GrainGenes

II. 11. Slender: an accelerated extension growth mutant of barley.

C. A. Foster, Welsh Plant Breeding Station, Aberystwyth, Wales, G. B. "R"

A mutant of potential biochemical interest, having greatly accelerated extension growth characteristics, has been isolated in the cultivar Herta, following treatment with diethyl sulphate.

The mutant phenotype is characterized by very rapid extension growth in the seedling and adult plant stages. The mature plant is tall, slender, extremely lax, and unable to support itself. At the first leaf stage the mutant plants are up to four times as tall as the normal phenotype, while at heading the difference in total height is only 25% to 35% in favor of the slender phenotype. Days to ear emergence are similar, but the ears of the mutant are up to twice as long as the non-mutant and are thin and fragile, having greatly elongated rachis internodes. The ears normally emerge through the fold of the flag leaf sheath, and are often somewhat compressed in a concertina manner, lacking the physical rigidity required to emerge through the flag leaf ligule region. Basal internode elongation occurs concurrently with tillering, resulting in an aerial branching habit, with root initials forming at the lower aerial nodes, in contrast to the pattern of tillering, crown development and subsequent stem elongation normally found. Stems and leaf laminae are narrower than normal, while anthocyanin pigmentation of the leaf sheaths and stem nodes is greatly enhanced m the mutant plants. Ears are generally at least twice as long as in the non-mutant phenotype. Floral parts are very reduced in size and completely sterile: no pollen is produced and no seed set on cross pollination.

Expression of the mutant phenotype, at least at the seedling stage, is relatively greater at low temperatures (less than 10°C) than at high temperatures (over 20°C).

M3 and M4 progeny tests of heterozygotes yielded a segregation of 551 N : 157 slender plants (X² 3 : 1 = 2.26; p = O.50 - 0.10) indicating monofactorial recessive inheritance of the slender character.

Mutant plants do not respond to exogenous gibberellins whereas nonmutant sibs respond in the usual manner - rapid stem and leaf extension growth occurring, resulting in plants which are phenocopies of the mutant.

The appearance of the mutant plants suggests that the mutated gene is one concerned with some aspect of gibberellin synthesis or utilization. Preliminary results of biochemical studies indicate that the mutation is concerned with gibberellin synthesis (J. L. Stoddart, pers. comm.).

'Gigas' and 'vine' type mutants of barley have been reported in the past, but none of these, except that recently described by Favret et al. (1976), seem comparable to this mutation. The symbol sln is being proposed for this gene and appropriate linkage studies initiated. Seed is available from the author.

Figure 1. Normal plant at tillering state (on left). Slender plant of same age (on right).

Figure 2. Slender mutant (on left) vs. normal (on right) at ear emergence.

Figure 3. Ears of slender mutant barley vs. normal (on right).

Reference:
Favret, E. A., Favret, G. C., and E. M. Malvarez. 1976. Genetic regulatory mechanisms for seedling growth in barley. Barley Genetics III, 37-42.

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