Plant diseases cost the global economy more than $220 billion US annually. Among them, diseases caused by oomycetes such as Phytophthora spp. have been historically devastating. For instance, the Irish Great Famine resulting from potato crops infested by Phytophthora infestans stands as a dramatic reminder of the impact plant diseases can have on society. One of the best approaches to prevent losses to plant pathogens is through the use of genetic resistance. This implies the exploitation of resistance genes that recognize the virulence factors (also called avirulence genes or Avr) of a pathogen to create an incompatible (resistant) interaction.
In the particular case of Phytophthora sojae, threatening soybean crops every year, specific resistance genes, called Rps (resistant to P. sojae), have been used for many years. These Rps genes interact with effectors (Avr) produced by P. sojae to generate incompatible interactions. However, the virulence profile of P. sojae is rapidly evolving as a result of the large-scale deployment of Rps genes in soybean, thus creating new races (variants) of the pathogen. For successful exploitation of Rps genes, it is recommended that soybean growers use cultivars containing the Rps genes corresponding to Avr genes found in P. sojae populations present in their fields. Determination of the virulence profile of P. sojae isolates is critical for the selection of soybean cultivars but this process has become challenging owing to the ever-increasing diversity of virulence profiles.
In a recent article, Dr. R.R. Bélanger and his team from Laval University in Québec, Canada exploited High resolution Melting curve analysis (HRM), first applied in medicine, as an original approach to discriminate effectors to differentiate P. sojae haplotypes for six Avr genes. High resolution melting analysis was performed on 24 P. sojae isolates with different haplotypes collected from soybean fields across Canada. The results confirmed that HRM assays discriminated different virulence genotypes. Moreover, the HRM assay was able to differentiate multiple haplotypes representing small allelic variations. HRM-based prediction was validated by phenotyping assays. This HRM assay provides a unique, cost effective and efficient tool to predict virulence pathotypes associated with six different Avr (1b, 1c, 1d, 1k, 3a, 6) genes from P. sojae, which can be applied for the deployment of appropriate Rps genes in soybean fields.
The technology was licenced by AYOS, a small biotech company, which now offers a diagnostic service to soybean growers across North and South America. Based on the results, growers can now make an educated decision about the best cultivars to deploy in their fields and thus increase their revenues by reducing losses to P. sojae.
A rapid molecular diagnostic tool to discriminate alleles of avirulence genes and haplotypes of Phytophthora sojae using high-resolution melting analysis
TITLE IMAGE: Phytophthora sojae on Soy Bean in the field.