On Regreening of Cucurbita pepo L. Fruit

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Cucurbit Genetics Cooperative Report 6:86-87 (article 43) 1983

A. Schaffer1 and C. D. Boyer2
Rutgers University, New Brunswick, NJ 08903

The effect of B on precocious yellowing of C. pepo fruits has been reported in detail (1). However, during our studies on the-pigmentation of C. pepo fruits (2) a number of significant observations regarding fruit coloring were made which indicate directions for further study. Whereas standard (bb) fruits were susceptible to regreening in storage, precocious (B-) fruits were relatively resistant. The most striking example of this difference was observed during the fall of 1982. Small Sugar (SS) pumpkins, bb and Bb genotypes, were grown in the field in New Brunswick, New Jersey during the summer of 1982 for experimental purposes and the remaining fruits were harvested in mid-September and distributed to departmental staff members for ornamental purposes. At the time of harvest, the bb and Bb fruits were indistinguishable on the basis of rind color, all falling within the 5 YR and 7.5 YR color classification of Munsell (3). Approximately ten fruits of each genotype were kept in fluorescent-lit offices, frequently in mixed bb and Bb groups of two or three fruits. By the end of November, all of the bb fruits, and none of the Bb genotype, had begun to regreen.

Another example of the effect of B on regreening was in the progeny of the cross Early Prolific (EP) Bb x Table King (TK) bb. Only two Bb and one bb fruit were observed over a long period of time. By 50 days past anthesis (d.p.a.), the three fruit were yellow (10 YR according to Munsell) but soon afterwards the bb fruit began to regreen and at 160 d.p.a. it was almost completely dark green while the Bb fruits were unchanged.

Not all bb genotypes, however, are equally susceptible to regreening. The most striking example of differences was observed between the EP x TK bb fruit previously described as regreening and the bb progeny of SS Bb x TK bb. Two bb fruit from the SS Bb x TK bb cross were observed to turn from green to orange at approximately 50 d.p.a. By 80 d.p.a., the two bb fruits were completely orange and hardly distinguishable from their Bb counterparts and remained orange at 160 d.p.a. Differences in regreening susceptibility were also observed with respect to intensity of regreening.

These observations may be explained in terms of plastid transformations. The reversion of chromoplasts to chloroplasts has been reported in C. pepo var. ovifera fruits (4) but only in tissue which had previously changed from green to yellow (chloroplast to chromoplast). However, Ljubesic (5, 6) observed that in bicolor C. pepo (from which B is derived (1)) the green portion contained chloroplasts which later developed into chromoplasts while the yellow portion was characterized by chromoplasts derived directly from proplastids. If the action of gene B in fruit skin is at the plastid transformation level rather than at the carotenoid biosynthesis level per se (2), then B may be viewed as effecting direct proplastid to chromoplast development as well as inhibiting either proplastid to chloroplast or chromoplast to chloroplast development. Accordingly, the term “regreening” is inappropriate for B-genotypes. However, B-fruits do occasionally express greening when stressed in some manner, e.g. water stress (7) and virus infection.

The process of regreening, or post-maturation greening, in C. pepo has yet to be studied in detail. The physiological genetics of plastid reversions in C. pepo bb, the effect of B on plastid development, and the physiological effect of virus and environmental factors in causing greening even in B fruit are all topics that warrant further investigation.

Literature Cited

  1. Shifriss, O. 1981. Origin, Expression and Significance of Gene B in Cucurbita pepo L. J. Amer. Soc. Hort Sci. 106:220–232.
  2. Schaffer, A. 1982. Characterization and Inheritance Studies of Fruit Pigmentation and Rind Development in Cucurbita pepo L. Ph.D. Thesis, Rutgers University, New Brunswick, NJ.
  3. Munsell Book of Colors, Glossy Finish Collection, 2.5 R-10 G. Munsell Color, Macbeth Division of Kollmorgen Corp., Baltimore, 1976.
  4. Devide, Z. and N. Ljubesic. 1974. The Reversion of Chromoplasts to Chloroplasts in Pumpkin Fruits. Z. Pflanz. 73:296–306.
  5. Ljubesic, N. 1970. Fine Structure of Developing Chromoplasts in Outer Yellow Fruit Parts of Cucurbita pepo L. var pyriformis. Acta Bot. Croatia 29:51–56.
  6. Ljubesic, N. 1972. Ultrastructural Changes of Plastids During the Yellowing of the Fruit of Cucurbita pepo var. pyriformis. Acta Bot. Croatia 31:47–53.
  7. Burger, Y., H. S. Paris, H. Nerson, Z. Karchi and M. Edelstein. 1983. Overcoming the Silvering Disorder of Cucurbita. Cucurbit Genetics Cooperative Report #6.

1Present address: The Hebrew University of Jerusalem, Rehovet 76-100, Israel.
2Present address: The Pennsylvania State University, University Park, PA 16802.