Alternate bearing has been and still is a major problem in fruit trees. From the point of view of a horticulturist it is a tree productivity syndrome which must be addressed by agro-technical means in order to eliminate or, at least, mitigate the alternation cycle. ‘Masting’ is a widespread forest tree irregular sexual reproduction pattern that has attracted ecologists who wonder about the survival-advantage of this behavior. From an evolutionary perspective alternate bearing and masting seem to be related and may share a common bio-evolutionary mechanism, responsible for ‘yield alternation’. A recently developed resource budget model, based on nonlinear chaos dynamics, seems to account for a broad spectrum of yield alternation patterns. From an evolutionary standpoint, one may envision a domestication-evolutionary continuum from extreme masting, through intermediate alternate bearing, down to regular yield of fully-managed fruit trees. Domestication records of pecan (Carya illinoiensis) support this hypothesis. The alternate bearing of fruit trees appears to be mediated by a ‘fruit overload’ signal but resource depletion still plays a critical role in the alternate bearing of numerous tree crops.

The molecular responses of plants to anaerobic stress have been extensively studied in roots during and after flooding; far less has been done with ripening fruits, and very little is known about the behavior of citrus fruit during postharvest storage under restricted O-2 availability conditions. Using 'Star Ruby' grapefruit and 'Murcott' mandarin as plant materials and N-2 atmosphere treatment as the major experimental system, we studied the molecular responses of citrus fruits to anaerobiosis. The major response of citrus fruit to anaerobiosis is a metabolic shift towards ethanol fermentation, and the regulation of ethanol fermentation takes place at both transcriptional and posttranscriptional levels. Ethylene is not a major player in the responses to anaerobiosis. 'Murcott' mandarin is more sensitive than 'Star Ruby' grapefruit to anaerobiosis, peel (flavedo) and juice vesicles respond differently to anaerobiosis. Taken together, our data reveal both general and citrus fruit-specific anaerobic-response mechanisms.

The pigment changes of citrus fruit peel [='colorbreak'] are the best visual markers of citrus fruit maturation. Pigment changes of most citrus cultivars consist of breakdown of chlorophyll and buildup of carotenoids, both of which are enhanced by ethylene and delayed by gibberellins. The degreening of citrus fruit by ethylene has served for more than 30 years as a model system for the study of chlorophyll catabolism. The abrupt upsurge of chlorophyllase enzyme activity in response to ethylene prompted further, molecular investigations. Citrus Chlase 1 overexpression was shown to initiate chlorophyll catabolism in several heterologous systems, supporting the notion that chlorophyllase is a rate limiting enzyme. Confocal microscopy localization has shown that both forms of chlorophyllase [ the longer precursor and the shorter, mature form] reside in citrus' plastids. In conclusion, the strong correlation between ethylene induction of citrus fruit colorbreak and chlorophyllase gene expression and protein maturation indicate that chlorophyllase initiates the chlorophyll catabolic pathway in this system.In Arabidopsis (Arabidopsis thaliana), on the other hand, recent work based on analysis of mutants questions the role of chlorophyllase in chlorophyll breakdown during senescence. Moreover, the Hortensteiner group identified an alternative enzyme from Arabidopsis leaves involved in dephytilation, pheophytin pheophorbide hydrolase (PPH), which exhibits specificity to the Mg-free form of chlorophyll (phein), and must, therefore, be preceded by a Mg removal step. This finding raises doubts regarding the role of chlorophyllase as the universal initiator of chlorophyll catabolism and points to the existence of two, alternative catabolic pathways. Examination of the actual roles of chlorophyllase and PPH in various plant systems is presently underway. The hypothesis that ripening fruits and senescing leaves represent distinct modes of chlorophyll catabolism deserves consideration.

