The effect of different levels of irrigation water salinity on received radiation, and the yield of some cotton genotypes

Introduction: Cotton (Gossypium hirsutum L.) is an indeterminate plant that growth and harvesting of multistage fibers along with the seed is possible in one crop season. Cotton, however, is a salt tolerant plant, but salinity, especially in dry and semi-arid regions of the world, can lead to a loss of production of this plant. Reduction of cotton yield due to use of saline irrigation water in surface irrigation methods was reported at 0, 10, 25 and 50% in salinity levels of 5.1, 6.4 and 8.4 and 12 dS m-1 respectively. Salinity stress can affect the growth of germination and plant growth, and reduce the amount of photosynthetic active radiation absorbed by the plant and consequently photosynthesis and yield. The purpose of this study was to evaluate the effect of irrigation water salinity on vegetative growth and yield of two cultivars and six cotton mutants produced in the nuclear power research institute.
Materials and Methods: This research was carried out in 2013 using split plot experiment in randomized complete block design with four replications at Rudasht salinity and drainage research station in Isfahan. Irrigation water treatments at three levels (4, 8 and 12 dS m-1) consisted of main plots and two varieties of Varamin and Shayan along with six mutants of cotton were sub plots. Saline water is supplied from drainage water with a salinity of 25 dS m-1 from the Rodasht saline research station, which was mixed at the site of the project with river water (maximum 2 dS m-1) in the place of special reservoirs and transferred to the sweets after delivery. It has been transmitted to the experimental plots by pipelines. The measured traits during the study were: the amount of light received in the middle and the bottom of the plant's canopy using a light meter at 7 am and 13 pm, the number of bolls per plant, lint percentage (fiber weight to seed weight ratio), harvest index and yield. All statistical analysis was performed using SAS software and means were compared by Duncan's multiple range test.
Results and Discussion: The effect of salinity treatments on number of bolls per plant and yield was significant at 5% level, but the effect of salinity interaction and genotype on yield and yield components were not statistically significant. Based on the results obtained in the morning, the amount of light received in the floor of canopy in treatments of 12, 8 and 4 dS m-1 were 329, 317 and 303 foot candle and at noon were 358, 348 and 310 foot candle, respectively. Shayan cultivar with the yield of 2852 kg ha-1 had the highest yield, but there was no significant difference between the yield of this cultivar and the other mutants used. One of the negative effects of salinity stress is the reduction of plant leaf area due to the reduction of plant cell pressure potential and the result of this process is the reduction of absorption of active photosynthesis radiation. In this case, the amount of light received to the canopy cover of the plant increases. Therefore, measurements of light in the floor of canopy can be considered as a measure of vegetation growth. In general, Varamin varieties and mutants such as LM1676 and LM1321 are among the genotypes with higher foliage than the other genotypes with less light in the center and floor of canopy. Therefore, less light in the floor of canopy (more foliage) does not necessarily mean more economic yield. The number of bolls per plant in salinity treatments of 4, 8 and 12 dS m-1 was 6.92, 6.75 and 4.49, respectively.
Conclusions: According to the results, most cotton mutants used in this study have good potential and can be considered as promising mutants to introduce new cultivars, especially in cases where available water sources are not of appropriate quality. Given that these mutants are produced by gamma rays, it seems that the use of this method can be considered as an appropriate approach in expediting the introduction of new cultivars of cottons.
Key words: Bolls per plant, Canopy, Lint percent