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Seed Dormancy and Tissue Culture Response in Wheat

Western Wheat Quality Lab., USDA-ARS, E-202 Food Sci. & Human Nutr. Facility East
Dept. of Crop and Soil Sciences, Washington State Univ., Pullman, WA 99164-6394

^* Corresponding author (wwql{at}wsuaix.csc.wsu.edu).

High levels of seed dormancy in wheat (Triticum aestivum L. em Thell) effect tolerance to pre-harvest sprouting conditions. An inverse relationship between the level of seed dormancy at maturity and growth of calli derived from immature embryo explants was previously observed among a small group of wheat genotypes. In this study, 24 genotypes representing a diverse genetic base were used to examine the relationship between seed dormancy and tissue culture response in wheat. Immature embryo explants were cultured on a modified Murashige and Skoog medium. Increase in callus fresh weight and subjective callus rating were determined after 30 and 60 d. Cumulative germination curves, percentage germination, a modified Promptness Index, and time to reach 50% germination were evaluated as methods of characterizing the relative level of dormancy among the genotypes. Visual assessment of cumulative germination curves categorized the genotypes into four dormancy groups. Numerical reduction of these curves indicated that genotypes differed most in percent germination and modified Promptness Index after 6 d (PG6 and MPI6, respectively). PG6 and MPI6 were.highly correlated (r = 0.98). Median germination produced a similar ranking of genotypes for seed dormancy with predicted population midpoints of 2.3 to 56 d. After 60 d in culture, calli ranged from an average of 0.29 to 1.00 g, and watery, loose and translucent to friable, compact and yellow-white in appearance. Callus ratings and weights were all significantly correlated. Wheat genotypes with good tissue culture response exhibited a wide range in mature seed dormancy and no correlation between the two biological phenomena was evident. Therefore, the level of mature seed dormancy and tissue culture response in wheat are largely independent traits, and wheat breeding programs may use tissue culture to develop sprouting-resistant cultivars.

Received for publication October 25, 1993.