Production of watermelons for seed consumption is popular in many regions of the world. In the Mediterranean area, large white seeds are preferred. Six breeding lines were selected for investigating the nature of black spot, an undesirable feature reducing the commercial value of the seeds. Black spot is expressed as blackened areas of the seed coat, mostly near the margin in mild cases, but extending over much of the seed coat in severe cases. Sowing date had a significant effect on expression of black spot. Seeds that developed in early summer (June) had low frequency and severity of black spot expression, whereas seeds that developed later in the summer (July–August) had markedly increased expression. Large differences were also observed among the breeding lines. There was a significant negative correlation between severity of black spot and seed weight, suggesting that black spot is a stress-related phenomenon.
Fruits of four cucurbit crops, cucumber, melon, watermelon. and squash, were harvested 25, 35 and 45 days past anthesis (dpa) and their seeds were extracted immediately or after 10 or 20 days of pre-extraction storage. Upon extinction, the seeds were subjected or not subjected to fermentation, washing and drying, The effects of these procedures on terminability was examined immediately after extraction or after up to 48 months of storage. Cucumber, melon and watermelon reached full germinability by 35 dpa, but squash required a longer period. Fermentation and drying were important for improving terminability of immature seeds of cucumber, melon and watermelon. Fermentation had a deleterious effect on immature squash seeds, but drying and washing improved terminability of squash seeds. Washing of cucumber, melon and watermelon seeds increased the rate of germination but not the percentage. Pre-extraction storage had a positive effect on terminability but was less effective than leaving the fruit on the vine for a comparable period of time. The seed coat completed its growth earlier than did the embryo.
Two field experiments were conducted in Bet Hashita (1992) and Newe Ya'ar (1993), Israel, in order to examine the possibility of using plant growth habit, chlorflurenol, and plant population density to concentrate yield of pickling cucumber (Cucumis sativus L.) under a simulated once-over mechanical harvest system. Two near-isogenic cucumber lines, WI 1983G normal and WI 1983G little leaf, were grown under three plant densities, 5, 10, and 20 plants/m2, and at flowering half of the plants were treated with 50 mg·L-1 chlorflurenol solution. The little leaf line produced a smaller canopy than the normal line under five plants/m2 but a larger canopy under 20 plants/m2. The average commercial yield of the little leaf line was higher than that of the normal leaf line by 28% and 55% in Bet Hashita and in Newe Ya'ar, respectively. The highest yield of each line was achieved under the highest plant density. The average commercial yields under 20 plants/m2 were 1.13 and 0.91 kg·m-2 in Bet Hashita and 1.86 and 0.92 kg·m-2 in Newe Ya'ar for little leaf and normal leaf, respectively. Chlorflurenol increased fruit number per unit area but did not increase yield. Nevertheless, it increased the proportion of small fruits, which are more valuable. The present study shows that the little leaf growth habit can increase the yield concentration in pickling cucumber and make this crop more suitable for a once-over mechanical harvest. Chemical name used: methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (chlorflurenol).
Field experiments were conducted in 1996 and 1997 to examine the effects of plant density on yield and quality of fruit and seeds of muskmelons (Cucumis melo L.). Two open-pollinated cultivars, Noy Yizre'el (Ha'Ogen type) and TopMark (western U.S. shipper type), were grown at plant densities ranging from 0.5 to 16.0 plants/m2 under commercial conditions. The highest marketable fruit yields were achieved with plant densities of 2 to 4 plants/m2. In contrast, the highest seed yields were obtained at 8 to 12 plants/m2. Seed yield index [seed yield (g)/fruit yield (kg)] was used as a parameter to define seed production efficiency. High seed yield was closely related to high value of the seed yield index. High seed yield indexes resulted from high plant densities (up to 12 plants/m2), at which the crops produced many, but relatively small fruit. In all cases, the seed yield per fruit (seed number and seed size) increased with increasing fruit weight. However, the sum of the seed yield of two small fruit was always greater than the seed yield of one, double-sized fruit. There was a clear exception with extremely small fruit (<500 g), which produced both low seed yields and poor seed quality. A positive relationship was found between fruit size and seed size in both cultivars. Nevertheless, relatively small seeds (25 to 30 mg) extracted from relatively small fruit (500 to 1000 g) showed the best performance in terms of germination and emergence percentages and rates, and in the vegetative development vigor of the seedlings.
