**4. Accessing drought tolerance of soybean**

To facilitate cultivation of soybean in semi-arid and arid regions, it is important to rank soy‐ bean cultivars according to their drought tolerance. Various parameters have been adopted to assess drought tolerance (Table 3). Due to different environmental and temporal factors, the results of assessment may be varied. Therefore, experiments have to be conducted con‐ secutively for a few years in the same regions with large sampling size using various assess‐ ment parameters in order to achieve a more reliable classification.



Reduction in leaf area is a convenient morphological parameter for measuring drought stress experienced by the plant. Commercially available leaf area meters provide a non-de‐ structive means to measure leaf area in the field. Alternately, the area of detached leaves can be measured simply by creating a digital image of the leaf using desk-top scanners followed

A Comprehensive Survey of International Soybean Research - Genetics, Physiology, Agronomy and Nitrogen

Drought stress also leads to a reduction in leaf relative growth rate [23], which can be calcu‐

where, FDW refers to the final dry weight; IDW refers to the initial dry weight; t2 refers to the time in days at the end of the experiment; t1 refers to the time in days at the beginning of

The degree of chlorophyll reduction in soybean leaves was correlated with the strength of drought treatments [24]. Chlorophyll can be simply extracted by immersing the plant tissue in N,N-dimethylformamide (DMF) [25]. After incubation and mixing, the DMF is subjected to OD determination. The total chlorophyll content is calculated as Ct = 8.24 *A*664 + 23.97 *A*647 – 16.64 *A*603, where Ct is the total chlorophyll content in µg/ml of the

To facilitate cultivation of soybean in semi-arid and arid regions, it is important to rank soy‐ bean cultivars according to their drought tolerance. Various parameters have been adopted to assess drought tolerance (Table 3). Due to different environmental and temporal factors, the results of assessment may be varied. Therefore, experiments have to be conducted con‐ secutively for a few years in the same regions with large sampling size using various assess‐

**Index Description Refs**

1. Average yield Average yield of certain germplasm in arid region or in the same region for several years.

2. Water usage efficiency Unit yield on the expense of a unit of water. [26] 3. Environmental index Yield at targeted region relative to the average yield of all regions

Yield at water deficit year/region relative to water sufficient year/

[26]

[26]

[26]

by image analysis by computer software [22].

lated using the following formula:

RGR = ln (FDW) – ln (IDW) / (t2– t1)

DMF subjected to measurement [25].

A. Direct yield scoring methods

B. Drought tolerance coefficient-based methods

1. Drought tolerance coefficient (I)

**4. Accessing drought tolerance of soybean**

ment parameters in order to achieve a more reliable classification.

tested.

region.

the experiment.

Relationships

214


**Table 3.** Common parameters for assessing drought tolerance of soybean cultivars.
