Soil salinity is a serious threat to cotton production worldwide, especially in arid and semi-arid regions. Excessive salts in the soil affect all most the whole living process of a cotton plant mainly through osmotic stress, iron toxity and nutrient imbalance, and finally leads to reduced cotton yield and fiber quality. Plant response to salinity stress may vary with genotypes and the growth stages in which the stress is imposed. However, it is still not clear if there exist difference in salt tolerance among current cotton cultivars at germination and seedling stages. The main objective of this study is to determine the salt tolerance of different types of cotton varieties. We attempted to develop easy and accurate methods for identifying cotton salt tolerance and screening genetic materials of cotton, with focus on difference in salt-tolerance of cotton between salt-tolerant cultivars and salt-sensitive cultivars at different stages during stand establishment.
To achieve this objective, we conducted box and pot experiments at the Cotton Research Institute (CRI),Anyang, Henan province in 2009. Seeds of 14 cotton varieties (lines) (sGKzhong980, Lumianyan21, CRI35, Lumianyan16, CRI 45, Jimian668, DPlcon215, Handan109, Zhong404A, Yumian21, CRI12, Yinshuangjia, Zhong9806 and Line44) were grown in either a box for germination or in a pot containing saline soil for emergence. The germination rate and the leaf leakage solution electrical conductivity were determined. Two typical varieties (CRI35 and Tamcot CAB-CS) with different salt tolerance were also studied at three-leaf age stage. For the germination stage study, the cotton seeds were planted in the mixture of NaCl and sterilized sand, and incubated in a growth chamber. For the juvenile seedling stage study, the seedling germinated on wet double layers filter paper towel were transferred to the sterilized sand mixture which contained 0.4% NaCl (w/w), and incubated in a growth chamber. For the three-leaf stage, the seedlings were grown in the non-salt soil pots in a growth chamber and treated with different salinity level of stress when the seedlings reached tree leaf sage. The results showed that there were significant differences in salt tolerance among the 14 varieties treated at the germination stage, with the maximum relative germination rate of 88.6% and the minimum of 9.1%. The germination rate of most varieties treated with salt at the juvenile seedling stage showed less difference than those treated at the germination stage among the 14 varieties, most of their germination rate being higher than 50%. It indicated that seedlings were more sensitive in germination stage than in juvenile seedling stage. Once the seeds germinated the salt tolerance increased over the growing time. The most appropriate stage for assessment of cotton salt tolerance was from germination to seedling stage.
Both varieties treated with salt at the three-leaf stage could survive under at least 0.55% NaCl, but their seedlings became shorter in length with smaller leaf and shorter epicotyl as the salt concentration increased. The two cultivars also differed significantly in response to salt stress. The sensitive variety was more severely inhibited than the tolerant one. The electrical conductance is an indicator of permeability of plant plasma membrane. Higher conductance shows the severer of intensity of membrane injury. The spatial sites of the two varieties response differed significantly. The salt injury intensity of different organs was different under the same salt concentration. For the salt-tolerant variety CRI35, the intensity of plasma membrane injury from high to low was true leaf > epicotyl >cotyledon. For salt-sensitive variety Tamcot CAB-CS, the intensity of injury was true leaf >cotyledon>epicotyl.