**3. Types of environmental sensitive genic male sterility (EGMS)**

Comprises mainly of four types namely*:*

#### **3.1 Photoperiod-sensitive genic male sterility (PGMS)**

This type of male sterility was discovered in rice by Professor Shi Ming Song in Hubei Province of China in 1973. Several male sterile plants were noticed in

*Progress and Prospects of Two Line Rice Breeding in India DOI: http://dx.doi.org/10.5772/intechopen.99545*

a late japonica cultivar Nongken 58, when exposed to photoperiod of more than 14 hours. The same sterile plants when grown in photoperiod of less than 13 hours and 45 minutes, turned to fertility. Subsequently detailed investigations were carried out and the findings have been reported by Shi [7, 8]. The male sterile mutant was originally designated as Hubie Photoperiod-Sensitive Genic Male Sterile Rice (HPGMSR). Subsequently the mutant was named as Nongken 58 S. Pioneering and extensive work has been done on this mutant at Wuhan in Hubei Province and at other centers in China. PGMS trait from Nongken 58 S has been transferred to several elite japonica and indica cultivars through backcrossing in China.

PGMS system is useful and can be deployed in temperate countries where the day length differs considerably during different seasons.

#### **3.2 Thermo-sensitive genic male sterility (TGMS)**

This type of male sterility which is controlled by the temperature prevailing at sensitive stage of the crop, was discovered in China [13, 14].

In most of the TGMS mutants reported so far, such as Annong – 1S from China, Norin PL-12 from Japan, IR 32364 TGMS from IRRI, Philippines and several mutants reported from India and Vietnam, the sterility is caused by higher temperatures (generally above 30°C) at the sensitive stage whereas at lower temperatures (generally below 24°C) fertility is observed. However, in few cases, sterility is observed at lower temperatures and fertility is observed at higher temperatures. Such type of male sterility is referred to as 'Reverse TGMS type'. Examples of reverse TGMS type reported are mutant Diaxin 1A and IV A and a mutant in variety 26 Zhaizao from China [15–17], JP-38S from India.

In tropical and sub-tropical countries, where there are large temperature differences across locations, regions, seasons and at different attitudes TGMS system can be utilized. India is one of the country with various regions and seasons and with attitude ranging from sea level to several thousand meters in hilly areas, is highly suitable for exploiting TGMS system for deployment and development of two-line hybrids.

#### **3.3 Photo-thermo-sensitive genic male sterility (PTGMS)**

Several japonica and indica male sterile lines have been developed, utilizing the Nongken 58S mutant. All such lines developed utilizing the PTGM mutant, were found to interact both with photoperiod as well as temperature. Such type of male sterility is called photo thermosensitive genic male sterility (PTGMS). In such a system, photoperiod is effective between critical fertility point (CFT) and critical sterility point (CSP). This range of temperature is called as Temperature Range of Photo sensitivity.

#### **3.4 Micronutrient-deficiency induced male sterility**

Deficiencies of copper, Boron and some other micronutrients are reported to cause male sterility in wheat and some other crops. High genetic variability has been reported in sensitivity to deficiency of these micronutrients. Very sensitive types are completely male sterile under micronutrient deficient conditions. It has been suggested that these sensitive genotypes can be used under deficient conditions as females and tolerant genotypes as males for producing F1 hybrid seed. The sensitive types can be multiplied by growing them under micro nutrient sufficient conditions.

The PGMS, TGMS and PTGMS lines are governed by 2–3 recessive genes, hence they can be easily transferred through backcrossing to known elite, good combining varieties. TGMS system can be utilized for tropical countries like India where low and high temperature prevails in high altitudes and in plains respectively, whereas PGMS system for the temperate countries like China and Japan where the daylength variation is significant. PTGMS can be utilized in both the tropical and temperate conditions. The sensitive stage to temperature, photoperiod or both is generally stage IV (stamen and pistil primordia), to stage VI (Meiosis) of the developmental stages of the rice plant.

On the basis of the critical sterility point (CSP) the temperature at which complete sterility is induced and critical fertility point (CFP) the temperature at which maximum fertility is achieved, it can be classified into four types.

#### *3.4.1 Type 1: High CSP (>32°C) Low CFP (<24°C)*

This type is recognized by Chinese as ideal, as it is safe for both hybrid seed production and multiplication of PTGMS. According to Yuan [18] such an ideal type still, remains to be identified. Although no one is certain as to where to draw the lines for high CSP and Low CFP, based on the prevalent temperature and photoperiod regimes in a region, a narrow range can be determined. Spontaneous Mutant lines SM3 and SM5 fall under this category. SM5 with a CSP of 32.3°C is just on the border line [19].

#### *3.4.2 Type 2: High CSP (>32°C) High CFP (>24°C)*

Chinese have reported several of the EGMS lines identified by them to fall under this category. Zhang *et al.,* [20] classified this category as 7001 S type. Under this category TGMS like 8902S and W7415S have been listed. It is not suited to Chinese condition, as it would introduce risk in hybrid seed production. Zhang *et al.,* [20] suggested their usefulness in tropics. JP 2 falls under this category [19].

### *3.4.3 Type 3: Low CSP (<32°C) – Low CFP (<24°C)*

By virtue of its stable sterility duration over a large region in China, it can be used in hybrid seed production without any problem. However in this type of EGMS lines, their seed multiplication becomes difficult and hence limits their wide utilization in China [20]. Nevertheless this type (Pei ai 64S type) was preferred until ideal lines were bred [18, 20]. In subtropical countries like India however this type would be most suited, as only sterile phase is required to be more stable in such situation. Most of the TGMS Lines viz., TNAU 45S, TNAU 60S, TNAU 95S etc., developed from Department of Rice, TNAU, India fall under this category.

*3.4.4 Type 4: Low CSP (< 32°C) - High CFP (>24°C)*

Some of the lines *viz*., GDR 38S, GDR 39S and GDR40S developed from Hybrid Rice Evaluation Centre recorded this type of category.

#### **4. Detection and identification**

A detailed procedure for identifying Thermo-sensitive genic male sterile (TGMS) lines under field conditions, from germplasm and mutagenised populations in rice, has been given by Virmani *et al* [21]. These populations are critically observed for occurrence of male sterility when the crop gets exposed under natural conditions after panicle initiation stage to temperatures of above 30–350 Male sterility can be easily identified in the field, by the presence of partially filled hanging panicles and completely sterile erect green panicles in the same plant. Those

*Progress and Prospects of Two Line Rice Breeding in India DOI: http://dx.doi.org/10.5772/intechopen.99545*

showing complete lack of seed formation in self pollinated crop or partial seed set in cross pollinated crops under sterility inducing phase and partial seed set both in self and cross pollinated crops under fertility inducing phase are suspected to be EGMS. Such suspected EGMS plants are them studied critically in phytotrons or growth chambers under appropriate environmental conditions to confirm the presence of EGMS. If such facilities are not available, then periodical sowings over a period of time can be resorted to with change in temperatures under natural conditions, to observe the transformation from fertility to sterility vice-versa.
