Climatic change could lead to expanded ranges for plant pathogens due to favorable wet and warm conditions in higher latitudes and altered dispersal patterns influenced by intensifed rain and wind, and shifting vector habitats. Many factors associated with climate change, including elevated temperatures, increased periods of drought, intensifted storms and elevated CO2 will likely influence the health of our crops directly, but also indirectly by shifting the balance of microbes that may inhabit them, including plant pathogens, human pathogens and beneficial or commensal organisms. For some plant-pathogen pairs, weather-based forecasting models are already in use, helping growers time pesticide applications efficiently for the highest effectiveness and lowest environmental impact. Similar decision support systems could be implemented for use in food safety, growing blueberries in containers providing recommendations to growers on safest harvest times following single and repeated rain events. The first step in achieving this goal is amassing an understanding of the community-level dynamics on harvestable fresh produce preceding and following rain events.
Pomegranate is a fruit tree grown today in a wide range of subtropical and tropical geographical locations spread all over the globe; these locations include many countries in Asia, Europe, South and North America, Africa, and Australia . Pomegranate is considered a minor fruit and is far from the top of the list of consumed fruits, such as apple, banana, grapes, and citrus; however, it is one of the most interesting fruits in terms of cultural, traditional, and potential therapeutic usage.The pomegranate fruit is a fleshy berry with a nearly round shape, crowned by a prominent calyx. Its relatively thick peel has an outer colored skin and the fruit’s inner structure contains multi-arils chambers separated by membranous walls . The edible part of the pomegranate fruit, the arils, contains seeds and a special layer of cells that are of epidermal origin and protrude from the outer epidermal cells of the seed . The external fruit color ranges from yellow, green or pink overlaid with pink to deep red or deep purple. The color of the juicy layer can vary from white to deep red . Various parts of the pomegranate fruit were traditionally used as treatments against various ailments including stomachaches and bacterial infections . The traditional usages were strengthened by modern scientific studies focused on health beneficial metabolites and their therapeutic effects and mechanisms of action on human and animal health.
These studies were thoroughly reviewed in recent years. Most of the therapeutic effects of the pomegranate fruit were attributed to its secondary and primary metabolites, such as polyphenols, including flavonoids, anthocynains and hydrolizable tannins, fatty acids, and lipids . These metabolites were found in all fruit parts, including the fruit peel , arils , seeds , and membranous walls . Anthocyanin biosynthesis occurs in parallel in the arils and in the fruit peel. These two tissues are not necessarily correlated in their activity with respect to color production, and often, the two tissues display different colors . The same situation could appear in other biochemical pathways responsible for other important metabolites. High variability was reported for pomegranate fruit that manifests, among other phenomena, considerable differences in size, shape, color, date of ripening, and taste. This external variability is interesting in view of the fact that the only edible species among the Punica, which include only two species, is the cultivated pomegranate . The only other pomegranate known to science is the non-edible species Punica protopunica, endemic to Socotra . The fruit of this species is small and not colorful and no biochemical, genetic, or molecular studies of its fruit were published. This high variability is also reflected in the content of primary and secondary metabolites.
Quite substantial work has been devoted in recent years to determining primary metabolites in the pomegranate fruit. These efforts include studies of sugar, organic acids, protein, amino acids, and lipid content and composition. In general, the pomegranate fruit consists of 50% peel, 40% arils, and 10% seeds . The arils contain 85% water, 10% total sugars, 1.5% metabolites and bioactive compounds such as organic acids, phenolics, and flavonoids . The seeds are a rich source of lipids; pomegranate seed oil comprises 12–20% of total seed weight . It appears that primary and secondary metabolites showed extensive variability due to the fact that the fruit used for the various studies originated from different varieties and highly variable climatic conditions and taken from trees grown under different agro-technical methods. While pomegranate reviews published up until now focused mainly on secondary metabolites , there are only few that focused on primary metabolites, despite their great importance to taste attributes and to the nutritional index of the fruit. In this review, we focus on primary metabolites and on secondary metabolites, anthocyanins and hydrolizable tannins, with special attention to the variability of their content and composition. A special effort was aimed at the developmental, genetic, and environmental effects on the content and composition of primary metabolites. Whenever available, primary metabolites in each of the fruit organ, peel, arils, and seeds, were specified.The pomegranate fruit is a rich source of sugars. The level of the sugars in pomegranate juice is highly correlated with the level of total soluble solids . Shwartz et al. and Dafny-Yalin et al. calculated a value of R 2 = 0.89, P < 0.01. The TSS level in the juice ranges from 4.2 to 8.5 g/100 g depending on cultivars, climatic conditions, and cultural techniques ; Amir et al.. Pomegranate juice contains a high amount of polyphenols such as flavonoids, ellgitannins, and the color molecules anthocyanins. A substantial fraction of these molecules are known to be conjugated to sugars, mostly glucose. The taste of arils from various pomegranate varieties is significantly variable, ranging from sour to sweet . Sugar content is an important parameter influencing taste, although it is highly influenced by organic acid content as well. Many studies examined the sugars in