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

Abstract

English: Extreme temperatures are detrimental to plant growth and development and thus affect the productivity of various crops around the world. In South Africa, nearly 544 000 hectares of wheat were insured against frost damage over the last 15 years. Wheat in most of the western parts of Free State, experiences high temperature stress in later stages of growth. In this study, 15 cultivars were evaluated to test their response to high and low temperature stress. Ten of the cultivars were tested to determine the influence of high and low temperature stress on yield and yield components. There was a high and positive correlation between total grain yield and other yield components. Some cultivars performed well and gave good yields under both high and low temperature stress, indicating stress tolerance. Other cultivars showed temperature stress sensitivity, as they yielded poorly. Low temperature stress proved to the most devastating as some cultivars failed to produce any seed and some had poor and shrunken seeds. Accumulation of metabolites during stress has been correlated with the level of stress tolerance. A study to evaluate the effect of high and low temperature stress on proteins and carbohydrate (glucose and sucrose) content in seedlings was done. There was a significant difference in the increase of protein content between high and low temperature stress. Protein content increased significantly more under low temperature stress than high temperature stress. All cultivars except PAN 3349 had increased protein content under low temperature stress but a few cultivars exhibited high temperature sensitivity as they failed to increase their protein content. Changes were also observed on carbohydrate level. There was a notable increase in glucose and sucrose content in certain cultivars. It was also noted that sucrose content increased significantly more than the glucose content and that not all the cultivars that exhibited increased sucrose content necessarily had a glucose content increase as well. Different screening methods were evaluated for their efficiency as measure of stress tolerance. Results from the cell membrane stability test from this study were inconclusive, which raises questions on the reliability and efficiency of this method as a measure of high temperature tolerance. Another test that was conducted is TTC, which gave good and reliable results It showed that there are definite high temperature tolerance differences in South African cultivars. Some cultivars proved to be high temperature tolerant as they had high TTC reduction under stress temperatures, whereas some cultivars showed sensitivity with low TTC reduction. It was also found that some cultivars are able to avoid stress, whereby they tolerate stress for only short periods. A crown survival study was also done and leaf-length and percentage survival were studied as measures of freezing tolerance. Results indicated a high level of freezing tolerance in cultivars, as they remained viable and were able to grow new leaves after exposure to stress. The cultivars in this study can be grouped as tolerant, intermediate and sensitive. On the bases of this study the tests were reliable and can be utilised as a measure for freezing tolerance. The use of pro line content as indication of tolerance to stress has been established and in use for a long time. The effect of high and low temperature stress was studied with the aim of evaluating proline content as a measure of temperature stress. Results showed increased levels of proline after temperature treatments in comparison to a control treatment in some cultivars. Some cultivars exhibited an increase of proline content after both high and low temperature treatments, whereas some had increased proline content for either low or high temperature stress. Proline content can be used as a screening tool for tolerance, but it must be used in conjunction with other screening methods like TTC.

Afrikaans: Uiterste temperature is nadelig vir plant groei en ontwikkeling, en affekteer dus produktiwiteit van verskeie gewasse in die wereld. In Suid Afrika is amper 544 OOOha koring teen koue skade verseker in die laaste 15 jaar. Koring in die meeste westelike dele van die Vrystaat ondervind hoe temperatuur stremming in later groei stadia. In hierdie studie is 15 cultivars geevalueer om huJ!e reaksie op hoe en lae temperatuur stremming te bepaal. Tien van die cultivars is getoets om die effek van hoe en Jae temperatuur stremming op opbrengs en opbrengs komponente te bepaal. Daar was 'n betekenisvolle positiewe korreJasie tussen opbrengs en opbrengs komponente gewees. Sommige cultivars het goeie opbrengs onder beide hoe- en Jae temperatuur stremming gehad, wat stremmings toleransie aandui. Ander cultivars was sensitief en het swak opbrengste geJewer. Lae temperatuur stremming het die grootste effek gehad deurdat sommige cultivars geen saad gevorm het nie, terwyl van die antler sade klein en verkrimp was. Die akkurnulasie van metaboJiete tydens stremming is met die vlak van stremmings toJeransie gekorreJeer. 'n Studie is gedoen om die effek van hoe- en Jae temperatuur stremming op proteYene en kooJhidrate (gJukose en sukrose) in saailinge te bepaal. Daar was betekenisvolle verskille in die toename van proteYene tussen hoe- en lae temperatuur stremming. ProteYen inhoud het betekenisvol meer toegeneem onder die Jae temperatuur as hoe temperatuur stremming. Alie cuJtivars behaJwe PAN 3349 het meer proteYen onder die lae temperatuur behandeJing gehad, maar 'n paar cultivars het hoe temperatuur sensitiwiteit getoon deur nie hulJe protelen inhoud te verhoog nie. Veranderings is ook in die vJak van kooJhidate gesien. Daar was 'n betekenisvolle toename in gJukose en sukrose inhoud in sekere cuJtivars. Die sukrose inhoud het ook betekenisvol meer as die glukose inhoud gestyg. Nie alle cultivars wat verhoogde sukrose inhoud getoon het, het ook verhoogde gJukose inhoud getoon nie. Verskillende evaluasie metodes is vergelyk vtr hulle vermoe om stremmings toleransie te meet. Resultate van die selmembraan stabiliteits toets in hierdie studie was onbevredigend en het vrae Jaat ontstaan oor die betroubaarheid en effektiwiteit van hierdie toets as'n meting van hitte stremming. Nog 'n toets wat gebruik is, is die TIC metode wat goeie en betroubare resultate gelewer het. Die toets het gewys dat daar verskillende vlakke van hitte toleransie in Suid Afrikaanse cultivars bestaan. Sommige cultivars was hitte tolerant omdat hulle hoe TTC reduksie het onder stremming gehad, terwyl antler cultivars sensitief was met Jae TTC reduksie. Ander cultivars het stremming vermy deur toleransie vir kart tye te toon. 'n Kroon oorlewings studie is ook gedoen en blaar lengte en persentasie oorlewing is gebruik om koue toleransie te meet. Daar was 'n hoe persentasie koue toleransie in die cultivars, aangesien hulle oorleef het en nuwe blare na koue behandeling gevorm het. Die cultivars in die studie kon as tolerant, intermedier en sensitief groepeer word. In hierdie studie was hierdie metodes betroubaar en kan gebruik word om koue toleransie te evalueer. Die gebruik van prolien inhoud as 'n indikasie van stremmings toleransie is lank reeds gevestig en steeds in gebruik. Die effek van hoe- en Jae temperatuur stremming is geevalueer om te bepaal of prolien as 'n metode om toleransie te toets gebruik kan word. Resultate het 'n toename in prolien inhoud gewys na temperatuur stremming in vergelyking met 'n kontrole behandeling. Sommige cultivars het 'n toename in prolien inhoud na hoe- en Jae temperatuur stremming getoon, terwyl antler verhoogde prolien inhoud vir of hoe- of Jae tempratuur stremming gehad het. Prolien inhoud kan as 'n evaluasie metode vir toleransie gebruik word, maar dit moet Jiewer saam met antler metodes soos die TTC gebruik word.