Grain and spike morphology in three pleiotropic barley mutants and their homozygous double combinations.
Grain and spike morphology in three pleiotropic barley
mutants and their homozygous double combinations.
A. R. Prina and M. del C. Arias. Instituto de Genética
"Ewald A. Favret", CICA, INTA, CC.25, (1712), Castelar, Argentina.

X-ray and sodium azide treatments were carried out on seeds of a two-row spring barley genotype carrying translocation T(6-7)a. The first generation was grown in a field nursery and it was harvested by the one seed per spike method (cf.Prina et al.1986). The main scope of those experiments was related with analysis of meiotic behaviour, reciprocal translocations and heritable sterility (Prina et al 1983;1986;Prina and Hagberg 1984). Additionally, twenty-two putative mutants regarding grain and/or spike characteristics were visually selected as individual plants on the M2 generation. After several generations of selfing three of those mutants,MC166, MC169, MC170 (mutant Castelar accession numbers) were characterized by measurements of grain weight, length, width and depth and spike internode density. Other differential characteristics, not considered here, were noticed on these "pleiotropic" mutants, including the length and the diameter of the straw and also its chemical composition, for which marked differences in lignin content were observed (Acevedo et al,1993). Experiments were carried out during three years. Morphological features of the grain were registered on the five biggest grains of the two main spikes of twelve plants each year, spike internode density was measured on the four main spikes of twelve plants each year.

The double combinations of the three mutants were obtained by crossing and selection in the F/2/ and the F/3/ generations. A similar experiment to those mentioned above for the single mutants was carried out with the double combinations in order to analyze the intergenic interactions in homozygous condition.

Results presented graphically (figs.1,2 and 3) clearly show the main tendencies observed in the single mutants and their combinations as double homozygotes. The main differential feature of MC170 was a marked reduction in spike internode density. However, according to this characteristic the other two mutants also belonged to the laxatum type (fig.1). The main differential characteristic of MC166 was the general increased size of the grain (fig.2) and the grain weight (Fig.3). For the last character, this mutant has shown a semidominant expression (Prina, 1989). MC169 presented a characteristical elongated grain(fig.2) and also showed other features in coincidence with lax-a mutants (cf.Larsson and Lundqvist, 1986).

In the double combinations positive interactions in internode density were observed in both of the combinations of MC169, while the combination of the other two mutants showed additive effects. MC166 was epistatic over MC170 for all the dimensions of the grain and, accordingly, the grain weight. While in combination with MC169, the most prominent interaction was the positive effect in relation with the length of the grain. MC169 was epistatic over MC170 for grain length, while, the contrary was observed for grain width, with the double mutant having a grain weight similar to those of both parental mutants(fig 3).

Results showed that even though measurements of grain sizes and weight are usually not practical characteristics for cultivar identification (Sparks and Malcolm,1978), this is not the case when dealing whith segregation of major genes affecting them. Moreover, they also allowed us to distinguish intergenic interactions, which were different for the same homozygous combination depending on which character was considered.

References.

Acevedo,A., Prina,A.R., Arias,M.C. and Casal,O.F. 1993. Análisis bioquímico e histológico del tallo en mutantes de cebada caracterizadas por la morfología del grano y/o la espiga. Actas del II Simp.Arg.de Biotecnol. Veg. Huerta Grande. Mayo 1993. (Abstr.0.2,2 p).

Larsson,H.E.B. and Lundqvist U. 1986. Description of genetic stocks. B.G.N.16 (Section VII):57-80.

Prina A.R. 1989. Consideraciones para la aplicación eficiente de mutagénesis inducida en Fitomejoramiento. Mendeliana 5-49.

Prina A.R.,Hagberg G. and Hagberg A. 1983. Reciprocal translocations in sodium azide treatments in barley. Barley Genetics Newsletter 13: 72-77.

Prina A.R. and Hagberg A. 1984. A barley mutant with chromosome condensation in late tetrad stage. Hereditas 101:261-263.

Prina A.R., Hagberg A. and Favret E.A. 1986. Inheritable sterility induced by X-rays and sodium azide in barley. Genetica Agraria 40: 309-320.

Sparks G.A. and Malcolm J.P. 1977. Barley identification by grain characters in New Zealand. N.Z.Journal of Experimental Agriculture 6: 1-10.


Fig 1. Means and standard deviations of spike internode length in mutants MC 166, 169 and 170, their mother line (X-T)² and their double homozygous combinations.




Fig.2. Means and standard deviations of the seed sizes (length,width and depth) in mutants MC 166, 169 and 170, their mother line (X-T)² and their double homozygous combinations.


Fig.3. Means and standard deviations of seed weight in mutants MC 166, 169 and 170, its mother line (X-T)² and their homozygous double combinations.