Variation for salinity tolerance during seed germination in diverse carrot [Daucus carota (L.)] germplasm

Authors: BOLTON, ADAM - University Of Wisconsin; Simon, Philipp

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2018
Publication Date: 1/1/2019
Citation: Bolton, A., Simon, P.W. 2019. Variation for salinity tolerance during seed germination in diverse carrot [Daucus carota (L.)] germplasm. HortScience. 54(1):38-44. https://doi.org/10.21273/HORTSCI13333-18.
DOI: https://doi.org/10.21273/HORTSCI13333-18

Interpretive Summary: The extensive use of irrigation in agriculture often results in an accumulation of salts in soils, especially in warmer climates which increase rates of evapotranspiration. Approximately 10 million hectares of land are becoming salinized annually to the point that these lands can no longer sustain adequate crop production. Most crops are stunted when grown in saline soils, but salt-tolerant varieties have been discovered in several crops that are generally saline-sensitive. Carrots are among the most salt-sensitive of crops, but very little screening for salt-tolerant varieties has been undertaken. In this study we evaluated 63 wild carrots and 231 cultivated varieties from 41 countries for salt-tolerance. Samples of carrot seed were germinated in water without salt added, and with salt added, roughly equivalent to 25% as much salt as in sea water. We discovered that salinity stress significantly reduced germination in most, but not all, carrots evaluated. Examples of salt-tolerance were observed from wild and cultivated carrots from around the world, but carrots from Southern and Eastern Asia displayed a higher average salt tolerance at the germination stage than did carrots from other parts of the world, and cultivated carrots usually had a higher incidence of salt tolerance than did wild carrots. The discovery of tolerant cultivated accessions is promising for carrot breeders, as they may be used to develop salt tolerant cultivars, and is of interest for plant physiologists and molecular biologists studying abiotic stress.

Technical Abstract: Global carrot production is limited by its high susceptibility to salinity stress. Little public research has been conducted to screen for genetic salinity stress tolerance in carrot and few resources exist to aid plant breeders in improving carrot salinity tolerance. The objectives of this study were to evaluate the response of diverse carrot germplasm to salinity stress, identify salt tolerant carrot germplasm that may be used by breeders, and define appropriate screening criteria for assessing salt tolerance in germinating carrot seed. Carrot plant introductions (210 cultivated; 63 wild) from the United States Department of Agriculture (USDA) National Plant Germplasm System representing 41 different countries, 16 inbred lines from the USDA Agricultural Research Service, and five widely grown commercial hybrids were screened for salinity tolerance under salinity stress and nonstress conditions (150 and 0 mM NaCl, respectively) by measuring absolute decrease (AD) in percent germination, inhibition index (II), relative salt tolerance (RST), and salt tolerance index (STI) of germinating seeds. All salt tolerance measurements differed significantly between accessions; AD ranged from -4.2% to 93.0%; II ranged from -8.0% to 100.0%; RST ranged from 0.0 to 1.08; and STI ranged from 0.0 to 1.38. Broad sense heritability calculations for these measurements were 0.87 or greater, indicating a strong genetic contribution to the variation observed. Six accessions identified as salt tolerant or salt susceptible were evaluated in a subsequent experiment conducted at salt concentrations of 0 50, 100, 150, 200, and 250 mM NaCl. Variation between mean AD, II, RST, and STI of tolerant and susceptible lines was greatest at 150 mM NaCl, validating the use of 150 mM NaCl concentrations in salt tolerance screening of carrot seed. Wild carrot accessions displayed little tolerance, and PIs 256066, 652253, 652402 and 652405 from Turkey were most salt tolerant.