**6. Inheritance of EGMS**

In most of the studies inheritance of EGMS has been reported as monogenic recessive. However, there are few studies, where it has been reported as digenic and in one case as dominant, depending upon the crosses in which inheritance has been studied. In PGMS mutant Nongken 58S, Shi [8] reported the inheritance of the character as monogenic recessive, whereas reported it as digenic. Oard and Hu [22] in PGMS mutant M-201S, reported this trait to be controlled by one to three recessive genes. Huang and Zhang [17] in the mutant CIS-25-10 S, reported a single dominant gene. However, Xue and Deng [23] reported that the PGMS trait was quantitatively inherited.

TGMS trait is reported to be monogenic recessive in 5460 S [14], R 59 TS [24] H89–1 [25, 26] and IR 32364 TGMS [25]. However, this trait was reported to be controlled by two recessive genes in Annong S-1 [27] and UPRI 95–140.

TGMS genes in 5460S and H 89–1 (later renamed as Norin PL-12) were designaed as tms1, and tms2 respectively Virmani and Borkakati [25] found TGMS gene in IR 32364 TGMS to best non-allelic with the gene in Norin PL-12 and tentatively designated it as tms3. For lack of accessibility to Chinese TGMS mutant 5460S, allelic test with tms1, could not be carried out. Subsequently, Reddy *et al.* [28] and Dong *et al.* [29] reported tms4(t) gene in their studies. Recently Wang *et al.* [30, 31] reported tms5 gene in Annong S-1 mutant.

Ashraf et al., [32] reported that pollen-mother-cell (PMC) formation, as well as meiosis stages, are induction detection sites for TGMS because at hightemperature wrinkled or abortive pollen grains were produced due to abnormal meiosis in microspore-mother-cells (MMC). Zhou et al. [33] quoted that, other TGMS-lines were also reported from Japan, The Philippines, India, and Vietnam [26, 34–36]. Mostly, reported TGMS-lines or mutants induce male sterility at high temperatures and male fertility at low temperatures [37–39]. The stated TGMS genes/lines are tms1, tms2, tms3, tms4, tms5, tms6, tms7(t), tms8, tms9, tms9–1, and tms10 [30, 31, 40–47] and Zao25S, Lu18S, N28S, 95,850 ms, XianS, Zhu1S, Meixiang851S, and HD9802S [48–53], that provide useful material for two-line HR production. Intriguingly, the reverse phenomena were also observed such as male sterility induced at low temperature and fertility restored at high temperature. Such kinds of TGMS rice-lines are termed as reverse TGMS (rTGMS) lines. Herein, the reported rTGMS genes/lines are rtms1, Diaxin-1A, and IVA and the mutant of Indica-rice variety 26-Zhaizao from China and JP-38S from India [16, 54–57]. The tms5 is an important factor that regulates thermosensitive sterility among many tgms lines.

#### **6.1 Linkage with molecular markers**

Linkage with morphological or molecular markers facilitates transfer of EGMS genes to desirable agronomical backgrounds, since mutants are rarely suitable for direct utilization in plant breeding programs. Linkage with morphological markers are rare. Secondly, this character of sensitivity to environmental factors is expressed only under certain specific ranges or conditions of these factors. Under such situation molecular markers are very handy and useful.

A summary of the molecular markers linked to the EGMS genes and the chromosomes on which they are located is given in **Table 1**.

The molecular mechanism underlying the TGMS Lines are studied by Pan *et al*., [61]. They reported the usefulness of thermosensitive genic male sterile (TGMS) lines and photoperiod-sensitive genic male sterile (PGMS) lines to improve rice yields. The male sterility in recently developed TGMS CO 27 is based on co-suppression of a UDP-glucose pyrophosphorylase gene (Ugp1). They studied Microarraybased transcriptome profiling by growing the TGMS-Co27 line and wild-type Hejiang 19 (H1493) line at high and low temperatures. A total of 8303 genes were differentially expressed in the two lines, under the two conditions, or both. Global gene expression was strongly affected by environmental factors. Some genes were strongly repressed in TGMS-Co27 at high temperature were important for pollen development. Notably, series-cluster analysis of differentially expressed genes (DEGs) between TGMS-Co27 plants grown under the two conditions showed that low temperature induced the expression of a gene cluster. This cluster was found to be essential for sterility transition. Many meiosis stage-related genes were included that are probably important for thermosensitive male sterility in TGMS-Co27. Temperature plays a major role in global gene expression and may be the common regulator of fertility in PGMS/TGMS rice lines.

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


#### **Table 1.**

*Molecular markers for EGMS genes.*
