Inheritance of light pigmentation in squash

The Journal of Heredity 76:305-306. 1985.

Inheritance of light pigmentation in squash H. S. Paris, H. Nerson, Z. Kerch), and Y. Burger

ABSTBACT: The Inheritance of light external fruit pigmentation of squash {Cucurttta pepo L.) was studied at two stages of growth: 2-5 days past anthesls (dpa) (young, edible summer squash stage) and 18-22 dpa (Intermediate stage of fruit development). Four cuitivars and their F,s and Fjs were studied: Early Prolific Stralghtneck (EPS), Slhl Lavan (= White Bush) (SLA), Bennlng's Green Tint (BGT), and Vegetable Spaghetti (VSP), all four of which are lightly pigmented 2-5 dpa and all except the first remain lightly pigmented throughout growth. The results Indicated that the four cuitivars carry the same gene (/) for light pigmentation at 2-5 dpa. Two of the four cuttlvars, SLA and VSP, also carry gene r that in concert with / determines light fruit pigmentation at 18-22 dpa. EPS and BGT carry R that conditions Intense fruit pigmentation at 1822 dpa. BGT is lightly pigmented at 18-22 dpa because It carries W (white fruit color), which Is epistatic to ft The genotypes of the four cuitivars are EPS, II RR wv^BCJ, II RR WW; and SLA and VSP, llrrww.

AN ARRAY of fruit colors occurs in Cucurbita pepo L., the species that includes summer squash as well as some winter squash, pumpkins, and gourds. The hues that occur are, principally, green and yellow-orange, which vary in intensity and shading from almost black to almost white. In addition, various kinds of striping, mottling, and bicolor patterns occur. To complicate matters further, fruits often change color during the course of development. The inheritance of some of these hues, intensities, shades, and patterns has been worked out, the most recent comprehensive review on the subject being that of Robinson et al.3. However, in some cases there remains considerable confusion with regard to color inheritance. This is due in part to genetically unrelated material being used by different investigators, and in part to the need for a developmental approach to fruit coloration. Various genes have been proposed as conditioning light or "white" pigmentation of fruit. The symbol W was assigned by Sinnott and Durham10 to a dominant gene determining white fruit color. Shifriss8 postulated the existThe authors are affiliated with the Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Experiment Station, P.O. Haifa, Israel. Contribution no. 1241-E, 1984 series, from the Agricultural Research Organization, Bet Dagan, Israel. © 1985, American Genetic Association.

Notes

ence of a recessive gene / for lightly pigmented fruit. Globerson2 later assigned the symbol c to a recessive gene for white fruit color. According to Globerson another recessive gene, r, was needed for the fruit to remain white throughout development; if its allele, R. occurred with cc, the fruit became green during later stages of development. Each of these proposed genes has been accepted in the gene list for Cucurbit^. The W gene appears to have been identified from crosses involving pedigrees from the scallop or "patty-pan" cultivar group. Shifriss cited Fordhook Zucchini and Early Prolific Straightneck as examples of intensely pigmented (LL) and lightly pigmented (II) genotypes, respectively. Globerson used for crossing an unspecified cultivar of the zucchini group and Sihi Lavan (= White Bush), a variable, open-pollinated Israeli cultivar of the vegetable marrow group, as examples of "green" (CC RR) and "white" (cc rr) genotypes. The aim of the present work was to clarify the inheritance of light external pigmentation of C. pepo fruit. For this purpose Early Prolific Straightneck (EPS) was crossed with Sihi Lavan (SLA) and Benning's Green Tint (BGT), the last being a light-green-colored cultivar of the scallop group. SLA also was crossed with Vegetable Spaghetti (VSP), another cultivar having lightly pigmented fruit. Fruit of reciprocal F] and F2 progenies of each of these crosses were then observed and scored at two developmental stages.

