Basil (Ocimum spp.) is one of the most economically important and widely grown herbs in the world. Basil downy mildew, caused by Peronospora belbahrii, has become an important disease in sweet basil (O. basilicum) production worldwide in the past decade. Global sweet basil production is at significant risk to basil downy mildew because of the lack of genetic resistance and the ability of the pathogen to be distributed on infested seed. Controlling the disease is challenging and consequently many crops have been lost. In the past few years, plant breeding efforts have been made to identify germplasm that can be used to introduce downy mildew resistance genes into commercial sweet basils while ensuring that resistant plants have the correct phenotype, aroma, and tastes needed for market acceptability. Fungicide efficacy studies have been conducted to evaluate current and newly developed conventional and organic fungicides for its management with limited success. This review explores the current efforts and progress being made in understanding basil downy mildew and its control.

2011. Variability among forecast models for (he apple sooty blotch/flyspeck disease complex. Plant Dis. 95:1179-1186.Several disease forecast models have been developed to guide treatment of the sooty blotch and flyspeck (SBFS) disease complex of apple. Generally, these empirical models are based on the accumulation of hours of leaf wetness (leaf wetness duration [LWD]) from a biofix at or near the phenological growth stage petal fall, when apple fiower petals senesce and drop. The models recommend timing of the initial fungicide application targeting SBFS. However, there are significant differences among SBFS forecast models in terms of biofix and the length of LWD thresholds. A comparison of models using a single input data set generated recommendations for the first SBFS fungicide application that differed by up to 5 weeks. In an attempt to improve consistency among models, potential sources for differences were examined. Leaf wetness (LW) is a particularly variable parameter among models, depending on whether on-site or remote weather data were used, the types of sensors and their placement for on-site monitors, and the models used to estimate LW remotely. When SBFS models are applied in the field, recommended treatment thresholds do not always match the method of data acquisition, leading to potential failures. Horticultural factors, such as tree size, canopy density, and cultivar, and orchard site factors such as the distance to potential inoculum sources can impact risk of SBFS and should also be considered in forecast models. The number of fungal species identified as contributors to the SBFS disease complex has expanded tremendously in recent years. A lack of understanding of key epidemiological factors for different fungi in the complex, and which fungi represent the most challenging management problems, are obvious issues in the development of improved SBFS models. If SBFS forecast models are to be adopted, researchers will need to address these issues.Sooty blotch and flyspeck (SBFS). a disease complex caused by numerous fungal species, impacts pome fruit production in humid regions worldwide (4,5.18,21.35.58,60). Although the disea.se is limited to waxy cuticles and does little damage to trees or fruit, the blemishes it causes can substantially decrease apple fruit quality and. therefore, value. In the eastern production regions of the United States, growers generally apply from 30 to 50% of a season's fungicides, usually from four to eight applications, to manage a set of summer diseases, including SBFS, black rot {Botryosphae-ria obtusa (Schwein.) Shoemaker), bitter rot {Glomerella cingutata (Stoneman) Spauld. & H. Schrenk), white rot or bot rot {B. dothidea (Moug.) Ces. & De Not.). Brooks fruit spot {Mycosphae-rella potni (Pass.) Lindau), and Alternaria blotch {Alternarla niali Roberts) ( 54). SBFS is the only consistent summer disease problem in northem regions such as New England but the other diseases become increasingly important going from north to south.Calendar-based management programs of ...

