Sex Expression in Vegetables

In majority of the vegetable crops hermaphroditism is rule. Staminate and pistillate flowers are also common in vegetable family. But there are also many vegetables like cucurbits, spinach, asparagus etc. which shows variety of sex forms or flowering habits. For an example, Dioecy is common in Asparagus, Beetroot, Spinach, Dioscorea, Ivy Gourd, pointed gourd and Sweet Gourd.

In addition to those staminate, pistillate and hermaphrodite there are various kind of sex forms like,

Trimonoecy, (Plant bearing staminate, pistillate and hermaphrodite flowers together),

Monoecy (Staminate and pistillate flowers together)

Androecy (Only staminate flower)

Andromonoecy (Plant bearing staminate and hermaphrodite flowers)

Gynoecy (Plant bearing only pistillate flowers)

Gynomonoecy (Plant bearing pistillate and hermaphrodite flower)

Hermaphrodite (Plant bearing hermaphrodite flowers)

Dioecy (Plant bearing male and female flower in separate plant)

Androdioecy (Gynoecious and Monoecious in separate plants)

Gynodioecy (Gynoecious and Hermaphrodite in separate plants)

Androdioecy (Androecious and Gynoecious flower in separate plant)

Cucurbits:

Cucurbits belongs to the family of Cucurbitaceae. The family shows almost all kind of sex forms. The table shown below may be helpful for understanding sex forms in cucurbits.

Sex form	Cucurbits	Remarks
Hermaphrodite	Cucumber, Muskmelon, ‘Satputia’ cv. of Ridge Gourd	Primitive sex forms of cucurbits
Trimonoecy	Cucumber, Muskmelon, Ridge Gourd	This form is rare and scarcely present in some breeding lines
Monoecy	Ash gourd, Bottle Gourd, Bitter Gourd, Cucumber, Muskmelon, Pumpkin, Ridge Gourd, Round melon, Sponge Gourd, Squashes & Watermelon	Predominant form.
Andromonoecy	Muskmelon, Watermelon, Ridge gourd, Smooth Gourd, Cucumber	Predominant in Muskmelon while rare in watermelon, smooth gourd, ridge gourd, cucumber
Androecy	Ridge Gourd, Cucumber, Muskmelon	Rarely seen in segregating population of the mentioned cucurbits, Can be used as pollen doner.
Gynomonoecy	Ridge Gourd, Cucumber, Muskmelon	Rarely seen in segregating population of the mentioned cucurbits
Gynoecy	Cucumber, Muskmelon and Ridge Gourd	Rarely found in Muskmelon and ridge Gourd. But at present time in cucumber, Gynomonoecy is assumed to be evolved from gynomonoecios sex form. Gynoecy is one of the major tool for creating hybrids.
Gynodioecy	Buffalo Gourd (Cucubita foetidissima), Cucumber	Artificially synthesized
Androdioecy	Cucumber	Artificially synthesized
Dioecy	Pointed Gourd, Ivy Gourd	Common in these cucurbits. Also found in wild species (Feral forms) like Luffa echinata, Citrullus naudinianus, Cucumis asper

 Sequence of flowering in Monoecious cucurbits:

Generally in monoecious plants staminate flowers appears first and later pistillate forms appear. The probable sequence is,

Underdeveloped Male→Normal Male→Normal Female→Inhibited Male→Giant Female→Parthenocarpic Female

Schematic representation of flowering in Squash

However the sequence may deviate minutely with genotypes and environmental factors. In monoecious cucumber staminate, mixed and pistillate flowers are normally noticed. Schematic representation of flowering sequence on the main shoot of squash.

Factors affecting Sex Expression of Cucurbits:

In angiosperms the basic flowering type is Hermaphroditism. Its been said that with the environmental spontaneous mutation other sex types evolved. The appearance of main flower types viz. staminate, pistillate and hermaphrodite in cucurbits, depends largely on environmental condition and certain plant growth substances that modifies sex expression.

1.    Environmental

• The appearance of main flower types viz. staminate, pistillate and hermaphrodite in cucurbits, depends largely on environmental condition and certain plant growth substances that modifies sex expression. Among environmental factors, temperature and photoperiod plays major role. Besides, nutrition, soil moisture and atmospheric humidity also have considerable contribution to the sex expression.
• High temperature and long photoperiod independently or in combination tends to shift femaleness towards maleness i.e. more number of staminate flower compared to pistillate flower for long duration (Undesirable for crop improvement) while low temperature and short photoperiod shift maleness to femaleness, i.e. more pistillate flower than male flower population for longer time (Desirable character for crop improvement). Example, Gynoecious and Gynomoecious lines of Muskmelon.
• High Nitrogen along with adequate soil moisture and high relative humidity promotes femaleness.

2.    Growth Regulators:

A number of Growth regulators (GRs) are also found to be affecting the sex expression of cucurbits.

• Ethrel (2-chloroethyl phosphonic acid) @ 250 ppm at 2-4 true-leaf-stage induces femaleness in cucurbits like cucumber, pumpkin and squash. Ethrel is also found to be inducing femaleness in andromonoecious cucumber. For hybrid seed production in many monoecious cucurbits Ethrel is used to regulate staminate and pistillate flowers. Surprisingly, Ethrel has no effect found in Luffa acutangula.
• NAA @100 ppm increases the female sex ration in Luffa cyllindrica.
• In some cases IAA and IBA also found to be increased femaleness.
• GA application induces maleness in gynoecious cucumber. It is most useful in hybrid seed production of cucumber.
• AgNO₃ promotes hermaphrodite flowers on monoecious muskmelon.

Asparagus:

Dioecy is rule. Asparagus plants possess three type of flower. Fully functional female, Normal male and fully male or Supermale. Supermales have high breeding value and is useful in production of hybrids. They are developed as a result of natural fertilization in fully functional female plants.

Read more: Genetic mechanism of sex expression in Vegetables