Male Sterility in plants - concise points

MALE STERILITY

• In male sterile plants the pollen grains are either inactive or non functional 
• Male sterility occurs in nature due to mutation that occurs sporadically

Classification of Male sterility

Genetic Male Sterility

• It is governed by a nuclear gene ms , which is recessive generally
• In F2 , 3 fertile and 1 sterile plant will be obtained
• GMS is maintained by crossing msms * MSms yielding 50 % of fertile  plants and 50 % Sterile
• GMS is used for hybrid seed production in Castor , Pigeonpea and Tomato

GMS is of 3 types --> Temperature Sensitive GMS (TGMS) , Photoperiod Sensitive GMS (PGMS)  and Transgenic GMS (TrGMS)

 PGMS

In PGMS male sterility expression depends on exposure of plants to varying photoperiodic light thresholds

eg : In Rice if the plant is exposed to  Long day conditions ie >13hr 45 min , it shows Male sterility
, If the plant is exposed to short day conditions (<13 hr 45 min ) it will be male fertile

TGMS

In TGMS male sterility expression depends on temperature

eg : In Rice variety  Pei - Ai 64S a high temperature (>23.3 degree) leads to male sterility while a low temperature leads to male  fertility

TrGMS

Male sterility is governed by a transgene

eg : Barnase Barstar system

-> Transgene Barnase encodes an RNAse in the tapetum (nutritive tissue of microsporangium of anther ) in Tobacco , Brassica napus and causes male sterility

-> Transgene Barstar is the inhibitor of barnase encoded RNAse and restores the fertility

Limits of GMS: Only 50 % is sterile  , others 50 % is  fertile and has to be removed for Hybrid seed production


Cytoplasmic male sterility

• Male sterility is controlled by plasmagenes in the mitochondrial DNA

• CMS line (A line)  is maintained by crossing it with a maintainer line (B Line)

• 6-7 Backcrosses makes the nuclear genotype of male sterile progeny same as that of the recurrent parent
• All F1 hybrids are male sterile in CMS

CMS is used for hybrid seed production in vegetatively propagated plants not in seed propagated species since all the F1 produced is male sterile

Cytoplasmic genetic male sterility

• Male sterility is determined by the cytoplasm and a nuclear gene called restorer gene restores male fertility
• Restorer gene is generally dominant
• Repeated backcrossing for transfer of male sterility to a maintainer line and transfer of restorer gene using backcross is also involved

• Plants having ms cytoplasm is sterile only if the nuclear restorer genes are recessive rr 

• If their nuclear genotype is RR or Rr they will be male fertile

• Male sterile line is maintained by crossing with maintainer line (B line ) having rr nuclear genotype

In the case of hybrid seed production MS line is crossed with the restorer line so that the F1 plants are sterile

Male sterile line --> A line
Maintainer line --> B line 
Restorer line     --> R line

Hybrid seed production in - Rice , Bajra , Cotton , Sorghum , 
Chemically induced Male sterility

• Male sterility is induced by treatment with male gametocides and is non heritable in nature

• Examples of male gametocides - Ethrel , GA3 , Maleic Hydrazide , NAA , Na/Zn methyl arsenate

Ethidium bromide is the potent mutagens of plasmagenes eg :  Petunia , Barley male sterility