Genetic control of frost tolerance in Pinus patula × Pinus tecunumanii (LE and HE) hybrid families

Malinga, Sithembile (2018-03)

Thesis (MScFor)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: In vitro artificial freeze testing procedures were used to investigate the frost tolerance and genetic control in some Pinus pure species and hybrids at three target temperatures (-3, -6 and -9°C). Genetic parameters such as heritability (h2), general hybridising ability (GHA), and specific hybridising ability (SHA) were determined and compared. Hybrid families were ranked for frost tolerance based on least square means. The electrolyte leakage (EL) and whole plant freeze testing (WPFT) were employed to screen unrooted shoots, and rooted cuttings (8- month old). Comparisons were drawn between field (in vivo) and laboratory (in vitro) results for frost tolerance, as well as between EL and WPFT screening methods. Needles of thirty-two interspecific hybrids families of P. patula × P. tecunumanii were screened as unrooted shoots and 8-month old rooted cuttings with the EL method at -3, -6 and -9°C. The same thirty-two families as 8-months old rooted cuttings were screened with the WPFT at -3, -6 and -9°C. An extra 38 families of P. patula × P. tecunumanii, 19 P. taeda × P. tecunumanii, two P. patula var. patula female parents and nine P. tecunumani as male parent were screened with the EL method at -6°C only. Field trials of the 32 families of P. patula × P. tecunumanii were also planted at three frost-prones sites in KwaZulu Natal and Mpumalanga. EL and WPFT screening were done by keeping samples at 4°C for three hours, an hour at 0°C, followed by six hours at target temperature. This was followed with one hour at 0°C and three hours at 4°C, after which they are put in the shaker for 16 hours. After the shaker the first electrical conductivity (EC) was measured before samples were placed in an oven for two hours at 85°C to kill plant tissues. The second EC was measured after another 16 hours in the shaker. Based on estimates of variance components, the male parent (P. tecunumanii) (Vdad between 29.0 and 149.5 for unrooted shoots, between 63.6 and 126.4 for rooted cuttings) contributed the most to the frost tolerance in the hybrids, while the P. patula (female) (Vmom between 0.41 and 22.6 for unrooted shoots, between 9.5 and 12.5 for rooted cuttings) contributed very little. Frost tolerance proved to be under moderate to strong genetic control in P. tecunumanii with higher genetic variation that is heritable (h2 between 0.34 and 1.26 for unrooted shoots, between 1.08 and 1.72) than P. patula (h2 between 0.0005 and 0.19 for unrooted shoots, between 0.13 and 0.20 for rooted cuttings). The negative GHAs of P. tecunumanii further confirmed this. All the P. tecunumanii high elevation (HE) parents had negative GHAs at -3 and 6°C indicating that it contributes more to the hybrids than P. tecunumanii low elevation (LE) by reducing the overall mean and thus adding to frost tolerance. The family P4×TH3 had the lowest injury index when screened as unrooted shoots and rooted cuttings. Therefore, it was frost tolerant at both -3 and -6°C. Similar trends were observed for ranking of families when using EL for both unrooted shoots and rooted cuttings. Moderate positive correlations between EL and WPFT indicated that both EL and WPFT are reliable artificial freeze testing methods that can be used to determine frost tolerance on juvenile and mature plant tissues. Furthermore, correlations strongly suggested that the Munsell colour chart has potential as an injury scoring tool. Results from in vivo planted trials were unfortunately not obtained due to relatively mild winter temperatures experienced in 2017. Even though mild frost occurred on the trial sites there was no visible damage, but the monitored field-trial temperatures still proved invaluable to this study and its conclusions and recommendations. In future studies it is still important to answer the question of correlation between artificial seedling screening and in-field frost screening.

