Prediction of heterotic groups and hybrid performance in South African sunflower (Helianthus annuus L.) germplasm using SSR analysis

Abstract

English: Breeders would prefer to be able to predict the outcome of crosses prior to the production and testing of lines derived from them in field trials. One way to do this would be to find a correlation between the genetic distances of inbreds and relative yield obtained from the hybrids. The aim of this study was to determine whether the SSR based dendrogram can be of value as a predictor for the best performing combinations between A- and R-lines in the context of South African germplasm as well to determine whether correlations existed between oil content and relative yield and genetic distance and oil content. The study analysed 93 inbred lines, consisting of 49 R-, 40 A- and four B-lines which were planted in a glasshouse at Greytown, KwaZulu-Natal (South Africa). Two experiments were performed on the sets of lines, namely SSR analysis to establish genetic distance and a dendrogram and the second was to establish yield trials with a subset of the lines. A dendrogram was constructed using 55 SSR markers widely distributed over the entire sunflower genome. The objective was to establish genetic distances of the lines involved in order to determine heterotic groups in the hybrid breeding programme. SSR cluster analysis separated lines into two main groups, one included A- and B-lines (females) and the other R-lines (males). The groupings represented the breeding history and basic heterotic pattern of sunflower. Genetic similarities were lower overall for female (A) line x restorer (R) line crosses than for A x A or R x R. The highest level of dissimilarity was found between A9 and A40 and the second highest between A23 and R8. The lowest level of dissimilarity was found between R14 and R41 and the second lowest between R42(HO) and R43(HO). The second experiment included crossing of 33 A-lines to 11 R-lines to produce FI hybrid seed. However, not all crosses were successful. The successful hybrids were planted as lattice designs in a total of 133 trials on six locations. The yield of the hybrids was calculated and expressed relative to the yield of the commercial hybrid PAN 7351 which was included in all trials. Relative yield and oil percentage was calculated. The line x tester analysis was used to determine the combining ability of the inbred lines and to determine if there existed correlations between genetic distance and relative yield, between genetic distance and oil percentage and between relative yield and. oil percentage. The highest yielding combination was A25/R34. Low to no correlations were found between genetic distance and relative yield, between genetic distance and oil percentage and between relative yield and oil percentage. Exceptions were significant correlations found between relative yield and oil percentage for the A-lines crossed to R32, for genetic distance versus relative yield and for relative yield versus oil percentage for the A-lines crossed to R48 and for relative yield versus oil content for the A-lines crossed to R44(RM). The female line A16 exhibited high oil content in most of the combinations it was involved in. The average genetic distance for the lines involved in the yield trials was 0.24. This indicated low differences between the lines used and a possible reason for the low correlations found between combinations. Differences were found in GCA effects with A34 being the best general combiner for relative yield. The combinations A6/R34 and A25/R34 were the combinations with the best SCA effects for relative yield. According to the GCA:SCA ratio the SCA was greater which indicated non-additive gene action. Narrow-sense heritability was found to be 52.98% for relative yield. This was caused by equal parts additive effects and dominant gene actions.

Afrikaans: Telers verkies om in staat te wees om die uitkoms van kruisings te voorspel voordat die toetsing en produksie van basters in die veld plaasvind. Een manier om dit te bewerkstellig is om 'n korrelasie tussen genetiese afstande van ingeteelde lyne en opbrengs van basters verkry vanuit die lyne, te bepaal. Die doel van die studie was om te bepaal of 'n mikrosatelliet gebaseerde dendrogram effektief gebruik kan word om die beste presterende kombinasies tussen A- en R-Iyne binne die konteks van Suid-Afrikaanse kiemplasma te voorspel, asook om te bepaal of daar 'n korrelasie bestaan tussen oliepersentasie en relatiewe opbrengs asook tussen genetiese afstand en oliepersentasie. Die studie het 93 ingeteelde lyne ingesluit, wat bestaan het uit 49 R-, 40 A- en vier B-Iyne wat in 'n glashuis in Greytown, Kwazulu-Natal (Suid-Afrika) geplant is. Twee eksperimente is op die stel lyne uitgevoer, naamlik mikrosatelliet analises om genetiese afstand te bepaal en 'n dendrogram op te stel en tweedens is 'n subset van hierdie lyne gebruik om opbrengsproewe te doen. 'n Dendrogram is opgestel deur 55 mikrosatelliet merkers wat oor die hele genoom versprei is, te gebruik. Die doel was om genetiese afstande van die lyne te bepaal met die oog om heterotiese groepe in die baster teelprogram te bepaal. Mikrosatelliet analises het die lyne in twee hoofgroepe verdeel, met een groep wat die A- en B-Iyne (wyfies) bevat het en die ander die R-Iyne (mannetjies). Hierdie groeperings dui die telingsgeskiedenis asook die basiese heterotiese tendense van sonneblom aan. Genetiese ooreenkomste was oor die algemeen laer vir wyfie (A) lyn x hersteller (R) lyn kruisings as in die geval van A x A of R x R. Die kleinste ooreenkomste is tussen A9 en A40 gevind en die tweede kleinste tussen A23 en R8. Die grootste ooreenkomste is tussen R14 en R41 gevind en die tweede grootste tussen R42(HO) en R43(HO). In die tweede eksperiment is 33 A-lyne met 11 R-Iyne gekruis om F I_bastersaad te produseer. Nie al die kruisings het egter gerealiseer nie. Die suksesvolle basters is in 'n rooster ontwerp in 133 proewe oor ses lokaliteite geplant. Die opbrengs van die basters is bereken en relatief tot die opbrengs van die kommersiële baster PAN 7351, wat in al die proewe ingesluit is, uitgedruk. Relatiewe opbrengs asook oliepersentasie is bereken. Die lyn x toetser analise is gebruik om kombineervermoë van die ingeteelde lyne te bereken en om vas te stelof daar korrelasies tussen genetiese afstand en relatiewe opbrengs bestaan, tussen genetiese afstand en oliepersentasie asook tussen relatiewe opbrengs en oliepersentasie.Die kombinasie met die beste opbrengs was A25/R34. Lae tot geen korrelasies is tussen genetiese afstand en relatiewe opbrengs, tussen genetiese afstand en oliepersentasie en tussen relatiewe opbrengs en oliepersentasie gevind. Uitsonderings was betekenisvolle korrelasies wat vir genetiese afstand teenoor oliepersentasie vir die A-lyne gekruis met R32 gevind is asook tussen genetiese afstand en relatiewe opbrengs en vir relatiewe opbrengs teenoor olie persentasie vir die Alyne gekruis met R48. Betekenisvolle korrelasies is vir relatiewe opbrengs teenoor olieopbrengs vir die lyne gekruis met R44(RM) gevind. Die wyfielyn Al6 het hoë olieinhoud getoon in kombinasie met die Rvlyne wat gebruik is. Die gemiddelde genetiese afstand van die lyne wat ingesluit is in die opbrengsproewe was 0.24. Die waarde dui op kleiner verskille tussen die lyne en is 'n moontlike rede vir die lae korrelasies tussen die kombinasies. Verskille is vir die GCA effekte met A34 gevind wat die beste algemene kombineerder vir relatiewe opbrengs was. Die kombinasies A6/R34 en A25/R34 was die kombinasies met die beste SCA effekte vir relatiewe opbrengs. Indien die GCA:SCA verhouding in ag geneem word, was SCA groter wat op nie-additiewe geenaksie dui. Nou-oorerfbaarheid is bereken as 52.98% vir relatiewe opbrengs. Dit word deur gelyke dele additiewe effekte en dominante geenaksies veroorsaak.