OCL 2021, 28, 58AgronomyDOI: 10.1051/ocl/2021047© S. Gontcharov and N. Goloschapova, Published by EDP Sciences, 2021

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Research Article

Evaluation of horizontal resistance of sunflower (Helianthus annuus L.) to downy mildew (Plasmopara halstedii)☆

Évaluation de la résistance horizontale du tournesol (Helianthus annuus L.) au mildiou (Plasmopara halstedii)

Sergey Gontcharov¹* orcid and Natalya Goloschapova²

¹ Kuban State Agrarian University, Department of Genetics, Plant Breeding and Seed Production, Kalinina, 13, Krasnodar 350044, Russia
² V.S. Pustovoit All-Russian Research Institute of Oil Crops (VNIIMK), Department of Hybrid Sunflower Breeding, Filatova, 17, Krasnodar 350038, Russia

* Correspondence: serggontchar@hotmail.com

Received: 15 September 2021 Accepted: 18 November 2021 Published online: 23 December 2021

Abstract

Downy mildew is one of the most important diseases of sunflower crop around the world caused by Plasmopara halstedii (Farl.) Berl.et de Toni. The aim of our study was to evaluate the horizontal resistance of elite and prospective lines to downy mildew in field conditions. Experiments were conducted at All-Russia Research Institute of Oil Crops (VNIIMK) in 2016–2020. Released and prospective sunflower lines bred at VNIIMK were studied, divided into four groups on the base of their race-specific resistance in laboratory tests. Experimental design was randomized blocks with two replications. Evaluation was made by recording all the recognizable symptoms of downy mildew from emergence till flowering. The results obtained allowed us to identify the lines with the highest race non-specific resistance to downy mildew: VK 678 (5.3%), VK 653 (7.3%), VA 760 (3.3%), VA 93 (2.0%) and VK 732 (6.3%). The final aim is the development of sunflower hybrids with the most durable resistance to downy mildew, combining one parental line with the major gene (Pl₁₅) most effective for the specific location and the second parental line with a high level of horizontal resistance to downy mildew.

Résumé

Le mildiou est l’une des maladies les plus importantes de la culture du tournesol dans le monde, causée par Plasmopara halstedii (Farl.) Berl.et de Toni. L’objectif de notre étude était d’évaluer la résistance horizontale au mildiou des lignées élites et prospectives dans des conditions de terrain. Les expériences ont été menées à l’Institut de recherche panrusse des oléagineux (VNIIMK) en 2016–2020. Des lignées de tournesol issues du programme de sélection du VNIIMK ont été étudiées, divisées en quatre groupes sur la base de leurs résistances race-spécifique déterminées par tests de laboratoire. Le plan expérimental était en blocs randomisés avec deux répétitions. L’évaluation a été faite en enregistrant tous les symptômes reconnaissables du mildiou, de la levée à la floraison. Les résultats obtenus nous ont permis d’identifier les lignées présentant la plus forte résistance horizontale (non spécifique d’une race du pathogène) au mildiou : VK 678 (5,3 %), VK 653 (7,3 %), VA 760 (3,3 %), VA 93 (2,0 %) et VK 732 (6,3 %). L’objectif final est le développement d’hybrides de tournesol présentant une résistance durable au mildiou, en combinant une lignée parentale avec un gène majeur de résistance (Pl₁₅) le plus efficace localement et une seconde lignée parentale dotée d’une résistance horizontale élevée au mildiou.

Key words: sunflower / line / resistance / downy mildew / breeding

Mots clés : tournesol / lignée / résistance / mildiou / sélection

☆

Contribution to the Topical Issue “Sunflower / Tournesol”.

