Modeling the effect of physiological responses to green pruning on net biomass production of Eucalyptus nitens

Green pruning of Eucalyptus nitens (Deane and Maiden) Maiden increases instantaneous rates of light-saturated CO(2) assimilation (A), and changes patterns of total leaf area and foliage distribution. We investigated the importance of such changes on the rate of recovery of growth following pruning. A simple process-based model was developed to estimate daily net biomass production (G(d)) of three-year-old plantation-grown trees over a 20-month period. The trees had been pruned by removal of 0, 50 or 70% of the length of green crown, equivalent to removal of 0, 55 or 88% of leaf area, respectively, when the plantation verged on canopy closure. Total G(d) was reduced by only 20% immediately following the 50%-pruning treatment, as a result of both the high leaf dark respiration and low A in the portion of the crown removed compared to the top of the crown. Pruning at the time of canopy closure preempted a natural and rapid decline in G(d) of the lower crown. Although leaf area index (L) was approximately 6.0 at the time of pruning, high light interception (95%) occurred with an L of 4.0. The 50%-pruning treatment reduced L to 3.5, but the physiological responses to pruning were sufficient to compensate fully for the reduction in intercepted radiation within 110 days of pruning. The 70%-pruning treatment reduced L to 1.9, and reduced G(d) by 77%, reflecting the removal of branches with high A in the mid and upper crown. Physiological responses to the 70%-pruning treatment were insufficient to increase G(d) to the value of unpruned trees during the study. Model sensitivity analysis showed that increases in A following pruning increased G(d) by 20 and 25% in the 50- and 70%-pruned trees, respectively, 20 months after pruning. Changes in leaf area/foliage distribution had a greater effect on G(d) of 50%-pruned trees (47% increase) than did changes in A. However, the reduction in photosynthetic potential associated with the 70%-pruning treatment resulted in only small changes in leaf area/foliage distribution, which consequently had little effect on G(d). The effects of physiological processes occurring within the crown and in response to green pruning on G(d) are discussed with respect to pruning of plantations.     

Überleben einerXanthomonas campestris pv.pelargonii-Mutante in einjähriger Komposterde

Zusammenfassung Das Überleben vonXanthomonas campestris pv.pelargonii wurde anhand einer Mutante in einjährigem Kompost untersucht. In der Versuchsvariante 1, bei der die Bakterien mit Komposterde vermischt wurden, konnte die Mutante Xc3b nach 15 Monaten nicht mehr nachgewiesen werden. Unter diesen Bedingungen war es den Bakterien möglich, 14 Monate im Kompost zu überleben. In der Versuchsvariante 2, bei der Komposterde mit Bakterien und zusätzlich noch mit infizierten Pelargonienstielen eingebracht wurden, konnten dieXanthomonas-Mutanten noch nach 26 Monaten nachgewiesen werden.

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Survival of a mutant ofXanthomonas campestris pv.pelargonii in one year old compost

Survival of phytopathogenicXanthomonas campestris pv.perlargonii in a one year old compost was investigated by use of a mutant. In the variant 1, in which the compost soil was mixed with the bacteria, the mutant Xc-3b could not be detected after 15 months. Under these conditions the bacteria were able to survive for 14 months in the compost. In the variant 2, in which the compost soil was mixed with bacteria andXanthomonas-infected geranium stems, it could be found even after 26 months.

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Morphology and rooting of shoots developing in response to decapitation and pruning of Caribbean pine

The effects of decapitation at various levels, combined with heavy pruning of remaining branches, were examined for Caribbean pine. This treatment stimulated the development of shoots with long primary needles at all levels in the crown of trees aged one, four and eight years. Although a significant positive relationship between primary needle length and rooting was demonstrated, the very juvenile appearance of these shoots was not a reliable guide to rooting. There was an over-riding effect on rooting of the ortet age × level in crown × decapitation height treatment. Decapitated trees provided shoots of higher rooting capacity than intact trees for the one and four, but not the eight year old trees. Shoots developing in the lower crown in response to decapitation and heavy pruning of four year old trees displayed a high level of rooting-equivalent to that of shoots from the decapitated and pruned one year old trees.     

