**11. Heterotic potential of two line hybrids**

The magnitude of heterosis in two line hybrid is also 5–10% higher than in three line hybrids as it does not have a cytoplasmic penalty. Reported that for most of the characters, the mean heterosis percent was in the order of indica/japonica F1 > Tropica japonica/indica F1 > indica/indica F1 > Tropical japonica/japonica F1.

A comparative studies on two - line, three - line and conventional hybrids of rice ( l.) was made at TNAU by [85]. To compare the efficiency of the available systems in hybrid rice technology, a study was conducted to evaluate 120 hybrids belonging to four different group of combinations using cytoplasmic genic male sterile lines (CMS), temperature sensitive genic male sterile lines (TGMS), temperature sensitive genic male fertile lines and well adapted varieties as female parents for their genetic potential related to yield and yield components.

The two line hybrids, TNAU (TGMS)4 x BPT5204, TNAU (TGMS)4 x JGL1798 and TNAU (TGMS)4 x Karnataka Deluxe Ponni were the high yielders and in CMS based hybrids, the hybrid IR 79156 A x Karnataka Deluxe Ponni possessed high yield and good restoration capacity. Of the conventional hybrids, IR 79156B x BPT5204, IR80151B x PSBRC82, IR80151B x WGL32100 and IR80151B x Karnataka Deluxe Ponni have exhibited significant *sca* and standard heterosis for yield [86]. Among the three groups of hybrids the two line hybrids were superior for yield compared to the CMS based and conventional hybrids and its application has great potential to revolutionize rice production in breaking the yield plateau.

Highly heteotic two line hybrids were identified by [87]. They studied three TGMS lines and 20 testers were used to generate 60 two line rice hybrids in a LxT mating design. All the three TGMS lines *viz.,* TNAU 18 S, TNAU 60 S and TS-29–150 GY and nine testers, *viz.*, CB 493, CB 55, CB 508, CB 513, CB 004, CB 921, CB-09–104, CB-09–106, CB 306 showed desirable general combining ability values for two or more characters of which three testers *viz.*, CB 044, CB 009 and CB 306 had positive and significant general combining ability values for single plant yield. Thirty eight hybrids had desirable *sca* effects for at least one of the eight characters. Top hybrids selected with high standard heterosis were TNAU18 S X CB 55, TNAU 18 S X CB 508, TNAU 18 S X CB 044, TNAU18 S X CB 921, TNAU 60 S X CB-09–106, TNAU 60S X CB 493, TNAU 60S/CB 55, TNAU60 S X CB 513 and TS-29–150 GY X CB 306 (**Table 4**).

Considering both physical and cooking quality traits primarily with head rice recovery, the four hybrids namely TNAU 60 S X CB 009, TNAU 60 S X CB-09– 106, TNAU 18 S X CB 921 and TNAU 18 S X CB 044 had acceptable grain quality traits with maximum phenotypic scores. These hybrids were studued for their adoptability under three environments. Comparing both Eberhart and Russell and AMMI models to all hybrids and checks, four two - line hybrid*s viz.,* TNAU 60 S X IET 21009, TNAU 60 S X CB-09–106, TNAU18 S X CB 921 and TNAU 60 S X CB 513 gave above average values and outperformed the checks thus showing considerable stability in the tested locations. On comparison of the two line rice hybrids with their test entries of similar maturity groups belonging to CGMS system and HYVs, obviously the two line rice hybrids gave additional per day productivity ranging from 3.23 to 44.53 percent increase. The hybrid TNAU 60 S


#### **Table 4.**

*Heterotic potential of Two line rice hybrids.*

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

X CB 55 significantly differed from other entries for six traits in initial hybrid evaluation and notably recorded 34.30 g of single plant yield. This hybrid also had medium slender grain type, high head rice recovery with intermediate amylose content and desirable pasting properties leading to a score of 40 in IRRI quality scale. This cross combination yielded fairly good amount of hybrid seed in mini seed production plot and also the female parent TNAU 60 S had acceptable outcrossing percentage. Multi location trials revealed that this particular hybrid fell under medium maturity group with 131 days of maturity, highest panicle length and also the highest yielded grain yield of 13082 kgha−1 with 99.6 kgha−1 day−1 productivity.

The hybrid combination was given with name TNTRH 55. The new two line rice hybrid TNTRH 55 with a duration of 125 days was synthesized using tgms line TNAU 60S with CB 55. The hybrid seeds were produced with minimum staggering between the parental lines. The hybrid was tested with station trials at Coimbatore and also at HREC, Gudalur the exclusive station for tgms line multiplication situated at 1500 MSL in Tamil Nadu for three seasons (Khariff 2014, 2015 & 20 (**Tables 5** and **6**) [88]. All the biometrical traits along with blast reaction were also studied with check varieties. Per day productivity of this hybrid was 39.7 kg/day.

This hybrid showed 13–25% yield increase over the check variety. It showed resistance to blast with the score of 1. The hybrid produces medium slender grain type with Intermediate amylose content and Gel consistency. In Multilocation Evaluation Trial it recorded a grain yield of 6562 kg/ha which was 17.4% over ADT 39 and on par with medium duration check TNAU rice hybrid CO 4 (6578 kg/ ha). At present the hybrid is under advanced stage of evaluation in Tamil Nadu. If this hybrid qualifies the criteria for release it will be the first two line rice hybrid ever released for cultivation in India. By the release of two line rice hybrid we can reduce the hybrid cost drastically as it involves only two parental lines for seed production [82].

Chandrasekhar [89] studied 1000 hybrids by crossing 500 germplasm lines (male) with one CGMS female line (IR79156A) and one TGMS female line (IR75589) and were evaluated in test cross nursery. Among the lines tested in test cross nursery on CGMS female, 60% lines are either partial restorers or partial maintainers. The maintainers proportion was 9% and restorer was 33%. TGMS female on an average across 161 combinations yielded 6.25 F1 seed yield per plant in comparison to 4.95 g F1 seed in CMS female. It was observed that TGMS females in general have higher seed production potential than the CMS female and TGMS female yielded 26% higher seed yield that CGMS female on an average across male lines in the study. For grain yield 187 hybrids recordedsignificant


#### **Table 5.**

*Evaluation of two line rice hybrids at HREC, Gudalur.*


#### **Table 6.**

*Performance of two line rice hybrid over seasons.*


## **Table 7.**

*Heterotic potential of the hybrids.*

positive heterosis over better parent and 128 hybrids over standard check. The top two line hybrids H137 (34.4%), H203 (31.9%) and H323 (26.7%) recorded the highest significant positive heterosis for grain yield (**Table 7**). TGMS hybrids exhibited higher average grain yield heterosis than the CGMS hybrids.
