Management of grape powdery mildew with an intelligent sprayer and sulfur

Wine grapes are an important agricultural commodity in the Pacific Northwest where grape powdery mildew (GPM) is one of the main disease problems. The efficacy of different sulfur concentrations and different output volumes from an air blast sprayer retrofitted with the Intelligent Spray System (ISS) were evaluated for the management of GPM. The ISS consists of a LiDAR sensor, Doppler speed sensor, embedded computer, flow controller, and individual pulse-width-modulation solenoid valves at each nozzle. GPM cluster severity ranged from 55% to 75% across all trials in the study when using the ISS at its default spray rate of 62.5 ml m-3 and micronized sulfur at 6 g L-1, which was significantly higher than all other fungicide treatments, but lower than non-treated controls. Similarly, leaf incidence values were highest on non-treated vines, followed by micronized sulfur at 6 g L-1 applied at 62.5 ml m-3 , with all other fungicide treatments being significantly lower in all trials. Using the ISS at the 62.5 ml m-3 rate and a rotation of locally systemic fungicides resulted in the lowest observed GPM leaf incidence, and average cluster severity of 11% in both 2019 and 2020, the lowest cluster severity of all fungicide treatments tested. GPM control using the ISS and micronized sulfur was equivalent to a constant-rate air blast treatment at 6 g L-1 when the spray rate of the ISS was increased to 125ml m-3, or if the concentration of sulfur was increased to 24 g L-1. In those cases, the amount of sulfur applied to vines was at or above the minimum label rate from bloom until the end of the season, or the entire season, respectively. This study has shown that sufficient disease control cannot always be expected when mixing pesticides at the same rate as would be used for a constant-rate sprayer in a variable rate sprayer, especially when using contact fungicides like sulfur . With appropriate adjustments, the variable-rate ISS can be a useful tool to reduce pesticide quantities, water required for mixing, and as a result labor, as fewer trips to refill for a given spray event are required.

Improvement of Cercospora leaf spot and powdery mildew resistance of mungbean variety KING through marker-assisted selection

The development of resistant mungbean varieties is one of the most efficient strategies to control major diseases such as Cercospora leaf spot (CLS) and powdery mildew (PM). The objectives of this study were to pyramid a CLS resistance gene and two PM resistance genes from the donor parent D2 into a susceptible variety KING through marker-assisted backcrossing (MABC) and to evaluate their agronomic traits and disease resistance under field conditions. Five markers linked to the resistance genes were used for foreground selection, while two marker sets [Set A containing 15 polymorphic simple sequence repeat (SSR) and expressed sequence tag-SSR (EST-SSR) markers and Set B containing 34 polymorphic inter-simple sequence repeat (ISSR) loci] were also used for background selection. Two pyramided backcross (BC) lines, namely H3 and H4, were homozygous at all five marker loci when confirmed in BC4F4 and BC4F5 generations. Their recurrent parent genome (RPG) recovery ranged from 96.4 to 100.0%, depending on the marker sets. During field evaluation, a moderate to high level of CLS and PM resistance was observed in both BC lines compared to the susceptible recurrent parent KING. One of these BC lines (H3) had all agronomic traits similar or superior to the recurrent parent KING at all environments, and had a higher yield than KING (18.0–32.0%) under CLS and PM outbreaks. This line can be developed into a new resistant mungbean variety in Thailand in the future. These results substantiate the usefulness of MABC for transferring multiple resistance genes into an elite variety.

Morphological and molecular identification of new records and new host plants of powdery mildews (Erysiphaceae) from Mexico

Powdery mildew is one of the most severe diseases affecting Cucurbitaceae. We identify the members of Erysiphaceae infecting cucurbits in three producing regions in Mexico. We determined that Golovinomyces ambrosiae, Neoerysiphe sechii, and Podosphaera xanthii infected cultivated and wild cucurbits species or subspecies. Leaf samples showing symptoms and signs of powdery mildew were collected from the northwestern, central western, and eastern regions of Mexico between 2017 and 2020. Species associated with the disease were identified based on morphology and ITS rDNA sequences. All powdery mildew specimens presented only the anamorph. Podosphaera xanthii was the predominant species; it was found in 85.7 % of the samples and in 13 out of 14 species or subspecies of cucurbits. Neoerysiphe sechii was found in 15.23 % of the samples and in only four cucurbit species from the central western and eastern regions of Mexico. Golovinomyces ambrosiae was documented for the first time in a Cucurbitaceae species (Sicyos deppei) from Central West Mexico. Three new hosts were registered for Neoerysiphe sechii (Cucurbita ficifolia, Echinopepon milleflorus, and Sicyos laciniatus) and eight for Podosphaera xanthii (Cucurbita argyrosperma, C. argyrosperma subsp. sororia, C. ficifolia, C. okeechobeensis subsp. martinezii, C. radicans, Sechium edule, Sicyos laciniatus, and S. deppei).

Evaluation of resistant genotypes and their characterization using molecular markers linked for powdery mildew resistance in cucumber (Cucumis sativus L.)

Powdery mildew (PM) is one of the most severe fungal diseases of cucumber that limits its production worldwide. In this study, 140 genotypes of cucumber were screened for disease resistance under field and artificial conditions, and then validated with eight known SSR markers linked to PM resistance. Among these genotypes, genotype GS140 was found resistant (R), whereas GS148, GS16 and GS70 were moderately resistant, and GS169 was found to be tolerant. Of all the eight markers, only C31, C80, C162, SSR16472 and SSR16881 amplified the reported linked allele. The 127 bp allele of SSR16881 was found to be associated with the lowest disease severity of 37.65%. The associated markers could further be verified for their usability using linkage studies and the contrast genotypes in the present study could serve as a tool for selection in future marker-assisted selection breeding strategies for PM resistance.

Polyketide Derivatives in the Resistance of Gerbera hybrida to Powdery Mildew

Powdery mildew is a common disease affecting the commercial production of gerbera flowers (Gerbera hybrida, Asteraceae). Some varieties show a certain degree of resistance to it. Our objective was to identify biomarkers of resistance to powdery mildew using an 1H nuclear magnetic resonance spectroscopy and chemometrics approach in a complex, fully factorial experiment to suggest a target for selection and breeding. Resistant varieties were found to differ from those that were susceptible in the metabolites of the polyketide pathway, such as gerberin, parasorboside, and gerberinside. A new compound probably involved in resistance, 5-hydroxyhexanoic acid 3-O-β-D-glucoside, was described for the first time. A decision tree model was built to distinguish resistant varieties, with an accuracy of 57.7%, sensitivity of 72%, and specificity of 44.44% in an independent test. Our results suggest the mechanism of resistance to powdery mildew in gerbera and provide a potential tool for resistance screening in breeding programs.