Assignmenton

Self-incompatibility

• self incompatibility refers to the inability of plant to set seed with functional pollen after self polllination.

• Koelreuter -1st reported S.I in Verbascum phoeniceumplants(18th century)

• Self incompatibility reported in about 70 family of angiosperm including several crop spp.

• It is importnant for outbreeding mechanism(cross pollintaion) for normal fruit set.

• It maintained high degree of heterozygosity and can take place any stage between pollination and fertilization.

• Self incompatible pollen grain may fail to germinate on the stigmatic surface.

• Some may germinate but fails to penetrate the stigmatic surface.

• Some pollen grains may produce pollen tube, which enters through stigmatic surface, but its growth will be too slow. By the time the pollen tube enters the ovule the flower will drop.

• Some time fertilziation is effected but embryo degenerates early.

• According to Lewis (1954) the self incompatibility is classified as follow

Self incompatibility

Heteromorphic system Homomorphic system

Distyl Tristylty Gametophytic S.I Sporophytic S.I

Other classification of S.I

S.R no Basis of classification

Types of S.I Brief description

1 Gene involved monoallelic S.I controlled by single gene

Diallelic S.I controlled by two gene

polyallelic S.I controlled by several genes

2 Site of expression Stigmatic S.I gene express in the stigma

Stylar S.I gene express in the style

ovarian S.I gene express in the ovary

3 Pollen cytology Binucleate The pollen grains have 2 nuclei

trinucleate The pollen grains have 3 nuclei

• In this case there will be difference in the morphology of the flowers. For example in Primula sp there are two types of distyly flowers namely PIN and THRUM.

(Pin flower) (Thrum flower)

Matingprogeny

Phenotype genotype genotype phenotype

Pin x Pin ssx ss incompatibility -

Pin x Thrum SS xSs 1:1(pin:Thrum) 1 pin and 1 Thrum

Thrum x Pin Ss x ss 1:1(pin:Thrum) 1 pin and 1 Thrum

Thrum x Thrum Ss x Ss incompatibilty -

is known in some plants like Lythrum salicaria. In this case the style of the flower may be short, long or medium length

Sporophitic S.I gametophitic S.I

(S.I is governed by genotype of (S.I is governed by the genetic

pollen producing plant). constitute of gamets)

• There are 2 type of events considered to constitute basic of S.I

a)stimulation of unlike genotype

b)inhibit of like genotype

• 2 hypothesis proposed for explaining this S.I mechanism(by bateman)

a)complementary hypothesis

b)oppositional hypothesis

• Proposed by bateman in 1952.

• S.I due to absence of stimulation by the pistil on pollen growth in the like genotype(S1S2xS1S2)

• Means S.I is due to absence of substance in the pistil or pollen which are essential for pollen tube penetration.

• It states that interaction between like alleles(S1S2xS1S2) leads to production of inhibitor which inhibit the growth of pollen tube in the pistil.

• Interaction between like alleles, a substance is produced in pollen and pistil which property to interfere with normal metabolism of pollen grain and tube(inhibit enzyme or auxin, block pollen tube membrane, inhibit enzyme necessary for penetration.)

1) Bud pollination:-pollination of immature buds with mature pollen.

2) Delay pollination:-pollination of aged pistlsseveral days after maturity with normal incompatible pollen.

3) Late season pollination:-self pollination at end of flowering season also lead to seed set.

1) Irradiation:-irradiation of style with X-ray immediately

before selfing reulst in break down of S.I.

2) High temp.:-treatment of high temp ranging from 30-60

degree leads to break down of S.I.

3) Mutilation of style:-S.I could be broken by mutilating

the stigma with steel wire brush during pollination.

4) Invitro-fertilization:-placing the pollen grains in direct

contact with ovules result in break down of S.I.

:-(cabbage and brussel sprout hybrid seed production)

• Hybrid seed production without emasculation and without resorting of CMS and GMS.

• Practiced in japan.

• S.I system permits combining of desirable genes in a single genotype from two or more different sources through natural cross pollination which is not possible in self-compatible spp.

very difficult to produce homozygous inbreed lines in a S.I spp.

S.I is affected by environment factor i.eTemperature and humidity and photo period.

Sometimes, bees visit only one parental line in the seed production plot resulting in sib matting.

• No seed set in self pollination but possible in cross pollination

• S.I can utilized during hybrid seed production

• S.I is less used because most of crop has no S.I

• Un-functional pollen failure to set seed both in self and cross pollination.

• M.S can utilized during hybridization programme of breeding.

• M.S can used more.