Objectives Common vetch ( Vicia sativa L.) growth is easily inhibited by drought at germination stage. Thus, there is need for screening of critical, sensitive drought-resistance indicators and assessing the drought-resistance capacity of common vetch germplasms for identification and breeding of drought-resistant germplasms.

Methods Fourteen common vetch germplasms were collected from the dominant common vetch planting regions in China. Four different PEG-6000 concentrations (2.5%, 5%,10% and 15%) were prepared to simulate different drought stress levels, while distilled water treatment was the control. Indicators such as germination rate, germination potential, germination index, seed germination index, radicle length, embryo length, radicle weight, embryo weight, ratio of radicle length to embryo length, ratio of radicle weight to embryo weight, vigour index and their drought-resistance indexes (DRI) were measured and calculated.

Results All the four stress treatments significantly decreased the values of tested indicators and drought-resistance coefficients of all tested germplasms, with CV range of 11.40%‒48.71% and 10.20%‒46.56% for indicators and drought-resistance coefficients, respectively. Most measured indicators showed significant correlation with r value range of 0.182 to 0.956. Based on the principal component analysis, the DRI of the measured indicators were reduced to three independent integrated indicators, of which three contributed 85.9% of the cumulative variance. According to fuzzy mathematics membership function, the average drought-resistance comprehensive evaluation index (D value) of the tested germplasms was 0.420 with CV of 50.6%, while the maximum and the minimum D values were recorded for code 9 and code 10 germplasms, respectively. The 14 tested germplasms were clustered into four drought-resistance grades, and the grade of each germplasm was in accordance with its D value. The highest drought-resistant germplasms were those with code 9 and code 14, respectively, while 85.8% of the germplasms fell into the moderate and weak drought-resistance category. Stepwise regression produced a significant relationship between D value and drought-resistance coefficients of indicators (D = 1.31X₁ + 0.566X₂ + 0.183X₃–1.068; R² = 0.991; P< 0.001; X₁, X₂, and X₃ represent DRI for germination index, embryo weight and embryo length, respectively).

Conclusions The D value is an effective index for indicating drought-resistance characteristics at germination stage. The drought-resistance coefficients of germination index, embryo weight, and embryo length explained 99.1% of drought-resistance variation of the assessed germplasms. Two common vetch germplasms with high drought-resistance were identified, while more than 85% of the tested germplasms exhibited moderate and weak drought-resistance at germination stage. Overall, this study demonstrates that drought-resistance screening and evaluation are highly important for choosing drought-resistant germplasm and efficient growth and production of common vetch.