Vigorous Shoot Growth Research Articles

Dormant Pruning Influence on Auxin, Gibberellin, and Cytokinin Levels in Apple Trees

Abstract The levels of auxin, gibberellin, and cytokinin were measured using bioassay methods in pruned and unpruned apple trees (Malus domestica Borkh. cv. McIntosh). Vigorous shoot growth following heavy dormant pruning was accompanied by an increase in cytokinin concentration in the tissues in the early spring. As cell division and cell expansion progressed, the levels of auxin and gibberellin increased. The gibberellin activity in samples from pruned trees was 3 times higher than in samples from unpruned trees. Pruning diminished the midsummer level of cytokinins in the annual shoots.

Canopy Dynamics of Eucalyptus Maculata Hook. I. Distribution and Dynamics of Leaf Populations

The canopy dynamics of a regenerated 16-year-old stand of pole and sapling E. maculata were studied for 2½ years by repetitive non-destructive measurements in tree crowns accessed from a 20 m high scaffold tower. Average canopy leaf area density over a sample plot of 36 m2 was 0.23 m2 m-3 at a leaf area index of 4.3. Some 75% of leaf area was held in the canopies of overstorey eucalypts above 10 m in height. Average size of leaves increased gradually from top to bottom of tree canopies. Foliage production was usually concentrated in the upper crowns of trees where there was a higher proportion of active shoots, more frequent growth flushes and more rapid turnover of leaves than in lower canopy layers. Leaf area in the upper canopy fluctuated widely but increased in the long term, in mid canopy was more or less maintained and in lowest canopy declined. Crops of developing flower buds present on uppermost branches delayed and/or reduced shoot growth. Foliage production occurred in all months of the year. There was a unimodal annual rhythm of growth rate reaching a maximum in summer and a minimum in winter. Variable water supply, however, influenced production to peak in spring, summer or autumn. No shoot growth occurs in E. maculata at Kioloa when daily mean temperature (averaged for weekly intervals) falls below c. 10½C in winter. An upper temperature limit for growth could not be defined. The species apparently lacks dormancy mechanisms. Shoot growth is 'opportunistic' and occurs whenever environmental conditions are favourable. Patterns of leaf production and leaf fall were variable but peaks showed a general synchrony. Leaf fall, however, tended to lag behind leaf production. Leaves of all ages were shed but main losses were from older cohorts. Some 49% (s.d.±18%) of new leaves were lost while still small or immature, mainly during periods of vigorous shoot growth or low water supply. Browse of immature foliage was light. Normal senescence and leaf fall accounted for almost the entire loss of mature foliage.

EFFECTS OF ENVIRONMENT ON RELATIONS BETWEEN EXTENSION AND CAMBIAL GROWTH OF POPULUS EUPHRATICA OLIV.

SummaryVariations in the xylem increment and vessel diameter were found among Populus euphratica Oliv. trees from habitats of different water regimes. Vigorous shoot growth under conditions of ample water supply was associated with wide annual xylem rings and diffuse porous wood. Restricted shoot elongation of trees on dry sites was associated with narrow annual rings and ring porous wood. The influence of environmental factors on xylem production appeared to be indirect and to be largely mediated through physiological activity of the shoot system.

Seasonal Changes in the Amounts of White Unsuberized Root on Pear Trees on Quince Rootstock

SummaryThe amounts of unsuberized white root observed in glass panels, from two young deblossomed pear trees on Quince A rootstock, were measured at weekly intervals over three years under irrigated soil conditions. In the two years for which comparison was possible, the spring increase in unsuberized white root, due to new root production, occurred later on the pear trees than on neighbouring apple trees. Although root production on one pear tree was reduced in one year when that tree was stimulated into more vigorous shoot growth by pruning and in another year during a period of secondary shoot growth, the typical white root curve for this kind of tree showed only a single peak in the summer and not the pronounced double peak typical of young Worcester Pearmain apple trees investigated earlier. It is suggested that this was due to the smaller numbers of growing shoots per 100 buds burst on the pear trees. The cortex of the quince roots turned brown within a few weeks, as has been described for apple tre...

Relation of Kind of Food Reserves to Regeneration in Tomato Plants

1. It was very noticeable that in cuttings high in nitrogen, grown in the light in a nutrient solution lacking nitrates, considerable shoot growth resulted, and that in some cases more growth resulted than if nitrates were present in the solution. 2. The presence of nitrates in the nutrient solution in the case of nitrogen-high cuttings appeared to be unfavorable for root growth. If the carbohydrate reserves are exceedingly limited, the nutrient solution containing nitrates may also be unfavorable for shoot growth. In striking contrast with this condition, the same sort of solution favored development of shoots from cuttings high in carbohydrates. In this case root growth was also favored, although to a less extent. 3. In general, it seems that when the carbohydrate reserve is high and the nitrogen supply within the plant or in the nutrient solution is low, there may be a vigorous root growth. When the relative percentage of nitrogen either within or without is slightly higher, there may also be a vigorous shoot growth.