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Raspberry root rot and wilting complex (RRWC), primarily caused by Phytophthora rubi, is the most important disease for raspberry producers in Canada. There is currently little to no information on phenotypic diversity or sensitivity to metalaxyl-m of P. rubi isolates affecting raspberries in Canada. This study was conducted to understand the diversity in virulence and sensitivity to metalaxyl-m of P. rubi populations collected from diverse raspberry cultivars, fields, and locations during 2018–2020. All isolates of P. rubi (n = 24) were pathogenic on 'Chemainus' raspberry and showed significant variation (P < 0.05) in days to first foliar symptom development (DFSD) and progress in wilting index, as indicated by relative areas under disease progress curves (rAUDPC). Principal component analyses identified that root rot index, rAUDPC, DFSD, and percentage reduction in root length and weight were important variables in assessing pathogen virulence. Metalaxyl-m sensitivity was assessed using a radial growth assay and effective concentrations that inhibited 50% of mycelial growth (EC50) were determined for 44 isolates. The EC50 values ranged from 0.035–4.71 µg mL−1 with a mean value of 0.793 µg mL−1. About 61% of the isolates were very sensitive (EC50 values <0.20 µg mL−1), 25% of isolates were considered sensitive (EC50 values of 0.21–1.18 µg mL−1), and 14% of isolates showed reduced sensitivity to metalaxyl-m (EC50 value range of 1.19–4.71 µg mL−1). Knowledge of pathogen phenotypic diversity will be useful for raspberry breeders in screening genotypes against RRWC and the results of the fungicide sensitivity study will be useful in developing management strategies for RRWC. [ABSTRACT FROM AUTHOR]

Phytophthora species are primary causal agents of raspberry root rot and wilting complex (RRWC), a disease complex that is of major concern to raspberry producers worldwide. Accurate identification of the causal agents is a first step for effective disease management. Advancements in molecular diagnostics can facilitate the detection of multiple pathogen species associated with this disease complex. We developed multiplex targeted-sequencing methods using degenerate primers for heat shock protein 90, elongation factor 1α and β-tubulin genes to identify Phytophthora species causing RRWC. One hundred and twenty-eight isolates recovered during 2018 to 2020 from diverse fields in major raspberry growing areas of British Columbia (BC) were sequenced and identified by comparing with known reference sequences of 142 Phytophthora species, 111 Pythium species, and nine Phytopythium species in the NCBI database. This multiplex targeted-sequencing method was highly specific and identified two species of Phytophthora associated with RRWC. These were P. rubi (85% of isolates) and P. gonapodyides (15% of isolates). Phytophthora rubi was predominantly isolated from the cultivars 'Chemainus' (51%), 'Rudi' (27%) and 'Meeker' (15%), whereas P. gonapodyides was predominately isolated from the moderately resistant cultivar 'Cascade Bounty'. Pathogenicity studies on intact plants and detached leaves confirmed that P. rubi and P. gonapodyides can cause symptoms of RRWC on raspberry, thus fulfilling Koch's postulates. To our knowledge, this is the first report of P. gonapodyides as a causal agent of RRWC on raspberry in BC. This study provides novel insights into the identification and species composition of Phytophthora associated with RRWC in raspberry production systems. [ABSTRACT FROM AUTHOR]

Red raspberry (Rubus idaeus L.) is an important fruit crop in British Columbia, Canada, and the Pacific Northwest (PNW) region of the USA, as well as in other regions of the world. Root rot and wilting complex (RRWC), primarily caused by Phytophthora rubi, is the most important biotic constraint responsible for declining raspberry production in these regions, causing millions of dollars in losses. Other root-infecting fungal species and the root lesion nematode (Pratylenchus penetrans) may also be found associated with the disease complex. The average lifespan of raspberry plantings in the PNW is 10 to 12 years, which is reduced to 5 years by the disease complex. Phytophthora spp. play a predominant role in the RRWC complex due to the persistent nature of oospores, rapid dispersal of inoculum, and the polycyclic nature of infection, all of which increase disease severity. In this review, we discuss the current understanding of Phytophthora spp. and other pathogens associated with the RRWC, including pathogen biology and the disease cycle, the impact of infection on the plant, as well as current and potential cultural, biological, and chemical options for management. In addition, we discuss breeding efforts for disease resistance, including conventional and molecular approaches to identify sources of resistance, molecular markers linked to potential resistance genes, and their incorporation into elite breeding materials or cultivars. We also present the current gaps in knowledge, unique challenges, and future perspectives in sustainable disease management of this important disease complex. [ABSTRACT FROM AUTHOR]

