Moshe A. Flaishman

This chapter describes the unique fig fruit growth and maturation and compares them with other fleshy fruits. In conclusion, the ripening process of matured fig fruit is tissue specific and mainly governed by the plant hormones ABA and ethylene. It is suggested that genome editing of the key ABA biosynthesis gene, FcNCED2, and the major ethylene-biosynthesis gene, FcACS4, in the future to alter the rapid ripening process of fig fruit, which may be helpful to extend the postharvest life. In addition, the relationship between pollination, organic acids, and the aroma of the fig fruit can be explored and breeding projects undertaken to develop early ripening-stage, sugar-accumulating varieties. For commercial purposes, exogenous ABA might be used in the fig orchard to enhance fruit color and ripening, and to synchronize the ripening process in mature fig fruits after field tests based on varieties and climatic conditions.

This chapter provides an overview of the current research on different topics, and discuss the major outputs of the research work to identify the existing knowledge gaps. The focus will be on research gaps, aiming to stimulate new directions of research and innovation, possibly for the short and medium term, as advances in science and technology may divert the targets. In addition, proposals are made to stimulate research cooperation between industry, academia, and producers in order to increase applied and participatory research and fast transfer of knowledge, and to create wider impact. Finally, directions to encourage fig education by development of research networks are discussed.

Although rather rare and not severe, multiple diseases have been identified in figs. In general, first-crop figs tend to have more fungal decay than main-crop figs. This chapter suggests a general guide for fig diseases based on their source - either fungal or bacterial.

Female fig (Ficus carica L.) fruit are characterized by a major increase in volume and sugar content during the final week of development. A detailed developmental analysis of water and dry matter accumulation during these final days indicated a temporal separation between the increase in volume due to increasing water content and a subsequent sharp increase in sugar content during a few days. The results present fig as an extreme example of sugar import and accumulation, with calculated import rates that are one order of magnitude higher than those of other sugar‐accumulating sweet fruit species. To shed light on the metabolic changes occurring during this period, we followed the expression pattern of 80 genes encoding sugar metabolism enzymes and sugar transporter proteins identified in fig fruit. A parallel comparison with male fig fruits, which do not accumulate sugar during ripening, highlighted the genes specifically related to sugar accumulation. Tissue‐specific analysis indicated that the expression of genes involved in sugar metabolism and transport undergoes a global transition.

Fire blight caused by the bacterium Erwinia amylovora, is the most critical disease of European pear. Breeding of resistant cultivars is a possible solution for a growing demand for healthier alternative practices for disease control. In this study, we present a pear fire blight genetic study using a large F1 population. Quantitative trait loci (QTLs) were detected using a high‐resolution genetic map, allowing detection of QTLs with small intervals. A total of 162 offspring crossbred between ‘Harrow Sweet’ (HS, low susceptibility cultivar) and ‘Spadona’ (SPD, high susceptibility cultivar) were studied. We detected a significant genotype effect (p < .0001), which explained 46.4% of the variance of the necrosis length. A major QTL of the main genotype effect (AVG) was detected at 8.8 cM in linkage group (LG) 2 (LOD = 7.7). Additional QTLs were detected in LGs 7, 13 and 15. These markers can greatly contribute to pear breeding programs in a Mediterranean climate and can shed light on potential candidate genes that control fire blight resistance.

