Raphael A. Stern

Bio: Raphael A. Stern is an academic researcher from Tel-Hai Academic College. The author has contributed to research in topics: Pyrus communis & PEAR. The author has an hindex of 24, co-authored 81 publications receiving 1546 citations.

Pollen Parent Effect on the Selective Abscission of 'Mauritius' and 'Floridian' Lychee Fruitlets

Abstract: Fruit produced by adjacent blocks of 'Mauritius' and 'Floridian' lychee (Litchi chinensis Sonn.) were sampled at four different stages of development and the embryos were analyzed for pollen parentage by phosphoglucos e isomerase (PGI; EC 5.3.1.9) isozyme system. Hybrid percentage increased significantly from ≈5 weeks after fruit set to maturity as follows: from 29.5% to 76.3% in 'Mauritius' and from 74.2% to 92.5% in 'Floridian'. These findings clearly indicate selective abscission of selfed fruitlets. In 'Mauritius', yield was not related to the distance from the pollenizer block or hybrid percentage. In 'Floridian', yield of trees adjacent to the 'Mauritius' pollenizer was higher by 36% than that of trees at a distance of 24 m. The correlation between 'Flordian' yield and hybrid percentage tended toward significance (r= 0.64, P = 0.08). In addition, in both cultivars, fruit and seed weights were affected by the pollen parent: outcrossed fruit were heavier and contained heavier seeds than selfed ones.

CPPU and BA increase fruit size of ‘Royal Gala’ (Malus domestica) apple in a warm climate

Abstract: SummaryThe effects of the synthetic cytokinins BA and CPPU on fruit size of the small fruited ‘Royal Gala’ apple were examined during four consecutive years (1999-2002) in the warm climate of Israel. CPPU at a concentration of 10 ppm and BA at a concentration of 50 ppm caused an appreciable (>50%) and significant increase in fruit size when applied two weeks after full bloom. The large increase in fruit size occurred with (BA) or without (CPPU) some thinning. Therefore, the main effect was attributed to the direct stimulation of fruit cell division. Both cytokinins increased fruit size without affecting fruit shape and seed number, and with no reduction in the return bloom or yield of the following year. Our findings demonstrate that BA and CPPU have a significant potential to improve fruit size of ‘Royal Gala’ apple without any negative effects on fruit quality at harvest or in storage of 0°C. Preliminary results with ‘Red Delicious’ apple indicate that these cytokinins may be used for other cultivars as...

A Comparison between Semi- and Fully Compatible Apple Pollinators Grown under Suboptimal Pollination Conditions

Abstract: set Abstract. Apple (Malus domestica) has a gametophytic self-incompatibility (GSI) system. Consequently, fertilization is achieved by cross-pollination with a compatible pollinator. Compatibility is governed by a multiallelic S locus. Cultivars are fully compatible when both of their S-loci differ and are semi compatible when one locus is identical and the other differs. In a previous study we found that the fruit set and yield of the apple cultivar 'Topred' was reduced when it was pollinated by a semi compatible cultivar. To examine if this occurrence is a general feature in apples grown under suboptimal conditions, three additional cultivars, 'Golden Delicious', 'Granny Smith' and 'Royal Gala', were studied as pollen recipients of semi and fully compatible pollinators. Based on PCR analysis of the S-RNase allele, it was determined that the pollination rate of the semi compatible was signifi cantly lower than that of the fully compatible pollinator in all cases. This was refl ected by the lower fruit set and seed set of 'Golden Delicious' and 'Royal Gala', but not of 'Granny Smith'. In hand pollination experiments, where pollen was in excess, no difference was found between the semi and fully compatible pollinators in all three cases. These results indicate that the low yield, conferred by semi compatible pollinators, is due to insuffi cient cross-pollination (and not to cultivar characteristics). Thus, low yields due to semi compatibility may be avoided by appropriate honeybee management that will increase pollination. Still, under suboptimal conditions, for growth and pollination, full compatibility is preferable. Apples (Malus domestica) are self-incom- patible, and therefore cross-pollination with a compatible cultivar is essential to achieve fruit set and yield (Dennis, 1979, 1986). In the gametophytic self-incompatibility (GSI) system, found in Solanaceae, Scrophularia- ceae and Rosaceae, pollen growth inhibition is controlled by the S locus, which contains, among other genes, a multiallelic RNase gene (S-RNase) (Anderson et al., 1986). The S-RNases play a crucial role in conferring the incompatibility: they enter the pollen tubes during their growth in the style (Luu et al., 2000), resulting in pollen growth arrest. Recent fi ndings suggest that the non-self S-RNases are degraded by the ubiquitin/26S proteasome pathway, while the self S-RNase remains active (Qiao et al., 2004). Depending on their S loci, pairs of apple cultivars can be either fully compatible, when they differ in both S loci, semi compatible, when they carry one different and one identi- cal S locus or incompatible, when both loci are identical. Use of the S-RNase alleles as markers provides an effi cient tool for deter- mining the level of compatibility. In addition, these markers also serve to identify the pollen source of a given fertilization event, and thus enable the measurement of the pollen fl ow in the orchard. Goldway et al. (1999) have found that the major reason for the low yields of 'Topred' apple (a sport of 'Red Delicious') in Israel was due to semi-compatibility with one of its pollinators ('Jonathan'). In the present study we questioned whether this observation was a common feature in apples cultivated in re- gions with suboptimal condition for growth and pollination. Materials and Methods Orchard design. All experiments were conducted in 10-ha commercial apple orchards in the north of Israel. Trees from all cultivars ('Golden Delicious', 'Red Delicious', 'Granny Smith', 'Royal Gala', and 'Jonathan') were of the same age (10 to 13 years), grafted on the rootstock Hashabi 13-4 and planted at a spacing of 2 × 4 m (1250 trees/ha). Row direction was north to south. The experimental plots consisted of a block of two rows of the fertilized cultivar and two adjacent rows of pollinator, semi or fully compatible, on each side.

