Field Crop 2018, Vol.1, No.4, 15-17
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heterotichybrids is superior among two-line hybrids than among three-line hybrids. This system is ideal for
developing indica/japonica hybrids because most japonica lines don’t have restorer genes.
(3) Better grain quality and higher yields. It was demonstrated that the TGMS was more effective in increasing
grain yield and seed production efficiency (Yuan, 1990).
(4) Absence of negative impacts of sterility-inducing cytoplasm.
(5) The TGMS and PGMS trait is usually controlled by one or two major nuclear genes, so it should be
comparably easy to transfer to diverse genetic backgrounds, which helps in diminishing potential genetic
vulnerability among the hybrids.
2 Classification of the EGMS System
Depending on the environmental factor affecting expression of the sterility-inducing gene, EGMS is classified in
following categories:
(1) PGMS: Photoperiod-Sensitive Genic Male Sterility
(2) TGMS: Temperature-Sensitive Genic Male Sterility
(3) PTGMS: Photothermosensitive Genic Male Sterility
TGMS lines are delicate to the temperature for the expression of male sterility or fertility (Figure 1). For example,
most TGMS lines stay male sterile at high temperature (day temperature > 30°C/night > 24°C) and they revert
back to partial fertility at a lower temperature (day < 24°C > 16°C night) (Virmani et al., 2003).
Figure 1 Rice Knowledge bank IRRI
PGMS lines are responsive to the spell of day length for the expression of sterility or fertility. For example,
most PGMS lines show male sterility under long-day (> 13.75 h) conditions and turn back to fertility under
short-day (< 13 h) conditions (Virmani et al., 2003; Sindhu and Kumar, 2018).
PTGMS lines are sensitive to both temperature and photoperiod. Temperature is the key factor since PTGMS lines
become absolutely male sterile or fertile beyond a particular temperature range, that is, > 30°C or < 24°C, without
any consequence of photoperiod (
. But, inside this temperature
range (24-32°C), photoperiod influences the PTGMS lines, that is, longer photoperiod will enhance male sterility
at lower temperatures vis a shorter photoperiod (14 h at 30°C will make the PTGMS line sterile in comparison
with 13 h at 30°C) (Virmani et al., 2003).
3 Procedure of Two-line (TGMS) Hybrid Rice Seed Production
The production of two-line hybrid involves two major steps
):
