II.11 A single gene determining two new aleurone colours in barley.
R.A. Finch and G.E. Porter, Plant Breeding Institute, Maris Lane, Trumpington, Cambridge, England. "R"
During routine screening of the Institute collection of primitive barleys for mature aleurone colour, two new colours, brick red and intense blue, were found in the Abyssinian lines, Ethiopian 637 and Ab 2231, respectively. The new phenotypes are of potential value as grain identification markers. Their expression is influenced by the environment in much the same way as that of normal blue, but they are reasonably distinct from normal blue and white aleurones in well grown material.
In the cross, Nigrinudum x Ethiopian 637, the F1 grains were normal blue, like Nigrinudum. Of sixty-four F2 grains from one F1 plant, 41 were normal blue, 9 were intense blue like those in Ab 2231, 13 were white and one was red. This fits a 9:3:3:1 ratio (X2 3d.f. = 3.8 n.s.) and suggests that the parental lines differed from each other at two unlinked loci governing aleurone colour. Nigrinudum has both the unlinked complementary dominant alleles, Bl and Bl2, determining normal blue aleurone (Myler and Stanford, 1942) and the F2 ratio, 3 blue:l non-blue, suggests that Ethiopian 637 is Bl, bl2 or bl, Bl2. Since one quarter of the blue and non-blue F2 grains were intense blue and red, respectively, and the F1 grain was normal blue, a recessive allele must have segregated which interacts with Bl and Bl2 together to give an intense blue aleurone, and with Bl or Bl2 (whichever is present in Ethiopian 637) alone to give a red aleurone. We propose the symbol ibl for the new allele. F3 data from 60 of the above F2 grains showed that the nine different F2 types expected on the basis of this interpretation were present in about the expected relative proportions (X2 8 d.f. - 7.7 n.s.).
The dominant Bl or Bl2 allele which is not in Ethiopian 637 probably does not interact on its own with ibl to give a red colour. The evidence for this is that no red aleurones were found in derivatives of crosses between Ab 2231 and two European white aleuroned varieties, Maris Concord and Deba Abed. Thus of 51 F2 grains from the cross Ab 2231 x Maris Concord, 30 were normal blue, 8 were intense blue and 13 were white. This fits a 9:3:4 ratio (X2 2 d.f. = 0.3 n.s.). Maris Concord probably has the genotype bl, Bl2 (Finch, unpub.) and so these data suggest that ibl does not interact with Bl2 to give a red aleurone. A similar 9:3:4 ratio (X2 d.f. = 0.6 n.s.) was found in 100 selfed progeny of a breeder's selection derived from the cross, Ab 2231 x Deba Abed. (This plant was selected after two backcrosses of the F1 to Deba Abed and grew from a normal blue grain). Deba Abed formed white F1 grains in a cross with a daughter variety, Maris Mink, which formed blue Fl grains with Ethiopian 637. Therefore Deba Abed and Maris Mink are probably complementary to Ethiopian 637 at the Bl and Bl2 loci.
The simplest explanation of the results described is that the genotypes
of the varieties and the interactions of the Bl, Bl2 and
ibl alleles are as
shown in the table and Figure 1. Figure 1
depicts a simple model, but one could invoke other interactions between
alleles at the Bl, Bl2 and Ibl loci such as competition
and inhibition to explain the colours observed.
Microscopic examination of undamaged normal blue, intense blue and red aleurones in surface view after chemical dehusking (Mullick and Brink, 1970) showed that a given aleurone has only one hue except occasionally in a few cells and that the pigment is concentrated in parts of numerous otherwise colourless compound granules in the cells. In white cells, these granules are similar but colourless.
Reference:
Mullick, D.B. and V.C. Brink. 1970. Can. J. Plant Sci. 50:551-558.
