J. Rudich

Increase in femaleness of three cucurbits by treatment with Ethrel, an ethylene releasing compound.

SummaryThe application of Ethrel (2-chloroethane phosphonic acid), an ethylene-releasing compound, to monoecious cultivars of cucumber and squash and an andromonoecious cultivar of muskmelon, caused a shift towards femaleness in all three species. The increase in femaleness manifested itself in several symptoms: a decrease in the number of staminate (male) flowers, an increase in the number of pistillate (female) or hermaphrodite (perfect) flowers, and a change in flowering pattern, namely, formation of female flowers at lower nodes in cucumber and squash, and formation of hermaphrodite flowers on the main axis in muskmelon where normally only male flowers are formed in this cultivar.

Enzyme polymorphism inCitrullus lanatus andC. colocynthis in Israel and Sinai

Electrophoretic and morphological variation was studied in 13 cultivars ofC. lanatus and 31 accessions ofC. colocynthis from Israel. Twelve enzyme systems were assayed, representing 19 loci. We found 12 commercially grown cultivars to be monomorphic at all loci. OneC. lanatus accession collected from Israel is highly polymorphic and carries alleles ofC. colocynthis; this accession is probably a representative of a locally cultivated land race grown by Bedouins for animal feed. Over a range of 500 km two forms ofC. colocynthis were identified: one which grows along the coastal plains of the Mediterranean and the other in the arid Negev and Sinal deserts. A high level of electrophoretic and morphological divergence was found between plants of the two regions, whereas within the ecotypes little variation was observed.

Auxin, biosynthesis of ethylene and sex expression in cucumber (Cucumis sativus)

Ethylene production, level of 1-aminocyclopropane-1-carboxylic acid (ACC) and activity of the ethylene forming enzyme (EFE) were higher in apices of gynoecious cucumber (Cucumis sativus cv. Alma) as compared to monoecious cucumber (C. sativus cv. Elem). Application of indole-3-acetic acid (IAA) enhanced ethylene and ACC production in both cultivars. The stimulatory effect of IAA was more pronounced in gynoecious apices. Induction of ethylene production and accumulation of ACC resulting from treatment with IAA were effectively blocked by aminoethoxyvinylglycine (AVG). Content of endogenous IAA, measured by an enzyme immunoassay, was lower in gynoecious cucumber as compared to monoecious one. Treatment of gynoecious plants with the antiauxins α-(p-chlorophenoxy)isobutyric acid (PCIB) and β-naphthaleneacetic acid (β-NAA) did not inhibit female sex expression.It appears that although exogenous IAA enhances ACC and ethylene production, endogenous IAA might not have a major role in the control of sex expression in cucumber of the Beit-Alfa type.

Frequency distributions and linkage relationships of 2-tridecadone in interspecific segregating generations of tomato

SummaryThe levels of the naturally occurring insecticide 2-tridecadone (2TD) were measured in leaves of Lycopersicon hirsutum f. glabratum, L. esculentum, the interspecific F1 hybrid, the F2 and backeross generations. The wild species contains 50 times more 2TD than the cultivated tomato and the frequency distribution of the substance indicates that there is dominance for low levels of the compound. The genotype of F2 plants was determined with respect to 6 codominant isozyme markers and 4 dominant/recessive markers. Significant associations were detected between 5 of the marker genes and the level of 2TD. We interpret these results as implying linkage between marker genes and genes that control the level of 2TD. The behavior of the gene for the determinant growth habit of the plants suggests that it has a pleiotropic effect on the level of 2TD.

Photoacoustic and fluorescence measurements of the chilling response and their relationship to carbon dioxide uptake in tomato plants

The response of tomato plants to various chilling treatments was studied using two approaches for the measurement of photosynthetic activity. One involved the use of a portable fluorometer for the measurement of in-vivo chlorophyll fluorescence, while the other employed a newly introduced photoacoustic system which allowed changes in oxygen evolution to be followed in a leaf disc. A strong correlation was found between results obtained by each system and those obtained by a conventional open gas-exchange system for the determination of CO2 uptake. Both systems of measurements could readily distinguish between the effects of chilling in the dark (at 3° C for 18 h) and chilling at high photon flux density (2000 μmol m-2 s-1 for 5h at 5° C). Chilling in the dark had practically no effect on the quantum yield of oxygen evolution, chlorophyll fluorescence or CO2 uptake, while chilling at excessively high photon flux density resulted in a sharp reduction (50–70%) in the quantum yields obtained. The results support the view that photosystem II cannot be the primary site of damage by chilling in the dark, although it is significantly affected by chilling at high light intensity.