Phytophthora root rot and wilt (PRRW), caused by Phytophthora rubi and potentially other species of Phytophthora , is a destructive disease of raspberry in Canada and worldwide. In this study, trials were conducted over multiple years (2019–2022) in two fields, with pathogen (P. rubi) inoculated (PI) and naturally infested (NI) fields, to evaluate foliar and soil applied fungicides with different modes of action and application timings to manage PRRW. In addition, PRRW progress was also monitored in one PI field and four NI fields. In PI field plots, PPRW foliage and wilting symptoms appeared 6–8 weeks later and disease index was significantly (p < 0.0042) lower in the cultivar 'Cascade Bounty' than the cultivars 'Meeker' and 'Tulameen', indicating that 'Cascade Bounty' showed field tolerance to the disease. The efficacy of foliar fungicides (fosetyl-Al and phosphites) and soil-applied fungicides (oxathiapiprolin, metalaxyl-m, and cyazofamid) were assessed on susceptible cultivars at both sites. In PI plots, the fungicide treatments significantly enhanced (p = 0.01 to < 0.0001) numbers of primocanes and floricanes, as well as weight, percent witling index, and fruit yield of floricanes. Soil application of a tank mix or rotation of oxathiapiprolin and metalaxyl-m, and alternating these products with cyazofamid, was more effective compared to other fungicides in reducing PRRW and improving plant vigor. Our study identified effective fungicide treatment options for PRRW, allowing growers to alternate new chemistries with currently registered fungicides to reduce the risk of fungicide resistance development. • Phytophthora root rot and wilt (PRRW) symptoms were more severe on raspberry cultivars 'Meeker' and 'Tulameen' than in 'Cascade Bounty'. • Tank mix of oxathiapiprolin and metalaxyl-m alone or in combination with cyazofamid significantly reduced PRRW and increased plant vigor. • Fungicide treatments increased numbers of primocanes, floricanes (FC), weight of FC, and fruit yield. • Host resistance and fungicide applications can be integrated for PRRW management. [ABSTRACT FROM AUTHOR]

Common root rot ( CRR) and spot blotch, caused by Cochliobolus sativus (Ito and Kurib.) Drechsl. ex Dast., are important diseases of barley ( Hordeum vulgare L.) and wheat ( Triticum aestivum L.) worldwide. However, the population biology of C. sativus is still poorly understood. In this study, the genetic structure of three C. sativus populations, consisting of isolates sampled respectively from barley leaves ( BL), barley roots ( BR) and wheat roots ( WR) in North Dakota, was analysed with amplified fragment length polymorphism ( AFLP) markers. A total of 127 AFLP loci were generated among 208 C. sativus isolates analysed with three primer combinations. Gene diversity ( H = 0.277-0.335) were high in all three populations. Genetic variation among C. sativus individuals within population accounted for 74%, whereas 26% of the genetic variation was explained among populations. Genetic differentiation was high ( ØPT = 0.261, corrected [ABSTRACT FROM AUTHOR]

Dry root rot (DRR) is an important emerging disease of mungbean caused by fungus Macrophomina phaseolina. The disease is seed and soil-borne and hence management is difficult. Exploitation of host resistance could be a good option to manage the disease. The objectives of this study were to characterize the isolates of M. phaseolina from three legume crops and to identify resistant sources against DRR of mungbean. Isolates of M. phaseolina from mungbean, urdbean, and vegetable soybean were identified using morphological characteristics and sequencing internal transcribed sequence (ITS) region of 18S rRNA. Isolates of M. phaseolina from urdbean and vegetable soybean were inoculated on susceptible check genotype of mungbean to assess their pathogenicity. Forty three mungbean genotypes were screened against M. phaseolina isolate of mungbean using the paper towel method to identify sources of resistance. Among these genotypes, 9 were resistant in repeated experiment, with disease score ranging from 1.9 to 3.0. Resistant genotypes showing lower disease score, namely IPM99-125, EC693368, and EC693369, were further screened using the sick pot method to confirm their resistance. Among these three genotypes, IPM99-125 showed consistently higher plant survival rate followed by EC693368 and EC693369 as compared to susceptible checks (VC3960-88, KPS1). In addition, these three genotypes were resistant when screened with two strains of M. phaseolina isolated from urdbean and vegetable soybean, with IPM99-125 having lower disease score. The mungbean genotype IPM99-125 could be useful in mungbean breeding programs to develop root rot-resistant varieties. • Macrophomina phaseolina isolated from mungbean, urdbean and vegetable soybean showed identical cultural and molecular characteristics. • Screening of 43 mungbean genotypes against DRR revealed resistance of IPM99-125, EC693368 and EC693369 genotypes. • The above three genotypes also showed resistance against M. phaseolina isolated from urdbean and vegetable soybean. • Genotype IPM99-125 exhibited higher plant survival could be useful in mungbean breeding programs to develop DRR resistant varieties. [ABSTRACT FROM AUTHOR]