SummaryLeaf and tiller production, ear development and ear growth were measured on a two-row and a six-row spring barley genotype, on the F1 between them and on the first backcrosses.Among the developmental differences between the parental genotypes the following appeared to be of particular significance: the two-row genotype bore more leaves on the main shoot than the six-row genotype and these were initiated more slowly, but emerged more rapidly; the two-row genotype had a proportionately longer ear initiation phase than the six-row; the apical dome was bigger in the six-row than in t he tworow; the two-row genotype produced more tillers.The association of characteristics with ear type may depend on a pleiotropic effect of the ear type (V – v) locus or, alternatively, some of these characteristics may be under independent genetic control. The latter hypothesis was supported by the developmental pattern of the F1.It may be that well-adapted two-row and six-row genotypes have patterns of development balanced for the particular ear type. Hybridization between ear types may disrupt these balanced developmental patterns producing a high frequency of poorly adapted genotypes in the progeny.

The effects on yield and on grain and malt characters, of drought stress applied at different stages of grain development and ripening were studied in three varieties of spring barley grown in a glasshouse. Differences between variety means were found for most of the characters studied, but only for wort filtration time was there a significant interaction between variety and irrigation treatment. Grain yield was reduced by all the treatments involving drought stress and the reduction was greatest when stress was applied at heading and maintained for at least 14 days. A similar response was found for the number of ears per plant. Number of grains per main-shoot ear was reduced by drought stress applied at heading but not when the stress was applied from 32 days after heading until harvest. Grain size was significantly reduced by all treatments. Raw-grain characters known to be correlated with malt extract were found to be affected by the treatments: grain nitrogen content, barley extract viscosity and the rate of sedimentation of barley flour in ethanol were all increased by drought stress, the degree of response varying with the length and timing of the period of drought. Malt extracts were reduced by drought stress whether this was applied early or late in grain development. Malting loss and germinative energy were reduced, and wort filtration time increased by late stress. =-Amylase activity in the germinating grain was unaffected by any of the treatments.

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SUMMARYThe theoretical changes in the mean and variance of a segregating population under single seed descent, a method of rapid generation advancement in self-pollinating crops, are discussed. The direction and magnitude of these changes are shown to depend on the genetical architecture of the character under consideration.Examples, using computer simulation, show that for situations where heterosis is exhibited, few homozygous lines will be produced which exceed the mean of the F2 distribution from which they were derived.The advantages of the method over the normal pedigree breeding method are discussed.

Mature plant characters and yield components were measured on a two-row (Proctor) and a six-row (Clermont) spring barley variety, the F x of the cross between them, and the first back-cross to each parent.Whereas shoot dry weight in the F 1 significantly exceeded the mid-parental value, and chaff dry weight, stem length and weight per grain showed positive heterosis, grain yield did not exceed the mid-parental value and number of grains per plant showed negative heterosis.A scaling test showed that an additive-dominance model fitted the data in all cases except possibly for dry weight per grain, where the x 2 * es t approached significance.The partial dominance of the two-row allele (V) for grains set per rachis node exhibited in the mature ears of the F x was not apparent at anthesis when all the lateral florets were found to have large, apparently normal stamens. However, the ratio of median to lateral grains set over all main shoot ears of the F 1 was 1:0-21 with an average of six lateral grains per ear.The results presented indicate that the factors determining total dry-matter production and grain yield are inherited in such a way that the restriction upon grain yield in the F x is due not to a deficiency of dry matter but to a limited capacity of the plant to store dry matter in the form of grain. This may indicate some developmental interdependence in the expression of yield component characters.