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.
SUMMARYYields of sweet potato tips varied from 10 to 16 t/ha in weight and 61 to 352/m2 in number, whilst yields of marketable roots varied from 1 to 16 t/ha. Cultivar differences in dry matter, fibre, ash, vitamin B2 and oxalate were also observed. The tips appeared to provide an excellent source of vitamin B2 which is important for Asian diets deficient in this vitamin. Application of 120 kg N/ha gave higher tip yields than no nitrogen, primarily due to increases in their number and size. Among the leaf types evaluated, Kinangkong (a fine leaf cultivar) produced the highest yield, and had the highest amount of protein, lowest oxalate, and fairly high dry matter, which makes it a very desirable leafy vegetable.
Wild relatives of domesticated Capsicum represent substantial genetic diversity and thus sources of traits of potential interest. Furthermore, the hybridization compatibility between members of Capsicum species complexes remains unresolved. Improving our understanding of the relationship between Capsicum species relatedness and their ability to form hybrids is a highly pertinent issue. Through the development of novel interspecific hybrids in this study, we demonstrate interspecies compatibility is not necessarily reflected in relatedness according to established Capsicum genepool complexes. Based on a phylogeny constructed by genotyping using simple sequence repeat (SSR) markers and with a portion of the waxy locus, and through principal component analysis (PCA) of phenotypic data, we clarify the relationships among wild and domesticated Capsicum species. Together, the phylogeny and hybridization studies provide evidence for the misidentification of a number of species from the World Vegetable Center genebank included in this study. The World Vegetable Center holds the largest collection of Capsicum genetic material globally, therefore this may reflect a wider issue in the misidentification of Capsicum wild relatives. The findings presented here provide insight into an apparent disconnect between compatibility and relatedness in the Capsicum genus, which will be valuable in identifying candidates for future breeding programs.
Male sterility is of high importance in hybrid seed production of hot and sweet peppers. Genic (or nuclear) male sterility (GMS) is a simply inherited (usually monogenic recessive) and highly stable trait. However, one major disadvantage of using GMS is 1:1 segregation of male sterile to male fertile plants in every subsequent generation. Molecular markers tightly linked to genic male sterility (ms) genes would facilitate an efficient and rapid transfer of ms genes into different genetic backgrounds through marker-assisted backcrossing. The two non-allelic genic male sterility genes ms3 and msw in hot and sweet pepper backgrounds, respectively, are monogenic recessive. Genotyping by sequencing (GBS) in an F2 population segregating for ms3 gene in hot pepper and in an F6 inbred near-isogenic line (NIL) population segregating for msw gene in sweet pepper yielded 9,713 and 7,453 single nucleotide polymorphism markers, respectively. Four candidate SNPs co-segregating with ms3 gene and one co-segregating with msw gene were identified by bulk segregant analysis and physically mapped to chromosomes 1 and 5, respectively. In hot pepper, two markers [HPGMS2 (CAPS) and HPGMS3 (dCAPS)] located 3.83 cM away from the ms3 gene and in sweet pepper the dCAPS marker SPGMS1 co-segregated (completely linked) with the msw gene were developed. These markers will increase the efficacy of the male sterility genes for pepper breeding, as they can be useful in developing the genic male sterile lines in parental inbred lines of commercial hybrids through marker-assisted backcrossing, hybrid seed production, and genetic purity testing of hybrid seeds.
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