Organic acids are important components of overall fruit quality through flavor, taste, nutritional and medicinal values. Pollinated fig (Ficus carica L.) fruit quality is enhanced by increased acidity. We quantified the major organic acids and characterized the expression pattern of organic acid metabolic pathway‐related genes in the reproductive part – inflorescence and non‐reproductive part – receptacle of parthenocarpic and pollinated fig fruit during ripening. Essentially, pollinated fruit contains seeds in the inflorescence, as opposed to no seeds in the parthenocarpic inflorescence. The major organic acids – citrate and malate – were found in relatively high quantities in the inflorescence compared to the receptacle of both parthenocarpic and pollinated fig fruit. Notably, pollination increased citric acid content significantly in both inflorescence and receptacle. Genes related to the phosphoenolpyruvate carboxylase (PEPC) cycle, tricarboxylic acid cycle, citrate catabolism and glyoxylate cycle were identified in fig fruit. Expression levels of most of these genes were higher in inflorescences than in receptacles. In particular, FcPEPC and FcFUM (encoding fumarase) had significantly higher expression in the inflorescence of pollinated fruit. Most importantly, expression of the glyoxylate cycle genes FcMLS and FcICL (encoding malate synthase and isocitrate lyase, respectively) was induced to strikingly high levels in the inflorescence by pollination, and their expression level was highly positively correlated with the contents of all organic acids. Therefore, the glyoxylate cycle may be responsible for altering the accumulation of organic acids to upgrade the fruit taste during ripening, especially in the pollinated, seeded inflorescence.

Deciduous trees require sufficient chilling during winter dormancy to grow. To decipher the dormancy-regulating mechanism, we carried out RNA sequencing (RNA-Seq) analysis and metabolic profiling of European pear (Pyrus communis L.) vegetative buds during the dormancy phases. Samples were collected from two cultivars that differed greatly in their chilling requirements: 'Spadona' (SPD), a low chilling requirement cultivar; and Harrow Sweet (HS), a high chilling requirement cultivar. Comparative transcriptome analysis revealed >8500 differentially expressed transcripts; most were related to metabolic pathways. Out of 174 metabolites, 44 displayed differential levels in both cultivars, 38 were significantly changed only in SPD, and 15 only in HS. Phospholipids were mostly accumulated at the beginning of dormancy, sugars between before dormancy and mid-dormancy, and fatty acids, including α-linolenic acid, at dormancy break. Differentially expressed genes underlying previously identified major quantitative trait loci (QTLs) in linkage group 8 included genes related to the α-linolenic acid pathway, 12-oxophytodienoate reductase 2-like, and the DORMANCY-ASSOCIATED MADS-BOX (DAM) genes, PcDAM1 and PcDAM2, putative orthologs of PpDAM1 and PpDAM2, confirming their role for the first time in European pear. Additional new putative dormancy-related uncharacterized genes and genes related to metabolic pathways are suggested. These results suggest the crucial role of α-linolenic acid and DAM genes in pear bud dormancy phase transitions.

The common fig bears a unique closed inflorescence structure, the syconium, composed of small individual drupelets that develop from the ovaries, which are enclosed in a succulent receptacle of vegetative origin. The fig ripening process is traditionally classified as climacteric; however, recent studies have suggested that distinct mechanisms exist in its reproductive and non-reproductive parts. We analysed ABA and ethylene production, and expression of ABA-metabolism, ethylene-biosynthesis, MADS-box, NAC, and ethylene response-factor genes in inflorescences and receptacles of on-tree fruit treated with ABA, ethephon, fluridone, and nordihydroguaiaretic acid (NDGA). Exogenous ABA and ethephon accelerated fruit ripening and softening, whereas fluridone and NDGA had the opposite effect, delaying endogenous ABA and ethylene production compared to controls. Expression of the ABA-biosynthesis genes FcNCED2 and FcABA2, ethylene-biosynthesis genes FcACS4, FcACOL, and FcACO2, FcMADS8, 14, 15, FcNAC1, 2, 5, and FcERF9006 was up-regulated by exogenous ABA and ethephon. NDGA down-regulated FcNCED2 and FcABA2, whereas fluridone down-regulated FcABA2; both down-regulated the ethylene-related genes. These results demonstrate the key role of ABA in regulation of ripening by promoting ethylene production, as in the climacteric model plant tomato, especially in the inflorescence. However, increasing accumulation of endogenous ABA until full ripeness and significantly low expression of ethylene-biosynthesis genes in the receptacle suggests non-climacteric, ABA-dependent ripening in the vegetative-originated succulent receptacle part of the fruit.