1Department of Environmental Sciences and Engineering, Ardabil Branch, Islamic Azad University, Ardabil, Iran
2Young Researchers Club, Ardabil Branch, Islamic Azad University, Ardabil, Iran.
Corresponding author email: Khayatnezhad@gmail.com
Article Publishing History
Today’s world is facing various challenges that impose remarkable stress on the very environment and species that man relies on for his existence. Drought, for instance, is one of the main sources of environmental stress. To tackle the environmental difficulties caused by drought, investigating types of plants with drought-resistant properties is both useful and, arguably, essential. The selection procedure of plant materials includes many formulas, such as SSI, STI, TOL, GMP, YI, YSI, and MP. Under drought stress and non-stress conditions, these formulas rely on seeds’ weight. Low viability of seeds can mislead research with inauthentic data for the selection of an optimal species of plants. Thus, this study suggested the inclusion of ‘seed viability’ in these formulas. Based on the results of other research projects, the Stress Tolerance Index (STI) is the most useful selection criterion. Since breeders have to meet the needs of both research laboratories and the breeding program, selecting a set of seed with high viability is vital, hence the final formula:
MSTI= ((Ypi xYsi)/Yp2)×SV
Ysi= yield of the cultivar in stress condition, Ypi= yield of the cultivar in normal condition,
Yp2= SV= seed viability.
*Note: SV is for the selected condition that we want to use seeds in
It should be noted that the provided formula here is only for the breeding program and laboratory experiments.
Msti, Drought Stress Tolerance, New Formula, Breeding Program
Khayatnezhad M, Gholamin R. A Modern Equation for Determining the Dry-spell Resistance of Crops to Identify Suitable Seeds for the Breeding Program Using Modified Stress Tolerance Index (MSTI). Biosc.Biotech.Res.Comm. 2020;13(4).
Khayatnezhad M, Gholamin R. A Modern Equation for Determining the Dry-spell Resistance of Crops to Identify Suitable Seeds for the Breeding Program Using Modified Stress Tolerance Index (MSTI). Biosc.Biotech.Res.Comm. 2020;13(4). Available from: https://bit.ly/38C6bFk
The drought-induced stress is of the main factors that limit the production of crops, including wheat on the national and international levels. The limiting role of drought becomes more prominent when it comes to dry and semi-arid regions (Kirigwi & Van Ginkel et al., 2004). The severity of this issue becomes clearer when statistics indicate about 1/4 of Earth’s land is dry, and an estimated 1/3 of the world’s arable land suffers mild to severe water shortage (Gholamin and Khayatnezhad 2020).
Drought tolerance is defined as the ability of crops to grow and produce under conditions of water shortage. If the drought persists over the long term, the stress that it causes can negatively impact plants’ metabolic reactions, physiological properties, unsettle the stages of growth, and damage soil’s water storage capacity. Crops indicate different drought tolerance in comparison with wild species. In reaction to a condition where access to water is severely limited, crops go through serious deficit-related trauma, perish, or significantly lose yield, whereas, in the wilderness, plants may fight the deficit and remarkably survive without yield decline. Nevertheless, breeders in dry areas, where land suffers a shortage of water, have always considered the drought-resistant properties of their crops a determining breeding factor, seeking ways to maximize production while keeping water consumption to the minimum, (Talebi, Fayaz et al., 2009).
While attempts at enhancing grain yield in areas with favorable environmental conditions have proven much successful, genetic modification of crops to maximize the yield in harsh environments remains a challenge to date (Richards, Rebetzke et al., 2002). Hall defines drought resistance as a genotype’s relative yield compared with other genotypes’ yield when subjected to the same level of drought stress (Hall 1993). Research studies often measure genotypes’ drought susceptibility as a function of yield reduction under drought-induced stress (Blum 1988) whilst the values are confounded with genotypes’ differential yield potential (Ramirez-Vallejo & Kelly, 1998) defined ‘stress tolerance’ as the different levels of yield under stress (Ys) and non-stress (Yp) conditions. They also defined mean productivity (MP) as the average yield of Ys and Yp. Fischer and Maurer proposed a new index that could help distinguish the more susceptible plants from others in an experiment: It was called the ‘stress susceptibility index’ or SSI (Fischer & Maurer, 1978).
