Evaluation of Salt Tolerance in Newly Developed Zhongdan Series Maize Hybrid Varieties and Their Parental Inbred Lines

The aim of the present study was to explore the correlation between seedling-stage salt tolerance in newly developed maize hybrids and salt tolerance in their parental inbred lines, evaluate the full growth-stage salt tolerance of hybrids with high seedling-stage salt tolerance, and provide resources and data support for development of maize hybrids suitable for saline-alkaline soils.

Sixteen hybrid varieties and 30 parental inbred lines were used as materials for evaluating seedling-stage salt tolerance in 2024. The experiments were conducted in greenhouses at the Institute of Crop Science, Chinese Academy of Agricultural Sciences. Two treatments were applied: CK (control) and SA (salt stress treatment). Seedling-stage salt tolerance and correlation analyses were performed by measuring seedling height and biomass. Salt-tolerant hybrids were selected, and leaf yellowing percentage and sodium ion (Na⁺) content were analyzed in the latest developed leaves to further validate their salt tolerance. Additionally, salt tolerance during the germination stage was tested in hybrid varieties Zhongdan 1130, Zhongdan 1112, and Zhongdan 1118, and yield measurements were carried out in saline-alkaline soils of Dongying City, Shandong Province.

Under 350 mmol·L^-1 NaCl stress, seedling height, fresh weight, and dry weight of the 16 hybrid varieties decreased by 53.73%-74.65% when compared with those in the control. Seven hybrids, including Zhengdan 958, Zhongdan 1130, Zhongdan 1112, and Zhongdan 1118, exhibited significantly higher morphological indices and salt tolerance coefficients than the average, demonstrating high salt tolerance. Under 250 mmol·L^-1 NaCl stress, salt tolerance was validated for some hybrids. Zhengdan 958 and Zhongdan 1130 exhibited significantly lower leaf yellowing percentages and Na⁺ contents in their aboveground parts than the salt-sensitive hybrids Zhongdan 153 and Zhongdan 123. Correlation analysis between the salt tolerance of the hybrids and those of their parental lines revealed that the salt tolerance coefficient of the aboveground fresh weight and seedling condition under salt stress of hybrids was significantly correlated with maternal line seedling condition (P<0.05). Kompetitive allele specific PCR analysis indicated no correlation between salt tolerance of hybrids and number of favorable allelic variations at the four salt tolerance loci in the parental inbred lines. In situ trials in moderately saline-alkaline soils throughout the entire growth stage showed that Zhongdan 1130 had a yield of 6 577.50-8 034.71 kg per hectare, which was 14.35%-20.99% higher than that of Zhengdan 958. Zhongdan 1112 yielded 6 415.11-7 720.73 per hectare, with either no yield reduction or an increase of 7.22%-34.22% when compared to that of Zhengdan 958. Zhongdan 1118 yielded 6 075.45-6 958.35 kg per hectare, with a yield increase of 5.62%-10.33% when compared to that of Zhengdan 958.

Salt tolerance of maize hybrids is correlated with that of parental lines; however, the correlation is significant only with the seedling condition of the maternal line. The number of favorable allelic variations in the salt-tolerance genes SOS1, HKT2, HAK4, and HKT1;2 in the parental lines was not significantly correlated with the salt tolerance of the hybrids. The newly developed hybrid Zhongdan 1130, which has high seedling-stage salt tolerance, exhibited a stable yield increase of > 14.35% in saline-alkaline soils in Shandong compared to that of Zhengdan 958, making it a suitable, high-yielding, salt-tolerant variety for adoption in the Huang-Huai-Hai region.