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.