II. 1 A mutant of barley: Triploid inducer.
H. Ahokas. Department of Genetics, University of Helsinki, P. Rautatiekatu 13, 00100 Helsinki 10, Finland. "R"
The P-4 stock was established from one plant selected from cv. Paavo (Tammi/OAC21/Gull). The P-4 plants are characterized by two kinds of seeds, thin and normal. A random sample of 10 heads gave the following distribution of seeds: 252 thins and 236 normals. This fits the 1 : 1 distribution (X2 = 0.525; P > .30).
The thin seeds can usually be germinated in Petri dishes. The result of a chromosome study is presented in Table 1. The thins have triploid roots, and apparently other parts of the embryo. The normal seeds continuously give plants with heads segregating 1 : 1.
Table 1. Number of chromosomes in root tips of the different seed types of P-4.
The triploids must arise from a fertilized cell, since the plants from the thin seeds are hybrids, as revealed by crosses with pollen parents carrying dominant markers (BGS 0019 cv Nepal; AHOR 2607 cv. Noire 2R Trifurquee). At least the dominant genes K, B, and V penetrate in the triploid. The anthers of the triploid plants usually dehisce, but the plants are highly sterile. A few seeds have been observed on them: seed set about 0.1%. A triploid stand can be raised from the thin seeds in the field under favorable conditions for emergence.
The reciprocal crosses with a glossy mutant, arbitrarily called Paavocer-l, gave F2 distributions fitting 9 : 3 : 3 : 1, and fitting 3 : 1 for normal and mixed-seeded plants (Table 2). In the first cross (Table 2), only normal F(1) seeds were planted for the F2 generation. P-4/Paavo-cer-l backcrossed by P-4 gave 4 normal-seeded and 3 mixed-seeded plants. This fits the 1 : 1 ratio. Thus, the triploid inducer phenomenon is most likely controlled by a recessive factor. The mutant might perhaps be classified as shrunken endosperm, xenia (sex), but the symbol tri (triploid inducer) provides more information, in accordance with the suggestion by Eslick and Hockett (1976). Some yield and chemical characteristics are given in Table 3.
Table 2. F2 segregation of triploid inducer.
Table 3. Yield and chemical characteristics of
P-4.
A simple explanation for the behavior of the mutant is the following: Either the fertilized egg cell or the fertilized triploid central cell of the embryo sac initiates the embryo, both at the probability of 0.5. This explanation is supported by the fact that triploids are born from a hybrid cell, and have a poor endosperm, which could be diploid.
The mutant can be used in studying the dosage effects of alleles, since triploids are easily obtained. The mutant may provide material for different kinds of chromosome manipulations.
The induction of a variable percentage of triploids and aneuploids was attributed to BSMV infection (Sandfaer 1973, 1975).
The P-4 stock is in addition to tri, bl2 N v Uz k b s R. Limited amounts of seed of the mutant are available upon request. The mutant was sent to Barley Genetic Stock Center (Fort Collins).
References:
Eslick, R. F. 4 Hocket, E. A. 1976. Suggestions for gene symbolization, g, m, and x. BGN 6:115.
Kakade, M. L. & Liener, I. E. 1969. Determination of available lysine in protein. Anal. Biochem. 27:273-280.
Sandfaer, J. 1973. Barley stripe mosaic virus and the frequency of triploids and aneuploids in barley. Genetics 73:597-603.
Sandfaer, J. 1975. The occurrence of spontaneous triploids in different barley varieties. Hereditas 80:149-153.
