II.31. Allelism testing of seven chlorina mutants in Trebi barley.
Michael McMullen. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80521, U.S.A.
The spontaneous chlorina mutants of Trebi barley collected by D.W. Robertson at Colorado State University were tested for allelism among themselves and with the collection of designated chlorina mutant stocks: f, fc, f3, f4, f5, f6, f7, f8, f9. The Trebi mutants, normal green plants, and designated chlorina stocks were crossed reciprocally in a sufficient number of combinations to determine the allelic relationship of the chlorina genes and the type of inheritance of the chlorina character.
The F1 phenotypes of crosses using Colsess V (fcfc) as the female parent and the Trebi mutants as the male parent are presented in Table 1. Using Trebi VI, Trebi X, Trebi XII and Trebi XIII as the male parent resulted in all green F1 progeny, indicating these mutants are not allelic to fc. The F1 progeny resulting from crosses using Trebi V, Trebi IX and Trebi XI as the male parent were all chlorina, indicating that these mutants are allelic to fc.
Table 1. F1 phenotypes of Colsess V (fcfc) x Trebi mutants.
The F1 phenotype of crosses among the Trebi mutants and normal green plants is presented in Table 2. The crosses among Trebi V, Trebi IX and Trebi XI resulted in all chlorina F1 progeny. This verifies allelism of these mutants which were previously shown to be allelic to fc.
Table 2. F1 phenotype of diallelic crosses among Trebi chlorina mutants. Number is number of F1 plants observed.
All of the F1 progeny resulting from crosses using Trebi VI, Trebi X, Trebi XII and Trebi XIII as the female parent were chlorina, while the F1 plants resulting from crosses using these mutants as the male parent were green, except in cases involving one of these mutants as the female parent. The reciprocal difference in those crosses is attributed to maternal inheritance of the chlorina character.
The mutants suspected of being maternally inherited, Trebi VI, Trebi X, Trebi XII and Trebi XIII were crossed reciprocally with normal green plants. All crosses using these mutants as the female parent and normal green as the male parent produced chlorina Fl progeny. The reciprocal crosses using normal green female parents produced only normal green progeny, verifying the maternal inheritance of these Trebi chlorina mutants.
Three other maternal chlorina stocks have been observed, Coast V (Robertson, 1937), Trebi VIII and Trebi 67-8043A (Tsuchiya and Robertson, 1971).
The F2 generation from crosses involving the maternally inherited Trebi chlorina mutants was grown to verify the maternal inheritance. The F2 of crosses using normal green as the female parent and maternally inherited chlorinas as the male were all normal green, exhibiting no segregation for the chlorina character and indicating no genetic control of the chlorina character. The F2 of crosses using the maternally inherited chlorinas as the female parent and normal green males were all chlorina.
Crosses using a maternal chlorina as the female and a nuclear chlorina as the male parent were all at least as light in color as the female chlorina parent. Plants ranging in color from albino to slightly lighter than chlorina were also observed in the F2 populations. These plants were attributed to the segregation of homozygous recessive nuclear chlorina genes interacting with the maternally inherited chlorina factor.
A particular segregating nuclear gene interacting with the various types of chlorina cytoplasm was expressed differently in the different maternally inherited chlorina cytoplasm types of Trebi VI, Trebi X, Trebi XII and Trebi XIII. Using this criterion, it was concluded that the four maternally inherited Trebi chlorina mutants are distinct from each other, conditioned by four separate maternal systems.
Since four types of maternal chlorina inheritance were found and 3 others have previously been observed, it seems likely that cytoplasmic inheritance may play an important role in the inheritance of chloroplast characters. Polymorphism may exist in chloroplasts, or at least in cytoplasmic factors controlling their development. Many, more subtle characteristics than color phenotype are probably inherited other than through nuclear genes. This being the case, the choice of a female parent to be used by breeders would be a fundamental concern.
Robertson, D. W. 1937. Maternal inheritance in barley, Genetics 22:104-113.
Tsuchiya, T. and D.W. Robertson. 1971. Two more cases of maternal inheritance of chlorina mutation in barley. Barley Genetics Newsletter 1:65.
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