Light-induced expression of a MYB gene regulates anthocyanin biosynthesis in red apples.

Abstract: Anthocyanins are secondary metabolites found in higher plants that contribute to the colors of flowers and fruits. In apples (Malus domestica Borkh.), several steps of the anthocyanin pathway are coordinately regulated, suggesting control by common transcription factors. A gene encoding an R2R3 MYB transcription factor was isolated from apple (cv Cripps' Pink) and designated MdMYB1. Analysis of the deduced amino acid sequence suggests that this gene encodes an ortholog of anthocyanin regulators in other plants. The expression of MdMYB1 in both Arabidopsis (Arabidopsis thaliana) plants and cultured grape cells induced the ectopic synthesis of anthocyanin. In the grape (Vitis vinifera) cells MdMYB1 stimulated transcription from the promoters of two apple genes encoding anthocyanin biosynthetic enzymes. In ripening apple fruit the transcription of MdMYB1 was correlated with anthocyanin synthesis in red skin sectors of fruit. When dark-grown fruit were exposed to sunlight, MdMYB1 transcript levels increased over several days, correlating with anthocyanin synthesis in the skin. MdMYB1 gene transcripts were more abundant in red skin apple cultivars compared to non-red skin cultivars. Several polymorphisms were identified in the promoter of MdMYB1. A derived cleaved amplified polymorphic sequence marker designed to one of these polymorphisms segregated with the inheritance of skin color in progeny from a cross of an unnamed red skin selection (a sibling of Cripps' Pink) and the non-red skin cultivar Golden Delicious. We conclude that MdMYB1 coordinately regulates genes in the anthocyanin pathway and the expression level of this regulator is the genetic basis for apple skin color.

Biodiversity, Ecosystem Functioning, and Human Wellbeing: An Ecological and Economic Perspective

Abstract: In an age of accelerating biodiversity loss, this timely and critical volume summarizes recent advances in biodiversity-ecosystem functioning research and explores the economics of biodiversity and ecosystem services. The book starts by summarizing the development of the basic science and provides a meta-analysis that quantitatively tests several biodiversity and ecosystem functioning hypotheses. It then describes the natural science foundations of biodiversity and ecosystem functioning research including: quantifying functional diversity, the development of the field into a predictive science, the effects of stability and complexity, methods to quantify mechanisms by which diversity affects functioning, the importance of trophic structure, microbial ecology, and spatial dynamics. Finally, the book takes research on biodiversity and ecosystem functioning further than it has ever gone into the human dimension, describing the most pressing environmental challenges that face humanity and the effects of diversity on: climate change mitigation, restoration of degraded habitats, managed ecosystems, pollination, disease, and biological invasions.However, what makes this volume truly unique are the chapters that consider the economic perspective. These include a synthesis of the economics of ecosystem services and biodiversity, and the options open to policy-makers to address the failure of markets to account for the loss of ecosystem services; an examination of the challenges of valuing ecosystem services and, hence, to understanding the human consequences of decisions that neglect these services; and an examination of the ways in which economists are currently incorporating biodiversity and ecosystem functioning research into decision models for the conservation and management of biodiversity. A final section describes new advances in ecoinformatics that will help transform this field into a globally predictive science, and summarizes the advancements and future directions of the field. The ultimate conclusion is that biodiversity is an essential element of any strategy for sustainable development.

In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

Abstract: In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

Regulation of floral initiation in horticultural trees

Abstract: The intention of this review is to discuss floral initiation of horticultural trees. Floral initiation is best understood for herbaceous species, especially at the molecular level, so a brief overview of the control of floral initiation of Arabidopsis (Arabidopsis thaliana (L.) Heynh.) precedes the discussion of trees. Four major pathways to flowering have been characterized in Arabidopsis, including environmental induction through photoperiod and temperature, autonomous floral initiation, and regulation by gibberellins. Tropical trees are generally induced to flower through environmental cues, whereas floral initiation of temperate deciduous trees is often autonomous. In the tropical evergreen tree mango, Mangifera indica L., cool temperature is the only factor known to induce flowering, but does not ensure floral initiation will occur because there are important interactions with vegetative growth. The temperate deciduous tree apple, Malus domestica Borkh., flowers autonomously, with floral initiation dependent on aspects of vegetative development in the growing season before anthesis, although with respect to the floral initiation of trees in general: the effect of the environment, interactions with vegetative growth, the roles of plant growth regulators and carbohydrates, and recent advances in molecular biology, are discussed.