Breeding of sunflower lines for resistance downy mildew in the setting of changing pathogenic races

Abstract

The aim and tasks of the study. The main objective of this study was to select starting material resistant to downy mildew pathogen for use in breeding programs. Phytosanitary monitoring of crop conditions for pathogen and races was concurrently performed.

Materials and methods. Resistance of sunflower lines – pollen fertility restorers to downy mildew pathogen was evaluated in the phase of calathidium formation. Resistance of sunflower accessions to disease was determined by the prevalence of disease. In winter, resistance of accessions to pathogen was evaluated by a rapid method. Plasmopara helianthi races were identified with a triplet set of lines-differentiators. In addition to resistance, we determined ripeness group, plant height and branching type. Variance and correlation analyses were used for statistical processing of experimental data.

Results and discussion. Maximum and average values of the disease prevalence fluctuated in the Eastern Forest-Steppe of Ukraine in 2007-2016 (at the maximum 17.5-100% of plants were affected). During half of the study years, the damage level was 1.4-3.3%. High prevalence (11.3-30.7%) was recorded during 3 years (2010, 2014 and 2016.) with excessive precipitation related to the multiyear average (by 14.0-42.4 mm). This is confirmed by close relationship between the average (r = 0.93) and maximum (r = 0.74) values of the disease prevalence and the precipitation amount. Negative correlation was found between these parameters and the average monthly temperature (r = -0.55).

Race 330 was the most common until 2006. Since 2010, race 730 has taken a dominant position. In the setting of a prolonged excessively wet spring of 2016, race 732 was identified by response of lines -differentiators to pathogen. The spread pattern of race 730 predicts a probable spread of race 732 for 2017, provided favorable the for pathogen development conditions.

Comparing the results of evaluation of sunflower breeding accessions for resistance to downy mildew pathogen in laboratory and field conditions, we identified 33 lines with resistance to 3 races of pathogen - 330, 730 and 732. Most of these sunflower lines - pollen fertility restorers (23) are mid-early; four lines are short-season; and six are early-ripening. They are characterized by various types of branching and plant height.

Conclusions. The efficacy of combination of assessment of starting material for resistance to downy mildew in the field conditions in years with wide prevalence and large-scale affection of plants with continuous annual evaluation of breeding material for virulent races in winter in the laboratory conditions was proved. We selected 33 sunflower lines-pollen fertility restorers belonging to different groups of ripeness, which are resistant to 3 races (330, 730 and 732) of downy mildew pathogen and are a basis for new resistant hybrids.