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  • Author or Editor: Oved Shifriss x
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The author of the article “A Gynoecious Line of B+B+Genotype in Cucurbita pepo” (HortScience 21:319, Apr. 1986), Oved Shifriss, wishes it noted that: “The genetic synthesis of gynoecism in Cucurbita is a subject of a pending application for a U.S. patent.”

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Squash (Cucurbita pepo L.) cultivars are monoecious. A phenotypically sensitive gynoecious line, NJ34, was developed through crosses of 3 monoecious inbreds and selection for increasing number of pistillate flowers in plants of several filial generations. NJ34 consists of female and predominantly-female plants under conditions favoring strong male expression. Predominantly-female plants differentiate sporadically 1–3 staminate flowers. The proportion of females is estimated at over 50% with a potential increase of up to 100% under conditions favoring strong female expression. The data show: 1) that NJ34 is later in time of flowering than its monoecious parents, 2) that its females can be converted into monoecism by spraying with an aqueous solution of 250 ppm GA3, and 3) that this line carries gene B for precocious fruit pigmentation.

Open Access
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A phenotypically sensitive gynoecious line of Cucurbita pepo L., NJ34, has been synthesized recently through crosses of monoecious inbreds and selection (3). NJ34 is 100% pistillate in some environments, but it differentiates a few staminate flowers in other environments. This line is BB, in which gene B conditions precocious yellow pigmentation of fruit. Since previous observations suggested that B can also increase female expression (1), a question arose: Is B essential for the synthesis of gynoecism in this species?

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The names squash and pumpkin are used interchangeably for fruit vegetables that belong to several cultivated species of Cucurbita. The species C. pepo consists of different groups of edible cultivars and a small group of inedible ornamentals known as yellowflowered gourds. In 1939, while leafing through L.H. Bailey's The Garden of Gourds (1937), I was fascinated by the illustrations of some bicolor gourd fruits. It occurred to me that the biocolor fruit pattern (Fig. 1) might be useful experimentally for studies of polarity in bioloy. However, the opportunity to initiate such studies did not come until about 10 years later.

Open Access
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Two systems of fruit pigmentation exist in Cucurbita pepo. In the standard B+-system, the onset of color differentiation (orange, yellow, cream, or white) occurs after the “bud phase.” In the precocious B-system, the onset of color occurs during the bud phase. The source of the precocious system is a group of bicolor-fruited cultivars of the ornamental gourds. The yellow portion of a bicolor fruit is precociously pigmented, but the extent of precocious pigmentation may vary greatly even among fruits borne on the same plant. Starting with a single bicolor-fruited plant of the ‘Pear’ gourd, a program of self-reproduction and selection was initiated in an attempt to establish true-breeding lines which differ in extent of precocious fruit pigmentation. Many plants of successive inbred generations proved to be unstable genetically or phenotypically or both. But 2 genetically stable plants of known breeding history were identified as BB and B w B w (B w for a “weak” allele). Inbred BB produces completely yellow fruits in one environment and somewhat variable fruits in another environment. Inbred BwBw produces fruits which exhibit a wide range of variation in extent of precocious pigmentation in different environments. Substitution of B for B + in several edible cultivars has revealed the following facts: 1) BB lines of some backgrounds produce completely yellow fruits in diverse environments. 2) BB + heterozygotes of different backgrounds differ from one another in extent of precocious fruit pigmentation and in the range of fruit variation on the same plant. 3) B is stable in some backgrounds and unstable in other backgrounds. 4) B can exert “secondary” effects on plant growth, sexuality, and fruit quality, some of which are detrimental and others, beneficial. 5) The secondary effects are separable in breeding experiments. It is suggested that the initial source of B and its precocious alleles is genetic instability which occurs spontaneously in some stocks during gametogenesis; that the extent of precocious fruit pigmentation depends on time at which B (or its allele) blocks chlorophyll synthesis during the bud phase; that the determination of this time is affected by the “strength” of the B alleles present, their dosage, modifier genes, and non-genetic factors; that the secondary effects of B result from different interactions between B and other genes; and that superior precocious cultivars could be developed in which the beneficical effects of B are enhanced and its detrimental effects are suppressed through selection of new gene recombinations.

Open Access
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Gene B. which conditions precocious yellowing of fruits, can also condition precocious yellowing of leaves. Data from a cross between BB parents, ‘Jersey Golden Acorn’ (yellow fruits, yellow leaves) and ‘NJ 260’ (yellow fruits, green leaves), indicate that a partially dominant gene, Ses-B, selectively suppresses the expression of B in leaves, but not in fruits.

Open Access

Abstract

Data from a cross between ‘Table King’, B +/B +, bearing green fruits, and ‘Precocious Small Sugar’, B/B, bearing yellow fruits, revealed the existence of 2 independent modifier genes, designated Ep-1 and Ep-2, each of which can extend the boundaries of precocious fruit pigmentation conditioned by gene B. The effect of these modifiers of B is cumulative, but the dosage of B plays an important role in controlling the extent of precocious pigmentation. Some commercial hybrids are B/+ and these tend to produce bicolor fruits, an undesirable feature in squash. The present findings suggest that B/+ hybrids can produce yellow fruits exclusively, provided they carry 2 or more Ep genes.

Open Access