Survival and spread of Phytophthora capsici in Coastal Peru.

Phytophthora capsici is a soilborne pathogen that causes significant losses to pepper production in Peru. Our objective was to investigate the mechanisms by which P. capsici is able to survive and spread. During 2005 to 2007, 227 isolates of P. capsici were collected from four species of pepper (Capsicum annum, C. baccatum, C. chinense, and C. pubescens) and tomato (Solanum lycopersicum) at 33 field sites in 13 provinces across coastal Peru. All 227 isolates were of the A2 mating type and amplified fragment length polymorphism (AFLP) analysis indicates that 221 of the isolates had the same genotype. Analyses of six polymorphic single nucleotide polymorphism (SNP) loci showed fixed heterozygosity suggesting a single clonal lineage is widely dispersed. Members of the same clonal lineage were recovered during 2005 to 2007 from geographically separate locations from each of the host types sampled. Our results indicate that clonal reproduction drives the population structure of P. capsici in Peru. The impact of continuous cropping and irrigation from common river sources on the population structure in Barranca Valley are discussed.

First Report of Phytophthora nicotianae Causing Asparagus Spear and Root Rot in Peru.

During 2006, spears, roots, and crowns of asparagus (Asparagus officinalis) exhibiting brown necrotic lesions with water soaking were collected from several sites across Peru (Ica, Lima, and Trujillo). Small infected tissue sections were washed thoroughly with tap and sterile distilled water and transferred to corn meal agar plates (CMA) amended with PARP (100 ppm of pimaricin, 100 ppm of ampicillin, 30 ppm of rifampicin, and 100 ppm of pentachloronitrobenzene) and incubated for five days at 25°C. Hyphal tips were subcultured from actively expanding mycelium. Sporangia produced on CMA were papillate and averaged 38 µm long × 29 µm wide. Chlamydospores were terminal or intercalary and averaged 35 µm in diameter. Isolates incubated in the dark for more than 3 weeks did not produce oospores in single culture. Mating with Phytophthora capsici tester isolates CBS 121656 = A1 and CBS 121657 = A2 indicate that all five isolates were A2. For pathogenicity tests, inoculum was generated by incubating 300 g of autoclaved wheat seeds with four agar plugs (7 mm) of expanding mycelium in polyethylene bags for 1 month at 25°C. Nine-week-old asparagus plants (UC151 F1) were transferred into pots containing autoclaved substrate (1 part sand, 1 part potting soil, and 1 part peat). Inoculum was added as 1 g of inoculum per kilogram of substrate. Plants were maintained in the greenhouse at 23°C and watered daily. Decline symptoms as well as root and spear rot were observed after 7 days and a Phytophthora sp. was reisolated from infected tissue. No symptoms were observed on asparagus plants inoculated with sterile inoculum. DNA was isolated from two representative isolates, and the nuclear ribosomal internal transcribed spacer (ITS) region was amplified with ITS4 and ITS6 primers and sequenced. ITS sequence was submitted for a BLAST search in the NCBI database, showing Phytophthora nicotianae strain UQ848 Accession No AF266776 as the closest match with 99% sequence similarity (1). The consensus ITS sequence was deposited in NCBI (Accession No. EU433396). These results, together with the morphological characteristics, indicate that the Phytophthora sp. isolated from asparagus in Peru is P. nicotianae (Breda de Haan) (2). To our knowledge, this is the first report of P. nicotianae infecting asparagus and represents a new threat for asparagus growers in Peru. Control methods such as moderate watering and metalaxyl application are being applied to reduce Phytophthora outbreaks. References: (1) D. E. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society. St Paul, MN, 1996.