Resistance to downy mildew among sunflower gerplasm.

The increase in the use of zero tillage and the early planting under cooler and wetter conditions favor the environment to downy mildew (caused by Plasmopara halstedii), one of the most destructive fungal disease on sunflower. Some resistant cultivars are available in Argentina, however, the development of new sources of resistance would reduce the crop vulnerability to fungal racial variation. The goal of this study was to detect new sources of resistance to downy mildew among the sunflower germplasm available at INTA Pergamino, involving local and exotic materials. The reaction of 1062 entries of sunflower germplasm of Pergamino Agricultural Experimental Station to downy mildew was evaluated under laboratory conditions at INTA Pergamino from 2001 until 2008, using local isolation (predominant race 770) by Gulya et al. (1991) method. Only 1.7% of the total evaluated lines were resistant to downy mildew. In the Exotic group, 1.99% of lines were resistant, in Local group, 0.34% and the Local × Exotic group, 2.29%. The resistance in the Exotic group came from HA 335/HA 412 (resistant 700, 730 and 770 Plasmopara halstedii races) and ND (North Dakota IMI resistant); in the local group came from P1(INTA Pergamino); and in the Local × Exotic group came from EstanzuelaxMP557/ NegroBellocq/KLM/HA300; HA 341/PEREDOVIK/P1 and P1/KLM/HA 300. It is a good screening for INTA lines to identify new sources of resistance to race 770 of Plasmopara halstedii. The selection on Local × Exotic group is the best option to obtain resistant lines. The number of selections of Estanzuela x MP 557/Negro Bellocq/KLM/HA 300 would have to be increased, for its good performance and different origin. The results are very useful for INTA breeding program. It will be continued with studies to identify the genes involved in the new source of resistance. The detection of the new sources of resistance would allow incorporating the character into hybrids, reducing the vulnerability of the sunflower crop to the disease.