Rate of leaf emergence of barley grown in the field in each of 2 years was affected by sowing date and, where direct comparisons were possible, it was found that leaves on late-sown plants emerged more quickly. Rate of leaf emergence fluctuated throughout the season, slowing almost to zero in the winter. Much of this variation in rate was removed when the number of leaves was plotted against accumulated temperature rather than time. When emergence rates for each sowing were calculated using a common base temperature they were found to be well correlated with rate of change of daylength. However, it was found that base temperature as well as temperature response was affected by date of sowing. The pattern of change of size of leaves was also affected by date of sowing. It appeared that in low temperatures and short days, there was no increase in leaf size from leaf position to leaf position. The responses of leaf emergence, extension and final size to date of sowing appear to adapt the plant to grow quickly when sown early but to cease growth and possibly frost-harden at low temperatures.
Rate of leaf emergence and number of leaves was measured on nine varieties of wheat and nine varieties of barley on four sowing dates in each of two years. Number of leaves declined the later the plants were sown, except for the February or March sowing when the number of leaves increased in the winter varieties. There were differences between varieties and a strong variety x sowing date interaction, which was probably due to differences in vernalisation response. The rate of leaf emergence was faster the later the sowing date and there were differences between varieties. Analysis by regression of number of leaves on accumulated temperature showed that the rate was up to 80 per cent faster in the last sowing, compared with the first. Differences of up to 18 per cent were found between varieties, but there was little or no interaction with sowing date. Leaves of barley emerged more quickly than those of wheat. There was a correlation between rate of leaf emergence and rate of change of daylength at the time of plant emergence, similar to that found by other workers. There was evidence that the base temperature varied with date of sowing. Additional key words : Vernalisation, accumulated temperature, rate of change of daylength, base temperature. RÉSUMÉ Effet de la date de semis et de la variété sur le rythme d'apparition des feuilles du brin-maître et leur nombre total chez l'orge et le blé. La vitesse d'apparition des feuilles et leur nombre ont été observés pour 9 variétés de blé et 9 variétés d'orge et pour 4 dates de semis au cours de 3 années successives. Le nombre final de feuilles diminue lorsque les dates de semis sont de plus en plus tardives, sauf pour le semis de février ou de mars pour lequel le nombre de feuilles est plus élevé chez les variétés d'hiver. On constate des différences entre variétés ainsi qu'une forte interaction variété x date de semis, qui sont probablement liées à des différences de sensibilité à la vernalisation. La vitesse d'apparition des feuilles augmente pour des semis plus tardifs et varie entre variétés. L'analyse, par régression linéaire, des relations entre le nombre de feuilles et les sommes de température accumulées montre une plus grande vitesse d'apparition des feuilles, de l'ordre de 80 %, pour le semis le plus tardif par rapport au plus précoce. Les différences entre variétés vont jusqu'à 18 %, mais l'interaction entre la date de semis et la variété est faible à nulle. Le rythme d'apparition des feuilles est plus rapide chez l'orge que chez le blé. Ce rythme est corrélé à la vitesse de changement de la durée du jour au moment de l'apparition du pied, selon une relation comparable à celle constatée par d'autres auteurs. On montre que la température de base (ou seuil) varie selon la date de semis. Mots clés additionnels : Vernalisation, température accumulée, vitesse de changement de la durée du jour, température de base.
A scheme to relate leaf emergence and tillering is described. It assumes that 3 phyllochrons elapse between the emergence of a leaf and the tiller in its axil (phyllochron interval) and that leaves emerge at the same rate on all shoots. These assumptions were examined in several varieties of wheat and barley sown on 4 different dates in each of 3 seasons. It was found that the phyllochron interval was generally about 3 but that it tended to be longer in the coleoptile tillers and the 1st secondary tiller. There were significant differences in the rate of leaf emergence amongst shoots. In spite of these considerations observed tiller production measured on a main shoot leaf number basis agreed well with the predicted production. The main shoot leaf number at which tillering ceased was correlated with total number of leaves on the main shoot. These results indicate that rate of tillering will vary with rate of leaf production and that genetic variation in rate of leaf production may be used to predict and select for different tillering patterns.
SUMMARYGrain growth and final weight per grain were measured in 12 genotypes of spring barley, the parents and progeny of two six-row × two-row crosses. Weight of carpels or grains from node 10 on the main shoot ear was measured from shortly after meiosis until grains were at maximum dry weight. Similar measurements were made at representative node positions along the ear of Proctor and of Midas spring barley cultivars.From about 10 days after anthesis grains grew at a constant rate for about 3 weeks. Amongst genotypes growth rate of the median grain ranged from 1·4 to 2'2 mg/day and there was a very highly significant positive correlation between growth rate and final grain weight. A similar relationship was found among grain positions on the ear. For about 10 days after anthesis growth was exponential and although relative growth rate did not differ between genotypes or grain positions there was a highly significant difference between caryopsis weights during this phase. There were significant correlations between final grain weight and carpel weight at anthesis and between final grain weight and husk weight at anthesis. In the period between meiosis and anthesis growth was exponential and the relative growth rate did not differ between genotypes or node positions on the ear. There were significant differences between carpel weights during this phase. Carpel weight at anthesis and carpel linear dimensions at meiosis were correlated.These data suggest that the initial size of carpel is an important factor in determining growth rate and potential grain weight. Potential grain size in barley may be determined by physical limitations imposed by the lemma and palea or may be causally related to the size of the carpel. The relative size of the carpel is determined by the time of meiosis and potential size may also be affected by pre-anthesis conditions.
Ear development and ear growth were studied in the progeny of two crosses between a six-row and two two-row spring barley varieties. There were no differences in the rates of primordium initiation amongst the progenies and parents. Duration of ear initiation and ear growth varied amongst the genotypes, and there was a strong negative correlation between the duration of these phases. Duration of ear initiation was correlated with number of leaves, as was the length of life cycle from sowing to anthesis. Survival of spikelets was related to the number of spikelet primordia initiated. However, the proportion of spikelet primordia that survived to form grains was less in ears with most spikelet primordia. This may be due to competition for resources in the ear. It is suggested that optimal ear size and life-cycle duration may be achieved by breeding for appropriate durations of the component phases of the life cycle.
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