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Yosef Mizrahi and Avinoam Nerd

Numerous species of cacti were introduced in an attempt to diversify the types of fruit trees cultivable under the conditions of the Israeli Negev Desert. The new species were tested in five introduction orchards varying in type of soil, climate and irrigation water. Fruits of the Hylocereus genus, which must be grown on a trellis system under netting, were found to be of an attractive shape, color, appearance and taste. Cereus peruvianus, which grows outdoors, produced beautiful tasty fruits which varied in color from yellow to deep red. Fruits of these species are of the nonclimacteric type and are capable of withstanding long-distance transportation. Some have to be cross-pollinated while others can be self-pollinated. They flower twice or three times a year, bearing fruits from June to November. These types are characterized by a CAM photosynthetic pathway, pointing to high water use efficiency.

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Avinoam Nerd and Yosef Mizrahi

Changes occurring during fruit ripening and duration of fruit development were studied in Selenicereus megalanthus (Scum. ex Vaupel) Moran (yellow pitaya), a climbing cactus grown in protected structures at three sites in the Israeli Negev desert. During ripening, peel color turned from green to yellow, fruit dimensions slightly changed, and pulp content markedly increased. Total soluble solids and soluble sugars in the pulp increased, while starch content decreased. Acidity decreased at the last stage of ripening. Fruit in which most of the peel area had turned yellow (stage 4) were given the highest taste grade by a panel of tasters. Measurements of ethylene and CO2 evolution indicated that fruit was nonclimacteric. The mean number of days from anthesis to fruit of stage 4 was negatively correlated with the mean of the maximum and the minimum temperatures during the growth period. Daily accumulation of heat units (HUs) was calculated as the difference between daily mean temperature and a base temperature of 7 °C. Sum of HUs for the period from anthesis to ripening was 1558±12 HUs.

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Avinoam Nerd, Avraham Karady, and Yosef Mizrahi

Field experiments were conducted to examine the effect of fertilization and short periods of drought on the out-of-season winter crop in prickly pear [Opuntia ficus-indica (L.) Mill.]. In addition, the winter and summer crops were compared regarding floral bud production and fruit characteristics. Under both continuous fertigation (N, P, K applied with the irrigation water) and continuous irrigation, the number of floral buds per plant was much lower in the winter than in the summer crop. Fertilization increased production of floral buds in both crops, but to a greater extent in the winter crop. The increase in floral bud production in fertilized plants was associated with an increase in NO3-N content in the cladodes. Suspension of fertigation for 4 or 8 weeks immediately after the summer harvest decreased cladode water content and delayed and reduced floral bud emergence as compared with continuous fertigation (control) or late drought (4 or 8 weeks) applied 4 weeks after the summer harvest. The plants subjected to early drought suffered from high mortality of floral buds. The fruits of the winter crop ripened in early spring, following the pattern of floral bud emergence the previous autumn. Mean fresh weight and peel: pulp ratio (w/w) were higher in fruits that ripened in the spring (winter crop) than in fruits that ripened in the summer.

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Avinoam Nerd, Vered Irijimovich, and Yosef Mizrahi

Argan is a wild 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 argan as an oil crop. Flowering of fertigated trees cultivated in the Negev Highlands of Israel was confined to the spring months. The flowers were found to be protogynous, the stigma protruding from the flower before anthesis. Stigma receptivity at the pre-anthesis phase was a third of that at anthesis. 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% to 9%) than in self pollination (0.5%). Since in-vivo pollen germination and pollen tube growth in the pistil were similar for foreign and self pollen, the lower fruit set obtained in self pollination may have been related to postzygotic discrimination. Pollen transfer by wind was restricted to short distances, and flies (family Calliphoridae), were proven to be involved in pollination. In contrast with stands in argan's native habitat, where fruit growth is inhibited in summer, fruits of the cultivated trees grew continuously throughout the summer. The pattern of growth of fruit fresh weight was similar to that shown for typical fleshy drupaceous fruits, with an initial and a final phase of rapid growth interrupted by a phase of slow growth.

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Julia Weiss, Avinoam Nerd, and Yosef Mizrahi

The reproductive biology of the climbing cacti Hylocereus polyrhizus (Weber) Britt. & Rose, H. undatus (Haworth) Britt. & Rose, H. costaricensis (Weber) Britt. & Rose, and Selenicereus megalanthus (Schum. ex Vaupel) Moran (syn. Mediocactus megalanthus) was studied with the aim of cultivating the cacti in Israel as fruit crops. Flowering in Hylocereus spp. occurred in two to three waves during the summer, whereas in S. megalanthus, flowering was concentrated at the end of autumn. Flowers of all species opened 1 to 1.5 hours before sunset and closed ≈6 hours after sunrise. In the Hylocereus spp., H. polyrhizus and H. costaricensis were self-unfruitful, and cross-pollination with other species led to high fruit set (100%). Hylocereus undatus was self-fruitful, setting fruit with self-pollen. Cross-pollination between the clones of S. megalanthus led to a high fruit set and each clone was self-fruitful. In contrast to H. undatus, S. megalanthus clones could set fruit without pollen vector involvement, although the set was slightly lower than with hand pollination. Pollen source influenced fruit weight. In the self-fruitful species of Hylocereus, fruit obtained by hand cross-pollination with other Hylocereus spp. were significantly heavier than fruit obtained by hand self-pollination. The largest fruit in each of the Hylocereus spp. were obtained by specific cross-combinations within the group. Fruit of S. megalanthus had a lower weight than fruit of the Hylocereus spp. Flowers of all species were visited by day-active honeybees only. Fruit set and fruit weight with open pollination was lower than with hand pollination in Hylocereus spp. Since stigma receptivity and pollen germinability stayed high during anthesis, the low pollination effectivity has to be related to other factors, such as the short bee visits and the absence of specific adaptation by the bees to the flower. In S. megalanthus, fruit set and fruit weight with open pollination were similar to values obtained with hand pollination. This similarity is probably related to the fact that pollen transfer in open pollination is achieved by bee visits and direct transfer of pollen to the stigma, which occurs via physical contact between anthers and stigma during flower closing.

