Table 1.
Reported methods and indices for drought tolerance in Brassica species
| Method or indicator | Species | Developmental stage | Traits | Drought regime | Literature |
|---|---|---|---|---|---|
| Biomass and water potential | B. napus, B. juncea, B. campestris, B. carinata | Seedling | Biomass, water content, osmotic potentials | Greenhouse | Ashraf and Mehmood 1990 |
| DSIa | B. juncea | Mature | Seed yield and component traits | Experimental field | Chauhan et al. 2007 |
| LS, PSS, RVIb | B. napus | Germination | Biological and biophysical traits | Petri dish, 10% PEG6000 solution |
Yang et al. 2007 |
| Principal component, clustering, subordinate function analysis | B. napus | Flowering | Morphological and agronomic traits | Rain shelter | Zhu et al. 2011 |
| Leaf wilting index (LWI) c | B. napus | Seedling | Biological and physiological traits | Pots in rain shelter | Li et al. 2012 |
| TDM, LAI, RGR, CGRd | B. napus | Whole stages | Physiological growth indices | Field | Moaveni et al. 2010. |
DSI, drought susceptibility index, which is calculated as (1 − As/Ai)/(1 − Bs/Bi), where As and Ai are traits for a given genotype measured under drought-stressed and irrigated conditions, respectively, and Bs and Bi are traits averaged across all genotypes measured under drought and irrigated conditions, respectively.
RVI, relative vigor index, which is calculated as (Cs × Ds)/(Ci × Di), where Cs and Ci are lengths of seedlings under drought-stressed and irrigated conditions, respectively, and Ds and Di are the percentage of surviving seedlings under drought and irrigated conditions, respectively. LS, length of seedlings (from root to leaf). PSS, percentage of seedlings surviving after drought stress.
LWI = (1 − E/F) × 100, where E is the number of wilting leaves and F is total number of leaves.
TDM, total dry matter of 10 plants. LAI, leaf area index, which is defined as the one-sided green leaf area per unit ground surface area in broad leaf canopies. RGR, relative growth rate. CGR, crop growth rate. Crop growth rate is a measure of the increase in mass over a period of time.
The increase can be plotted as a logarithmic or exponential curve. The CGR is the slope of the curve, while RGR is the slope of the curve that represents logarithmic growth over a period of time.