A new advanced index, the Stress Tolerance Index, which is used for the identification of an optimal genotype with the highest production under stress and non-stress conditions, was introduced by ’90s (Fernandez, 1992). The list of criteria used in determining drought resistance is not limited to STI, though, as other research studies use geometric mean (GM), mean productivity (MP), and tolerance (TOL) (Gholamin and Khayatnezhad 2020). Not all breeders use the geometric mean as only those interested in improving the relative performance tend to employ it. The reason for this tendency lies within the unstable nature of the stress caused by drought or harsh conditions as it can change in severity in the long run (Ramirez-Vallejo and Kelly 1998, Sallam et al 2019).
In a research study for evaluation of pattern variance of stress resistance in wheat genotypes, they found that SSI for genotypes and their ranking pattern varies every year (Clarke & DePauw et al., 1992). Studying spring wheat plants, Guttieri and his team found that an SSI value more than 1 meant an above-average susceptibility to the stress caused by drought (Guttieri & Stark et al., 2001). (Golabadi & Arzani et al., 2006), and (Sio-Se Mardeh & Ahmadi et al., 2006) proposed that high mean productivity (MP), geometric mean productivity (GMP), and the stress tolerance index (STI) can facilitate the selection of a drought-tolerant genotype under stressed and non-stressed conditions.
Breeders mainly seek new ways of selecting suitable genotypes with high resistance to drought-induced stress so that they can enrich their genotypes storage with new modified variations with improved performance under harsh conditions. (Clarke, DePauw et al., 1992). Other research studies in this field utilized different indexes for identifying the plant with optimal resistance to water deficit (Khayatnezhad and Gholamin 2010), however, but in breeding program and laboratory experiments we need alive seeds and seed viability is important than seed weight. Thus, seed viability is included in the Stress Tolerance Index equation (Eq.1).
MSTI= ((Ypi xYsi)/Yp2)×SV/100
Ysi= yield of cultivar in stress condition, Ypi= yield of Ysi= yield of the cultivar in stress condition, Ypi= yield of the cultivar in normal condition, SV= seed viability in stress.
*Note: SV is for the selected condition that we want to use seeds in.
Depicted below, is the explanation of this new idea:
Table 1. Stress tolerance values for example
Based on the conventional methods, EXP 2 is more resistant than EXP1 (Table 1), so we can select this genotype for the food program because EXP 2 has more seeds, thus more useful. We measured the seed viability of both samples (Table 2).
Table 2. values of seed Viability in stress condition for examples
The study conducted the measurement using the suggested formula:
MSTI= ((Ypi xYsi)/Yp2)×SV/100
Ysi= yield of cultivar in stress condition, Ypi= yield of cultivar in normal condition, SV= seed viability in stress.
*Note: SV is for selected condition that we want to use seeds
Table 3. Percentage of growth ability and Stress tolerance
|Genotype||STI||MSTI||Percentage of growth ability and Stress tolerance|
As depicted in Table.3, the impact of seed viability on STI’s percentage of growth in EXP 1 and EXP 2 was respectively 90.56% and 66.90%. The results find EXP2 unsuitable for the breeding program seed. Also, the EXP2 genotype is only suitable for food, but EXP 1 is stronger than EXP 2. Therefore, this genotype had fewer 1000-seeds weight, which meant it wasn’t a fitting candidate for food consumption, while it proved more suitable for the breeding program.
Based on the findings of these studies below, it is proposed that these indexes are relatively limited in terms of selecting the optimal genotype: (Khayatnezhad & Hasanuzzaman et al., 2011), (Khayatnezhad, Khayatnezhad, & Gholamin 2012) (Khayatnezhad, Gholamin, & Khayatnezhad, 2010), (Gholamin et al., 2010), (Khayatnezhad & Zaeifizadeh et al., 2010), and (Khayatnezhad & Zaefizadeh et al., 2011).Since this study needs alive seeds for the breeding program and relevant experiments, it will select high-viable seeds. Hence, these two factors, drought-resistance, and seed viability can play a vital role in helping ensure successful experimental projects to maximize yields and minimize water consumption.
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