Phytophthora capsici, 100 Years Later: Research Mile Markers from 1922 to 2022.

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.

Occurrence of Bacterial Spot on Pumpkin and Squash Fruit in the North Central Region of the United States and Bacteria Associated with the Spots.

Since 2006, a bacterial spot disease has been widely observed on pumpkin and squash fruit in the North Central region (NCR) of the United States. Surveys were conducted during 2011 to 2013 to determine the occurrence of the disease on pumpkin and winter squash in the NCR. In each state, at least five commercial pumpkin and squash fields were visited each year within 3 weeks of harvest, and 60 fruit were inspected in each field. In nine states surveyed, 217 of 245 fields had fruit with bacterial spot. The average incidence of the symptomatic fruit in all pumpkin fields surveyed was 27.1, 30.3, and 25.3% in 2011, 2012, and 2013, respectively. The average incidence of fruit with bacterial spot in all squash fields surveyed was 20.2% in 2012 and 16.9% in 2013. The incidence of symptomatic fruit was more than 90% in some fields. Xanthomonas cucurbitae and non-X. cucurbitae bacteria were isolated from all of the symptomatic fruit collected. X. cucurbitae was identified based on colony characteristics on yeast extract-dextrose-CaCO3 agar, a polymerase chain reaction test using primers RST2 and RST3, and pathogenicity on pumpkin leaves. All X. cucurbitae isolates tested were pathogenic on 'Howden' pumpkin. In total, 312 non-X. cucurbitae isolates were identified into 10 genera based on the restriction fragment length polymorphism analysis. None of the non-X. cucurbitae isolates was pathogenic on Howden. In vitro studies of interactions between non-X. cucurbitae and X. cucurbitae showed that Pantoea isolates had antagonistic activity against X. cucurbitae. Identified Pantoea agglomerans showed the highest antagonistic activity against X. cucurbitae.

Morphology, Molecular Identity, and Pathogenicity of Verticillium dahliae and V. longisporum Associated with Internally Discolored Horseradish Roots.

During 2008 to 2009, 255 isolates of Verticillium were obtained from internally discolored horseradish roots collected from California, Illinois, and Ontario. Twenty representative isolates were selected according to morphological features and geographic origin for further characterization. Based on the conidial size, the isolates were divided into two groups: Verticillium dahliae (4.4 ± 1.23 µm) and V. longisporum (7.8 ± 1.76 µm). Genetic diversity of the isolates was determined by sequence analysis of the internal transcribed spacer (ITS) and two mitochondrial genes (cytochrome oxidase subunit III [cox3] and NADH dehydrogenase subunit I [nad1]). Based on ITS analysis, Verticillium isolates were divided into two clades: V. dahliae and V. longisporum. However five isolates of V. longisporum (identified based on conidial size) were clustered with a V. dahliae clade, whereas the other five isolates formed a distinct V. longisporum clade. Combined analysis of the mitochondrial genes cox3 and nad1 showed that the two genetic clades of V. longisporum in ITS region analysis corresponded to the previously reported V. longisporum lineage A1/D3 and A1/D2. Pathogenicity tests revealed that all tested Verticillium isolates caused internal discoloration of horseradish roots, and there were no significant differences in either incidence or severity of root discoloration among the genetic groups.