Yiftach Vaknin

The potential of milk thistle (Silybum marianum L.), an Israeli native, as a source of edible sprouts rich in antioxidants

The potential of wild plants in Israel as sources of edible sprouts has not been investigated until now. Milk thistle (Silybum marianum L.) is native to the Mediterranean basin and is now widespread throughout the world; its young fleshy stems are traditionally eaten by the local Arab sector in Israel, and its sprouts are rich in antioxidants and have been used as a traditional medicine for diseases of the liver and biliary tract. The active extract of milk thistle, silymarin, is a mixture of flavonolignans and is a strong antioxidant that has been proved to promote liver cell regeneration, to reduce blood cholesterol and to help prevent cancer. The present objective was to investigate the potential of milk thistle as a source of edible sprouts rich in antioxidants. We found that seed germination within 3–4 days was high (96%, except for striated seeds). Exposure to light significantly reduced sprout growth and significantly increased the polyphenol content and antioxidative capacity. The polyphenol content was 30% higher in seeds originating from purple inflorescences than in those from white ones. We thus found milk thistle to be a good candidate source of healthy edible sprouts.

The Significance of Pollination Services for Biodiesel Feedstocks, with Special Reference to Jatropha curcas L.: A Review

The importance of pollination services for insect-pollinated crops in general, and for the major biodiesel crops, such as Jatropha curcas L., in particular, is reviewed. The dependence of the major biodiesel feedstocks on pollinators ranges from almost zero to low dependence in soybean, through low to medium dependence in rapeseed, and up to high dependence in the African oil palm and in J. curcas. Currently, the basic requirement of J. curcas for pollination services is largely neglected. In light of the enormous scale of existing and future plantations of J. curcas, and of the effective pollination by native pollinators in most commercial crops, it is clear that the local insect fauna of any given habitat, on any continent, will not be able to satisfy the pollination requirements of any plantation, once it becomes established and starts blooming. It is suggested that the best way to address the pending catastrophe of severely reduced yields in J. curcas plantations that would result from reduced reproductive success would be to use honeybees as the prime pollinators, regardless of the pollination services provided by the local insect fauna. Basic research on the contribution of honeybees to the reproductive success of J. curcas should be carried out and used as a guideline for planning future provision of proper honeybee pollination services in any given plantation, characterized by its specific size, age, planting density, soil type, irrigation, fertilization, and climatic conditions.

Can ants equal honeybees as effective pollinators of the energy crop Jatropha curcas L. under Mediterranean conditions

Jatropha curcas L. is the subject of many research and breeding programs concerned with its potential as an oil crop for biodiesel production. Despite an increasing amount of information regarding this relatively new crop, pollination requirements of this plant are largely neglected. The aim of the study was to evaluate the relative significance of ants and honeybees as potential pollinators of J. curcas grown under Mediterranean conditions. Jatropha curcas plants bloomed throughout the summer and fall, peaking twice, in early summer and late fall. During this period, the plants were visited by 70 species of insects representing 45 families from seven orders, with most species rarely being observed. Ants and Honeybees were the most common species, accounting for >95% of all flower visits. The foraging behavior of the honeybees followed the pattern of bloom phenology, especially during the summer, and mostly promoted cross‐pollination. Ants on the other hand, mostly promoted self pollination showing no such correlative behavior, reacting often too late to nectar availability, and were highly susceptible to climatic changes. Pollinator exclusion treatments revealed that during summer, fruit and seed sets, as well as seed size and oil and protein contents, were relatively similar for ant and bee‐pollinated flowers. During fall, however, reproductive success of bee‐pollinated flowers was relatively high (66%), while fruit set of ant‐pollinated flowers was significantly reduced from 71 to 11%. In conclusion, while both groups are equal in their pollination effectiveness in the summer, during the fall the honeybees are almost the sole pollinators of the plant. Based on bloom phenology and pollination activity data, the honeybees are responsible for the pollination of more than 80% of the annual reproductive potential of J. curcas, under Mediterranean conditions.

Effects of Pot Size on Leaf Production and Essential Oil Content and Composition of Eucalyptus citriodora hook. (Lemon-Scented Gum)

The influence of pot size on plant height, stem diameter, dry leaf biomass, essential oil content, and composition of Eucalyptus citriodora was investigated in this experiment. Both the physical and the chemical properties of pot-grown plants were significantly affected by pot size. Plants grown in larger pots were generally taller, had thicker stems and wider canopies, grew more branches, and produced more leaves that were larger than plants grown in smaller pots. The highest essential oil concentrations (∼ 1.2%) were observed in plants grown in 1-liter (20-cm diameter) and 5-liter (11 cm diameter) pots. Essential oil composition was fairly similar for all pot sizes. We conclude that Eucalyptus citriodora can be grown in pots, preferably in 10- or 5-liter pots, and thus provide fresh leaves on a daily basis.