Vorwort

Ohne Zusammenfassung     

Activity ofBacillus thuringiensis Berl. on the lesser cotton leafwormSpodoptera exigua Hbn. (Lep., Noctuidae) in corn and sunflower cultivations in Egypt

Field applications usingBacillus thuringiensis (Dipel 2 X) againstSpodoptera exigua infesting corn and sunflower cultivations were carried out in two different localities in Egypt. The percentage of infested corn plants decreased to 2.5%, seven days after treatment with Dipel 2x, (250 g/fed) and the yield was significantly increased compared with untreated plots. The carbamate insecticide (Lannate) at 300 g/fed caused complete kill to the larvae and the highest yield was obtained. Application of Lannate, Dipel (250 g) or a combination of both (150 g/each/fed) caused a high reduction of the larvae existing in sunflower after seven days from application, while Dipel at 200 g/fed gave a lower effect. Ten days after application, the number of larvae and infested plants increased significantly in plots treated with Lannate alone, while plots treated with either Dipel (250 g) or Dipel combined with Lannate (150 g/each) still maintained a lower infestation. The estimated yield showed the highest increase in plots treated with Lannate followed by Dipel (250 g) and then a combination of both.     

Untersuchungen zur Bekämpfung der Bienenmilbe,Varroa jacobsoni Oud.

Comparative study of 8 treatments was done to controlVarroa jacobsoni (Oudemans) infesting Carniolan honey beeApis mellifera L. colonies, including Apistan, Lactic acid, and Formic acid, using some methods of application. Experiments were carried out in the experimental apiary of the Faculty of Agriculture, Shebin El-Kom Egypt during the period from August to October 1991. Results showed that Apistan was the best material for controlV. jacobsoni followed by Lactic acid and Formic acid. Apistan completely controlled varroa mite at the 4 different doses (0.5, 1.0, 1.5, and 2.0 strips/colony) and no significant differences were found between the different doses. Lactic acid and Formic acid (at the rate of 1.5 cm³/frame) were slightly effective against the varroa mite in both methods of application (above and under the frames). The application of acids under the frames had better results than the application above the frames.     

Effects of Fencing and Ground Preparation on Natural Regeneration of Native Pinewood over 12 years in Glen Tanar, Aberdeenshire

An enumeration was carried out in 1989 to assess the effectsof fencing and ground treatment 11 years previously on survivaland growth of naturally disseminated Scots pine seedlings inthe native pinewood at Glen Tanar, Aberdeenshire. Results showeda significant difference between unfenced and fenced plots onpine seedling density and height in 1989. Initial effects ofseedbed treatment on Scots pine seedling density, 2 years afterthe experiment began had largely disappeared by 1989. If removalof ground cover is used to enhance pine seed germination, theexposed seedlings may need to be protected from browsing byfencing. Received 19 March 1990.     

Crop load and water stress effects on daily stem growth in peach (Prunus persica)

We investigated crop load and water stress effects on diurnal stem extension growth of field-grown peach (Prunus persica (L.) Batsch) trees. Neither the presence of fruit nor reduced irrigation significantly altered the timing of diurnal fluctuations in stem growth rate. Stems with subtending fruit had significantly reduced growth compared to stems with no subtending fruit. Crop load had no significant effect on relative stem extension rates and the majority of the reduction in absolute growth was the result of a smaller zone of elongation in fruit-bearing stems than in stems with no subtending fruit. Fruit removal did not increase growth rates within 24 h. When irrigation was reduced, the length of the stem elongation zone and total daily stem growth were significantly decreased relative to well-irrigated controls and the decreases were highly correlated with stem water potential. Compared with well-irrigated controls, relative stem extension rates of water-stressed trees were reduced at several times during the 24-h period, but the degree of reduction was not proportional to the difference in stem water potentials between the treatments.