The use of amplified fragment length polymorphism (AFLP) and morphological data to determine heterotic groups in sunflower (Helianthus annuus)

English: Breeders would like to predict the outcome of crosses, before producing and testing lines derived from them in field trials. One way to ensure this is by finding a correlation between the genetic distances of inbreds and the amount of heterosis obtained by such a hybrid. The aim of this study was to determine the genetic distances between 12 sunflower inbred lines with the use of the AFLP technique and to correlate these results with the amount of heterosis obtained in F1-hybrids. Twelve inbred lines, consisting of six females (lines) and six males (testers), was planted in a glasshouse at the University of the Free State (UFS) in Bloemfontein, South Africa. Two experiments were done on these parental lines. Young leaves were collected from each line. DNA was extracted from the leaves and AFLP analysis was performed on the DNA. Six different primer combinations were used, namely: Mse-Cn + Eco-ACA; Mse-CAG + Eco- ACA; Mse-CTC + Eco-ACA; Mse-Cn + Eco-AAC; Mse-CAG + Eco-AAC and Mse-CTC + Eco-AAC. The objective was to determine the genetic distances of the 12 lines with the use of the AFLP technique and different primer combinations. These results would then be used to identify heterotic groups in a hybrid breeding program. The genetic similarities were lower overall for CMS (A) x restorer (R) crosses than for AxA or RxR. This was confirmed by Hongtrakul et a/ (1997). Msecn + Eco-ACA, Mse-CAG + Eco-ACA and Mse-CTC + Eco-AAC identified the highest amount of dissimilarity between female lines 1A and 4A. The highest amount of dissimilarity between male lines 14R and 16R were identified by Mse-CTC + Eeo-ACA and Mse-CTC + Ecc-AAC. According to Hongtrakul et al (1997), the cluster analysis separated lines into two groups, one for A-lines (females) and another for R-lines (males). This was also found in this study. These groupings illustrate the breeding history and basic heterotic pattern of sunflower. In the second experiment, all six testers were individually crossed with each line to produce F1 hybrid seed. Thirty six crosses were made and sufficient seed was generated, except from the cross between parental lines 4A and 16R that resulted in a sterile hybrid with no seed. Therefore, 4Ax16R was replaced with a standard, HV3037. The 36 F1 hybrids were planted according to a randomized complete block design with three replications. The plant height, flowering date, head diameter, 1000-seed weight, yield and oil percentage of each hybrid was determined with the Line x Tester analysis. The aim was to determine the combining ability of the inbred lines, to determine if there are genetic correlations between the different characteristics and to determine the expression of heterosis for the different characteristics. Hybrid 6Ax13R had the latest flowering date and the highest yield. The F1 hybrid that had the highest head diameter and highest oil percentage was 1Ax12R. Some crosses performed equally or better than their best parents indicating the presence of heterotic effects. If yield is the most important selection criteria, the hybrid 6Ax13R would perform the best in a breeding . program as it ranked the highest. Line 1A could be used to improve head diameter, 1000-seed weight, yield and oil percentage, as it had the highest or second highest GCA effects for these characteristics. The tester 13R could also be used to increase plantheight and yield. To increase flowering date and 1000-seedweight, one can use 16R. F1 hybrid 3Ax15R was the only hybrid that had positive SCA effects for all the characteristics measured. The hybrid 4Ax14R was the best specific combiner for 1000-seed weight and yield, while 1Ax11R had the highest positive effects for oil percentage. According to the GCA:SCA ratio the SCA was greater, indicating non-additive gene action. This was found in the studies of Merinkovic (1993) who concluded that non-additive gene effects controlled yield. Putt (1966) also found that non-additive gene effects controlled the inheritance of flowering date, head diameter and 1000-seed weight. Correlations of interest were that when selecting for increased plant height one would increase the head diameter, 1000-seed weight and yield, but it would however, result in a decrease in the oil percentage. By increasing the flowering date, one would increase the oil percentage, but reduce the head diameter. Doddamani et al (1997) also found that head diameter, 1000-seed weight and plant height had a significant positive correlation with yield. They also found that flowering date had a negative correlation with yield. The results of this study thus confirm their results. Flowering date had the highest broad-sense heritability, followed by 1000- seed weight and plant height. Oil percentage had the highest narrow-sense heritability, followed by 1000-seed weight and flowering date. The hybrid with the highest MP and HP heterosis for yield was 6Ax13R. Hybrid 1Ax12R had the highest MP heterosis while 5Ax12R the highest HP heterosis for oil percentage. The three hybrids that expressed the highest heterosis overall, were 1Ax12R, 1Ax13R and 6Ax13R. Seetharam et al (1977) observed a significant positive heterosis for flowering date, plant height, head diameter, oil percentage and yield. According to Schuster (1964), heterosis for yield for the hybrids was up to 70% better than that of the parents. Half the hybrids showed heterosis for plant height (47% better) and heterosis for head diameter was 60%. Popov and Lazarov (1963) as well as Shuravina (1972) found that only a few hybrids exceeded the parents for oil percentage (heterosis of 4.8%). Above is all similar to the results found in this study. Correlations between genetic distance, heterosis, and hybrid performance for yield in sunflower were estimated. Genetic distances from AFLP fingerprints were correlated with the amount of heterosis found in F1 hybrids. Mse-CTT + Eco-ACA had the highest correlation with the amount of heterosis in the F1 generation. It can therefore be recommended that this primer combination can be used to identify heterosis for flowering date, head diameter, yield and oil percentage in hybrids. Therefore, it is possible to correlate the genetic distances found with AFLP data with the amount of heterosis that can be expected in F1 hybrids. This makes it possible to screen thousands of inbred lines and shorten the hybrid breeding program. The number of crosses, trails and amount of labor will decrease and will result in a lower farm price for hybrid seeds.