Because of their high yield and high level of uniformity, hybrid varieties are quite
desirable in crop production. Hybrid seed production depends on pollination between
two specific homozygous lines and the prevention of self-fertilisation of female plants.
Possible prevention techniques include inducing male sterility that disables production
of fertile pollen. For hybrid seed production, genic (nuclear) and cytoplasmic male
sterility are used. Genic male sterility is caused by the genes encoded in the nuclear
genome while cytoplasmic male sterility is caused by the genes found on mitochondria,
together with the nuclear genes. To prevent the increasing loss of genic diversity, plant
breeders must constantly search for new sources of male sterile lines. In the case of
brown/indian mustard, a new male sterile line, which produced fertile offspring when
crossbred with normal lines, has been developed. In the case of oilseed rape, a sterile
line, which did not produce fertile offspring when crossbred with normal lines, has also
been developed recently. To pollinate this line, a wild-type genotype will have to be
found. In the case of sorghum, the first gene causing nuclear male sterility has been
identified. This will enable the development of two-line hybrids. In the case of maize
and rice, a completely new hybrid-seed-production system has been developed. It
requires only one male sterile line, the fertility of which is restored by inserting a
transgene.
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