Avinoam Nerd

Ripening and postharvest behaviour of fruits of two Hylocereus species (Cactaceae)

Abstract Fruit growth and ripening, and the effect on fruit quality of various storage temperatures, were studied with Hylocereus undatus and Hylocereus polyrhizus plants growing in Beer-Sheva (Israeli Negev desert) under greenhouse conditions. Fruit growth was sigmoidal with a strong decline in growth rate after the onset of peel colour change. The first change in peel colour was recorded 24–25 days after anthesis in H. undatus and 26–27 days in H. polyrhizus . In both species, the peel turned fully red 4–5 days after the first colour change (mean temperature for the study period was 26.6±2.1°C). The slow growth phase was characterised by a decrease in the proportion of peel and concomitant increase in that of pulp, increase in the concentration of soluble solids and soluble sugars and a decline in firmness and the concentration of starch and mucilage. The surge in acidity prior to colour change indicated the beginning of the ripening processes. For H. polyrhizus , which has a red–violet pulp, the increase in pulp pigment paralleled the development of peel colour. Fruits were non-climacteric, and when harvested at close to full colour, they retained market quality for at least 2 weeks at 14°C or 1 week at 20°C. Storage at 6°C is not recommended, because transfer from that temperature to room conditions caused fruits to lose their firmness and flavour rapidly.

Cytology and mating systems in the climbing cacti Hylocereus and Selenicereus

Chromosome numbers and meiotic behavior are reported for the climbing cacti species Hylocereus undatus, Hylocereus polyrhizus, and Selenicereus megalanthus. The Hylocereus spp. are diploid (2n = 22), while S. megalanthus is a tetraploid (2n = 44). Irregular chromosome disjunction at anaphase I in pollen mother cells of S. megalanthus is probably the major cause of its reduced pollen viability and may contribute to low seed set, low number of viable seeds and, consequently, low fruit mass. A pollination study confirmed self-incompatibility in H. polyrhizus and a weakened incompatibility reaction in H. undatus and S. megalanthus. Major crossability barriers do not exist between the Hylocereus spp. investigated. Reciprocal intergeneric crosses were successful between Hylocereus spp. and S. megalanthus, suggesting that an Hylocereus sp. might be one of the diploid progenitors of the tetraploid S. megalanthus. The implications of the results on cacti nomenclature and systematics are briefly discussed.

Responses of two hemiepiphytic fruit crop cacti to different degrees of shade

Selenicereus megalanthus and Hylocereus polyrhizus, hemiepiphytic cacti of shady habitats, have recently been introduced as fruit crops to the Negev Desert of Israel. Since they become bleached and die when they are grown in full sunlight, the shading responses of these cacti were studied. Both species showed typical CAM CO2 fixation, namely CO2 was fixed during the night, followed by acid accumulation. Nocturnal acid accumulation and the concentration of photosynthetic pigments (chlorophyll and carotenoids) were determined in short term experiments in the summer under full sunlight or in net houses with 30, 60 or 90% shade. The effect of shading on morphological traits, growth and fruiting was determined in long term experiments, in net-houses only, since plants usually degenerate under full sunlight. S. megalanthus was found to be more sensitive to high light flux density and better adapted to deep shade than H. polyrhizus, as judged from the more marked decrease in both nocturnal acid accumulation and in the concentrations of chlorophyll and carotenoids under full sunlight in the former species. In addition, under 90% shade the stem biomass of S. megalanthus was reduced less than that of H. polyrhizus. In response to the shade, stem ribs became shallow, root dry weight decreased and shoot water content increased in both species. The most favorable conditions for growth and fruit production were found to be 30% shade for H. polyrhizus while for S. megalanthus 60% shade seemed to be preferable, since it facilitated higher acid accumulation, carotenoid and chlorophyll content, and better stem appearance. H. polyrhizus was distinguished by its higher fruit yield, estimated at 16 ton ha−1 vs. 3.8 ton ha−1 for S. megalanthus in the second year after planting when both species were growing under optimal conditions. The differences between the species in terms of light adaptation may be partially related to the wax layer coating the stem and sunken stomata of H. polyrhizus compared to S. megalanthus, which had neither wax nor sunken stomata.

