Whole detached citrus leaves (Citrus sinensis [L] Osbeck) were subjected to water stress by allowing them to lose water until their initial fresh weight decreased by about 15%. Ethylene production in water-stressed leaves increased significantly reaching a peak 4 h after termination of the stress treatment and decreased rapidly to control level thereafter. The enhancement in ethylene production was the result of an increase both in the synthesis of 1-aminocyclopropane-l-carboxylic acid (ACC) and in the activity of ethylene-forming enzyme (EFE). The increase in ACC level peaked 2 h after termination of the stress treatment, whereas EFE activity increased gradually with time. Pretreatment with abscisic acid (ABA) had no effect on ethylene production in whole detached leaves subjected to water stress. In water-stressed leaf discs, ABA pretreatment stimulated ethylene production. Norbornadiene, a competitive inhibitor of ethylene, enhanced the ethylene production rate in water-stressed leaves and delayed its subsequent reduction. Propylene, an ethylene analog, had no effect on ethylene production in stressed leaves. The possible involvement of an autoinhibition of ethylene production in regulating the level of water-stress-induced ethylene in citrus leaves is discussed.

In: Israel Journal of Plant Sciences

The irrigation and fertilization regime of different varieties of Grevillea in Israel are based on existing knowledge for growing various varieties of the Proteaceae family for production of cut flowering branches. However, growers face problems in cultivating Grevillea “Spiderman,” such as leaf chlorosis, prolonged growth until flowering, and reduced quality of cut flowering branches. The present study aimed to examine whether these problems stem from deficiency or excess of Fe, Mn, Zn, P, and Mg, focusing on the effect of these nutrients on growth, flowering, and appearance of visual leaf symptoms and on yield, quality, and vase life longevity of cut flowering branches. The nutrient treatments significantly affected plant development and flowering. Increasing the Fe concentration from 1 to 2 or 3 mg l–1 resulted in improved leaf color, from slightly yellow to dark green. The combination of 2 mg l–1 Fe + 1.8 mg l–1 Mn resulted in early flowering, highest yield, and development of long lateral branches. Low levels of P caused in the first year of treatment leaf chlorosis, which was intensified during the third year, resulting in severe yellowing of the flowering branches. Leaf necrosis and tip burn appeared in treatments with high concentrations of Zn, Mn, and Mg. Deficiency of Fe and Mn and high concentration of P and Mg led to the development of a large number of branches without flowers. The optimal fertilization treatment that yielded the highest quality of flowering branches after harvest was 2 mg l–1 Fe. Branches of this treatment had green foliage at harvest and the longest vase life (10 days) following the recommended postharvest treatment and air transport simulation. Based on the findings of the present research, it can be concluded that the problems in the cultivation of G. “Spiderman,” such as leaf chlorosis, delayed flowering, and reduced quality of flowering branches, result from improper fertilization.

In: Israel Journal of Plant Sciences

Forest trees possess high genetic diversity and high heterozygosity which allow adaptation to changing environmental conditions. There is a tendency to propagate successful and unique genotypes, which are identified at their mature stage in the forests, for future improvement programs and conservation purposes. However, vegetative propagation of mature forest trees is still a challenge in many conifers. In this study, we focused on improving the rooting of cuttings of mature and old Pinus halepensis and its hybrids. We observed that storage of cuttings before rooting at 4°C for 4 weeks and prolong immersion of cuttings in a solution containing 400 mg/l of indole-3-butyric acid, 5 mg/l of the auxin conjugate 2-(2,4-dichlorophenoxy)propanoic acid-glycine methyl ester, and 0.01% of Amistar fungicide significantly improved rooting of mature cuttings. The active ingredient in Amistar is azoxystrobin, an uncoupler of respiration, which seems to directly promote rooting. Rooted cuttings of selected clones demonstrated unique and uniform growth performance, most likely delivering the intrinsic growth parameters of the mother trees. It was also observed that trees growing under drought stress possess improved rooting ability. By using rooted cuttings, it will be possible to study the relationship between growth rate and adaptation to semi-arid climate conditions. The ability to clonal propagate mature and old P. halepensis trees not only enables vegetative propagation of elite trees for improvement programs, but also provides an opportunity to preserve unique naturally occurring old P. halepensis genotypes.

In: Israel Journal of Plant Sciences

Eucalyptus silver dollar (Eucalyptus cinerea) is cultivated under intensive agronomic practices for production of cut foliage branches for the floriculture industry. A range of damage symptoms, suspected to be related to unoptimized mineral nutrition, routinely occur in the leaves at the production plantations and reduce yield quality. No information is available about the nutritional requirements of Eucalyptus silver dollar, or of any other Eucalyptus species under intense cultivation for cut foliage branches production. In this study we evaluated the hypotheses that: (1) leaf damage symptoms in the Eucalyptus silver dollar plantations might be related to the nutritional status of the leaves; and (2) they are affected by environmental and growing conditions, and will therefore differ between seasons and location of the plantations. To test these hypotheses we studied the seasonal and location variations in the ionomics of damaged and healthy leaves, physiological parameters, and postharvest attributes of cut foliage branches during vase life in four plantations of Eucalyptus silver dollar in Israel. The observed leaf symptoms were also characterized anatomically. The range of concentrations for individual macronutrients in the leaves was (in g kg–1): N (18–40); P (1.2–3.0); K (5.5–17.0); Ca (3.5–14.0); Mg (1.1–2.8); S (1.3–2.6). The concentrations range for micronutrients was (in mg kg–1): B (10–100); Fe (30–170); Zn (14–27); Mn (38–190); Cu (3.5–5.9). None of the identified leaf symptoms correlated with a consistent increase or decrease of the content of a specific mineral nutrient or heavy metal compared to the healthy leaves, suggesting that they were not caused by mineral deficiency or toxicity. The leaf ionomics was affected by season and varied between locations. The main damage symptoms observed in the four examined plantations during the four harvests were red and purple spots, and oil stains. Postharvest experiments showed that the quality of branches was reduced during 7–15 days of vase life following transport simulation to the local market. The degree of reduced quality during vase life was also dependent on the location of the plantation and the season of harvest. The oil stains appeared in the two most southern locations during summer, suggesting that this symptom might be derived from the summer conditions such as the high temperatures and high light intensities occurring in the southern part of Israel.

In: Israel Journal of Plant Sciences