Changes in sugars,acids, and volatiles during ripening of koubo [Cereus peruvianus (L.) Miller] fruits

The columnar cactus Cereus peruvianus (L.) Miller, Cactaceae (koubo), is grown commercially in Israel. The unripe fruits are green, and the color changes to violet and then to red when the fruit is fully ripe. The content of soluble sugars was found to increase 5-fold during ripening. Glucose and fructose were the main sugars accumulated in the fruit pulp, and each increased from 0.5 to 5.5 g/100 g fresh weight during ripening. The polysaccharides content decreased during ripening from 1.4 to 0.4 g/100 g fresh weight. The titratable acidity decreased and the pH increased during ripening. The major organic acid found in the fruit was malic acid, which decreased from 0.75 g/100 g fresh weight at the mature green stage to 0.355 g/100 g fresh weight in ripe fruits. Citric, succinic, and oxalic acids were found in concentrations lower than 0.07 g/100 g fresh weight. Prominent accumulation of aroma volatiles occurred toward the end of the ripening process. The main volatile found in the ripe fruit was linalool, reaching concentrations of 1.5-3.5 microg/g fresh weight.     

Spatial heterogeneity of a microbial community in a sandy soil ecosystem

A fieldwork was carried out in Caesarea sand dunes, Israel, to determine the influence of fine-scale landscape-patch abiotic-factor heterogeneity on microbial activity in a Mediterranean region. Soil organisms in terrestrial systems are unevenly distributed in time and space, and are often aggregated. Spatio-temporal patchiness in the soil environment is thought to be crucial for the maintenance of soil biodiversity, providing diverse microhabitats that are tightly interwoven with resource partitioning. Determination of a ‘scale unit’ to help understand ecological processes has become one of the important and most debatable problems in recent years. To better understand the distribution of soil microbial communities at multiple spatial scales, a survey was conducted to examine the spatial organization of the community structure in two sandy soil ecosystems. One-hundred forty-four soil samples were collected from two patches 4000 m apart from each other. Basal respiration (CO₂ evolution without the addition of any external substrate), microbial biomass, functional diversity, and community-level physiological profile (CLPP) in soil were measured with a MicroResp? system. Soil abiotic analysis was performed by soil standard analytical methods. The results demonstrated that bacterial distributions can be highly structured, even within a habitat that appears to be relatively homogeneous at the plot and field scale. Different subsets of the microbial community were distributed differently across the plot. This is due to spatial heterogeneity associated with soil physical, chemical, and biological properties. Although spatial variability in the distribution of soil microorganisms is generally regarded as random, this variability often has a predictable spatial structure. This study provided evidence that a spatially explicit approach to soil ecology can enable the identification of factors that drive the spatial heterogeneity of populations and activities of soil organisms, at scales ranging from meters to hundreds of meters. Furthermore, there is increasing evidence that spatial soil ecology can yield new insights into the factors that maintain and regulate soil biodiversity, as well as on how the spatial distribution of soil organisms influences plant growth and plant community structure.     

Quality attributes of stored koubo (Cereus peruvianus (L.) Miller) fruit

Cereus peruvianus (L.) Miller (koubo, also known as apple cactus) is a new fruit crop in Israel. When the fruit reach full maturity, they tend to crack due to uncoordinated growth of the different fruit tissues. This phenomenon normally causes heavy fruit losses, as much as 90% of the total yield. To prevent this problem, fruit are usually harvested before they reach full ripening, i.e. at the violet stage, a practice that effectively prevents cracking, but also reduces the overall quality of the marketed fruit. In order to establish optimal harvesting protocols and storage conditions, we characterized fruit ripening under storage, comparing purple-harvested fruit, stored fruit (purple and red-ripe) and tree-ripened red-split fruit. Organoleptic tests indicated that the overall flavor increased concomitantly with the development of the red peel color. During ripening, the pH slightly increased, while titratable acidity and the content of malic acid decreased. These changes were more marked in stored than in tree-ripened fruit. The levels of polysaccharides, glucose and fructose did not change significantly during storage. The content of linalool and linalool derivatives increased dramatically during storage, being much higher than that of cracked tree-ripened fruit. Our results indicated that the overall quality of the fruit increased during storage as expressed by color change, decreased acidity and enhanced levels of aroma compounds, while the content of carbohydrates was practically unaffected.     

Emergence of Culicoides obsoletus from indoor and outdoor breeding sites

Culicoides obsoletus (Diptera: Ceratopogondae) is considered as the probable main vector of Bluetongue virus (BTV) in northern Europe. Its breeding sites are poorly documented at the present time. We report numerous emergences of C. obsoletus s. str. from soil samples collected in two holdings between August and September 2010. Specimens were collected regularly in the laboratory during 80 days. In one holding, 1584 C. obsoletus midges emerged from used litter collected inside a dairy cow building and 211 C. obsoletus midges emerged from manure left outside the farm buildings. In the second holding, the number of emergences observed was much lower, especially for indoor samples. We discuss the impact of the farming practices on the abundance of emergence between both holdings on one side and between indoor and outdoor breeding sites on the other side. The observation of a peak in emergence and high emergence rates recorded in the laboratory for indoor samples let us assume that these breeding sites are of great importance, especially when it comes to understand the biology of this widespread species and its role in the transmission of BTV.     

Characterization of monkey orange (Strychnos spinosa Lam.), a potential new crop for arid regions

The green monkey orange (Strychnos spinosa Lam., Loganiaceae), a tree indigenous to tropical and subtropical Africa, produces juicy, sweet-sour, yellow fruits containing numerous hard brown seeds. The species has recently been introduced into Israel as a potential new commercial crop. However, little is known about its agronomical performance, fruit development and ripening, or postharvest physiology. The current study shows that during ripening in storage, the peel color changes from green to yellow, accompanied by a climacteric burst of ethylene and carbon dioxide emission. Total soluble solids slightly increased during storage, whereas total titratable acidity and pH did not change significantly. The major sugars that accumulated during ripening in storage were sucrose, glucose, and fructose, and the main acids, citric and malic acids. The main volatiles present in the peel of ripe fruits were phenylpropanoids, trans-isoeugenol being the major compound.