Pollen Source Effects on Fruit and Seed Traits of Jatropha curcas L.—A Renewable Biodiesel Feedstock

The effects of the pollen source on fruit and seed traits of Jatropha curcas and on potential biodiesel traits were investigated using analysis of breeding system and reciprocal pollination of various genotypes. The field experiments were carried out under Mediterranean conditions in Bet-Dagan, Israel. The breeding system was investigated by comparison of self-pollination with cross, open, and spontaneous self-pollination. Self-pollination, compared with cross-pollination, resulted in significantly lower levels of seed weight, oil concentration, oil content, and linoleic acid concentration in the seed-oil and with higher concentration of oleic acid. These seed traits were measured by near infrared reflectance spectroscopy (NIRS) as previously calibrated for J. curcas. Spontaneous self-pollination resulted in extremely low fruit and seed sets, and apomixis was totally absent. Pollen source effects were investigated by reciprocal pollination of selected genotypes; ‘Ethiopia,’ ‘Niger,’ and ‘Suriname’ both receiving and donating pollen. In addition, the genotype Brazil was used only as pollen source for the above mentioned genotypes. We found that most seed and oil traits were determined by the pollen recipient regardless of the type of pollen source. Additionally, when pollinated with Brazil, Ethiopia resulted in lower seed set, Niger resulted in higher content of seed protein and lower concentration of stearic acid in the seed oil, and Suriname resulted in higher concentration of linoleic acid and lower concentration of oleic acid. We suggest that enhancement of oil yield and oil quality in future plantations should be based either on a single elite genotype with nondetrimental self-pollination traits or on several elite genotypes with improved compatibility both as pollen sources and pollen recipients.

Global maximization of Jatropha oil production under semi-arid conditions by balancing vegetative growth with reproductive capacity

Jatropha curcas L. is a drought tolerant crop that is globally cultivated under semi‐arid conditions as a biodiesel feedstock. Despite its great potential, however, many projects failed to reach commercially viable seed and oil yields. The aim of the study was to provide globally applicable solutions for maximization of Jatropha oil production under semi‐arid conditions. Under extremely low irrigation (10% of potential evapotranspiration; ETp), fruit production was very low and a surprisingly significant portion of the fruits delayed their maturity up to six months post‐bloom. Increasing irrigation to mid‐level (60% ETp) significantly elevated fruit production and speeded up the ripening rate, whereas further increasing irrigation to a higher level (90% ETp) decreased seed and oil yields, probably due to the increased investment in vegetative growth. Nevertheless, maximal seed and oil yields at 60% ETp remained far below targeted yields. Coupling irrigation at 60% ETp, with induction of vegetative arrest, by soil application of a commercial gibberellin synthesis inhibitor, brought forward the second bloom period by two months, reduced vegetative growth, promoted floral production and significantly enhanced reproductive capacity by more than doubling oil production. The results show that under semi‐arid conditions, commercially viable seed and oil yields of Jatropha can be achieved by carefully balancing vegetative growth with reproductive capacity through the combined application of optimal irrigation regimes and induced vegetative arrest.

Shade Effects on Leaf Production and Essential Oil Content and Composition of the Novel Herb Eucalyptus citriodora Hook.

Abstract The influence of light conditions on plant growth and essential oil production of the novel herb Eucalyptus citriodora (Lemon-Scented Gum) was investigated. Pot-grown plants were grown either directly exposed to sunlight or ‘shaded’ with the least exposure to sunlight (75 % shade) or with intermediate exposure to sunlight (50 % shade). Shaded plants were generally taller, had thicker stems and wider canopies, grew more branches, produced larger leaves, produced more essential oils per plant, produced similar concentrations of the major essential oil components (citronellal, β-citronellol and trans-caryophyllene) in the leaves and produced record high concentrations of (±)-p-menthane-3,8-diol, a component having superior insect repellent properties, than the ones grown under full sun. Plants grown under ‘50% shade’ were likely to be the most productive of leaves and essential oils, either for personal use in tea infusions or for production of leaf-essential oils, potentially having improved capacity for insect repellency.

Electric field imposed by pollen vectors as a selective force in the evolution of floral morphology - an evolutionary hypothesis.

The hypothesis presented in this article is that electrostatic forces, which have been proven to promote enhanced pollen transfer even without direct contact with the stigma or anthers, have played a role in the evolution of generalized entomophilous flowers.