In 1922, Phytophthora capsici was described by Leon Hatching Leonian as a new pathogen infecting pepper ( Capsicum annuum), with disease symptoms of root rot, stem and fruit blight, seed rot, and plant wilting and death. Extensive research has been conducted on P. capsici over the last 100 years. This review succinctly describes the salient mile markers of research on P. capsici with current perspectives on the pathogen's distribution, economic importance, epidemiology, genetics and genomics, fungicide resistance, host susceptibility, pathogenicity mechanisms, and management.

The basil (Ocimum spp.) genus maintains a rich diversity of phenotypes and aromatic volatiles through natural and artificial outcrossing. Characterization of population structure and genetic diversity among a representative sample of this genus is severely lacking. Absence of such information has slowed breeding efforts and the development of sweet basil (Ocimum basilicum L.) with resistance to the worldwide downy mildew epidemic, caused by the obligate oomycete Peronospora belbahrii. In an effort to improve classification of relationships 20 EST-SSR markers with species-level transferability were developed and used to resolve relationships among a diverse panel of 180 Ocimum spp. accessions with varying response to downy mildew. Results obtained from nested Bayesian model-based clustering, analysis of molecular variance and unweighted pair group method using arithmetic average (UPGMA) analyses were synergized to provide an updated phylogeny of the Ocimum genus. Three (major) and seven (sub) population (cluster) models were identified and well-supported (P < 0.001) by PhiPT (ΦPT) values of 0.433 and 0.344, respectively. Allelic frequency among clusters supported previously developed hypotheses of allopolyploid genome structure. Evidence of cryptic population structure was demonstrated for the k1 O. basilicum cluster suggesting prevalence of gene flow. UPGMA analysis provided best resolution for the 36-accession, DM resistant k3 cluster with consistently strong bootstrap support. Although the k3 cluster is a rich source of DM resistance introgression of resistance into the commercially important k1 accessions is impeded by reproductive barriers as demonstrated by multiple sterile F1 hybrids. The k2 cluster located between k1 and k3, represents a source of transferrable tolerance evidenced by fertile backcross progeny. The 90-accession k1 cluster was largely susceptible to downy mildew with accession ‘MRI’ representing the only source of DM resistance. High levels of genetic diversity support the observed phenotypic diversity among Ocimum spp. accessions. EST-SSRs provided a robust evaluation of molecular diversity and can be used for additional studies to increase resolution of genetic relationships in the Ocimum genus. Elucidation of population structure and genetic relationships among Ocimum spp. germplasm provide the foundation for improved DM resistance breeding strategies and more rapid response to future disease outbreaks.

Considerable progress has been made in managing Peronospora belbahrii, an oomycete pathogen that causes basil downy mildew, since 2007, when it was first detected in the United States. Conventional fungicides have been registered and shown effective against P. belbahrii in replicated experiments in recent years. Unfortunately, because of their specific modes of action and P. belbahrii biology, some are at risk for resistance development, which has been documented outside the United States. Sweet basil varieties have been developed and commercialized, with most exhibiting good to high levels of resistance to basil downy mildew. Knowledge about conditions favorable for infection and disease development has resulted in the identification of cultural practices for managing basil downy mildew in the greenhouse. Practices being implemented include fans to move leaves, thus preventing water deposition and decreasing relative humidity, lighting at night to mitigate sporulation, and temperature modification to suppress disease development. Although downy mildew can be more effectively managed today, growers still experience losses, particularly when conditions are highly favorable for disease development. None of the organic fungicides or programs tested have provided adequate control for susceptible varieties, and limited testing has been done on resistant varieties to date. This review aims to summarize effective basil downy mildew management tools, in particular downy mildew-resistant varieties, environment modifications, and fungicide applications.

Fusarium wilt of basil (FOB), caused by Fusarium oxysporum f. sp. basilici , is an economically damaging disease of field- and greenhouse-grown sweet basil. Growers have observed a resurgence of FOB and susceptibility in FOB-resistant cultivars. Because currently available chemical, biological, and cultural control methods are costly, unsustainable, ineffective, or challenging to implement, new strategies of FOB control are needed. Cold plasma is becoming an increasingly important experimental technology in the food and agricultural industry for pathogen decontamination. To understand the effect of cold plasma treatment on FOB incidence and severity, experiments were conducted by treating FOB mycelium, inoculated sweet basil seedlings, and seeds with various experimental cold plasma treatment devices, all using helium as a feed gas. Initial results indicated that while the cold plasma jet treatment did not result in a significant reduction in mean mycelial growth rate or virulence of the pathogen, direct cold plasma jet treatments on seedlings, as well as a cold plasma dielectric barrier discharge treatment on seeds, did exhibit varying efficacies against FOB. Control of FOB appeared to be strongly dependent on the exposure time to cold plasma. These findings can aid in the standardization of a cold plasma treatment for the commercial basil seed and transplant industry.

We previously reported an outbreak of bacterial leaf spot (BLS) caused by Pseudomonas cichorii occurring on sweet basil in New Jersey during the summer of 2018 (Patel et al. 2019), a growing season...

An estimated 500 acres of basil varieties are grown annually for fresh and wholesale markets in New Jersey. In July of 2018, leaf spot disease symptoms were observed on several sweet basil cultivars and breeding lines grown in university field trials at the Rutgers Agricultural Research and Extension Center near Bridgeton, NJ. Disease incidence was less than 10%; no differences in susceptibility were observed between varieties or breeding lines of sweet basil within the field. Symptoms were observed as irregularly shaped blackened necrotic spots on leaf margins ranging from 2mm-7mm in diameter, which coalesced as lesions expanded over time. Margins of diseased tissue were excised, macerated in sterile water, and then quadrant-streaked for single colony isolations onto Nutrient Agar (NA) and King’s medium B agar (KMB) (Schaad et al., 2001). Cream-colored circular bacterial colonies with undulated margins predominated growth on both agar media. Colonies on KMB fluoresced blue under 365nm UV light. Two repre...