Growth and oil production of argan in the Negev Desert of Israel

Abstract Argan (Argania spinosa L.) is a wild tree native to southwestern Morocco. It bears a plum-sized fruit with one to three kernels rich in oil. The oil is highly prized as an edible and cooking oil by the local people. Our study was carried out to investigate the possibility of domesticating the species. Seedlings were planted in the Negev Desert of Israel at the location Qetura with a high summer temperature and brackish water and at the location Ramat Negev with a low winter temperature and good-quality water. Average tree height in the seventh year was 4.0±0.6 m at Qetura and 4.6±0.6 m at Ramat Negev. Best yielders produced dry fruits between 20 and 25 kg/tree at both sites in the sixth and seventh years, and average orchard yield was three-four-times lower as a result of high variation between the trees. Kernels comprised 6.5% of fruit weight and contained 55% of oil. In the seventh year, oil yield was 0.6 kg/tree at Qetura and 50% lower at Ramat Negev. The higher oil yield at Qetura is related to higher average fruit yields, higher kernel weights and higher oil content of the kernels than the values for Ramat Negev. Characteristics of the fruits and fatty acid composition of the argan oil and the chemical composition and quality characteristics of the defatted argan kernel meal are being presented. Fruit components, such as the pericarp (45% of fruit weight), and the defatted meal (3.5% of fruit weight) can be used as animal feeds. The meal is characterized by a high protein content (46%) and a high in vitro digestibility (96%).

The effect of ripening stage on fruit quality after storage of yellow pitaya

Abstract Some physicochemical properties and flavour quality were determined in yellow pitaya ( Selenicereus megalanthus ) fruits harvested either at the beginning of ripening (colour break), or when they reached good eating quality (advanced colour stage), and then stored for up to 4 weeks at either 10 or 20°C. Colour-break fruits stored at 10°C ripened only after being transferred to 20°C. During ripening such fruits attained the physical properties of fruits ripened on the plant, but they contained significantly lower concentrations of soluble sugars and acidity, and had an inferior taste. Fruits harvested at the advanced colour stage and stored at 10 or at 20°C were also inferior to those of freshly-harvested fruits with respect to soluble sugars and acidity as well as taste quality, but their physical properties changed only slightly during storage. In both groups of fruit water was translocated from the peel to the pulp during storage. The lower weight loss, higher soluble sugar concentrations, and lower susceptibility to pathogens of advanced colour fruits as compared with colour-break fruits, suggest that the former stage is the correct one for harvest.

Adaptation of five columnar cactus species to various conditions in the negev desert of Israel

