The evaluation and characterisation of South African wheat cultivars for temperature stress tolerance

[摘要] English: Extreme temperatures are detrimental to plant growth and development and thusaffect the productivity of various crops around the world. In South Africa, nearly 544000 hectares of wheat were insured against frost damage over the last 15 years. Wheatin most of the western parts of Free State, experiences high temperature stress in laterstages of growth. In this study, 15 cultivars were evaluated to test their response tohigh and low temperature stress.Ten of the cultivars were tested to determine the influence of high and lowtemperature stress on yield and yield components. There was a high and positivecorrelation between total grain yield and other yield components. Some cultivarsperformed well and gave good yields under both high and low temperature stress,indicating stress tolerance. Other cultivars showed temperature stress sensitivity, asthey yielded poorly. Low temperature stress proved to the most devastating as somecultivars failed to produce any seed and some had poor and shrunken seeds.Accumulation of metabolites during stress has been correlated with the level of stresstolerance. A study to evaluate the effect of high and low temperature stress onproteins and carbohydrate (glucose and sucrose) content in seedlings was done. Therewas a significant difference in the increase of protein content between high and lowtemperature stress. Protein content increased significantly more under lowtemperature stress than high temperature stress. All cultivars except PAN 3349 hadincreased protein content under low temperature stress but a few cultivars exhibitedhigh temperature sensitivity as they failed to increase their protein content. Changeswere also observed on carbohydrate level. There was a notable increase in glucoseand sucrose content in certain cultivars. It was also noted that sucrose contentincreased significantly more than the glucose content and that not all the cultivars thatexhibited increased sucrose content necessarily had a glucose content increase as well.Different screening methods were evaluated for their efficiency as measure of stresstolerance. Results from the cell membrane stability test from this study wereinconclusive, which raises questions on the reliability and efficiency of this method asa measure of high temperature tolerance. Another test that was conducted is TTC,which gave good and reliable results It showed that there are definite hightemperature tolerance differences in South African cultivars. Some cultivars proved tobe high temperature tolerant as they had high TTC reduction under stresstemperatures, whereas some cultivars showed sensitivity with low TTC reduction. Itwas also found that some cultivars are able to avoid stress, whereby they toleratestress for only short periods.A crown survival study was also done and leaf-length and percentage survival werestudied as measures of freezing tolerance. Results indicated a high level of freezingtolerance in cultivars, as they remained viable and were able to grow new leaves afterexposure to stress. The cultivars in this study can be grouped as tolerant, intermediateand sensitive. On the bases of this study the tests were reliable and can be utilised as ameasure for freezing tolerance.The use of pro line content as indication of tolerance to stress has been established andin use for a long time. The effect of high and low temperature stress was studied withthe aim of evaluating proline content as a measure of temperature stress. Resultsshowed increased levels of proline after temperature treatments in comparison to acontrol treatment in some cultivars. Some cultivars exhibited an increase of prolinecontent after both high and low temperature treatments, whereas some had increasedproline content for either low or high temperature stress. Proline content can be usedas a screening tool for tolerance, but it must be used in conjunction with otherscreening methods like TTC.

[发布机构] University of the Free State