Association analysis of SSR markers with leaf morphology in maize (Zea mays) under diverse watering regimes

The leaf morphology of maize (Zea mays) is closely related to its drought resistance. The molecular markers correlated with leaf morphology traits under different watering regimes may provide insights into the genetic mechanisms and identify the breeding varieties. In this study, changes in the leaf length (LL), leaf width (LW), leaf angle (LA), leaf orientation value (LOV), leaf size (LS), leaf shape coefficient (LSC), and leaf rolling index (LRI) of 187 maize inbred lines were analyzed under different watering regimes. A genome-wide scan and the genetic diversity were analyzed with simple-sequence repeat (SSR) markers, and the associations between the markers and the leaf morphological traits were assessed via a general linear model (GLM). The results showed that:1) the coefficients of variation for the leaf morphological traits of the 187 inbred lines were 13.21%-59.23% and 9.62%-28.22% under normal water and dry conditions, respectively, indicating abundant genetic variation. There were significant differences in the seven leaf morphological traits, so the leaf morphology was adjusted by the hereditary character of the inbred line. LL, LW, LA, and LS decreased significantly under drought stress, whereas LOV, LSC, and LRI increased, and the variance rate of the seven traits was 30.53%-198.31%. 2) A total of 652 alleles were detected using 145 SSR markers. The polymorphism information content (PIC) ranged from 0.201 to 0.966, with an average of 0.478. The tested materials were divided into five groups based on unweighted pair group method with arithmetic mean clustering and population structure; the Luda red cob group, Tangsipingtou group, Lancaster group, P group, and Reid group. 3) A total of 15 SSR markers were associated with seven leaf morphologies under different watering regimes (GLM, P < 0.01), and the amount of explained phenotypic variance was 2.25%-27.30%. Approximately 72.97% of the SSR markers were detected under drought conditions. The umc1124, umc2363, umc1742, phi331888, umc1378, bnlg1863, umc2134, and umc1345 markers were simultaneously associated with multiple leaf morphologies under different watering regimes, indicating pleiotropy. These results provide useful information for the genetic improvement of leaf morphology and marker-assisted selection breeding programs for maize drought resistance and optimization.