Table L

Generation

Materials and Methods EPS, BGT, SLA, and VSP were obtained from Otis S. Twilley Seed Co. (Trevose, PA), Northrop King Co. (Minneapolis, MN), Aratan Co. (Haifa, Israel), and Sakata Seed Co. (Yokohama, Japan), respectively. Reciprocal Ft and F2 progenies were obtained for crosses between EPS and SLA, between EPS and BGT, and between SLA and VSP. Flowers were covered on the day before anthesis. Covers were removed for a few brief seconds for pollination, carefully replaced over the pistillate flowers, and the flowers were tagged. Each of the parents and the Fi and F2 progenies were seeded in the field at Newe Ya'ar in • April 1984. Field preparation was as described by Paris et al.4. One pistillate flower on each plant was tagged and the day of its anthesis recorded. Color of the fruit was recorded at two stages of development: 2 to 5 days past anthesis (dpa), which is the prime edible summer squash (young fruit) stage, and 18 to 22 dpa, which is a stage of fruit development intermediate between the summer squash stage and the mature fruit stage. The mature fruit stage, some 40 to 50 dpa, is not pertinent to the scope of the present work. Results and Discussion Fruit color of EPS was light yellow at 2-5 dpa, intensified to yellow-orange by 14 dpa, and remained yellow-orange thereafter; this con-

Inheritance of fruit-color intensity 2-5 day* put anthesis

Description

No. plants intense-pigmented light-pigmented fruit fruit

Early Prolific Straightneck

0

22

Pj

Sihi Lavan

F, F, F, F2 F2 F2

(Pi X P2) (P2 X Pi)

0 0 0 0 0 0 0

21 15 14 29 107 102 209

0 0 0 0 0 0 0

11 13 15 28 93 108 201

0 0 0 0 0 0 0

10 15 15 30 112 111 223

Total (Pi X P2) 9 (P 2 X P,) ®

Total

P3

Benning's Green Tint

F, F, F, F2 F2 F2

(Pi X Pj) (Pj X P,)

P« F, F, F, F2 F2 F2

Total (Pi X P3) 9 (P3 X P,) 9

Total Vegetable Spaghetti (P2 X P 4 ) (P4 X P2)

Total (P 2 X P4) ® (P 4 X P 2 ) ® Total

July/August 1985

305

forms with the description by Shifriss7, who assigned this cultivar to color group IV, the persistent yellows. BGT, SLA, and VSP were light green at 2-5 dpa, gradually becoming almost white by 14 dpa, and turning yellow at fruit maturity (40-50 dpa); this conforms with Shifriss' color group IX, subgroup B. Each of the four cultivars was uniform for fruit color. The inheritance of fruit coloration at 2-5 dpa (summer squash stage of fruit development) is summarized in Table I. In all three sets of reciprocal crosses, only lightly pigmented fruits were obtained with color no more intense than the yellow of EPS or the green of BGT, SLA, and VSP. There were no plants that had intensely pigmented fruits at this stage of development. This indicates that all four cultivars have in common a gene conditioning lightly pigmented fruit at the summer squash stage. Thus, the gene symbols c and / are synonymous. The inheritance of fruit coloration at 18-22 dpa (intermediate stage of fruit development) is summarized in Table II. In both sets of reciprocal crosses involving EPS, plants having intensely pigmented fruits, whether yellow or green, were observed in the progeny. For yellow fruit, intensely pigmented was defined, according to the color guide of Kornerup and Wanscher3 as hue (page) 4, shade (column) A, intensity (row) 5 or more intense (similar to EPS), and for green fruit, more intense (darker) than the three green-fruited cultivars, e.g., of the 205 F2 progeny obtained from reciprocal crosses of EPS with SLA, there were 119 with intensely pigmented yellow-orange fruit, 38 recombinants with intensely pigmented green fruit, and 48 with lightly pigmented (yellow or green) fruit. These results are consistent with the interpretation that these two cultivars differ genetically in color intensity at the intermediate stage of fruit development and that the intensely pigmented fruit of EPS are conditioned by a single dominant gene, probably the gene designated R by Globcrson2. The lightly pigmented fruit of SLA would be conditioned by rr. In the reciprocal crosses of EPS and BGT, the results obtained were the opposite of those obtained by crossing EPS with SLA: the Fi was lightly pigmented and most of the F2 progeny were lightly pigmented (Table II). This is explained by assuming that BGT carries the dominant gene W, designated by Sinnott and Durham10. Like EPS, BGT carries a gene for intense pigmentation at this stage, probably R, with W epistatic to R. The data do notfitthe expected 13:3 ratio (x 2 - 16.94, P