QTL mapping of partial resistance to Phoma basal stem and root necrosis in sunflower (Helianthus annuus L.)

Phoma macdonaldii infects different tissues of sunflower and causes reduction in yield and oil content. The aim of present research was to identify genomic regions involved in partial resistance of sunflower to four Phoma macdonaldii basal stem and root necrosis isolates using our improved map constructed with 191 SSR and 304 AFLP markers. The experiment was conducted using F9 recombinant inbred lines (RILs) from a cross between 'PAC2' and 'RHA266'. Results showed that 'PAC2' was more resistant than `RHA266' to basal stem necrosis isolate `TA6' and root necrosis isolate 'TA4'. By contrast 'RHA266' was more resistant than 'PAC2' to basal stem necrosis isolate `TA9' and root necrosis isolate 'TA2'. Transgressive segregation was observed for partial resistance to all four isolates. Some recombinant lines presented partial resistance or susceptibility to all isolates. Twenty-seven QTL with phenotypic variance ranging from 7 to 29% were detected. Among them 13 were 'isolate-specific' and others were common for partial resistance to different isolates (isolate-non-specific). Most of the QTLs in common have major effects for resistance to each isolate. The 'isolate-non-specific' QTLs were located on linkage groups (LG) 5, 6, 8, 12, 13 and 15. The markers 'HA3555' on LG12 and 'E33M48_26' on LG6 as well as 'E33M48_20' on LG13, which are each linked to QTLs of different basal stem and root necrosis isolates, could be used in marker-assisted selection to introduce tolerance to four Phoma macdonaldii isolates into elite sunflower breeding lines. (c) 2006 Elsevier Ireland Ltd. All rights reserved.