engleski

Gene mapping and QTL analysis in faba bean (Vicia faba L.)

The development of saturated linkage map in any species has become widely recognized as an essential tool for efficient quantitative trait loci (QTL) mapping and marker-assisted selection (MAS). In faba bean (Vicia faba L.), the use of a recurrent parent (Vf6) allowed the development of the composite map by joining data from different segregating progenies. Moreover, some linkage groups were assigned to their respective chromosomes by means of trisomic stocks. A skeletal map with uniform distribution of markers has been extracted from the composite map and applied to detect loci underlying quantitative traits as resistance to broomrape (Orobanche crenata) and Ascochyta fabae. The molecular analyses were carried out in 9 F2 families derived from trisomic plants and in 2 F2 disomic populations. In all the crosses the same line (Vf6) was used as a female parent, while 6 different lines were used as pollen donors. Vf6 was an asynaptic line and it was used as a source of trisomy (1, 2). Morphological markers (3), isozymes (2, 4), RAPDs (5), seed-protein genes (6, 7), and physically located SSRs (8) were surveyed in the parental lines involved in the crosses. The F2 progeny derived from the Vf6 x Vf136 cross was used in QTL analysis of broomrape (Orobanche crenata) and Ascochyta fabae resistance. The maternal parent, Vf6, was highly susceptible to O. crenata while having a fair level of resistance to A. fabae infection. In order to maximize genetic variation of the resistance traits in F2 generation, the line Vf136 was chosen showing the opposite resistance scores form Vf6. A set of 196 F2-derived F3 lines was grown in a field plot heavily infested with O. crenata seeds. Broomrape resistance was scored as the number of broomrapes per plant and the resistance index was constructed (9). Yet another set of 196 F3 lines was grown in a growth chamber. The seedlings were inoculated by spraying a suspension of A. fabae spores. Disease resistance was scored by a visual scale that considered the percentage of symptomatic area of the whole plant (10). The composite map incorporates morphological marker, isozyme, RAPD, seed protein genes and SSR data from 11 F2 families (2, 3, 4, 5, 7, 9, 10) for a total of 654 individuals all sharing the common parent Vf 6. The integrated map is arranged in 14 major linkage groups (LGs), five of which were assigned to specific chromosomes. The LGs include 192 loci and cover 1559 cM with an overall average marker interval of 8 cM. The Vf 6 x Vf 136 cross data yielded a map consisting of 121 markers arranged into 16 LGs, nine of which were assigned to specific chromosomes. Broomrape resistance QTLs, Oc1, Oc2, and Oc3, were identified on chromosome 1 and 6, and on unassigned LG XI, respectively, and jointly explained 74 % of the total phenotypic variance. Two A. fabae resistance QTLs, Af1 and Af2, were identified on chromosome 3 and 2, respectively, and jointly accounted for 46 % of the total phenotypic variance. In all the cases the resistance-enhancing alleles originated from the resistant parent. Since V. faba possesses one of the largest genomes among legumes (cca. 12.000 Mb), the map useful for MAS requires further saturation. Thus, future research goals include the extension of the genome coverage to attach all currently unassigned markers. Detected QTLs will be tested in different genetic backgrounds and in multiple environments. F2 populations segregating for broomrape and A. fabae derived from different crosses have been developed and surveyed. The F2 populations have been selfed to obtain recombinant inbred lines (RILs).

Vicia faba; composite map; QTL; Orobanche crenata; Ascochyta fabae

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