**9.2 Stability of TGMS lines under fertility inducing and sterility inducing environments**

In Tamil Nadu, there is an exclusive centre for two line hybrid rice research under Tamil Nadu Agricultural university, Coimbatore. The centre was established during 1996 at Gudalur, Nilgiris District. The seed production procedure mentioned above is followed for evaluating tgms line at Gudalur and Coimbatore. For exploiting the two line breeding system a stable TGMS Lines are needed and seed production to be standartised based on the line to be used and prevailing weather parameters in the particular location.

Manonmani *et al.,* [82] studied the stability of new TGMS lines for sterility and standardized the seed multiplication of tgms lines at sterility and fertility favoring Environments. The experiments were conducted at Paddy Breeding Station, Coimbatore, Farmers field at Sathiyamangalam and Hybrid Rice Evaluation Centre, Gudalur during the *rabi and khariff* seasons in 2013 & 2014 to assess the pollen fertility expression under different temperature regimes in new generation temperature sensitive genic male sterile lines of TNAU. Weather parameters at Coimbatore and Gudalur during for the past fifteen years was analyzed for fixing the sowing season (**Figure 5** and **6**).

*Tgms* lines were evaluated under sterility inducing Environments *viz.*, Coimbatore and Sathiyamangalam during the month of December 2013 & 2014 (Rabi 2013 & 2014). The same lines were stubble planted and evaluated for pollen sterility under pollen fertility inducing Environment during the month of July 2014 at high altitude (1500 MSL) with cool climate at Hybrid Rice Evaluation Centre, Gudalur. The new TGMS lines developed at TNAU *viz*., TNAU 45S, TNAU 60S, TNAU 95 S, TNAU 19S and TNAU 39S were evaluated for their stability of pollen sterility under different temperature regimes were given in the **Table 2**.

At sterility inducing Environments the lines showed 100% pollen sterility. These lines were seeded during December at Coimbatore and Sathiyamangalam to expose them to a sterility inducing temperature (>29°C /< 23°C day night) during panicle initiation to flowering stage to test their sterility behavior so that their critical stage

#### **Figure 5.** *Mean Weather data at Coimbatore Location.*

#### **Figure 6.**

*Mean Weather data at Gudalur Location.*


#### **Table 2.**

*Pollen sterility of different TGMS lines in Rice.*

of flowering coincides with more than 29°C. Mean weather data for both locations was provided in the **Figures 6** and **7** and it showed that the temperature recorded in both the places exceeded >25°C during the month of March, April and May. During the flowering stage all these lines showed 100% pollen sterility at both the locations for more than 60 days and was test verified for next year also.

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

**Figure 7.** *Mean Weather data at Coimbatore and Sathyamangalam.*

The daily mean temperature of 24 to 26°C was found to be the critical temperature for fertility alteration. The sterile stubbles of these lines were planted at HREC, Gudalur during May to induce fertility for their seed multiplication and were exposed at critical stages to fertility inducing temperature (24°C / 18°C day / night). Maximum, minimum, and mean temperature significantly influenced the pollen and spikelet fertility in all five TGMS lines at high altitude. At Gudalur the temperature range during the month of July and August was less than 20°C. The appropriate sowing date of TGMS lines was fixed during June–July in such a way that the critical stages of panicle development would be exposed to the required temperature. The individual lines were maintained under isolation and genetically pure seeds were produced at Gudalur.

The above TGMS lines with wider pollen sterility period under plains can be very well exploited for developing two line rice hybrids during the period of December to April at Coimbatore. The same lines can be easily seed multiplied at Gudalur during July to November.

## **10. Two line hybrid rice seed production**

The TGMS seed produced from high altitude can be brought to locations like Coimbatore as proved above, where stable high temperature prevails during its sensitive stage for nearly 30 days. TGMS plants are planted in 6 rows and sandwiched with two rows of non TGMS good combiner lines on either sides. TGMS line must be randomly checked for complete pollen sterility during its sterile phase at high temperature. Supplementary pollination techniques as applied to three line system must be adopted such as GA3 spray, rope pulling, flag leaf clipping etc. to increase hybrid seed production. At the time of harvest care must be taken to harvest separately the non TGMS lines first. Seeds harvested from the TGMS line must be cleaned, packed, labeled, and sold to farmers as two line hybrid seed.

Hence Coimbatore and Gudalur locations were identified for the TGMS Seed multiplication and hybrid seed production in Tamil Nadu.

Based on the studied conducted at Department of Rice, Coimbatore and Hybrid Rice Evaluation Centre, Gudalur with Stability of TGMS lines compared with weather parameters over the ten years study resulted in the identification of season for seed multiplication and hybrid seed production as follows in the **Table 3**.


**Table 3.**

*Standardization of sowing season for the TGMS lines.*
