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Materials and methods

Crosses were made among four white-grain varieties. Brevor (BV), Clark's Cream (CC) and Losprout (LS) express grain dormancy. Greer (GR) expresses low dormancy (Walker-Simmons 1987; Hagemann et al. 1988). Progeny and parents were grown near Pullman, WA. In 1989, 180 to 200 F2:3 lines of crosses CC/GR, BV/GR, LS/GR, LS/BV and LS/CC were grown in single row plots of 0.7m2, about 50 seeds were sown per plot. Each of the four parents was included 3 to 4 times among the progeny of each population set. When harvest-ripe, the F2:3 lines and parental plots of each population set were harvested and immediately threshed using a thresher having a rubber cylinder to minimize mechanical damage to the grain, The F4 grain was directly stored at -5C to preserve dormancy. In 1993, F2:4 progenies and their parents of the five populations were grown in a similar manner as the F2:3 progenies; the F5 grain was harvested, threshed and stored in the freezer. Between anthesis and harvest in 1989 and 1993 mean daily temperature were 17.3 and 16.4C, respectively. Precipitation received between anthesis and harvest was 123 and 103 mm, in 1989 and 1993, respectively.

Grain germinability was measured at 30C as the optimum temperature for assessing grain dormancy according to George (1967). For all progeny and parents, 50 grains were placed on blotting paper in a petri dish containing distilled water. Progeny and parents were replicated with 2 to 4 sub-samples of grains taken from each F4, F5 line and parental sample. The petri dishes were incubated in the dark. Once plates of GR commenced germination, four consecutive daily counts were made.

Two measures of dormancy were made. Germination % (G%) was the value attained by the fourth count. Rate of germination was estimated by the germination index (GI) using a method similar to that described by Hagemann and Cilia (1984). After count four, dishes were incubated at 16C for 7 days and samples having fewer than 40 viable seeds were not included in the results.

Data were analyzed using SAS procedure. The 5% LSD for each population set was used to determine the number of progeny having similar or different G% and GI values to the parental means of each population. Frequency distributions for G% and GI were made for the F5 progeny of each cross. The F5 generation was used because it was more homozygous than the F4 and the 1993 season produced greater dormancy than the 1989 season. The progeny distribution patterns were tested for normality by chi-square test (Snedecor and Cochran 1967). Narrow sense parent-offspring heritability (h2) estimates were calculated by the regression method (Falconer 1981) and by the standard unit method (Frey and Horner 1957).

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