1 Introduction

Downy mildew (DM) is one of the most important diseases of sunflower around the world caused by Plasmopara halstedii (Farl.) Berl. et de Toni (Novotelnova, 1962; Goossen and Sackston, 1968; Sackston, 1992; Gulya et al., 1997; Jocić et al., 2012). There are a few ways to control DM including agrotechnical, chemical, and breeding methods. Seed chemical treatment and cultivation of resistant sunflower hybrids to DM are the most effective control measures (Gulya et al., 1997; Vear et al., 1997). Breeding for resistance to DM usually concentrates on the search for and incorporation of major genes designated Pl into elite sunflower lines. Simple inheritance of DM genes was discovered rather early (Vranceanu and Stoenescu, 1970; Zimmer, 1974), with different race-specific single dominant resistance genes used worldwide by sunflower breeders (Vear et al., 2008a). This causes the DM pathogen to evolve new races (Ahmed et al., 2012). After race 100 and 300 appeared, then 710, 730, 304, 307, 314, 334, 704 and 714 evolved (Carson, 1981; Gulya et al., 1991b; Molinero-Ruiz et al., 1998, 2002; Tourvieille de Labrouhe et al., 2000; Gulya, 2007). Now 35 Pl genes have been discovered and incorporated into commercial sunflower hybrids (Tourvieille de Labrouhe et al., 2008; Qi et al., 2016, 2019; Trojanova et al., 2017).

Identification of races is based upon the reaction of the host (an internationally accepted set of differential lines) to the pathogen (Gulya et al., 1991a; Gulya, 1995; Tourvieille de Labrouhe et al., 2000, 2012). Molecular markers have been used in P. halstedii race differentiation (Roeckel-Drevet et al., 2003; Gascuel et al., 2015) and in sunflower maker assisted selection for resistance (Mulpuri et al., 2009).

Wild sunflower species are often used as a source of new DM resistance genes (Seiler, 1992; Vear, 2004, 2010; Vear et al., 2008a; Kaya et al., 2012).

Appearance of new races forces sunflower growers to use chemical control with seed-applied fungicides. Usually, seeds are treated by metalaxyl or mefenoxam (Melero-Vara et al., 1982; Albourie et al., 1998; Gulya, 2002; Molinero-Ruiz et al., 2005). However, in 1995 metalaxyl tolerant isolates were discovered (Molinero-Ruiz et al., 2005; Spring et al., 2006) and a little later – mefenoxam-tolerant isolates (Molinero-Ruiz et al., 2005).

Durable resistance could be achieved by combining race-specific (vertical) and non-race-specific (horizontal) resistance in a single hybrid (Tourvieille de Labrouhe et al., 2004; Vear, 2004; Vear et al., 2008b). To accomplish this, it is possible to use one parental line with the most effective major gene for the specific location and the second parental line with high horizontal resistance to DM.

The aim of this study was to evaluate the horizontal resistance of elite and prospective VNIIMK breeding lines to DM under field conditions.

2 Material and methods

The experiments were conducted at the Central Station of All-Russia Research Institute of Oil Crops (VNIIMK), Krasnodar, Russia in 2016–2020. The Krasnodar region is situated in the Southern part of Russia near the Black Sea. Climatic conditions are very favorable for sunflower production. Sunflower production usually covers about 0.5 million ha in this region. Downy mildew is one of the most dangerous pathogens for sunflower in the region. During the last decade, new races of DM (710, 730 and later 334) (Iwebor et al., 2016) appeared to become common and all the commercial VNIIMK hybrids (resistant to only race 330) became susceptible to DM (Gontcharov, 2014).

Released and prospective sunflower lines of the VNIIMK breeding program were used in the study and divided into four Groups based their race-specific resistance in laboratory tests. All lines used in the study are the property of the V.S. Pustovoit All-Russian Research Institute of Oil Crops (VNIIMK), and could be available through a specific agreement. The first Group includes 18 lines without any major genes for resistance to DM. The lines in this Group were highly susceptible to race 330 laboratory tests. The second Group included 17 lines resistant to the race 330, but susceptible to the race 710 and 730 consisted of 17 lines resistant to the mixture of races – 330, 710 and 730 (mainly with Pl₈). The fourth Group included five lines with Pl₁₅, resistant to all the downymildew races identified in the region up to 2016. All the pathogen samples used in the experiment were collected in the field of the Krasnodar region and identified as to race.

The experimental design was a randomized block with two replications. Each replication had two rows for each line with an area of 12.2 m². Seeds were not treated with any chemicals. Evaluation was made by recording all the visible symptoms of DM from emergence until flowering. Low air temperatures and an abundance of precipitation at emergence and early growth stages produced favorable conditions for the pathogen (Cohen and Sackston, 1973) in both 2016 and 2017. However, in 2018, 2019 and in 2020 they were unfavorable for DM with higher temperatures and low precipitation in the early growth stages.

