International Journal of Horticulture, 2017, Vol.7, No.22, 180-204
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Entomophilous ornamentals: Poppy, Liatris.
Zoophilous ornamentals: Willow.
Cross pollination leads in the improvement and preservation of heterozygosity in a population. Cross pollination
species are highly heterozygous and they show a certain degrees of heterosis with low to high inbreeding
depression. Such type of pollination is useful in the production of hybrids or synthetics.
3.3 Various mechanisms involved in cross pollination
Monoecious plants
: Male and female flowers occur in the same plant either in the same inflorescence or separate
inflorescence. It occurs in
Casuarina eqisetifolia
, pine,
Begonia, Petunia.
Dioecious plants
: Male and female flowers occur on different plants. It is observed in
Juniperus
spp.,
Polygonum
cuspidatum
.
Protogyny
: In this case, pistils mature earlier than stamens. Protogyny is found in petunia and antirrhinum.
Protoandry
: In this case, stamens mature before pistils. It occurs in salvia, marigold.
Heterostyly
: This condition is due to different lengths of styles and filaments leading cross pollination. It occurs
in antirrhinum, primula, Limonium, Pentas.
Herkogamy:
This mechanism is attributed to the physical barriers between the anthers and stigmas of a flower. It
is reported in Narcissus, Peperomea,
Ruellia brevifolia, Viola.
Genetic Male Sterility:
This type is determined by the single recessive gene, ms carried in the nucleus. It occurs
in Vinca, Pelargonium, Ageratum.
Cytoplasmic Male Sterility:
This type of sterility is determined by cytoplasmic factors and progeny of male
sterile plants become always sterile. It occurs in sunflower, petunia, impatiens.
Cyto-genetic Male Sterility:
This type of Male sterility is determined by the interaction of genes and cytoplasm.
It is found in petunia, zinnia, cosmos, marigold.
Self –incompatibility:
It is incapability of viable pollen grains to fertilize the same flower. It may be due to the
failure of pollen germination, pollen tube growth and degeneration of embryo after fertilization.
Gametophytic incompatibility
: It is influenced by a single gene with multiple alleles located in pollen, styles
and ovule which is independent in action and do not show any dominance relationship. It occurs in
Nicotiana
alata
, Petunia, Rose.
Sporophytic incompatibility
: It is influenced by a single gene with multiple alleles which are not independent
and show dominance relationship. It is found in Cosmos, Ageratum, Chysanthemum.
Heteromorphic incompatibility
: It is due to the presence of two or three types of morphologically distinct
flowers which are incompatible and their style and filament length are influenced by two alleles linked with genes.
In Primula, out of two flowers, Pin flowers have long style, short filament, large stigmatic cells and small pollen
and ‘Thrum’ flowers have short style, long filament, small stigmatic cells and large pollen. Both flower types are
self incompatible but cross compatible. This situation is called as ‘Distyly’ and governed by a single gene s, Ss
for Thrum and ss for Pin flowers. In Lythrum, ‘Tristyly’ situation is occurred with three types flowers, long, mid
long and short and each type has two positions of anthers.
Long style: mmss
Mid style: Mmss or MMss
Short Style: MmSs, mmSs, MMSS, MMSS, MmSs
