In barley 85 eceriferum (cer) complementation groups have been identified which affect the synthesis and deposition of the epicuticular (surface) waxes (Lundqvist and von Wettstein, 1988; Sogaard and von Wettstein-Knowles, 1987). Of these Cer-yy is unique in that all mutant alleles are dominant. Only the spikes of Cer-yy plants appear to lack wax. An additional 151 mutants with the same general phenotype distributed among 11 other cer complementation groups are all recessive. Despite the non-waxy (glossy) appearance of Cer-yy spikes epicuticular wax is present, and a detailed analysis of the latter revealed a close resemblance to leaf blade wax. Combining all information led to the suggestion that Cer-yy is a regulatory gene whose product turns on the synthesis in the spikes of the normally quiescent leaf blade wax genes (Lundqvist and von WettsteinKnowles 1982).
One possible approach toward isolating this interesting gene depends on the knowledge of its position in the barley genome. Thus, I was most interested in Netsvetaev and Sozinov's (1982) report that the glossy spikes of Cristal and Ametyst were due to a dominant gene located on chromosome 5 distal to the Hor5 (Hrd F) locus: 3-4% recombination. The gene was designated Gle1 (glossy spike), inferring that the rest of the plant had a normal wax coat. Six additional varieties were reported to have dominant mutations of the same gene. Since seeds of two of these, namely Carina and Maris Mink, were present in the Carlsberg Plant
Breeding collection, these varieties were chosen as experimental material to test the hypothesis that Gle1 and Cer-yy are allelic.
As the Maris Mink stock turned out to have waxy spikes, only the cross Carina (female) × Cer-yy437 (male) was made. The F1 and all 345 F2 plants had normal waxy coats except for the spikes which appeared waxless. The F2 population also segregated for time of maturity. Very early maturity being a characteristic of the Cer-yy437, but not of Carina, supports the contention that the desired cross had been made. The most likely explanation of these results is that the glossy spikes of Carina are due to a mutation of the Cer-yy849 locus. While this note was being prepared Franckowiak informed me that when he crossed the variety Estate (CI3410) and Wolfe's multiple dominant marker stock with Cer-yy , all the spikes of the F1 and F2 progeny appeared waxless revealing that both these barley lines also carried mutant alleles of the Cer-yy locus.
Until now only three of the glossy sheath gs loci have been definitively assigned to cer complementation groups (Sogaard and von Wettstein-Knowles, 1987). Pertinent genetic analyses to remedy this have been initiated. The first positive results were obtained in the summer of 1990 from the cross cer-b2 , Hex-v (female) × gs2d, hex-v (male). That is, the uppermost leaf sheaths and internodes plus spikes of the F1 and all of the circa 180 F2 plants were non-waxy. In addition the row character segregated in the F2. These observations infer that gs2 is most likely an allele of cer-b. In this connection it is puzzling that Eslick (1974) deduced non-allelism from the F1 phenotype of a cross between unspecified alleles of gs2 and cer-b. No additional information was given in the report.
How many mutant alleles of Cer-yy and cer-b have been identified? Our induced cer mutant collection includes 18 of the former and 39 of the latter or 1.1 and 2.5%, respectively, of the cer mutants assigned to complementation groups (Lundqvist and von Wettstein, 1988; Sogaard and von Wettstein-Knowles, 1987). If we exclude the multifunctional cer-cqu locus with 522 mutations, then Cer-yy and cer-b are the 16th and 11th most frequently mutated cer complementation groups. The relatively low frequency of Cer-yy mutations suggests that the number of different Cer-yy mutant alleles in the waxless spike barley varieties is probably quite small. Gula and Rosie are two additional varieties that on the basis of phenotypes might also have mutant alleles at Cer-yy (J. Larsen, personal communication). At least five gs2 mutants have been described that did not originate in Sweden (McProud, 1971; Konishi, 1973), and hence must be different from all cer-b mutants. The proportion of gs2 among total gs mutations is similar to that of cer-b among total cer mutations.
References:
Eslick, R. 1974. Allele tests of gs and cer mutants. BGN 4:9-11.
Konishi, T. 1973. Genetic analyses of EMS-induced mutants in barley. BGN 3:28-29
Lundqvist, U., and D. von Wettstein. 1988. Stock list for eceriferum mutants. BGN 18:88-91.
Lundqvist, U. and P. von Wettstein-Knowles. 1982. Dominant mutations at Cer-yy change barley spike wax into leaf blade wax. Carlsberg Res. Commun. 47:29-43
McProud, W. L. 1971. Genetics, phenotypes, agronomic and malting performance of glossy sheath mutants in barley, Hordeum vulgare L. Ph.D. thesis, Montana State University, 72pp.
Netsvetaev, V. P., A. A. Sozinov. 1982. Linkage studies of genes Gle1 and Hrd F in barley chromosome 5. BGN 12:13-18.
Søgaard, B. and P. von Wettstein-Knowles. 1987. Barley: genes and chromosomes. Carlsberg Res. Commun. 52:123-196.