3 Results

Many sunflower plants had DM symptoms in the field in 2016 and 2017. Favorable weather conditions stimulated the pathogen development. This allows for the identification of all the sunflower material with resistance to DM in the field without any artificial inoculation. Downy mildew infection was present in all Groups, except one, Group 4 (lines with Pl₁₅ gene) where there was no infection (Tab. 1).

Sunflower lines from Group 2 (resistant to the race 330) were damaged to a greater extent than those from Group 1. Therefore, this major gene for resistance to DM was no longer effective. Sunflower lines from the Groups 1 and 2 were analyzed together.

Sunflower lines from Group 3 (resistant to the most frequently appearing races) were damaged by DM to a lesser extent.

The situation in the following years (2018–2020) was quite different with DM rarely occurring, indicating a low infection pressure.

Sunflower lines included in Groups 3 and 4 have major gene(s) effectively protecting them from DM attacks. Lines from Groups 1 and 2 demonstrated rather high damage rate depending on year condition and their level of horizontal resistance (Tabs. 2 and 3).

The results allowed for the identification of lines with the highest nonspecific race resistance to DM: VK 678 (5.3%), VK 653 (7.3%), VA 760 (3.3%), VA 93 (2.0%) and VK 732 (6.3%). Presence of horizontal resistance can vary greatly depend on the quantity of available spores for infection and proper environmental conditions. Some lines were damaged up to 100%. It demonstrates that weather conditions were favorable for the pathogen development and a sufficient quantity spores were available in the field for infection.

Similar results were obtained for the Group 2. In general estimation of sunflower resistance was close to the previous Group (Tab. 3). Race 330 is no longer the predominant race so the major gene for resistance to DM is no longer effective.

Field evaluation from the favorable years (2016 and 2017) allowed for the differentiation of susceptible lines for horizontal (race-nonspecific) resistance to DM. Lines with the less than 10% of infected plants were considered to be resistant, with 10 to 40% of infected plants, mildly resistant, and with more than 40% of infected plants susceptible (Fig. 1).

Field evaluation made in the unfavorable years (2018 and 2019) for pathogen development were not useful since all lines showed resistance (Fig. 1).

The final aim of the study was the development of sunflower hybrids with durable resistance to DM, combining one parental line with the most effective major gene (Pl₁₅ for example) for the specific location and the second parental line with a high horizontal resistance to DM.

Table 1

Resistance of sunflower lines Groups to downy mildew (VNIIMK, Krasnodar, Russia).

Table 2

Evaluation of sunflower lines horizontal resistance to downy mildew (VNIIMK, Krasnodar, Russia).

Table 3

Evaluation of sunflower lines horizontal resistance to downy mildew (VNIIMK, Krasnodar, Russia).

thumbnail
Fig. 1

Differentiation of susceptible sunflower lines for horizontal (race nonspecific) resistance to downy mildew depending on the year. Green: Resistant, less than 10% of damaged plants; Yellow: Medium resistant, 10 to 40% of damaged plants; Red: Susceptible, more than 40% of damaged plants.

4 Discussion

Field evaluation during favorable years showed the presence of high genetic variability for horizontal resistance to DM in a set of sunflower inbred lines developed by VNIIMK. This has been shown in different materials reported by other researchers (Tourvieille de Labrouhe et al., 2008; Vear et al., 2008b; Ahmed et al., 2012; Gontcharov, 2014).

To evaluate the horizontal resistance properly, it is necessary to test the number of susceptible to DM sunflower lines during at least three years in a field conditions. However, we didn’t meet any published material with such kind of information.

This study agrees with other researchers (Tourvieille de Labrouhe et al., 2004; Vear, 2004; Vear et al., 2008b) that durable resistance in sunflower could be achieved by combining race-specific (vertical) and non-race-specific (horizontal) resistance in one hybrid. To achieve this, it is possible to use one parental line with the most effective specific location gene and the second parental line with a high horizontal resistance to DM.

