A. Cucurbits:
i. Trimonoecious:
ü In cucumber controlled by ‘Tr’ gene.
ü In muskmelon ocuurs with an interaction between ‘a’ and ‘g’ gene.
ii. Androecious:
ü In cucumber, controlled by ‘a’ gene (monogenic recessive), influenced by ‘acr’ locus.
ü “mmff” controls andromonoecy in cucumber—‘aa’ for androecy and ‘mm ff” hermaphroditism exists in cucumber.
ü In Muskmelon-
‘A’- gene converts perfect flower to pistillate flower and ‘G’ converts perfect flower to staminate flower.
AG-Monoecism
Ag-Gynomonoecism
aG-Andromoecism
ag-Hermaphroditism
iii. Monoecious:
ü Monoecy controlled by a monogenic dominant gene in cucumber, muskmelon and watermelon.
ü In Ridge gourd sex is determined by ‘A’ (determines the both maleness and femaleness) and ‘B’ (determines the female sex only).
ü In Luffa two independent suppressor gene ‘A’ (Suppress maleness) and ‘G’ (supress femaleness) controls the sex mechanism.
Thus,
A/- G/- (Trimononecious)
a (Monoecious)
a/a G/- (Andromonoecious)
A/- g/g (gynoecious)
a/a g/g (Hermaphrodite)
ü In Cucurbita pepo
aa→ Andrecious
AA→ Andromonoecious
iv. Gynoecious:
Important mechanism for hybrid seed production in cucurbits, especially cucumber.
ü Genes associated with femaleness in cucumber→ ‘F’, ‘Acr’, ‘st’, acr(F), ‘gy’ and ‘M’. These genes are influenced by the same modifier gene and environmental factors.
ü Gene combination, Aa intensifies the maleness with stst.
ü Gynoecism is controlled by the interaction of alleles at 2 loci, M and F. The MM FF genotype produces all female flowers.
M locus→ Triggers the development of pistillate flowers, strong linkage with bacterial wilt resistant gene ‘Bw’. ‘Mm’ controls perfect flowers and crossing two such line produces an F1 with pistillate flower.
ü ‘gy’ (Recessive factors) controls gynoecisn and is closely linked with ‘acr’ . The pistillate flowers in gynoecious lines may occur in cluster or in solitary.
ü st+/st shifts overall flowering pattern basipetally or acropetally.
ü Gynoecism in Muskmelon is governed by MM gg gene, in the presence of Tr gene.
ü In Luffa femaleness is controlled by A/- g/g.
ü In Summer Squash a gynmoecious line has been identified, named NJ34. The line was developed by crossing 3 monoecious inbred line and thereafter selection for maximum number of female flowers for several filial generations. The line was maintained by GA3 @200 ppm for incorporating maleness and subsequent crossing.
ü Gynomonodioecism, gynodioecism, androdioecism and dioecism are also genetically controlled. Both gynodioecism and dioecism can be artificially synthesized in cucumber. In Cucurbita foetidissima, gynoecism is controlled by heterozygous dominant gene and monoecism is controlled by homozygous recessive gene. Acr accelerates the female tendency and reduces the male tendency during flower development. It also brings change in growth habit in plants.
v. Dioecious:
ü In cucurbits, Coccinea indica, trichosanthes dioica and T. japonica are naturally occurring dioecious plant. In T. japonica femaleness is controlled by 2A + 2X and maleness was controlled by 2A + XY.
ü In Ivy gourd sex determination is controlled by a pair of heteromorphic chromosomes, viz. X & Y. the Y chromosome appears to have dominant female suppression gene SuF with 2 more genes or set of genes M1 & M2. It controls the early and M2 controls the late stage of development of male organs in plant. The X chromosome carries their normal alleles, suF, M1 & M2.
B. Asparagus:
Ø In asparagus, theoretically male and female plants should be in equal proportion. Asparagus are generally dioecious. There are female (YY) and two type of male, viz. normal male (XY) and Supermale (XX). Supermale are not much productive in respect to the production but on the breeding point of view it is valuable. Generally supermale occurrence is erratic, sometime produced in functional female flower naturally or through pollen culture.. The male plants are more productive and often produces hermaphrodite flowers and even small berries. The sex is controlled by a single factor. X-Y pattern is also found in sex determination in Asparagus. Maleness is controlled by single dominant gene. Mm for male (located at Y chromosome) and mm for female.
Ø Self-seeds of andromonoecious plants produced male:female ratio of 3.:1. Among the male plants 2/3 is heterogametic (Mm) and 1/3 is homogametic (mm), also known as supermale which can be maintained vegetatively.
Ø Andromonoecy is mainly controlled by a gene located at Y chromosome which causes degeneration of stigma and style. Hermaphroditism is controlled by three complementary genes located in X chromosome.
Ø Three types of hermaphrodite plants produced by XHXH, XHX and XHY.
C. Spinach:
Ø Spinach is tetramorphic and sex expression ranges from maleness to complete femaleness. Though males are predominant, generally male, monoecious and female types occur in nature.
Ø Among these monoecious forms are of significantly important for crop improvement program as along with male, female and monoecious forms, the progeby of monoecious species produces high amount of female plants. This female plants can be increased by selection.
Ø X-Y system is found to be involved in sex expression of spinach. The Y chromosome controls maleness.
Ø The X-Y system is influenced by a pair of autosomal genes
Ø The sex genes are found to be located on the short arm of the longest chromosome (chromosome1).
Ø Female plants are homozygous (XX) for translocation and male plants are heterozygous (XY) for translocation.
Ø The longest chromosome pair decides the sex of plant either in homomorphic or in heteromorphic condition in one of the sexes, possibly the male.
D. Dioscorea (Yam):
Ø In Yam, most of the species are dioecious.. In D. sinnata femaleness is controlled by 2A + 2X and maleness by 2A + X.
Ø It’s been concluded that a strong Y chromosome is involved in the sex determination of the plant.
Why the different female lines have different sex expression and different degrees of response to GA?
It is because, the Acr-gene has multiple alleles to control the expression of pistillate flower and accelerate the rate of conversion from staminate to pistillate. M/m is the most important modifier controlling the trigger mechanism for floral bud differentiation.
How to synthesize artificially male and female plants in monoecious cucumber?
- Gynodioecisn can be synthesized by incorporating Acr gene. Dioecism can be synthesized by combining Acr with de gene (controls determinate growth habit of plant). In monoecious cucumber, acr acr produces male flower at early lodes and pistillate flowers at later stage. But the plant is with indeterminate growth habit (controlled by De De). Gene de controls the determinate habit and terminates the main stem early in plant development. So, acr acr de de plants are obvious male because the plant never got chance to develop female flower as the growth was terminated early. In this way in a dioecious population Acr Acr de de as female and acr acr de de as male plants can be synthesized.
- Inheritance of sex expression involving dioecious cucumber reveal that, 2 main loci ‘a’ and ‘acr’, with epistatsis were proposed to control sex expression. a-locus for maleness and acr-locus for femaleness
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