Five species of columnar cacti were examined with the aim of introducing new orchard crops to the Negev desert of Israel. The species comprisedStenocereus gummosus, S. griseus, S. thurberi andPachycereus pringlei, all found in semi-arid regions of Mexico, andCereus peruvianus, which is grown in sub-tropical regions. Young seedlings were planted at four sites in the Negev. The sites differ in climatic conditions and water quality. Growth data, expressed as total stem length and stem biomass, was obtained after five to six years in the orchards. They showed thatC. peruvianus grew best in the site with moderate temperatures and good-quality water, whereas the other species also did well under more extreme conditions of high temperatures and brackish water. Growth of all species was significantly retarded at the site having water with the highest NaCl content. In the sixth year a severe drop in temperature at one of the sites caused extensive injury toC. peruvianus andS. griseus plants, raising doubts as to the suitability of that site for their cultivation. At this stageC. peruvianus is the most promising candidate for domestication. Its growth rate was much higher than that of the other species, yield was precocious and fruit of good quality. Stem tissue ion concentrations (dry weight basis) showed that accumulation of K+was similar at all four sites and that Na+and Ct were significantly higher (probably in toxic concentrations) at the site with the highest concentrations ofNa+and Cl~ ions in the water. At all sites Cl~ concentration inC. peruvianus was much lower than that in the other species indicating that the exclusion of Cl- from the stems was not correlated to salt tolerance.RésuméCinco especies de cactaceas columnares fueron examinadas con el objeto de introducir nuevos cultivares en el Desierto del Negev de Israel. Las especies fueron:Stenocereus gummosus, S. thurberi yPachycereus pringlei, todas nativas de las regiones semiaridas de Mexico,S. griseus, cultivada y naturalizada en Oaxaca, México yCereus peruvianus que se encuentra en regiones tropicales y subtropicales de Sudamérica. Plántulas fueron sembradas en cuatro sitios del Negev, todos diferiendo en sus condiciones climáticas y en la calidad de agua. Datos de crecimiento, expresados en la longitud total del tallo y su biomasa obtenidos después de seis anos de cultivo, indican queC. peruvianus crece mejor en sitios con temperatura moderada y buena calidad de agua, encuanto que las otras especies tambien se desarrollan bien bajo condiciones extremosas de altas temperaturas y agua ligeramente salina. El crecimiento de todas las especies fue significativamente retardado en el sitio con mayor concentración de agua salina (NaCl). En el sexto año hubo severas heladas que dañaron extremadamente las plantas de C. peruvianus yC. griseus, lo que indujo dudas de su potencial de cultivo en esta localidad. Hasta lafecha se consideraC. peruvianus como el candidato más promisor para la domesticacián. Su taza de crecimiento fué mucho mayor que las otras especies y se obtuvieron cosechas precoces confrutos de buena calidad. Medidas de la concentracián de iones en el tallo (basadas en peso seco), indican que la acumulacidn de K+fue similar en las cuatro localidades y que Na+y Cl- fueron significativamente superior en la localidad con mayor concentracidn de iones de Na+y Cl- en el agua (probablemente con excesiva concentracidn tóxica). En todas las localidades la concentraci]’on de Cl- enC. peruvianus/we mucho inferior que en las otras especies, indicando que la exclusion de Cl- de los tallos no está correlacionada con la tolerancia a la salinidad.

Salt tolerance of prickly pear cactus (Opuntia ficus-indica)

In view of the need to exploit saline water resources in agriculture in arid zones, we investigated the salt tolerance of Opuntia ficus-indica in plants growing in solution culture. Salt (NaCl) was added in concentrations ranging from 5 (control) to 200 mol m-3. Cladode growth was sensitive to salinity, being 60% of the control at 50 mol m-3 NaCl. The root-to-stem ratio decreased significantly only at 200 mol m-3. Various other parameters were studied, such as water content, Na, K and Cl content, osmotic pressure, and CO2 uptake. Of these parameters the decreases in cladode water content and CO2 uptake were related to the decrease in cladode growth. Raised salinity increased cladode osmotic pressure, which was associated with tissue dehydration. We concluded that osmotic adjustment does not occur in prickly pear under salt stress.

Properties and postharvest behavior of the vegetable cactus Nopalea cochenillifera