Effect of high temperature on quality of processing-tomatoes of various genotypes ripened off the vine

Abstract High-temperature effects on tomato fruits of various genotypes ripened on the vine in the greenhouse were studied. A significant reduction in fruit quality was found in fruits ripened in a greenhouse where the temperature was greater than 30°C for an average of 9 h/day. The parameters studied included colour, total soluble solid content and acidity. There was no significant change in the major carotenoid pigments concentrations in these fruits compared with fruits ripened at optimal temperatures. This finding was not in agreement with that obtained in an earlier study using detached fruits ripened in incubators. Diurnal temperature fluctuation and translocation processes in the plant are suggested as the major factors accounting for these differences. “White tissue”, a colour disorder, was a major factor affecting fruit quality at high temperature. Fruits of a breeding line UCX100 15-2-2 had the highest quality, did not develop colour disorders and were relatively insensitive to high-temperature effects.

The growth rates of fruits on different parts of the tomato plant and the effect of water stress on dry weight accumulation

Abstract The rate of dry-weight accumulation was found to be higher in early- than in later-setting fruits and was unaffected by the water regime. Water stress shortened the duration of fruit growth and accelerated ripening. When expressed as final dry-weight yield, the proportion of fruit set during the first week of flowering was significantly higher than that of later-setting fruit. Under water stress more than 40% of the final dry-weight yield was contributed by fruits set during the first week of flowering, as compared with 30% under non-stress conditions. The competition for assimilates between the various fruits is discussed.

Sex expression in watermelon as affected by photoperiod and temperature

Abstract The effect of environmental factors on sex determination of flowers of watermelon (Citrullus lanatus) was studied under controlled conditions. Short days (8 h) and a day temperature of 27° C increased the tendency towards female flowers. Day length of 16 h and a day temperature of 32° C inhibited the development of female flowers.

Changed sex expression and possibilities for F1-hybrid seed production in some cucurbits by application of Ethrel and Alar (B-995)

SummaryExperiments were performed to study the effects of the ethylene releasing compound Ethrel on sex expression in cucumbers and squash, and of Alar (B-995) plus Ethrel in muskmelons. As a result of foliage sprays with one or both of the above compounds normally monoecious plants produced female flowers only, for the first 2–3 weeks of flowering. The optimum treatments for cucumbers were two foliage sprays with Ethrel 250 ppm or 500 ppm applied at the second and the fourth true leaf stages. The optimum treatments for squash were Ethrel 250 ppm and 500 ppm applied at the first and the third true leaf stages.High doses (1000 ppm) or repeated applications of Ethrel retarded growth of muskmelons and cucumbers. Applications of B-995 (5000 ppm) plus Ethrel (500 ppm) at the second true leaf stage inhibited male flowering for 2–3 weeks of the flowering period. F1-hybrid seeds of muskmelons were experimentally produced in large isolation cages in the field, using two monoecious lines as female parents. The merits and some of the problems associated with the production of F1-hybrid seeds by the above methods are discussed.

Growing of processing-tomato plants under water-deficiency conditions: Mulching with transparent polyethylene

Abstract Processing-tomatoes, Lycopersicon esculentum Mill., were cultivated in an area devoid of summer precipitation without irrigation. A method was tested which included soil mulching with transparent polyethylene, augmented phosphorus fertilization, plant population, planting-dates and cultivars which produced 60 tons per hectare. Under dry cultivation, fruit quality was superior, particularly as expressed in parameters of total soluble solids (TSS, 7–8° Brix), high acidity amounting to 0.5% total titrated acid, and high viscosity. Soil mulching and intensified phosphorus fertilization influenced yield of red fruit for canning, and also affected yield of TSS per hectare.