AFRIKAANSE OPSOMMING: In vitro kunsmatige vriestoets prosedures word gebruik om ryp verdraagsaamheid en die genetiese beheer daarvan in sommige Pinus spesies en hibriede by drie teiken temperature (-3, -6 and -9°C) te ondersoek. Genetiese grense soos oorerflikheid (h2), algemene hibridisaie vermoë (GHA), en spesifieke hibridisasie vermoë (SHA) was bepaal en vergelykings tussen spesies en hibriede getref. Hibried gesinne was ingedeel volgens ryp verdraagsaamheid wat gebaseer was op die gemiddeldes. Die elektroliet loging (EL) en heelplant vriestoets (WPFT) was gebruik om wortelose lote en bewortelde steggies (8-maande oud) te ondersoek. Vergelykings was getref tussen die veld (in vivo) en laboratorium (in vitro) rypskade, asook die EL en WPFT ondersoek metodes. Twee en dertig interspesifieke gesinne van P. patula × P. tecunumanii se naalde van onbewortelde lote en 8-maand oue steggies was ondersoek met behulp van die EL metode by -3, -6 en -9°C. Dieselfde 32 gesinne was ook getoets met die WPFT metode met 8-maand oue steggies by -3, -6 and -9°C. ‘n Verdere 38 gesinne van P. patula × P. tecunumanii, 19 P.taeda × P. tecunumanii, twee P. patula var. patula as vroulike ouer en nege P. tecunumani as manlike ouer, was getoets met die EL metode by slegs -6°C. Veldproewe van die 32 gesinne van P. patula × P. tecunumanii was ook aangeplant by drie veskillende rypvrye groeiplekke in KwaZulu Natal en Mpumalanga. EL en WPFT toetse was gedoen deur die naalde by 4°C vir drie ure te verkoel, gevolg deur ‘n uur by 0°C, en dan ses ure by die teiken temperatuur. Hierna is die naalde weer vir een uur geplaas by 0°C en drie ure by 4°C waarna dit in ‘n skudmasjien geplaas is vir 16 ure. Die eerste elektriese geleiding (EC) is dan gemeet waarna die naalde in ‘n oond by 85°C vir twee ure gesit is om die plant weefsel te vernietig. Die tweede EC is gemeet na ‘n volgende sarsie van 16 ure in die skudmasjien. Gebasseer op beramings van die variasie komponente, het die manlike ouer (P. tecunumanii) (Vpa tussen 29.0 en 149.5 vir onbewortelde lote, tussen 63.6 en 126.4 vir bewortelde steggies) die meeste bygedra tot ryp verdraagsaamheid in die hibriede. Pinus patula (vroulike ouer) (Vma tussen 0.41 en 22.6 vir onbewortelde lote, tussen 9.5 en 12.5 vir bewortelde steggies) het min bygedra tot ryp verdraagsaamheid. In P. tecunumanii was ryp verdraagsaamheid onder matige tot sterk genetiese beheer met ‘n hoër geneties variasie (h2 tussen 0.34 en 1.26 vir onbewortelde lote, tussen 1.08 en 1.72) in vergeleke met P. patula (h2 tussen 0.0005 en 0.19 vir onbewortelde lote, tussen 0.13 en 0.20 vir bewortelde steggies). Negatiewe GHAs van P. tecunumanii HE en LE het dit ook bevestig. Al die P. tecunumanii hoë opstand (HE) ouers het ‘n negatiewe GHA by -3 en 6°C gehad wat aangedui het dat dit meer bygedra het tot die hibriede as P. tecunumanii lae opstand (LE) omdat die algemene gemiddelde verlaag is en dus bydra tot ryp verdraagsaamheid. Die gesin P4×TH3 het die laagste beserings indeks gehad wanneer onbewortelde lote en bewortelde steggies getoets was. Daarom was dit ryp verdraagsaam by beide -3 en -6°C. Soortgelyke tendense was waargeneem met die rangorde van gesinne vir die EL metode vir beide onbewortelde lote en bewortelde steggies. ‘n Matige positiewe korrelasie was bereken tussen die EL en WPFT metodes. Die twee metodes is dus betroubare kunsmatige vriestoetse wat kan help om ryp verdraagsaamheid in jong en meer volwasse plant weefsel te bepaal. Verder het ‘n korrelasie tussen die Munsell kleurkaart en visuele waarnemings potentiaal getoon as ‘n beseringsindeks waarnemingsmetode. Veldproewe het egter geen resultate opgelewer nie weens matige winter temperature gedurende die winter van 2017. Alhoewel matige ryp wel voorgekom het, was geen plantweefsel skade sigbaar nie. Toekomstige studies sal egter die korrelasie tussen kunsmatige saailing toetse en veldproewe verder moet ondersoek aangesien dit ‘n waardevolle metode is om jong saailinge se ryp verdraagsaamheid te toets.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103903
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