Pl2 resistance gene differentiates the pathogenicity in four "Plasmopara halstedii" (sunflower downy mildew) races 304, 704, 314 and 714

Nachaat Sakr

doi:10.5209/rev_bocm.2015.v39.49130

Abstract

In order to clarify the role of Pl2 resistance gene in differentiation the pathogenicity in Plasmopara halstedii (sunflower downy mildew), analyses were carried out in four pathotypes: isolates of races 304 and 314 that do not overcome Pl2 gene, and isolates of races 704 and 714 that can overcome Pl2 gene. Based on the reaction for the P. halstedii isolates to sunflower hybrids varying only in Pl resistance genes, isolates of races 704 and 714 were more virulent than isolates of races 304 and 314. Index of aggressiveness was calculated for pathogen isolates and revealed the presence of significant differences between isolates of races 304 and 314 (more aggressive) and isolates of races 704 and 714 (less aggressive). There were morphological and genetic variations for the four P. halstedii isolates without a correlation with pathogenic diversity. The importance of the Pl2 resistance gene to differentiate the pathogenicity in sunflower downy mildew was discussed.

Highlights

Downy mildew is one of the major diseases for sunflower cultivation (Helianthus annuus L.)
The two sunflower inbred lines XRQ and RHA340 were resistant to all P. halstedii isolates tested
In sunflower downy mildew, there are no studies about the genetic background for avirulence Avr genes correspondent to Pl resistance genes (Viranyi & Spring 2011)

Summary

Introduction

Downy mildew is one of the major diseases for sunflower cultivation (Helianthus annuus L.). The causal agent is Plasmopara halstedii, an obligate biotroph oomycete from the Peronosporaceae family, diploid, homothallic, and can reproduce sexually and asexually. This disease is found in most parts of the world where the crop is cultivated and where a co-evolution between H. annuus and P. halstedii has taken place. Virulence has been defined as specific disease-causing abilities and aggressiveness as non-specific disease-causing abilities (Van der Plank 1968). It displays a gene-for-gene interaction with its host plant and shows physiological races

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Conclusion