Konishi and Matsuura (1988) found that the Ga2 gene for certation is linked with the complex locus (Estl, Est2, and Est4) for esterase isozymes which are located on a terminal portion on the long arm of chromosome 3 (recombination value = 11.7 ± 4.1%). The present authors aimed to examine geographical distribution of the Ga2 gene, using F₂ populations crossed between 171 varieties collected from different regions of the Old World and an Afghan variety, 487, as the common parent for topcrosses. For finding the varieties having the Ga2 gene, 100 F₂ seedlings of each cross were grown under a 12 h illumination in a growth cabinet kept at 180C for 10 days, and the crude extract from the first leaf of the individual was electrophoresed to examine the genotype for esterase isozymes. In each of the F₂ populations, the genotypes of individuals were easily detected by banding patterns of esterase isozymes, and classified into three groups, namely, those of the parent tested (P₁), the common parent 487 (P₂) and their heterozygote (F₁). When the certation did not occur, segregation of genotypes for esterase isozymes (P₁:F₁:P₂) was compared to a ratio of 1:2:1.

Relationship between frequencies of P₁ and P₂ genotypes in F₂ populations is indicated in Fig. 1. When the frequency of P₁ genotype increased more than 25% and that Of P₂ genotype decreased significantly, the variety tested (P₁) was thought to have the Ga2 gene, shown as a black circle. Meanwhile, the open circles indicate that the certation did not occur in these F₂ populations, scattering around the cross point of theoretical frequencies of 25%.

As is apparent in Table 1, 16 (9.4%) of 171 varieties tested possess the Ga2 gene for certation, and are found in Asia, mainly in Japan and Nepal. It is noteworthy that almost all these Japanese varieties are distributed in the southern parts of Japan, and all of the Nepalese varieties possessing the Ga2 gene are naked ones, with only one exceptional covered barley.

The result suggests that the skewness of segregation for marker genes located near the terminal of the long arm of chromosome 3 might be observed in hybrid populations crossed with Asian varieties having the Ga2 gene. Furthermore, the common parent 487 is thought to be a suitable one to examine the varieties having the Ga2 gene, because its genotype for esterase isozymes is rare pong the barley varieties, composing of three alleles of Est1^1A, Est2^null, and Est4^null .

Reference:

Konishi, T. and S. Matsuura. 1988. A new certation gene, Ga2 on the long arm of chromosome 3 in barley. BGN 18:33-36.