Different basils (Ocimum sp.) and cultivars (28 in 2009 and 32 in 2010) were evaluated for susceptibility to basil downy mildew (Peronospora belbahrii) at the Rutgers Agricultural Research and Extension Center near Bridgeton in southern New Jersey. At the end of each growing season, seed was collected from individual plants and stored for potential downy mildew pathogen detection using real-time polymerase chain reaction (PCR) analysis. Most of the basil cultivars and breeding lines were showing symptoms of basil downy mildew infection at the time of seed collection before the first frost near the end of the production season. Symptoms of basil downy mildew were present on 25 of the 28 (89%) basil lines evaluated in 2009 and 26 of 32 (81%) basil lines tested in 2010 at the time of seed harvest, with sporulation evident on the abaxial surface of infected leaves. Real-time PCR analysis of seed collected from various infected plants detected P. belbahrii on seed of 14 of 25 (56%) basil lines tested in 2009 and 8 of 32 (25%) tested in 2010. Importantly, P. belbahrii was not only detected on seed of sweet basil (Ocimum basilicum) phenotypes but also on seed of ‘Spice’ basil (Ocimum americanum) in 2009 and ‘Sweet Dani Lemon Basil’ basil (Ocimum citriodorum), ‘Holy Red and Green’ basil [Ocimum tenuiflorum (form. sanctum)], ‘Lime’ basil (O. americanum), and again on ‘Spice’ basil in 2010 where no symptoms (i.e., no chlorosis or sporulation) were present on the leaves when seed were collected. This work demonstrates that basil seed, regardless of basil species and whether symptoms are visible on foliage of the basil plant or the plant is immune or resistant to downy mildew, can test positive for the presence of P. belbahrii using a real-time PCR assay following exposure of plants to the pathogen during the natural development of downy mildew under field conditions.

Current and emerging plant diseases caused by obligate parasitic microbes such as rusts, downy mildews, and powdery mildews threaten worldwide crop production and food safety. These obligate parasites are typically unculturable in the laboratory, posing technical challenges to characterize them at the genetic and genomic level. Here we have developed a data analysis pipeline integrating several bioinformatic software programs. This pipeline facilitates rapid gene discovery and expression analysis of a plant host and its obligate parasite simultaneously by next generation sequencing of mixed host and pathogen RNA (i.e., metatranscriptomics). We applied this pipeline to metatranscriptomic sequencing data of sweet basil (Ocimum basilicum) and its obligate downy mildew parasite Peronospora belbahrii, both lacking a sequenced genome. Even with a single data point, we were able to identify both candidate host defense genes and pathogen virulence genes that are highly expressed during infection. This demonstrates the power of this pipeline for identifying genes important in host–pathogen interactions without prior genomic information for either the plant host or the obligate biotrophic pathogen. The simplicity of this pipeline makes it accessible to researchers with limited computational skills and applicable to metatranscriptomic data analysis in a wide range of plant-obligate-parasite systems.

A Plectosphaerella sp. was isolated from an undescribed root rot of the herbaceous ornamental Heuchera sanguine (Coral Bells) in Massachusetts. Morphological examination and phylogenetic analysis using DNA sequences derived from internal transcribed spacer (ITS) of rDNA, large subunit (LSU) of rDNA, calmodulin (CaM), β-tubulin 2 (Tub) and transcription elongation factor 1 (Ef-1α) loci identified the fungus as a member of Plectosphaerella cucumerina. A test of Koch's postulates on an isolate of P. cucumerina indicated that it was a pathogen causing root rot in Heuchera sp. The pathogen caused greatest damage to small transplants (1-4 g) as opposed the larger transplants (9-13 g) and in separate studies was found to infect seedlings of cucumbers, melons and pumpkins. Plectosphaerella cucumerina is reported for the first time in Heuchera sp. Given the importance of Heuchera to the ornamental industry, and the rapid dissemination that can occur with propagated material in the horticultural trade, caution should be exercised to prevent the spread of P. cucumerina. K E Y W O R D S Heuchera, multilocus and morphological classification, Plectosphaerella cucumerina | 57 ELMER Et aL. Koch's postulates and to assess the effect of plant age on disease development. S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section. How to cite this article: Elmer W, Li D, Yavuz S, Madeiras A, Schultes N. Heuchera root rot, a new disease for Plectosphaerella cucumerina. J Phytopathol. 2020;168:56-62.