The potency of 12 new volatile cyclopropenes to inhibit ethylene action synthesized at the laboratory of Edward C. Sisler was assessed. The inhibitory effect was evaluated in the following test systems: ethylene-induced ripening of climacteric fruits, ethylene-induced growth modifications in etiolated pea seedlings and abscission of citrus leaf explants. In some of the test systems, the new compounds were found to be more potent ethylene antagonists than 1-MCP, whereas in other systems they were less potent. A novel water soluble inhibitor of ethylene action 3-(cycloprop-1-enylpropanoic acid, sodium salt (CPAS, IL patent application 184729, WO 2009/010981 A1)), was synthesized by D-Pharm, Israel, from one of the new cyclopropene derivatives. CPAS was found to counteract ethylene-induced abscission of citrus leaf explants and of avocado fruit peduncles, to inhibit ethylene-induced leaf epinasty in tomato seedlings, and to prolong the vase-life of carnation and petunia cut flowers. It also considerably delayed fruit ripening processes, such as skin colour change in 'Hass' avocado and banana fruit and softening of peach fruit. Banana and avocado fruit softening were delayed by CPAS to a lesser extent, probably due to insufficient penetration.

To elucidate the role of ethylene receptors in avocado ripening and storage, we have isolated avocado (Persea americana Mill. 'Arad') homologues of the ethylene receptor genes, referred to as PaETR and PaERS1. The basal levels of PaETR and PaERS1 mRNA in avocado mesocarp were very low at harvest and were hyperinduced by exogenous ethylene treatment. The expression of both genes also increased in parallel to the onset of climacteric ethylene peak, suggesting that increase in endogenous ethylene leads to increase in these genes' expression. Application of the ethylene inhibitor, 1-methylcyclopropene (1-MCP) at harvest delayed ethylene production and down-regulated expression of PaETR and PaERS1 genes. PaETR mRNA expression in tissues taken from various distances from the seed revealed that the expression was highest close to the base of the seed and was reduced gradually toward the blossom end. We suggest that ethylene receptors are involved in regulation of ethylene responsiveness during ripening and act to protect the tissue against ethylene injury.

The potency to inhibit ethylene action of twelve new water-insoluble volatile cyclopropenes was assessed. This inhibitory effect was tested on the following test systems: ethylene-induced ripening of climacteric fruits, ethylene-induced growth modifications in etiolated pea seedlings and abscission of citrus leaf explants. In some of the test systems, the new putative inhibitors were found to be more potent ethylene antagonists than 1-MCP, whereas in other systems they were less potent. A novel water soluble, non-volatile inhibitor of ethylene action (WS-CPD, patent pending), was synthesized from one of the new cyclopropene derivatives. It was found to counteract ethylene-induced abscission of citrus leaf explants and peduncles of avocado fruits. It also inhibited ethylene-induced leaf epinasty in tomato seedlings, and prolonged the vase-life of carnation and petunia cut flowers. It considerably delayed fruit ripening processes, like skin color changes in ‘Hass’ avocado and banana fruit, as well as softening of peach fruit. WS-CPD delayed to a lesser extent banana and avocado fruit softening, probably due to insufficient penetration. INTRODUCTION Ethylene-induced accelerated ripening and senescence account for most of the preand postharvest losses of perishable agricultural commodities. Ethylene is a natural product of plant metabolism and plants respond to both endogenous and exogenous ethylene (Abeles et al., 1992). Antagonists of ethylene action are considered to be very beneficial for agricultural use, since they protect the tissues from both endogenous and exogenous ethylene. Ethylene antagonists inhibit the action of ethylene at the molecular level by blocking its receptor site (Sisler and Wood, 1988; Sisler. and Serek 1997). Thus, application of effective inhibitors of ethylene action may allow extending the harvest season of crops, and improving the keeping quality and prolonging the storability and shelf life of fruits, herbs, leafy vegetables, and flowers. Antagonists of ethylene action have been described in the past. Of the inhibitors of ethylene action developed so far, 1-methylcyclopropene (1-MCP) is considered to be the most promising antagonist for commercial use (Serek et al., 1995; Sisler et al., 2000). However, its practical use is limited, mainly due to the following reasons: (a) very low solubility in water; (b) it is a gas at temperatures above 0C and must be applied as such in sealed systems, (c) as a gas it cannot be used for dip loading of cut flowers or applied as a spray in the field (d) attempts to use 1-MCP as a spray revealed that very high concentrations are required to render it effective, which pose a threat to other plants and crops in the environment. In addition, being volatile, the compound dissipates rapidly depending on the wind velocity, and therefore its effectiveness is totally unpredictable. Consequently, it is obvious that a potent, water-soluble, broad-spectrum ethylene antagonist is required by the agriculture industry. MATERIALS AND METHODS The studies were conducted following the procedures described in Goldschmidt et al. (2007). The cyclopropenes tested are listed in Table 1. Table 1. List and structure of 1-MCP and twelve 1-substituted cyclopropene (cp) analogous newly synthesized and tested for potency as antagonists of ethylene action. RESULTS AND DISCUSSION In this communication we present results of two lines of research. The first stage was aimed to broaden the spectrum of volatile water-insoluble antagonists of ethylene action that can protect plants and fruits from ethylene for various lengths of time. The second stage of the research was aimed to develop a water soluble non-volatile ethylene antagonist. 3-Methylamine-1-cp-2-carboxylic acid N-(1-Methyl-cp)-ethyl-amine 3-(1-cp)-Propanoic acid-isopropyl amine salt 3-(1-cp)-Propanoic acid 1-(3-Hydroxypropyl)-cp 2 Structure Inhibitor No. Name -CH2N(CH2)3CH3 -COOH 3

