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Developing a screening tool for osmotic stress tolerance and classification for rice using in vitro seed germination


Farmers around the world are considering dry direct seeding of rice which not only reduces labor and time involved in land preparation but also sustains rice production in rainfed conditions. Rice producers in the U.S. Mid-South practice dry drill seeded rice seed where the permanent flood is set at the fourth-leaf stage. However, one of the primary concern is that the dry soil conditions, sometimes, may result in non-uniform seed germination and poor stand establishment.

An in vitro study was conducted characterizing seed germination traits of 15 commercially grown rice cultivars in response to wide range of osmotic potentials (0 to -1.0 MPa, with -0.2 MPa increments) using polyethylene glycol as a method to mimic soil moisture content. Time-series of seed germination data at different osmotic potentials were used to estimate seed germination traits; maximum germination percentage (MSG) and seed germination rate (SGR), maximum osmotic potential when seed germination rate was zero (GROPmax), and maximum osmotic potential when seed germination was zero (MSGOPmax).

The study found significant cultivar differences for seed MSG, SGR, MSGOPmax, and GROPmax. The MSG and SGR declined significantly with decreasing osmotic potential in all the cultivars. Cumulative drought response indices (CDRI) were developed to evaluate genetic variability among the cultivars for drought tolerance based on germination traits; which provided a method to numerically assign a value for the genotype and classify them into various of tolerance; low, moderate and high. Among the tested cultivars, Cheniere and RU1204122 were identified as the least and the most drought-tolerant cultivars, respectively.

The identified tolerance scoring system will benefit rice producers in selecting a cultivar suitable for a particular production environment. Also, the technique provides a method for rice breeders to screen and develop genotypes best suited for environments affected by drought stress.

Read the full article in Crop ScienceFree preview Feb 24 - March 3