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Avinoam Nerd, Fania Gutman, and Yosef Mizrahi

Fruit growth and ripening and the effect of various storage temperatureson fruit quality were studied in Hylocereus undatus and H. polyrhizus growing in Beer-Sheva (Israeli Negev desert) under greenhouse conditions. Dimensional growth of the fruit had a sigmoid pattern with a negligible growth after the onset of peel color change. The first change in peel color was recorded 24-25 d after anthesis in H. undatus and 26-27 d after anthesis in H. polyrhizus. In both species, peel color turned fully red 4-5 days after first color change (mean temperature for the study period was 26.6 ± 2.1 °C). Parallel to color changes the content of pulp, SSC and soluble sugars increased while firmness and the content of starch and mucilage decreased. The surge in acidity before color change indicated the beginning of ripening processes. In H. polyrhizus fruit, which have a red-violet pulp, the pigment increased in parallel to the development of peel color. The fruit were proved nonclimacteric, and when harvested at close to full color, they kept their marketing quality at least 2 weeks at 14 °C or 1 week at 20 °C. Storage at 6 °C is not recommended because fruit transferred from 6 °C to room conditions lose their firmness and flavor rapidly. In H. undatus chilling injury symptoms appeared.

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Christiane Metz, Avinoam Nerd, and Yosef Mizrahi

Hylocereus undatus (Haw.) and H. polyrhizus (Weber) are new fruit crops of the Cactaceae. In Israel, flowers of the two species, which are self-incompatible, are hand cross-pollinated. In order to ensure a current supply of compatible pollen and guarantee good yields, we have developed a procedure for long-term storage of pollen. Pollen for storage was collected in the evening or in the morning. Its moisture content ranged between 45% to 50% in the evening and between 18% to 22% in the morning. Pollen was first dehydrated in a vacuum desiccator until the moisture content was reduced to 5% to 10% and then stored at various temperatures (+4, –18, –70, –196 °C) for 3 or 9 months, after which it was used for cross-pollination. Percent fruit set and fruit fresh weight (FW) were affected by the temperature but not the duration of pollen storage; storage at +4 °C reduced fruit set, fruit FW, and seed number more than did storage at subfreezing temperatures. The FW of fruits produced by frozen pollen was similar to that produced by fresh pollen in commercial orchards. The rate of seed germination was high (≈90%) regardless of the temperature during pollen storage.

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Christiane Metz, Avinoam Nerd, and Yosef Mizrahi

Hylocereus undatus (Haw.) and H. polyrhizus (Weber) are new fruit crops of the Cactaceae. In Israel, flowers of the two species, which are self-incompatible, are hand cross-pollinated. In order to ensure a current supply of compatible pollen and guarantee good yields, we have developed a procedure for long-term storage of pollen. Pollen for storage was collected in the evening or in the morning. Its moisture content ranged between 45% to 50% in the evening and between 18% to 22% in the morning. Pollen was first dehydrated in a vacuum desiccator until the moisture content was reduced to 5% to 10% and then stored at various temperatures (+4, -18, -70, -196 °C) for 3 or 9 months, after which it was used for cross-pollination. Percent fruit set and fruit fresh weight (FW) were affected by the temperature but not the duration of pollen storage; storage at +4 °C reduced fruit set, fruit FW, and seed number more than did storage at subfreezing temperatures. The FW of fruits produced by frozen pollen was similar to that produced by fresh pollen in commercial orchards. The rate of seed germination was high (≈90%) regardless of the temperature during pollen storage.

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Israel Weiss, Yosef Mizrahi, and Eran Raveh

This study examined the response of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus to two CO2 regimes [enrichment (1000 μmol·mol−1) vs. ambient control (380 μmol·mol−1)] and to two fertilization regimes [0.5- vs. 0.1-strength Hoagland's solution (designated high and low, respectively)]. CO2 enrichment increased total daily net CO2 uptake, nocturnal acid accumulation, shoot elongation, and total dry mass by 39%, 24%, 14%, and 6% (averaging the two fertilization regimes) versus ambient CO2 treatment, respectively. Plants exposed to high fertilization demonstrated 36%, 21%, 198%, and 79% (averaging the two CO2 regimes) increases versus those receiving the low fertilization regime in total daily net CO2 uptake, nocturnal acid accumulation, stem elongation, and total dry mass, respectively. Plants exposed to high fertilization and elevated CO2 demonstrated 108%, 77%, 264%, and 111% increases versus those receiving the low fertilization regime at the ambient CO2 concentration in total daily net CO2 uptake, nocturnal acid accumulation, stem elongation, and total dry mass, respectively. This response was 25% to 71% higher than the summed effects of the separate responses to each factor, indicating a synergistic effect of elevated CO2 and high fertilization. Thus, it is apparent that H. undatus crops grown under a high-fertilization agromanagement regime may benefit from elevated CO2 to a greater extent than those grown with low fertilization.

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Varda Kagan-Zur, Yosef Mizrahi, Dan Zamir, and Nir Navot

A spontaneous tomato (Lycopersicon esculentum Mill.) triploid hybrid was analyzed by isozyme and restriction fragment length polymorphism profiles. The double chromosome complement donor was shown to be the male parent, contrary to the prevailing hypothesis.