Harnessing Wild Potato Species for Combatting Late Blight: A New Era in Potato Breeding
by Jorge Luis Alonso with ChatGPT
The journal Plant Breeding has published a review article that examines the recognized sources of P. infestans resistance in wild potato species and the identified loci of corresponding resistance genes in the genome. The following is a summary of the article.
Introduction
Potato is the world’s fifth most important crop, with an annual production of approximately 360 million tons. However, it remains highly susceptible to disease, particularly late blight caused by Pythophthora infestans.
This disease causes significant yield losses, with an estimated global cost of $6.7 billion per year. While fungicides are currently used to control the disease, more environmentally friendly alternatives are needed. Breeding resistant varieties is essential, but achieving long-term resistance remains elusive.
Wild relatives of cultivated potatoes have been identified as valuable sources of resistance. The primary goal of potato breeding is to establish quantitative resistance to a wide range of races via multiple quantitative trait loci (QTL) and/or stacking of different resistance genes.
This review summarizes the known sources of P. infestans resistance in wild potato species and the known loci of corresponding resistance genes in the genome, with the aim of informing breeders and researchers about the diversity of potential resistance sources. Numerous untapped sources of resistance could be exploited for potato cultivar improvement.
Late Blight Resistant Wild Relatives of Potato
The genus Solanum contains about 1500 species, many of which are tuber-bearing and can provide resistance genes for potato varieties. Two taxonomic systems classify these species, with the Hawkes system still used by many scientists and institutions. Over the past four decades, 85 wild potato species have been identified as resistant to P. infestans, including 33 new species discovered since 2013.
Resistance identification has primarily relied on detached leaf tests, whole plant tests, or field tests, with tuber slice tests used in some cases. For many species, there is a lack of studies on the genomic location of their resistance. Further investigation is needed to determine whether newly discovered resistances may be homologues of previously characterized R genes.
Resistance Mechanisms Against P. Infestans
The majority of the identified resistance genes follow the classical gene-for-gene interaction model and are NLR genes encoding receptors for the detection of pathogen-specific effector proteins. All detected P. infestans effectors belong to the RXLR class, which plays a role in suppressing plant defense mechanisms. Several models of host-pathogen interaction have been proposed to explain resistance and susceptibility, including the Zigzag model, which characterizes the interaction as a multistep process.
Recently, a mechanism was uncovered that allows earlier pathogen detection by receptor-like proteins (RLPs) and receptor-like kinases (RLKs) found in two accessions of S. microdontum. This mechanism is consistent with the category of MAMP-triggered immunity (MTI) in the context of the Zigzag model. However, the practicality of using pattern recognition receptor genes for P. infestans resistance breeding in potato remains to be demonstrated.
R Genes and Qtl for P. Infestans Resistance in Wild Potato Species
A total of 61 R genes and 37 QTL were identified in 27 and 11 wild potato species, respectively. R genes are predominantly located on chromosomes 4, 9, and 11, while QTL are evenly distributed. R genes are organized in clusters, with 12 clusters detected on 10 chromosomes. RenSeq analysis can provide detailed information on the identity and location of known R genes, as well as the identification of new ones. Merging R genes from different clusters could lead to improved durable resistance in new varieties.
Interspecific Hybridisation With Wild Potato Species
A variety of P. infestans resistance donor species with different ploidies, such as diploid, tetraploid and hexaploid, are available. Research on cross-compatibility between species with similar and divergent ploidies has led to the identification of distinct ploidy and endosperm balance number (EBN) groups. Techniques such as chromosome doubling and unreduced gamete production can facilitate hybridization with incompatible species. Although 85 wild potato species show resistance to P. infestans, only 13% of them can be used for resistance breeding in tetraploid potato cultivars without ploidy manipulation or alternative methods to overcome hybridization barriers.
Opportunities for Diploid Breeding
Diploid potato varieties offer advantages in recessive allele selection and multiple trait improvement, with 40 of 85 potential P. infestans resistant donor species being diploid. Inbred diploid lines can be developed for hybrid breeding and propagation using true potato seed. Diploid cultivars facilitate resistance to introgression and allow for better control of undesirable traits.
However, challenges include inbreeding depression and natural self-incompatibility among diploid potato species. Self-compatibility inducers have been identified and used to create the first homozygous diploid potato inbred lines. Reciprocal recurrent selection and the use of inbred lines offer the potential to develop elite diploid lines and F1 hybrids with significant heterotic potential. In addition, diploid potato breeding offers advantages for scientific research.
Late Blight Resistance Through Genetic Engineering
The use of genetic engineering offers advantages in the development of resistant potato varieties, although it may face regulatory and consumer acceptance challenges. Cisgenesis has been used to create varieties with resistance genes, including Fortuna” and Innate®. This method could reduce disease problems and facilitate the rapid combination of multiple R genes without the disadvantage of linkage drag. However, the potential to develop long-lasting resistance through genetic engineering remains a topic of debate.
Conclusion
Here are some action-oriented bullet points based on the review article:
- Stack resistance genes from multiple sources to develop durable resistance in potato varieties.
- Incorporate quantitative resistance for longer-term protection against pathogens.
- Consider breeding at the diploid level for faster results and higher quality material for breeding resistant varieties.
- Explore alternative methods for sustainable agriculture that reduce the use of synthetic pesticides and improve carbon neutrality.
- Re-evaluate genetic modification technologies for potential use in developing more sustainable agriculture.
Source: Blossei, J., Gäbelein, R., Hammann, T., & Uptmoor, R. (2022). Late blight resistance in wild potato species — Resources for future potato (Solanum tuberosum) breeding. Plant Breeding, 141( 3), 314– 331.
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