Physiological and molecular evidence supported the autocatalytic ethylene production in young “Star Ruby” grapefruit and “Murcott” mandarins, and the autoinhibitory ethylene production in mature fruit. Ethylene upregulated expression of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) in both fruitlets and mature “Star Ruby”, and increased acetaldehyde (AA) and ethanol production, while ethylene action inhibitors counteracted the effect. N2 not only changed the expression of genes for ethylene biosynthesis but also genes for ethylene perception in both young and mature fruits.

Understanding the influence of reductions in solar radiation on crop physiology, growth and yield is important because of the widespread practice of protected cultivation under various light reducing covers. Parts of a commercial bearing grapefruit orchard (Citrus paradisi L.) were covered with aluminized reflective screens during three consecutive summers in southern Israel. Screens were installed shortly after fruit set and removed a week or 2 before harvest. Screens were of two types, 30 and 60% shade, erected horizontally over the rows. Shading reduced mid-day direct radiation reaching the trees and reduced exposed leaf temperatures, but increased their net CO2 uptake (A) and conductance (gl). The increased gl was reflected by decreases in carbon isotope ratios (δ13C) of leaves from under both shades and of fruit flavedo from the 60% shade. Final leaf area index (LAI), determined by gap fraction inversion, was 10% higher in 30% shade than in the control and canopy volume increased similarly. Trunk cross-section, total yield and size distribution of fruit were little affected by shade. During the second year, however, early shading presumably induced more than normal fruit abscission, leading to fewer but larger fruit. Fruit in the middle of the canopy of shaded trees were consistently heavier and also larger in the first 2 years, but peel width was not affected by shade. Juice content was reduced in the second and third years, but the ratio of sugar to acid was not affected. Mid-day leaf water potentials in August and September under 60% shade increased by 13%. Shading did not significantly reduce fruit yield.

Thioredoxins are ubiquitous small proteins with a redox-active disulfide bridge; they participate in redox regulation of selected target proteins, such as transcription factors, receptors and various metabolic and regulatory enzymes. In the present study, we isolated by PCR cDNA subtraction analysis a grapefruit 135-bp polymerase chain reaction (PCR) fragment whose expression was enhanced in the fruit peel tissue following the application of Candida oleophila yeast cells, an elicitation treatment that induces resistance towards the green mold pathogen Penicillium digitatum (Pers.:Fr.) Sacc., and that showed high sequence homology with various thioredoxin h (TRXh) genes. The full-length cDNA sequence of cTRXh (for citrus TRXh) was further isolated by screening a grapefruit flavedo cDNA library; it had a total length of 785bp with an open reading frame of 369bp, and encoded a predicted polypeptide of 123 amino acids with a molecular mass of 13.4kDa. Expression analysis studies revealed that cTRXh mRNA levels increased in grapefruit peel tissue upon infection by P. digitatum, and following the elicitation of fruit disease resistance by application of C. oleophila yeast cells, wounding, exposure to ethylene, and a hot water rinsing and brushing treatment. These results indicate that cTRXh may be part of the molecular mechanisms involved in the induction of pathogen defense responses in grapefruit, and may be involved in the signaling cascades leading to enhanced resistance.

