Several herbicides are designed to function by the involvement
of activated oxygen. These herbicides promote the accumulation of metabolic
intermediates the plant. These herbicides are described as photobleaching herbicides.
Other herbicides that depend on light and chlorophyll are paraquat and diquat. So
far, few plants have been selected for tolerance to oxygen free radicals.
Flood stress
Whereas some plants are adapted to water-logged conditions,
most plants need well-drained soils to grow properly.
Concepts associated with water-logging stress
In soybean, stress due to water-logging can reduce crop
yield by 17–43% when it occurs at the vegetative stage and about 50–56% if the
stress occurs at the reproductive stage. Floods are often caused by excessive rainfall
due to a prolonged seasonal rainfall, or excessive rainfall after a long period
of drought. The excessive amount of water quickly creates anoxic soil conditions causing flood-sensitive plants
to suffer anoxia or hypoxia. Fermentation occurs in plant roots under such
conditions. Photosynthetic capacity of plants is significantly inhibited. Flood-tolerant
species have certain adaptive mechanisms, such as the formation of aerenchyma
and adventitious roots. Some studies indicate that root tissue survival under
hypoxia depends on the fermentation rate and sufficient sugar supply to
maintain cell
energy and membrane function.
Breeding efforts
Tolerance to water-logging appears to be quantitatively
inherited. QTLs for tolerance to waterlogging have been reported in rice and
soybean. Researchers at the International Rice Research Institute isolated the
SUB1 locus that promotes tolerance to flooding. In conjunction with the
Central. Rice Research Institute in India
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