Browsing by Author "Mphahlele, Lebogang Ivonne"
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- ItemGenetic control of Fusarium circinatum tolerance in Pinus patula x P. tecunumanii hybrid families(Stellenbosch : Stellenbosch University, 2020-04) Mphahlele, Lebogang Ivonne; Ham, Hannel; Nel, Andre; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.ENGLISH ABSTRACT: This study concentrated on the genetic control of Fusarium circinatum in Pinus patula × P. tecunumannii high elevation (HE) and P. patula × P. tecunumannii low elevation (LE) hybrid families. A greenhouse method of artificial inoculation screening was employed. The genetic material used included 37 P. patula × P. tecunumanni LE and 32 P. patula × P. tecunumannii HE hybrid families together with their parental families of two P. patula, four P. tecunumannii LE, five P. tecunumannii HE and four P. taeda. Greenhouse screening were performed with the inoculation of three cultures simultaneously onto the abscission growth tip of seedlings. After eight weeks, plant height and lesion length were measured to calculate stem-kill percentage as an indicator of F. circinatum tolerance. The smaller the stem-kill percentage, the higher the F. circinatum tolerance. A strong positive correlation (93.6%) was observed between stem-kill percentage and lesion length, while a weak negative correlation (40.6%) was observed between stem-kill percentage and plant length. Genetic parameters such as narrow sense heritability (h2), general combining ability (GCA) and specific combining ability (SCA) was employed to determine which parental family contributed the most to F. circinatum tolerance. Analyses were conducted on two categories. The first one combined both hybrid families (combined dataset for PPTH and PPTL) and the second one separated hybrid families (PPTH separated from PPTL). The assumption was PPTL might mask PPTH hybrid families. Least square means were also calculated to rank hybrid families and species in terms of F. circinatum tolerance. Significant differences (p < 0.0001) were obtained for hybrid families and species tested for all genetic parameters tested. Variance components estimates indicated that the male variance components (o2m)of P. tecunumanii HE and P. tecunumanii LE contributed more to F. circinatum tolerance with a gene frequency of 4.30%, while the female variance components (o2f) indicated that P. patula, as female parent, contributed less with a 1.60% gene frequency. Obtained narrow sense heritability h2 also indicated that h2 male had a strong genetic control for both male parents, while the h2 female indicated a low genetic control. This was confirmed with the GCA obtained by most of the male and female parents. The parental family (TL2) from P. tecunumanii LE population had a negative and low GCA (-11.42), indicating more genetic effect contribution to P. patula and thus, a high level of F. circinatum tolerance. Hybrid family P5 × TL1 achieved a low and negative SCA (-20.02), indicating a high level of tolerance thus, additive and non-additive interaction between genes influenced the phenotype of hybrids. As a novelty, this study’s results were compared to the frost tolerance of the same genetic material of a previous study by Malinga (2019). Although a negative correlation in general was observed between frost and F. circinatum tolerance, two hybrid families indicated stronger F. circinatum and frost tolerance. Therefore, breeders should consider crossing P. patula with P. tecunumanii (LE and HE) families screened in this study based on the GCA and SCA values obtained. However, the combination of frost and F. circinatum resistant commercial hybrids might be more difficult to obtain.