Menahem Edelstein and Haim Nerson
The effects of plant spacing (5,000-40,000 plants per hectare) on watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production for seed consumption were evaluated in two breeding lines, 203 and 239-4, and in the standard cultivar Malali in three field experiments in northern Israel. The two breeding lines produced more, but smaller fruits than did `Malali', resulting in nearly double the seed yield per unit area. Seed size was not affected by fruit size, unless fruit size was <500 g. The total number of fruits per unit area was the most important component in determining seed yield. Increasing the plant population increased the seed yield in all three accessions. Breeding and agricultural practices that maximize fruit number per unit area are expected to be most beneficial in maximizing the yield of watermelon grown for seed consumption.
Menahem Edelstein and Haim Nerson
Germination percentage and germination rate were examined in two melon accessions differing in their ability to germinate under low temperature and in their reciprocal F1, F2, and BC1 progeny. The seedcoat structure, pressure force required for seedcoat splitting, and the response to hilum sealing of the reciprocal F1s were examined as well. The purpose of this study was to elucidate the effects of embryonic genotype and seedcoat characteristics on the ability of melon seeds to germinate under low temperature. The results of the study point out that both components are strongly involved in low-temperature germination. The cold tolerant parent, ‘Persia 202’ (P202), germinated greater than 90% at 15 °C, whereas the cold-sensitive parent, ‘Noy Yizre'el’ (NY), did not germinate at all. The P202 × NY F1 and the reciprocal F2 germinated 80% to 90%, whereas the NY × P202 F1 germination percentage was only 71%. Backcrosses of the reciprocal F1 to the parents revealed that if the cross was to the tolerant one, the seeds germinated greater than 90%, but if the F1s were backcrossed to the sensitive parent, the seeds had only 56% to 60% germination. Data collected suggest that several dominant genes are carried by P202 for low-temperature germination. On the other hand, the difference in germination percentages between the reciprocal F1 demonstrates that the different seedcoats also play a role.
Harry S. Paris, Haim Nerson, and Yosef Burger
Precocious Caserta is a summer squash (Cucurbita pepo L.) of the vegetable marrow type. Unlike other vegetable marrows, its fruit are yellow with yellow broken stripes, and the flesh is bright golden yellow. Plant characteristics resemble those of ‘Caserta’, but leaves may exhibit much yellow spotting.
Harry S. Paris, Haim Nerson, and Nurit Zass
The effects of gene B in Cucurbita moschata Poir. were studied by comparing 2 near-isogenic lines, PI 165561 (B+B+ ) and Precocious PI 165561 (BB) at 2 locations in Israel. B significantly increased femaleness and number of fruits, but decreased fruit size and yield and numerically decreased seed yield at one or both locations. Fruits of B+B heterozygotes were distinctly bicolor. There was a deficiency in the number of bicolor-fruited plants in BC6 progeny, the deviation from the expected 1:1 ratio of green-fruited to bicolor-fruited being significant. Overall, the effects of B in C. moschata were no different from its effects in C. pepo L.
Harry S. Paris, Haim Nerson, and Yosef Burger
Gene B of Cucurbita pepo L. conditions precocious yellow-fruit pigmentation and is incompletely dominant to its allele, B + (3). This gene is found in representatives of several C. pepo cultivar groups, including ornamental gourd, zucchini, straightneck, pumpkin, and acorn. In addition to its primary effect, gene B can have a number of secondary effects, such as yellow spotting of leaves, decreased fruit size, reduced yields, bright orange flesh color, increased carotene content of the flesh, and improved flavor. The extent to which a particular secondary effect is manifested is dependent upon the genetic background.
Zvi Karchi, Anneke Govers, and Haim Nerson
‘Alena’ is an open-pollinated, tetraploid watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) of excellent quality, adapted for conditions of intensive cultivation and fertilization. Fruit size ranges up to 4 kg with about 70 seeds per fruit. The flesh is dark red, very firm, and with a sugar content ranging up to 12.5%. Rind color is black-green, with maturity about 7 to 10 days later than ‘Sugar Baby’.