Environment-Friendly Control of Cucumber Downy Mildew Using Chlorine Dioxide

Pseudoperonospora cubensis (downy mildew) is highly virulent to various Cucurbitaceae crops, including cucumber (Cucumis sativus). We tested chlorine dioxide application in a plastic greenhouse for environmentfriendly control of downy mildew disease. Spraying diluted chlorine dioxide suppressed downy mildew disease with 41.2% control efficacy. Thermal fogging with chlorine dioxide had a high control efficacy of 80.9%, confirming that this approach is useful for environment-friendly downy mildew control. Using thermal fogging to control diseases that are greatly affected by humidity, such as downy mildew, may be more effective compared with conventional dilution spray control methods.

Eucalyptus staigeriana essential oil can control downy mildew in grapevine

Downy mildew (Plasmopara viticola) is the primary disease in viticulture worldwide, and your control requires synthetic fungicides applications to avoid quality and yield loss in the grapevines. However, alternatives to reduce synthetic fungicides are needed to ensure the consumer’s health and the environment. Essential oils (EOs) are amongst the most promising natural plant protection alternatives because of their antifungal properties on several crop diseases. The present study objective was to determine the effect of Eucalyptus staigeriana EO in vitro and in vivo against P. viticola. The EO exhibited the highest activity in vitro, inhibiting 90% of the incidence and severity of disease caused by P. viticola in leaves of grapevines in the greenhouse. In the field (in vivo), treatment with EO could not control the disease; however, treatment with EO in consortium with conventional treatment reduced approximately 50% of the incidence and more than 90% of the severity of downy mildew disease in leaves, decreasing the application of synthetic fungicides by 50%.

Screening of South Indian Culinary Melon (Cucumis melo subsp. agrestis var. acidulus) Accessions for Downy Mildew Disease under Natural Epiphytotic Condition

Culinary melon also known as non dessert cucumber (Cucumis melo subsp. agrestis var. acidulus) belongs to the family Cucurbitaceae. It is widely cultivated in Southern parts of Indian subcontinent. It is mainly utilized for preparation of lentil soup, sambar, dosa, palya and chutney. 70 accessions were collected from six South Indian states namely Karnataka, Kerala, Andhra Pradesh, Tamil Nadu, Telangana and Goa. The accessions were evaluated for incidence of downy mildew resistance during Kharif 2018 under natural condition. The percent disease index (PDI) for downy mildew ranged from 3.70 to 48.64%. 10 accessions showed resistance to downy mildew. Among them, accession MS21 showed resistance with average least PDI of 3.70 followed by MS 6 (6.54). 50 accessions were found to be moderately resistant with average PDI ranging from 20 to 39.80. 12 accessions were found susceptible with PDI ranging from 41 to 49. None of the accession was found highly susceptible to the disease. The resistant accessions can be utilized as donor parents for resistant breeding in the improvement of culinary melon as well as melon group of vegetables.

Ancestral chromosomes for the Peronosporaceae inferred from a telomere-to-telomere genome assembly of Peronospora effusa

We report the first telomere-to-telomere genome assembly for an oomycete. This assembly has extensive synteny with less complete genome assemblies of other oomycetes and will therefore serve as a reference genome for this taxon. Downy mildew disease of spinach, caused by the oomycete Peronospora effusa, causes major losses to spinach production. The 17 chromosomes of P. effusa were assembled telomere-to-telomere using Pacific Biosciences High Fidelity reads. Sixteen chromosomes are complete and gapless; Chromosome 15 contains one gap bridging the nucleolus organizer region. Putative centromeres were identified on all chromosomes. This new assembly enables a re-evaluation of the genomic composition of Peronospora spp.; the assembly was almost double the size and contained more repeat sequences than previously reported for any Peronospora spp. Genome fragments consistently under-represented in six previously reported assemblies of P. effusa typically encoded repeats. Some genes annotated as encoding effectors were organized into multigene clusters on several chromosomes. At least two effector-encoding genes were annotated on every chromosome. The intergenic distances between annotated genes were consistent with the two-speed genome hypothesis, with some effectors located in gene-sparse regions. The near-gapless assembly revealed apparent horizontal gene transfer from Ascomycete fungi. Gene order was highly conserved between P. effusa and the genetically oriented assembly of the oomycete Bremia lactucae. High levels of synteny were also detected with Phytophthora sojae. Many oomycete species may have similar chromosome organization; therefore, this genome assembly provides the foundation for genomic analyses of diverse oomycetes.