5 Conclusion

Results of this study allowed for the identification of lines with the highest nonspecific race resistance to DM: VK 678 (5.3%), VK 653 (7.3%), VA 760 (3.3%), VA 93 (2.0%) and VK 732 (6.3%). The major Pl₁₅ gene was highly effective in preventing DM infection. The final aim was the development of sunflower hybrids with durable resistance to DM, combining one parental line with the specific effective major (Pl₁₅) gene and the second parental line with a high horizontal resistance to downy mildew.

Conflicts of interest

The authors declare that they have no conflicts of interest in relation to this article.

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Cite this article as: Gontcharov S, Goloschapova N. 2021. Evaluation of horizontal resistance of sunflower (Helianthus annuus L.) to downy mildew (Plasmopara halstedii). OCL 28: 58.

All Tables

Table 1

Resistance of sunflower lines Groups to downy mildew (VNIIMK, Krasnodar, Russia).

In the text

Table 2

Evaluation of sunflower lines horizontal resistance to downy mildew (VNIIMK, Krasnodar, Russia).

In the text

Table 3

Evaluation of sunflower lines horizontal resistance to downy mildew (VNIIMK, Krasnodar, Russia).

In the text

All Figures

thumbnail
Fig. 1

Differentiation of susceptible sunflower lines for horizontal (race nonspecific) resistance to downy mildew depending on the year. Green: Resistant, less than 10% of damaged plants; Yellow: Medium resistant, 10 to 40% of damaged plants; Red: Susceptible, more than 40% of damaged plants.

In the text

Table 1

Resistance of sunflower lines Groups to downy mildew (VNIIMK, Krasnodar, Russia).

Group
Average percent downy mildew infection

2016
2017
2018
2019
2020

Group 1
(without major genes for resistance)
21
22
6.6
0.9
0.8

Group 2
(resistant to race 330)
30
24
6.4
1.6
0.9

Group 3
(resistant to a mixture of races (330, 710 and 730)
2
1
2
0
0

Group 4
(with Pl₁₅ gene)
0
0
0
0
0

Table 2

Evaluation of sunflower lines horizontal resistance to downy mildew (VNIIMK, Krasnodar, Russia).

Line of the Group 1
(without major genes of resistance to downy mildew)
Infected plants (%)

2016
2017
2018
2019
Average

VK 276
70
77
15
0
40.5

VK 585
100
20
0
1
30.3

VK 700
46
34
5
2
21.7

VA 760
0
6
6
1
3.3

VA 93
4
1
1
2
2.0

VK 905
29
51
25
0
26.3

SL 24
8
16
22
0
11.5

SL 4
14
16
9
0
9.8

VK 934
15
26
0
1
10.5

VK 678
7
10
3
1
5.3

VK 935
17
19
0
1
9.3

VK 934
15
25
0
1
10.3

VK 101
16
23
2
0
10.3

SL 3844
4
16
4
1
6.3

VK 653
1
9
19
0
7.3

VK 732
5
16
0
4
6.3

VK 680
10
25
2
1
9.5

Average
21.2
22.9
6.6
0.9

Table 3

Evaluation of sunflower lines horizontal resistance to downy mildew (VNIIMK, Krasnodar, Russia).

Line of the Group 2
(without major genes of resistance to downy mildew)
Infected plants (%)

2016
2017
2018
2019
Average

VK 580
23
18
15
1
14.3

VK 794
17
31
0
0
12.0

VK 551
13
3
5
0
5.3

VK 591
13
13
6
1
8.3

VD 541
32
19
1
0
13.0

VK 989
39
18
25
2
21.0

VK 536
5
9
22
1
9.3

VK 941
36
41
9
2
22.0

VK 776
6
36
0
0
10.5

VK 780
34
30
3
0
16.8

VK 787
69
47
0
1
29.3

VK 788
6
14
0
1
5.3

VK 930
72
30
2
1
26.3

VK 914
30
35
4
1
17.5

VK 915
62
33
19
2
29.0

VK 917
11
8
0
2
5.3

VK 920
44
29
2
2
19.3

Average
30.1
24.4
6.6
1.0

Fig. 1

Differentiation of susceptible sunflower lines for horizontal (race nonspecific) resistance to downy mildew depending on the year. Green: Resistant, less than 10% of damaged plants; Yellow: Medium resistant, 10 to 40% of damaged plants; Red: Susceptible, more than 40% of damaged plants.