II.32. Genetics of frosthardening ability in 2 crosses between spring and winter barley.
E. Schwarzbach, Technische Universität München, Institut fur Pflanzenbau und Pflanzenzüchtung, 805 Freising-Weihenstephan, Bundesrepublik Deutschland.
Two crosses were made between varieties differing in following complementary characters:
On seedlings of randomly selected progenies of F2-plants the frosthardening ability (HA) was determined according to following procedure:
Seedlings were grown in complete darkness in water culture to the stage at which about 50% of coleoptiles are penetrated by the 1st leaf. Then roots were clipped 15mm below the kernels and the seedlings were hardened 5 days in darkness at 1°C. Then the temperature was lowered by 1°C/h to -12°C and held so for 10 hours. After raising the temperature slowly to 1°C the coleoptiles were clipped 15mm above the kernel. After a recovery of several hours at 16°C the temperature was lowered again slowly to 1°C. By means of a simple direct current ohmmeter the electric resistance between the rootlet and coleoptile cutting surface was measure To prevent polarization, the electrode polarity was continuously changed with a frequency of 2 Hz. By this procedure 1000 seedlings can be measured in 1 hour. The electric resistance proved to be a good measure of vitality, totally killed seedlings having a resistance of about 30 kohms, whereas not damaged ones have up to 1 Mohm.
In addition, growth habit, rachilla character and ear row number of the progenies were determined.
Whereas the F2-population of both crosses had a mean HA highly significantly lower than that of any parent, as partly mentioned in the previous issue (Schwarzbach 1972), the F2-progenies of both crosses showed a mean HA similar to the respective spring parent and a continuous distribution with transgression in both directions. The progeny distribution in HA in the cross 'Dura' x 's(Bonus)' is shown in Figure 1.
Figure 1.: F2-Progeny Distribution in hardening ability in the cross 'Dura' x 's(Bonus)'.
The growth habit segregation fitted in both crosses a segregation expected from the spring genotype ++Sh2Sh2Sh3Sh3 and differed significantly from segregations expected from other possible spring genotypes described by Takahashi and Yasuda (1970). In the cross 'Dura' x 's (Bonus)' from 680 F2-progenies 51 were homozygous for winter habit, in the cross 'MK10' x 'Tria' 18 progenies from 198 showed winter habit.
The relation between growth habit and HA, although significant, was not close. In both crosses spring progenies could be found exceeding the winter habit parent in HA. In contrast, winter habit progenies could be found with lower HA than the spring parent.
In both crosses there are 3 significantly interrelated characters: growth habit, HA and rachilla hairness. When picked out, these correlations can be arranged as follows:
The finding that the correlation between winter habit and rachilla hairness is positive in the cross 'Dura' x 's(Bonus)' and negative in 'MK10' x 'Tria' confirms with the known linkage between the genes Sh2 and s. It is interesting, that the relation of HA to winter habit and to rachilla hairness is more close than between winter habit and rachilla hairness. A physiologic relation between HA and rachilla hairness can be excluded, because the correlation is of opposite direction in the two crosses. So it seems to be fairly logical to conclude that at least several of the genes for hardening ability are located on a segment of chromosome 7 between the genes Sh2 and s. Unfortunately, two unlinked genes for growth habit and an unknown number of genes for HA are involved. Therefore, progenies will be selected in future heterozygous only in single genes for HA to study more exactly their relation to Sh2 and s.
References:
Schwarzbach, E. 1972. Frost hardiness in spring barley and negative heterosis for this character in a cross of spring x winter barley. Barley Genetics Newsletter 2:74.
Takahashi, R. and S. Yasuda. 1970. Genetics of earliness and growth habit in barley. Barley Genetics II:388-408.