The share of brand-name fruit and vegetables is much lower than that for general foods or processed industrial foods. The paper analyzes consumers' choice between generic and brand-name products and shows that consumers' preferences for horticultural brands increase with their appreciation of quality and with a low quality of the generic products, and that brand preferences are affected by socio-economic variables. The theoretical findings are supported by an orange (Citrus sinensis) consumer survey held in the UK and Israel. We found that in both countries consumers assign a relatively low value to orange brands. Consumers who are willing to pay for better quality are those who perceive brands as more important.

Chapter 1 Girdling: Physiological and Horticultural Aspects R. Goren, R. Goren rgoren@agri.huji.ac.il Kennedy-Leigh Centre for Horticultural Research, The Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, IsraelSearch for more papers by this authorM. Huberman, M. Huberman Kennedy-Leigh Centre for Horticultural Research, The Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, IsraelSearch for more papers by this authorE. E. Goldschmidt, E. E. Goldschmidt Kennedy-Leigh Centre for Horticultural Research, The Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, IsraelSearch for more papers by this author R. Goren, R. Goren rgoren@agri.huji.ac.il Kennedy-Leigh Centre for Horticultural Research, The Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, IsraelSearch for more papers by this authorM. Huberman, M. Huberman Kennedy-Leigh Centre for Horticultural Research, The Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, IsraelSearch for more papers by this authorE. E. Goldschmidt, E. E. Goldschmidt Kennedy-Leigh Centre for Horticultural Research, The Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, IsraelSearch for more papers by this author Book Editor(s):Jules Janick, Jules Janick Purdue University, USASearch for more papers by this author First published: 29 October 2003 https://doi.org/10.1002/9780470650837.ch1Citations: 15 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Girdling Concepts and Techniques Girdling and Physiological Studies Endogenous Plant Hormones Girdling in Horticultural Practice Concluding Remarks Literature Cited Citing Literature Horticultural Reviews, Volume 30 RelatedInformation

Up to now fruit tree models have been primarily concerned with various aspects of plant development and yield. Problems of fruit quality have only rarely been approached. In the present study we address the fruit quality problem, as revealed with fresh orange fruit. Definition of fruit quality is complicated. Quality of oranges (as with most commodities) reflects numerous internal and external attributes. Integration of these attributes within a quality model requires that a) each attribute can be expressed in a quantitative manner, and b) that the relative contribution of each attribute to overall quality can be assessed. Different perceptions of desirable fruit quality parameters by growers, retailers and consumers, as revealed in the weighting of internal and external quality attributes creates major difficulties in addressing fruit quality issues. Further complications arise when different segments of the consumer population are taken into account. This study demonstrates a marketing approach to these problems using an extensive consumer survey of the perceptions of orange fruit quality conducted in the UK and Israel in 1999. Identification of consumer quality preferences is important for both short and long term management and planning of fruit tree crops.

Progress in the understanding of chlorophyll breakdown was very slow until the identification of major catabolites and enzyme systems by Matile and coworkers (Matile et al., 1999). The recent identification of the gene for chlorophyllase from ethylene-treated Valencia orange peel (Jacob-Wilk et al., 1999) was an important step towards elucidation of the developmental and hormonal regulation of chlorophyll catabolism in senescing plant systems.Notwithstanding the functional similarities between senescing leaves and ripening fruits, the evolutionary significance of chlorophyll decomposition in these systems seems to be different. Whereas in senescing leaves chlorophyll breakdown appears to be a component of the retrieval of nitrogen from dying organs, in fleshy fruits the disappearance of chlorophyll exposes the bright pigments, carotenoids and anthocyanins, which render the fruit attractive for seed dispersing animals. There are, however, important fruits which retain their chlorophyll throughout, or, at least, until the very late stages of ripening. Following Cipollini et al. (1991), it seems that such stay-green fruits have the potential advantage of extended photosynthesis; which presumably outweighs the seed-dispersal advantage of the attractive, bright colored fruit.