= grain yield under normal conditions.

Figure 1. Diagram of STI index in eight cultivars of the maize .

References

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2.                  Farshadfar E, Sutka J .2002. Multivariate analysis of drought tolerance in wheat substitution lines. Cereal Res. Commun. 31: 33-39.

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9.                  Ramirez P, Kelly JD .1998. Traits related to drought resistance in common bean. Euphytica 99: 127-136.

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Поступила в редакцию 02.02.2010 г.