Race Characterization of Phytophthora Root Rot on Capsicum in Taiwan as a Basis for Anticipatory Resistance Breeding

Abstract

Peppers (Capsicum sp.) are an increasingly important crop because of their use as a vegetable, spice, and food colorant. The oomycete Phytophthora capsici is one of the most devastating pathogens to pepper production worldwide, causing more than $100 million in losses annually. Developing cultivars resistant to P. capsici is challenging because of the many physiological races that exist and new races that are continuously evolving. This problem is confounded by the lack of a universal system of race characterization. As a basis to develop a global anticipatory breeding program, New Mexico recombinant inbred lines (NMRILs) functioned as a host differential for Phytophthora root rot to characterize the race structure of P. capsici populations in Taiwan. Using the NMRILs, 24 new races were identified, illustrating the utility and usefulness of the NMRILs for anticipatory breeding. Virulence of P. capsici was observed to be geographically specific and in two virulence clusters. Interestingly, all but two isolates collected in 2016 were the A2 mating type, which is a shift from the predominantly A1 mating type isolates collected prior to 2008. The NMRILs host differential provides an approach for scientists to work together on a global scale when breeding for resistance as well as on a local level for regional gene deployment. Additionally, we propose that the current race numbering system, which has no biological meaning, be supplemented with the virulence phenotype, based on the susceptible NMRILs to a given isolate. This work provides insights into the population dynamics of P. capsici and interactions within the highly complex Capsicum-Phytophthora pathosystem, and offers a basis for similar research in other crops.

Overview of Biotic Stresses in Pepper (Capsicum spp.): Sources of Genetic Resistance, Molecular Breeding and Genomics

“…Recently, novel races have been identified based on the differential reactions of a set of New Mexico Recombinant Inbred lines (NMRILs) [54]. Identification of pathogen races using NMRILs suggests supplementing the term "race" by the term "virulence phenotype", to designate the virulence of P. capsici isolates to the various host resistance genes [58]. Several C. annum accessions resistant to P. capsici and carrying a single dominant gene [59], or multiple genes with additive or epistatic effects [60] have been identified (Table 1).…”

“…Among them, Serrano Criollo de Morelos (CM334) has the highest resistance level to all the disease stages [51]. Host-parasite coevolutionary relationships have been demonstrated [58]. Indeed, both P. capsici and resistant germplasm sources have the same geographical origin.…”

Virulence Phenotypes on Chili Pepper for Phytophthora capsici Isolates from Michoacán, Mexico

“…Among the alternatives to control P. capsici, the development of resistant cultivars could be the best method to reduce the losses associated with this plant pathogen (G omez-Rodríguez et al, 2017). However, the development of resistant cultivars and varieties to P. capsici has been difficult due to the presence of diverse virulence phenotypes of this pathogen (Barchenger et al, 2018b;Jiang et al, 2015;Oelke et al, 2003;Sy et al, 2008).…”

“…The NMRILs have been used to characterize P. capsici physiological races from isolates of different regions and are a valuable tool to characterize P. capsici isolates at a global scale. Recently, the term ''race'' has been replaced by the term ''virulence phenotype'' to characterize the interaction of P. capsici isolates on RILs carrying various host resistance genes (Barchenger et al, 2018b). By using the NMRILs, 12 P. capsici root rot virulence phenotypes were characterized from isolates recovered from New Mexico, 11 from isolates recovered from Brazil, and 24 from isolates recovered from Taiwan (Barchenger et al, 2018b;da Costa Ribeiro and Bosland, 2012;Jiang et al, 2015).…”

“…Recently, the term ''race'' has been replaced by the term ''virulence phenotype'' to characterize the interaction of P. capsici isolates on RILs carrying various host resistance genes (Barchenger et al, 2018b). By using the NMRILs, 12 P. capsici root rot virulence phenotypes were characterized from isolates recovered from New Mexico, 11 from isolates recovered from Brazil, and 24 from isolates recovered from Taiwan (Barchenger et al, 2018b;da Costa Ribeiro and Bosland, 2012;Jiang et al, 2015). The NMRILs have also been used to characterize foliar blight virulence phenotypes (Monroy-Barbosa and Bosland, 2010;Monroy-Barbosa and Bosland, 2011).…”