1 Introduction
17
resistance at seedling stage. The method is simple and feasible, and can be carried
out in large quantities, but it is inconvenient to identify the drought resistance in the
later stage. The hyperosmotic solution method is to germinate the seeds in hyperosmotic solution. The drought resistance of varieties at seedling stage was evaluated
by the percentage of seed germination or germination percentage. Because of the
different standards, there are two views at present. One is that the germination rate
in hyperosmotic solution cannot represent the drought resistance at seedling stage,
but there is little relationship between them. On the other hand, it is considered that
the germination and extension period of seeds in hyperosmotic solution is related to
drought resistance at seedling stage.
Drought resistance evaluation index: drought resistance is a complex biological
character, which is reflected in a series of physiological and morphological changes,
and has a certain impact on yield. Therefore, it is difficult to identify drought resistance. Scholars at home and abroad have done a lot of work in the identification
of drought resistance of corn, and put forward a variety of drought resistance identification indicators. Morphological indexes such as root number, root dry weight,
maximum root length, root–shoot ratio, radicle number, leaf size, shape, angle, leaf
curl degree and male panicle size can be used as identification indexes of crop drought
resistance. Physiological and biochemical indexes include leaf water potential, leaf
relative water content, exosmosis conductivity, aab content, sod activity, mda content,
osmotic regulation ability and so on. The common indexes for identifying drought tolerance of maize by CIMMTY were leaf extension index, time between male heading
and silking, leaf necrosis grade and yield, etc. The leaf extension index was measured before anthesis, and the formula was as follows: leaf extension index = (leaf
length under irrigation condition-leaf length under drought condition)/leaf length
× 100% under irrigation condition. The small leaf extension index indicates that
drought has little effect on leaf growth, and such varieties are more drought-resistant
than drought-resistant varieties, on the contrary, drought resistance is poor.
After drought, the drought resistance of the varieties with short drawing delay time
and short drawing interval time was stronger, on the contrary, the drought resistance
of the varieties with short drawing delay time and short drawing interval time was
stronger, but on the contrary, the drought resistance of the varieties was poor. The
grade of leaf tissue withering was investigated at filling stage. According to the degree
of leaf senescence and death during drought, where the cell water holding capacity
was strong, the leaf senescence was slow after drought, and the drought resistance of
the varieties with long leaf functional period was stronger, on the contrary, the drought
resistance was poor. Drought resistance refers to the adaptability and resistance of
crops to drought. For crop production, drought resistance and drought resistance
are mainly reflected in yield. Therefore, many scholars believe that the evaluation
of crop drought resistance should be based on whether it can stabilize the yield
and high yield under the condition of drought, among which the following are the
most important ones. Although the drought resistance coefficient (dryland yield)water field yield proposed by Chinoy [21] has been used by many researchers to
measure the drought resistance of crops, this index can only indicate the stability
of dryland crop varieties. However, it cannot explain the plasticity of high yield or
17
resistance at seedling stage. The method is simple and feasible, and can be carried
out in large quantities, but it is inconvenient to identify the drought resistance in the
later stage. The hyperosmotic solution method is to germinate the seeds in hyperosmotic solution. The drought resistance of varieties at seedling stage was evaluated
by the percentage of seed germination or germination percentage. Because of the
different standards, there are two views at present. One is that the germination rate
in hyperosmotic solution cannot represent the drought resistance at seedling stage,
but there is little relationship between them. On the other hand, it is considered that
the germination and extension period of seeds in hyperosmotic solution is related to
drought resistance at seedling stage.
Drought resistance evaluation index: drought resistance is a complex biological
character, which is reflected in a series of physiological and morphological changes,
and has a certain impact on yield. Therefore, it is difficult to identify drought resistance. Scholars at home and abroad have done a lot of work in the identification
of drought resistance of corn, and put forward a variety of drought resistance identification indicators. Morphological indexes such as root number, root dry weight,
maximum root length, root–shoot ratio, radicle number, leaf size, shape, angle, leaf
curl degree and male panicle size can be used as identification indexes of crop drought
resistance. Physiological and biochemical indexes include leaf water potential, leaf
relative water content, exosmosis conductivity, aab content, sod activity, mda content,
osmotic regulation ability and so on. The common indexes for identifying drought tolerance of maize by CIMMTY were leaf extension index, time between male heading
and silking, leaf necrosis grade and yield, etc. The leaf extension index was measured before anthesis, and the formula was as follows: leaf extension index = (leaf
length under irrigation condition-leaf length under drought condition)/leaf length
× 100% under irrigation condition. The small leaf extension index indicates that
drought has little effect on leaf growth, and such varieties are more drought-resistant
than drought-resistant varieties, on the contrary, drought resistance is poor.
After drought, the drought resistance of the varieties with short drawing delay time
and short drawing interval time was stronger, on the contrary, the drought resistance
of the varieties with short drawing delay time and short drawing interval time was
stronger, but on the contrary, the drought resistance of the varieties was poor. The
grade of leaf tissue withering was investigated at filling stage. According to the degree
of leaf senescence and death during drought, where the cell water holding capacity
was strong, the leaf senescence was slow after drought, and the drought resistance of
the varieties with long leaf functional period was stronger, on the contrary, the drought
resistance was poor. Drought resistance refers to the adaptability and resistance of
crops to drought. For crop production, drought resistance and drought resistance
are mainly reflected in yield. Therefore, many scholars believe that the evaluation
of crop drought resistance should be based on whether it can stabilize the yield
and high yield under the condition of drought, among which the following are the
most important ones. Although the drought resistance coefficient (dryland yield)water field yield proposed by Chinoy [21] has been used by many researchers to
measure the drought resistance of crops, this index can only indicate the stability
of dryland crop varieties. However, it cannot explain the plasticity of high yield or