the pomegranate fruit, mainly in the juice, revealing glucose, and fructose as the main component of the juice sugars . Sugars found in the fruit peel were in some controversy among studies from different countries. It should be noted that those studies were done for different purposes and therefore followed different procedures of extraction and detection that might explain this disagreement. Some of the studies indicated glucose and fructose as the main sugars while others found that xylose and arabinose are the main sugars .Arils are a rich source of sugars. Studies obtained from different countries have shown that the composition of sugars among pomegranate varieties might differ. Analyses of the sugars in pomegranate aril juice from 29 worldwide varieties grown in Israel and 19 cultivars from Spain have shown that fructose and glucose were the major sugars found in the arils, square pots while sucrose and maltose were detected in lesser amounts. In some varieties, these two former sugars are the only sugars that were detected . In many studies the levels of fructose were similar to those of glucose in pomegranate juices, and both varied in different varieties by a factor of up to two-fold ranging from 4.2 to 8.5 g/100 g . In 76 Turkish varieties glucose levels showed a range of 4.2–8.3 g/100 g juice . Forty Spanish varieties showed a range of 5.5–7.8 g/100 g , 29 Israeli varieties showed a range of 4.8–6.6 g/100 g , and 30 Tunisian varieties showed a range of 5.7–8.5 g/100 g . In addition to the main fructose and glucose sugars, some other sugars were also detected in several varieties at a relatively negligible level .Determination of sugar contents in 6 Spanish varieties has shown that they all contain maltose and sucrose, but possess 45- and 70- fold lower quantities of glucose, respectively . Sucrose was also found in an about 33-fold lower quantity than glucose in 6 Turkish varieties and an up to 13- fold lower quantity in 53 out of 76 varieties . Maltose was only detected in one of 29 Israeli varieties . Several studies specifically measured the level of sugars and TSS in the fruit peel . Notably, the major sugars that were detected in the peels differed between the varieties grown in Tunisia, Iran and Israel. In the 12 Tunisian varieties, xylose and arabinose represented more than 60% of the total content, followed by galactose , glucose , mannose , rhamnose , and fucose .
Peels from one Iranian variety showed that the main sugar is glucose , followed by galactose , mannose , arabinose , and rhamnose . However, in the 29 worldwide varieties grown in Israel, the major sugars were glucose and fructose. The level of glucose varied in the range of 0.9–4.8 g/100 g , and that of fructose in 0.9–6.6 g/100 g . The level of fructose was higher than that of glucose in most of the varieties. Maltose was found at an about 50-fold lower concentration than that of glucose and fructose, in a range of 0.8–48.9 mg/100 g, while sucrose was detected in only 6 varieties at relatively low levels . Mannitol was also detected in all the varieties, ranging from 10 to 300 mg/100 g . As expected from these results, the TSS varied between the different collections. In 12 Tunisian cultivars, it ranged from 16.8 to 19.6 g/100 g , which was more than the range of three Indian varieties that show a range of 13.7– 14.5 g/100 g . However, these values were much higher than the results reported for 4 Turkish varieties that ranged from 3.8 to 6.4 g/100 g , and the 29 varieties grown in Israel, which showed a range of 5.2–11.3 g/100 g. In these varieties, the peels had a 2- to 3-fold lower level of TSS compared with the aril juice .Several studies followed the changes in the levels of sugars and TSS in aril juice during fruit development. The results taken from three cultivars in South Africa , and two cultivars from Israel have shown that the level of TSS rose during the development process in accordance with the levels of glucose and fructose. The increase shown in the two Israeli grown varieties and in “Wonderful” in South Africa was significant . The presented data indicate that the developmental stage of the pomegranate fruit is associated with sugar accumulation.Analysis of TSS and sugar content in different collections revealed that their values depended on climate and growth conditions. To gain more knowledge on the effect of the environmental conditions on the levels of sugars, 11 varieties from the Israeli collection in the Jezreel Valley were planted in Israel’s southern Arava Valley . Arils from both habitats were analyzed. The varieties grown in Mediterranean climate showed significantly higher levels of glucose and fructose in the juice than those grown in a hotter habitat . Similar results were also reported from the analyses of the 10 Chinese cultivars that grew in four different habitats . “Wonderful,” which was grown in Israel in two habitats , as well as in three habitats in South Africa , showed that relatively higher temperatures can decrease sugar content, whereas cooler temperatures apparently promoted the increase in glucose and fructose. Thus, temperatures appear to play an important role in the sugar content of pomegranate juice.Total titratable acidity values were shown to be affected by climate and growth conditions. Arils from 11 varieties grown in the Jezreel Valley and in the Southern Arava Valley were analyzed to study the effect of environmental and climatic conditions on the arils’ acid content. The cultivars grown in Mediterranean climate had higher acidity levels compared to the acidity levels found in desert climate. This was in accordance with the higher contents of citric and malic acids, the two main organic acids in the arils . Generally sour cultivars are mostly grown in northern cold regions, while sweet cultivars with low acidity values are mostly found in regions having hot dry conditions. In Southern Spain and North Africa most of the commercialized cultivars have a sweet taste , while in North Turkey and Russia sour cultivars are commercialized . In northern regions such as Russia, Macedonia, Georgia, and Turkey, the total acidity ranged from 0.5 to 2.3% , 0.6 to 2.2% , 0.4 to 2.8% , and 1.7 to 4.6% , respectively. However, in hot climates such as in India, Egypt, and Saudi Arabia, total acidity values dropped to 0.12–0.13% , 0.03–0.10%, and 0.02–0.14%, respectively .