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Harry S. Paris

Summer squash (Cucurbita pepo L.) is grown in many temperate and subtropical regions, ranking high in economic importance among vegetable crops worldwide. A native of North America, summer squash has been grown in Europe since the Renaissance. There are six extant horticultural groups of summer squash: cocozelle, crookneck, scallop, straightneck, vegetable marrow, and zucchini. Most of these groups have existed for hundreds of years. Their differing fruit shapes result in their differential adaptations to various methods of culinary preparation. Differences in flavor, while often subtle, are readily apparent in some instances. The groups differ in geographical distribution and economic importance. The zucchini group, a relatively recent development, has undergone intensive breeding in the United States and Europe and is probably by far the most widely grown and economically important of the summer squash.

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Harry S. Paris

Most cultivars of acorn squash (Cucurbita pepo), such as `Table Queen', have fruit that are light green when young, become dark green by intermediate age, and remain dark green through maturity, carrying genotype D/D l-l/l-1 L-2/L-2. Many other forms of C. pepo that carry this genotype, the most familiar being the Halloween and pie pumpkins, turn orange at maturity. The genetic basis for green color retention of acorn squash was investigated by crossing `Table Queen' with `Vegetable Spaghetti', `Fordhook Zucchini', and accession 85k-9-107-2 (the parental, filial, backcross, and testcross generation progenies being grown out in the field and observed and scored for fruit color at maturity, between 40 and 44 days past anthesis). The results indicated that the three stocks crossed with `Table Queen' carry two recessive genes, designated mature orange-1 (mo-1) and mature orange-2 (mo-2), which act in concert to result in complete loss of green color before maturity in 1-1/1-1 plants. `Table Queen' is Mo-l/Mo-1 Mo-2∼o-2. Genes D and mo-2 are linked, ≈15 map units apart.

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Harry S. Paris

The fruits of Cucurbita pepo cv. Table Queen are light green when young, turn dark green by intermediate age (15-18 days past anthesis) and remain dark green through maturity. Three major genes are known to affect developmental fruit color intensity in C. pepo: D, 1-1, and 1-2. Table Queen was crossed with cv. Vegetable Spaghetti and with tester stocks of known genotype in order to determine the genetic basis of its developmental fruit coloration. The results from filial, backcross. and testcross generations suggest that Table Queen carries gene D, which confers dark stem and fruit color from intermediate fruit age through maturity. Table Queen also carries L-2. which confers Light Type 2 (a pattern of grayish green hue) fruit color from intermediate age, but D is epistatic to L-2. The genotype of Table Queen is D/D 1-1/1-1 L-2/L-2. Clear-cut results were not obtained -- regarding the genetic basis of the retention of green color through maturity of Table Queen fruits.

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Harry S. Paris and Aviva Hanan

Most summer squash, Cucurbita pepo L., produce one flower bud per leaf axil, whereas some genotypes can produce two or more. The former genotypes are referred to as single-flowering, whereas the latter are referred to as multiple-flowering. The objective was to determine the mode of inheritance of multiple flowering. The zucchini ‘True French’, which is single-flowering, was crossed with Accession 1777, a nearly isogenic line of this cultivar, which is multiple-flowering. Parental, filial, and back-cross plants were grown in pots in the greenhouse and each of their first 15 leaf axils was scored for the number of flower buds. Nearly all F1 plants, regardless of the direction of the cross, and plants resulting from back-crossing to ‘True French’ were single-flowering. Approximately one-fourth of the F2 plants, regardless of the direction of the cross, and half of the plants of the back-cross to 1777 produced two flowers at one or more leaf axils. These results indicate that the ability to produce more than one flower per axil is conferred by a single recessive gene, herewith designated multiple flowering, symbol mf.

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Harry S. Paris and Rebecca Nelson Brown

Pumpkin and squash (Cucurbita L. spp.) are important cucurbit crops and are grown in almost all arable regions of the world. The three economically important species, Cucurbita pepo L., Cucurbita moschata Duchesne, and Cucurbita maxima Duchesne are highly polymorphic in fruit characteristics, inspiring much research into their inheritance. A comprehensive list of genes for Cucurbita was last published more than a decade ago. This new gene list for pumpkin and squash includes descriptions of gene interactions and the genetic background of the parents that had been used for crossing to allow easy confirmation of previous work and provide a sound foundation for further investigation. This gene list includes 79 loci for phenotypic/morphological traits and 48 polymorphic allozyme loci. Linkage and mapping are discussed.

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Harry S. Paris, Peter J. Stoffella and Charles A. Powell

Summer squash (Cucurbita pepo L.) plants were grown in pots with high (290% capacity) or low (45% to 70% of capacity) soil moisture. The plants were exposed or not exposed to sweetpotato whiteflies (Bemisia tabaci Genn.). Only the plants exposed to whiteflies developed leaf silvering. Silvering was more severe in plants subjected to low soil moisture.

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Harry S. Paris, Peter J. Stoffella and Charles A. Powell

`Striato d'Italia' (cocozelle group) and `Clarita' (vegetable marrow group) summer squash were grown in the greenhouse and field in the presence of sweetpotato whiteflies (Bemisia tabaci Germ.) and their susceptibility to leaf silvering was compared. Silvering was less severe in `Striato d'Italia' in the greenhouse and field.

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Charles A. Powell, Peter J. Stoffella and Harry S. Paris

Zucchini squash (Cucurbita pepo L.) fruit yield and the incidence of sweetpotato whitefly (SPWF) [Bemisia tabaci (Gennadius)], squash silver leaf (SSL) disorder, and zucchini yellow mosaic virus (ZYMV) were measured during Spring and Fall 1991 in experiments containing various plant populations. In both experiments, as the within-row spacing increased from 30.5 to 76.2 cm or the number of plants per hill decreased from three to one, the number of marketable fruit per hectare decreased, and the marketable fruit per plant increased. Adult SPWF populations increased with decreased within-row spacing in the spring but not the fall experiment. The incidence of SSL or ZYMV infection was not affected by plant population in either experiment. The results indicate that increasing zucchini squash plant population can increase yield without affecting the incidence of SSL or ZYMV.

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Yosef Burger, Uzi Saar, Nurit Katzir, Harry S. Paris, Yelena Yeselson, Ilan Levin and Arthur A. Schaffer

Fruit sweetness is the major determinant of fruit quality in melons (Cucumis melo L.) and reflects the concentration of the three major soluble sugars, sucrose, glucose, and fructose, present in the fruit flesh. Of these three sugars, sucrose is the prime factor accounting for both the genetic and the environmental variability observed in sugar content of C. melo fruit. Faqqous (subsp. melo var. flexuosus), a cultivar having a low sucrose and total sugar content, was crossed with Noy Yizre'el (subsp. melo var. reticulatus), a cultivar having a high sucrose and total sugar content. F1 plants had a sucrose content averaging slightly higher than that of the low-sucrose parent, indicating that low sucrose content is nearly completely dominant. Segregation in the F2 and backcross progenies indicated that high sucrose accumulation in melon fruit flesh is conferred by a single recessive gene herein designated suc. When the high-sucrose parent was crossed with the moderate-sucrose landrace known as Persia 202 (subsp. melo var. reticulatus), the segregation in the filial and backcross progenies suggested that additional genetic factors affect the amount of sucrose accumulation.