Abstract Flattened stem segments (cladodes) of certain cactus species are eaten in Mexico as a vegetable, when still at the young tender stage (nopalitos). This study focuses on the properties and response under storage of vegetable cladodes of a spineless cactus species newly introduced to Israel, Nopalea cochenillifera (L.) Salm-Dyck. Cladodes of N. cochenillifera were found to be suitable for harvest at the end of the rapid growth phase, at which time they were 11–13 cm long, weighed about 40 g, and had a chemical composition similar to that of certain Opuntia species used as a vegetable. The cladodes exhibited typical acidity changes of CAM plants, with titratable acidity measured at harvest fluctuating from a morning high level of 620 mmol H + m −2 to an evening low level of 69 mmol H + m −2 (155 and 17 mmol H + kg FW −1 , respectively). Acidity of fresh morning-harvested cladodes stored in an open place or a room declined to an acceptable level of 400 mmol H + m −2 (100 mmol H + kg FW −1 ) by the second day. Storage studies (dark conditions) indicated that cladodes have to be protected from low temperature (4 °C) because of chilling injuries and maintenance of acidity, and also that CO 2 -free air does not influence acidity changes. In a long-term storage study, cladodes were either left uncovered, placed in polyethylene bags, or wrapped in PVC film, then kept in darkness for up to 21 days at 12 or 20 °C. Acidity, while declining with time, tended to be higher at the lower temperature and in cladodes placed in plastic bags. It dropped markedly when the cladodes were transferred from dark storage to a room held at 20 °C and a light regime of 12 h dim light/12 h dark (4 days). Plastic bags significantly reduced weight loss, but they were not recommended for storage because cladodes under this treatment tended to be wet and to develop roots. With respect to both acidity and weight loss, the most favourable treatment for long-term storage is wrapping the cladodes in PVC film and storing them at either 12 or 20 °C.

Phenology, breeding system and fruit development of argan [Argania spinosa, Sapotaceae] cultivated in Israel

Argan (Argania spinosa) is an evergreen tree native to southwestern Morocco appreciated for its edible, high nutritional oil, extracted from the kernels of the drupe-like fruit. Aspects of its reproductive biology were studied with the aim to domesticate the tree as an oil crop. Flowering offertigated trees cultivated in the Negev Highlands of Israel was confined to the spring months. The flowers were protogynous. Results of different pollination treatments showed that a pollen vector was necessary for pollination and that fruit set was significantly higher in cross and open pollination (7–9%) than in self pollination (0.5%). The lower fruit set obtained in self pollination was related to postzygotic discrimination. Pollen transfer by wind was restricted to short distances. Flies, mainly of the family Calliphoridae, visited the flowers and were found to be covered with argan pollen. Fruits ripened nine months after anthesis, exhibiting bisigmoidal growth curve.RésuméL’arganier (Argania spinosa) est un arbre endémique du Sud-Ouest marocain apprécié pour I’huile comestible et á haute valeur nutritive extraite des graines de son fruit á caractére de faux drupe. Nous avons étudié certains aspects de la biologie reproductive de I’arganier dans le but de domestiquer cet arbre pour son huile. La floraison d’arbres irrigués poussant en Israël dans les hauteurs du Negev est restreinte au printemps. Les fleurs sont protogynes, le style emergeant de la fleur avant I’anthése. Les résultats de différents traitements de pollinisation demontrent la nécessité d’un vecteur pour la pollinisation, et aussi que le nombre de fruits posés est significativement plus élevé dans les cas de croise-ments et de pollinisation ouverte (7–9%) que dans les cas d’auto-pollinisation (0.5%). La reduction ohservée dans le nombre de fruits posés par I’auto-pollinisation est attribuable á une discrimination post-zygotique. Le transport du pollen par le vent est restreint á de courtes distances, et Vintervention de mouches (Calliphoridae) dans la pollinisation a été démontrée. Les fruits exhibent une courbe de croissance bisigmoïde et atteignent I’état mûr neufmois aprés I’anthése.

Molecular typing of Cereus peruvianus clones and their genetic relationships with other Cereus species evaluated by RAPD analysis

Summary RAPD analysis was used to fingerprint 29 genotypes of Cereus species and examine their genetic diversity. Some modifications were made to the DNA extraction procedure with a view to assuring higher DNA yield and purity. A dissimilarity matrix and dendrogram were constructed to help visualize genetic relationships between different genotypes. The results show that C. peruvianus has only a limited genetic base and that further improvement of this crop may require the introduction of additional germplasm into breeding programmes. RAPD markers were shown to be a valuable tool for clone identification in Cereus species and for detennining genetic relationships.