Evaluation of Salt Tolerance at Germination Stage in Cowpea [Vigna unguiculata (L.) Walp]

Abstract

<jats:p>Cowpea is a leguminous and versatile crop which provides nutritional food for human consumption. However, salinity unfavorably reduces cowpea seed germination, thus significantly decreasing cowpea production. Little has been done for evaluating and developing salt-tolerant cowpea genotypes at germination stage. The objectives of this research were to evaluate the response of cowpea genotypes to salinity stress through seed germination rate and to select salt-tolerant cowpea genotypes. The seed germination rates under nonsalt condition and salinity stress (150 m<jats:sc>m</jats:sc> NaCl) were evaluated in 151 cowpea genotypes. Four parameters, absolute decrease (AD), the inhibition index (II), the relative salt tolerance (RST), and the salt tolerance index (STI) were used to measure salt tolerance in cowpea. The results showed that there were significant differences among the 151 cowpea genotypes for all parameters (<jats:italic>P</jats:italic> values &lt;0.0001). The AD in germination rate was 5.8% to 94.2%; the II varied from 7.7% to 100%; the RST ranged from 0 to 0.92; and STI varied from 0 to 0.92. A high broad sense heritability (H<jats:sup>2</jats:sup>) was observed for all four parameters. High correlation coefficients (r) were estimated among the four parameters. PI582422, 09–529, PI293584, and PI582570 were highly salt tolerant at germination stage. In addition, genotypes from the Caribbean and Southern Asia exhibited better tolerance to salinity, whereas those from Europe and North America were the most salt-susceptible.</jats:p>

Variation for Salinity Tolerance During Seed Germination in Diverse Carrot [Daucus carota (L.)] Germplasm

“…These multiple criteria for quantifying salt tolerance demonstrated wide phenotypic variations in salt tolerance during the seed germination stage among diverse carrot accessions. Exposure to 150 mM salt solution significantly reduced the percent of germination for most of the carrot diversity panel, thus agreeing with the results of similar studies of other species (Abel and MacKenzie, 1964; Cuartero and Fern andez-Muñoz, 1998; Ravelombola et al, 2017) and with smaller studies involving carrots (Rode et al, 2012;Schmidhalter and Oertli, 1991). This evaluation found a wider range of variations for salt tolerance in carrot during the germination stage than did previous studies.…”

“…H 2 values were 0.87, 0.88, 0.88, and 0.93 for AD, II, RST, and STI, respectively. The heritability of traits estimated for the carrot accessions evaluated in this analysis was higher than that displayed by cowpea (0.84) (Ravelombola et al, 2017) and by tomato (0.76) (Foolad and Jones, 1992), indicating a significant genetic basis for these traits. These genetic factors warrant further investigation, as has been performed for cowpea (Ravelombola et al, 2018), which was found to have a significant quantitative trait locus (QTL) associated with salt tolerance during the germination stage in mapping populations.…”

“…Screening for salt tolerance at the germination stage is the first step in identifying tolerant genotypes because it is a critical stage for plant development. A number of studies of several crop species, including alfalfa, barley, corn, red kidney bean, and sugar beet (Abel and MacKenzie, 1964), tomato (Cuartero and Fern andez-Muñoz, 1998;Foolad and Lin, 1997), grain sorghum (Francois et al, 1984), sugar beet, cabbage, amaranth, and pak choi (Jamil et al, 2006), corn (Maas et al, 1983), cowpea (Ravelombola et al, 2017), and lettuce (Xu and Mou, 2015) have demonstrated that the percent of germination is adversely affected as salinity increases, decreasing the osmotic potential and thus lowering the water potential. Fortunately, screening for salinity tolerance at the germination stage is one of the most rapid and economical stages of development to evaluate a large number of diverse germplasm accessions for tolerance.…”

“…Each accession-treatment combination was present in six total replications in a randomized complete block design, with each bin acting as a replication. The design and conditions were similar to those used in other studies (Maas et al, 1983;Ravelombola et al, 2017).…”

“…At each measurement time, any seed that had germinated was counted and removed from the petri dish. Standard criteria for determining the performance of carrot accessions under salinity included: 1) final percent of germination under nonstress conditions (PG Control ); 2) final percent of germination under salt stress (PG NaCl ); 3) absolute decrease (AD) due to salt; 4) inhibition index (II); 5) relative salt tolerance (RST); and 6) salt tolerance index (STI) (Ravelombola et al, 2017). These measurements were calculated using the following equations: AD = PG Control -PG NaCl ; II = 100 * (PG Control -PG NaCl )/(PG Control ); RST = PG NaCl /PG Control ; STI = (PG NaCl *PG Control )/(PG Average ) 2 , where PG Average is the average percent of germination of all carrot accessions evaluated under no salt stress.…”