Male sterility: types and uses
Male Sterility:- When the pollens of a plant are dead and inactive, while the female gametes are alive and active, it is called male sterility. This occurs very rarely. This occurs due to mutation. There are three types of male sterility: -
1. Genetic Male Sterility (GMS)
2. Cytoplasmic Male Sterility (CMS)
3. Cytoplasmic Genetic Male Sterility (CGMS)
1. Genetic Male Sterility (GMS):- When male sterility is controlled by a recessive gene present in the nucleus, it is called genetic male sterility (GMS).
MS gene = For male fertility
ms gene = For male sterility
MS MS = Male fertile plant
MS ms = Male fertile plant
ms ms = Male sterile plant
Maintenance:- For maintaining GMS, male sterile plants are cross heterozygous male fertile plants. As a result, 50 percent male sterile plants are obtained in each generation.
Application in hybrid seed production:- For hybrid seed production, the male sterile line is used as the female parent and crosses with the appropriate male parent line. Hybrid seeds are produced using GMS in Castor and Pigeon pea crops.
EGMS (Environment sensitive GMS):- The environment has a great impact on genetic male sterility. Genetic male sterility is determined by photo period and temperature. This property is used in hybrid seed production in paddy crop. Thus, there are two types of EGMS:
i. TGMS (Temperature sensitive GMS)
ii. PGMS (Photoperiod sensitive GMS)
i. TGMS (Temperature sensitive GMS):- Temperature has an effect on genetic male sterility in paddy crop. At temperatures below 28 ° C, paddy plants are completely male fertile while at temperatures above 30 °C, paddy plants are completely male sterile.
Maintenance of TGMS line:- For this, paddy plants are grown in an area where the day temperature remain below 28 ° C. At this temperature, paddy plants are fully male fertile. Now allow self-pollination in plants, resulting in the production of TGMS line seeds and then plants.
Hybrid Seed Production:- For this, paddy plants are grown in an area where the temperature is above 30 ° C. At this temperature paddy plants are fully male sterile which can be used as female parent. Now these male sterile female parent plants are crossed with the appropriate male parent plant, resulting in the production of hybrid seeds.
ii. PGMS (Photoperiod sensitive GMS):- Photo period also has an effect on genetic male sterility in paddy crop. Paddy plants are fully male fertile at 10 hours of light period, while at 14 hours of light, paddy plants are completely male sterile.
Maintenance of PGMS line:- For this, paddy plants are grown in an area where light period remain available for 10 hours. Paddy plants are fully male fertile in this condition. Now allow self-pollination in plants, resulting in the production of PGMS line seeds and then plants.
Hybrid Seed Production:- For this, paddy plants are grown in an area where the light period lasts for 14 hours. Paddy plants are fully male sterile in this condition which can be used as female parent. Now these male sterile female parent plants are crossed with the appropriate male parent plant, resulting in the production of hybrid seeds.
2. Cytoplasmic Male Sterility (CMS):- When male sterility is controlled by cytoplasm, it is called cytoplasmic male sterility (CMS). When fertilization occurs, only the nucleus comes from the male parent, while both the nucleus and cytoplasm come from the female parent. So when the male sterile female parent is crossed with the male parent, all the plants produced from the hybrid seeds are male sterile as shown in the diagram below.
Hybrid Seed Production:- CMS cannot be used for hybrid seed production in crops in which seed is of economic importance. But in crops where a somatic part is of economic importance rather than seed, CMS is used for hybrid seed production. Such as onion, garlic, carrot, radish etc.
3. Cytoplasmic Genetic Male Sterility (CGMS):- When male sterility is controlled by both nucleus and cytoplasm, it is called cytoplasmic genetic male sterility (CGMS). Cytoplasm is the main controller. The dominant gene present in the nucleus is called restorative gene, which acts to restore male fertility by preventing the male sterile effect of cytoplasm. We denote this as R letter. While r is the inactive gene.
R gene = For male fertility
r gene = For male sterility
RR = Male fertile plant
Rr = Male fertile plant
rr = Determined by cytoplasm.
Different combinations of nucleus and cytoplasm are given in the following diagram: -
Hybrid Seed Production:- CGMS is most commonly used in hybrid seed production. A three line system has been developed for hybrid seed production using CGMS which consists of the following three lines:
i. A – line:- It is a male sterile line that is used as a female parent.
ii. B – line:- It is a male fertile line which is used as a male parent. It is the maintainer line that works to maintain the male sterile A - line.
iii. R – line:- It is a male fertile line which is used as a male parent. It is a restore line that works to restore the male fertility in hybrid plants.
To maintain the A-line, its cross is made with the B-line. For hybrid seed production, the A-line crosses with the R-line as shown in the diagram below.
