Studies On Screening Of Barley Genotypes With Frost Tolerance: Physiological And Genetic Aspects

Low temperature is a major environmental stress for cereal crops worldwide, reducing yield potential and grain quality of barley in sensitive reproductive stages. Barley (Hordeum vulgare L.) is a major world crop ranked the fourth in planting areas among cereal crops. In general, extreme low temperature in winter does not cause considerable damage to barley seedlings in the winter-barley growing areas. However, frost or low temperature frequently occurring in spring affects barley grain production significantly, because the plants at reproductive stage are quite sensitive to low temperature. Developing of frost-tolerant barley in reproductive stages is one of basic and effective approaches to fignt against the low temperature during spring. This study is going to developing potential methods of screening barley germplasm with low temperature tolerance. Meanwhile a comprehensive study was undertaken to compare the difference in low temperature tolerance between vegetative and reproductive stage of barley plants.One of the most important agronomic traits in barley is freezing tolerance, which can be enhanced by cold acclimation. In order to clarify the mechanisms of alleviating injury by cold acclimation in vegetative stage, two winter barley cultivars with different cold tolerance in vegetative stage were used to study the effect of irradiance on leaf H₂O₂ accumulation and ROS scavenging systems after removal of unlethal freezing stress. Moreover, the functions of photosynthetic apparatus in leaves were measured by chlorophyll fluorescence during recovery. The results indicated that some chlorophyll fluorescence parameters during recovery from freezing treatment might be used as the indicators in identification and evaluation of cold tolerance in barley. The functions of photosynthetic apparatus were affected by irradiance after freezing stress. It can be concluded that cold acclimation may not directly enhance cold tolerance of barley plants, but it increased recovery ability from freezing injury, and the ability to cope with excess energy and photoinhibition was much improved in cold-acclimated plants.The primary sites of chilling action appear to be plant membranes, and the membrane stability in root plays a central role in cold stress tolerance and recovery from cold injury. MIFE technique, developed by Newman in University of Tasmania, Australia, was employed to determine the effect of low temperature stress on ion flux from barley roots. Root H⁺ and K⁺ flux of three barley cultivars were measured and the effect of low temperature on K⁺ uptake by barley roots was studied. As a effective, non-invasive, and laboratory-based technique, MIFE technique can detect minimum fluctuation of ion flux caused by low temperature stress in barley roots. The possibility of using MIFE technique as a potential screening tool in identification and screening of barley genotypes with high frost tolerance was tested. The results showed the potential value of the technique. Meanwhile, it was proved that the ability of K⁺ uptake by barley roots was significantly inhibited by low temperature stress, and it can be reversed dramatically after removal of un-lethal low temperature.The functions of photosynthetic apparatus were affected by irradiance and temperature. In order to clarify the variation of genotypes and mechanisms of frost tolerance at reproductive stage of barley, two winter barley cultivars with different frost tolerance at reproductive stage were used in this study. Photosynthetic apparatus were measured during recovery stage after low temperature stress. The results showed that growth chamber could be used to simulate low temperature stress at reproductive stage of barley, and to evaluate frost tolerance of barley genotypes. Moreover, In vitro culture method was employed to investigate the photosynthetic apparatus responses of detached flag leaves to low temperature stress. The evaluation of the differences among barley genotypes in their responses to low temperature occurring at reproductive stage is limited by uncertainty in a course of weather and different growth rate. The results indicated that In vitro culture may provide an effective method of screening and evaluating barley germplasm in low temperature tolerance at reproductive stage. Meanwhile, In vitro culture method was used to evaluate frost tolerance of a double haploid population, and the analysis of QTLs controlling frost tolerance was conducted. A QTL relevant to frost tolerance was located on chromosome 3H.