A Diagnostic Guide for Basil Downy Mildew

Standish, Jeffrey R.; Raid, Richard N.; Pigg, Stacey; Quesada‐Ocampo, Lina M.

doi:10.1094/php-09-19-0062-dg

Cited by 4 publications

(1 citation statement)

References 37 publications

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“…Gradually, large chlorotic lesions with soft margins develop, that turn necrotic, leading to a slight curvature of leaves. Moreover, if environmental conditions are favourable, leaf wetness and 15-20 °C temperature, sporangiophores and sporangia, with a characteristic fuzzy, dark grey to purple growth, can be observed mainly on the abaxial leaf surface (Falach-Block et al 2019;Zhang et al 2019;Standish et al 2020; Topolovec-Pintaric and Martinko 2020; Abdullah et al 2022).…”

Section: Introductionmentioning

confidence: 99%

Cropping system support in downy mildew control in basil in organic farming: a two-year open field experiment

La Placa,

Cornali,

Bertinaria

et al. 2024

J Plant Pathol

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Basil Downy Mildew (BDM), caused by the oomycete Peronospora belbahrii, is a major issue for sweet basil (Ocimum basilicum L.) production worldwide. Currently, the disease is mainly controlled by chemical fungicides, but the development of populations of the pathogen which are resistant to the most widely used compounds is leading to the research of alternative crop protection strategies. Therefore, in this paper, some cropping variables were tested in a field trial conducted in two consecutive years (2021 and 2022) in Northern Italy in organic farming conditions, with the overall objective to optimize basil productivity and quality and limit BDM occurrence. These include two basil varieties, two sowing densities (dense, 30 kg/ha, and sparse, 15 kg/ha), and two irrigation systems (drip and sprinkler). A higher incidence and severity of BDM in 2022 compared to 2021 was observed, mainly due to the different climatic conditions that occurred in the two years. Year 2022 was characterized by high temperatures and repeated drought phenomena that led to basil stress and BDM severe outbreak. Moreover, variety 1 (considered resistant to P. belbahrii) was confirmed to be completely resistant in 2021 but it was found to be susceptible the following year, with disease incidence and severity comparable to variety 2 (medium susceptible). No differences were detected in terms of BDM occurrence and crop yield between the two sowing densities (mean of 58.4% and 26.6% of BDM incidence and severity, respectively; mean yield 1.4 kg/m2), while it emerged that drip irrigation can be useful in reducing BDM (−23.1% BDM severity). Therefore, this study suggests that the crop protection strategies tested, even if not definitive solutions, can significantly contribute to manage BDM more effectively, while preserving basil productivity and quality.

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Section: Introductionmentioning

confidence: 99%

Cropping system support in downy mildew control in basil in organic farming: a two-year open field experiment

La Placa,

Cornali,

Bertinaria

et al. 2024

J Plant Pathol

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Joint Action of Pb1 and Pb2 Provides Dominant Complementary Resistance Against New Races of Peronospora belbahrii (Basil Downy Mildew)

Ben-Naim

Weitman

2022

Phytopathology®

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Sweet basil (Ocimum basilicum, 2n=4x=48) is susceptible to downy mildew caused by Peronospora belbahrii. Pb1 gene exhibit complete resistance to the disease. However, Pb1 became prone to disease due to occurrence of a new virulent races. Here we show that Zambian accession PI 500950 (O. americanum var pilosum) is highly resistant to the new races. From an interspecies backcross between PI 500950 and the susceptible cv ‘Sweet Basil’ we obtained, by embryo rescue, a population of 131 BC1F1 plants. This population segregated 73 Resistant: 58 Susceptible (1: 1, P=0.22), suggesting the resistance is controlled by one incompletely dominant gene called Pb2. To determine whether allelic relationship is existing between Pb1 and Pb2, we used two differential races, race-0, avirulent to both PI 500945 (Pb1) and PI 500950 (Pb2) and race-1, virulent to PI 500945 but avirulent to PI 500950. F1 plants obtained from ‘12-4-6’ (BC6F3 derived from PI 500945) and ‘56’ (BC3F3 derived from PI 500950) showed resistant superiority to both races due to dominant complementary interaction. F2 plants segregated to race-0 as follow; 12:3:1, immune: incomplete resistant: susceptible, as against to 9:3:4 to race-1, indicating Pb1 and Pb2 are not alleles. Since joint action is contributed in F1 plants and in advanced (BC3F3(56) x BC6F3(12-4-6) F4) populations who carrying both genes, it can be assumed that both accessions carry two unlinked genes but share a common signal transduction pathway which leading to dominant complementation superiority of the resistance against different races of BDM.

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Development, Validation, and Utility of Species-Specific Diagnostic Markers for Detection of Peronospora belbahrii

et al. 2022

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Peronospora belbahrii is an oomycete and cause of basil downy mildew, one of the most destructive diseases affecting basil production worldwide. Disease management is challenging due to wind-dispersed sporangia and contaminated seed, therefore, identifying P. belbahrii in seed-lots before sale or planting, or in the field before symptoms develop could allow for timely deployment of disease management strategies. In this study, a draft genome assembly and next generation sequencing reads for P. belbahrii, and publicly available DNAseq and RNAseq reads of several other downy mildew pathogens, were incorporated into a bioinformatics pipeline to predict P. belbahrii-specific diagnostic markers. The specificity of each candidate marker was validated against a diverse DNA collection of P. belbahrii, host tissue, and related oomycetes using PCR. Two species-specific markers were identified and used to develop a highly sensitive probe-based real-time qPCR assay that could detect P. belbahrii in leaf tissue and seed samples. Both markers were capable of reliably detecting as low as 500 fg/µl of P. belbahrii genomic DNA and as few as 10 sporangia. The qPCR assay was then validated with seed samples collected from a basil cultivar experiment. In total, 48 seed samples were collected and tested; P. belbahrii was detected in samples of all cultivars at estimated concentrations of 600 fg/µl up to 250 pg/µl and at as few as 10 sporangia up to >1,000 sporangia. The markers and assays are valuable for diagnostics and for identifying P. belbahri-contaminated seed-lots, to mitigate the effects of future basil downy mildew epidemics.

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A Diagnostic Guide for Basil Downy Mildew

Cited by 4 publications

References 37 publications

Cropping system support in downy mildew control in basil in organic farming: a two-year open field experiment

Cropping system support in downy mildew control in basil in organic farming: a two-year open field experiment

Joint Action of Pb1 and Pb2 Provides Dominant Complementary Resistance Against New Races of Peronospora belbahrii (Basil Downy Mildew)

Development, Validation, and Utility of Species-Specific Diagnostic Markers for Detection of Peronospora belbahrii

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