Effect of different inoculum levels of P. arborescens in disease development and yield losses of opium poppy

Downy mildew (DM) caused by Peronospora arborescens is the most alarming disease of opium poppy which hampered the production of opium crop in major growing areas of India. The pooled data taken from Rabi 2016-17 and 2017-18 demonstrated that chemical protected un-inoculated plot had a minimum per cent disease severity (9.83) with maximum dry latex yield (31.25 kg ha-1), seed yield (801.31 kg ha-1) and husk yield (889.66 kg ha-1). However, plots inoculated with Peronospora arborescens at high inoculum density of 9×105 spores ml-1 had considerably higher per cent disease severity (67.00) and minimum dry latex yield (6.94 kg ha-1), seed yield (548.42 kg ha-1) and husk yield (590.86 kg ha-1) with maximum 77.79,31.56 and 33.58 per cent loss as compared to un-inoculated chemical protected plot, respectively. The severity of the downy mildew disease was found to rise in direct conflict with the level of inoculum concentration with significant reduction in dry latex yield, seed yield and husk yield.

CRISPR/Cas9-mediated mutagenesis of sweet basil candidate susceptibility gene ObDMR6 enhances downy mildew resistance

Sweet basil (Ocimum basilicum) is an economically important allotetraploid (2n = 4x = 48) herb whose global production is threatened by downy mildew disease caused by the obligate biotrophic oomycete, Peronospora belbahrii. Generation of disease resistant cultivars by mutagenesis of susceptibility (S) genes via CRISPR/Cas9 is currently one of the most promising strategies to maintain favored traits while improving disease resistance. Previous studies have identified Arabidopsis DMR6 (Downy Mildew Resistance 6) as an S gene required for pathogenesis of the downy mildew-causing oomycete pathogen Hyaloperonospora arabidopsidis. In this study, a sweet basil homolog of DMR6, designated ObDMR6, was identified in the popular sweet basil cultivar Genoveser and found to exist with a high copy number in the genome with polymorphisms among the variants. Two CRISPR/Cas9 constructs expressing one or two single guide RNAs (sgRNAs) targeting the conserved regions of ObDMR6 variants were generated and used to transform Genoveser via Agrobacterium-mediated transformation. 56 T0 lines were generated, and mutations of ObDMR6 were detected by analyzing the Sanger sequencing chromatograms of an ObDMR6 fragment using the Interference of CRISPR Edits (ICE) software. Among 54 lines containing mutations in the targeted sites, 13 had an indel percentage greater than 96% suggesting a near-complete knockout (KO) of ObDMR6. Three representative transgene-free lines with near-complete KO of ObDMR6 determined by ICE were identified in the T1 segregating populations derived from three independent T0 lines. The mutations were further confirmed using amplicon deep sequencing. Disease assays conducted on T2 seedlings of the above T1 lines showed a reduction in production of sporangia by 61–68% compared to the wild-type plants and 69–93% reduction in relative pathogen biomass determined by quantitative PCR (qPCR). This study not only has generated transgene-free sweet basil varieties with improved downy mildew resistance, but also contributed to our understanding of the molecular interactions of sweet basil-P. belbahrii.

The Incidence and Severity of Downy Mildew Disease on Local Madurese Maize Crops in Sumenep district, East Java, Indonesia

In Madura island, corn is the main commodity that is widely planted with an area of 301,725 ha or about 30% of the area of maize in East Java. Madura Island has local cultivars, such as: Tambin, Talango, Guluk-guluk, Manding, and Kretek. Efforts to increase production are continuously being made, starting from improving varieties until managing plant pests. One of the main diseases in maize is downy mildew. However, information about the incidence, incidence, severity, and species that cause downy mildew in local cultivars has not been reported. So, this study aims to identify the causes of downy mildew in local cultivars of Madura and disease severity in the field. The research method is a survey on local maize centers. Sampling was done by using the diagonal sampling method. Each plant sample was observed for symptoms of disease and scoring to calculate the value of disease severity. Fungi identification was carried out by microscopic observation of the fungus. The results showed that the cause of downy mildew in Madura local maize in Sumenep Regency was P. maydis. The highest incidence, disease severity, and AUDPC value after 4 MST were found in Guluk-guluk cultivars in Padangdangan Village, but had the lowest disease progression rate values. Meanwhile, the highest rate of disease progression was found in the Manding cultivar in Mandala Village. Based on the resistance category, Talango cultivar had the best resistance when compared to other cultiva.Keywords: AUDPC, downy mildew, disease progress, Madurese maize, Peronosclerospora maydis

CRISPR-Editing of Sweet Basil (Ocimum basilicum L.) Homoserine Kinase Gene for Improved Downy Mildew Disease Resistance

Sweet basil (Ocimum basilicum L.) downy mildew disease (DM) caused by Peronospora belbahrii is a worldwide threat to the basil industry due to the lack of natural genetic resistance in sweet basil germplasm collections. In this study, we used CRISPR-gene editing to modify the sweet basil DM susceptibility gene homoserine kinase (ObHSK). Gene-edited plants challenged with P. belbahrii displayed a significantly reduced susceptibility to DM, based on phenotypic disease indices and on in planta pathogen load. These results suggest that ObHSK plays a role in conditioning DM susceptibility, similar to that observed for the AtHSK gene in Arabidopsis. These results demonstrate the utility of CRISPR-gene editing in enhancing DM resistance and contributing to sweet basil breeding programs.