A preliminary study highlights the potential diversity within the Australian Bgt population and emphasises the importance of continuous monitoring to support the effective deployment of resistance resources, ultimately reducing reliance on fungicides.
Abstract
The obligate biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), the causal agent of wheat powdery mildew, has become increasingly prevalent in Australia. Recent reports of fungicide-resistant Bgt isolates further highlight the need for effective management strategies. However, only a few studies have investigated the Australian Bgt population, limiting the effective deployment of resistant cultivars for disease management.
To evaluate the virulence complexity of the Australian Bgt population and to identify lines with currently effective wheat powdery mildew resistance genes.
To investigate virulence diversity, 30 Australian Bgt isolates from various geographical locations and hosts were collected between 2020 and 2024 and screened against a panel of 24 wheat lines carrying defined major resistance genes.
Virulence complexity did not differ between eastern and western Bgt populations (P = 0.695), although Pm3a, Pm16, Pm17, and Pm4b were effective only in the western region, whereas Pm3d was effective only in the eastern region. Khapli (Pm4a) and Tabasco (Pm2), both carrying additional unknown resistance gene(s), were highly resistant to all isolates. Similarly, European cultivars Alchemy, Cordiale, and Einstein remained resistant to representative Australian Bgt isolates.
Virulence profiling showed substantial diversity within the Australian Bgt population. However, wheat varieties carrying defined resistance genes and their combinations are available and remain effective against contemporary Australian Bgt isolates.
This preliminary study highlights the potential diversity within the Australian Bgt population and emphasises the importance of continuous monitoring to support the effective deployment of resistance resources, ultimately reducing reliance on fungicides.
Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a major constraint to wheat production in China. Although the disease occurs in Tibet every year under the favorable weather conditions, the virulence diversity and population structure of the Pst population in this region remain poorly understood. In this study, 312 Pst isolates collected in 2025 from five major wheat-growing regions of Tibet (Qamdo, Nyingchi, Lhasa, Shannan, and Shigatse) were characterized using virulence phenotyping and the Pst 5K genotyping-by-target-sequencing (GBTS) platform. Virulence testing on 19 Chinese differentials identified 139 races, including 88 previously reported and 51 novel races, with Su11-3, HY-009-1, and CYR34 being the predominant races. Testing the isolates with 18 Yr single-gene differentials identified 190 virulence phenotypes. None of the isolates were virulent to Yr5 or Yr15, whereas virulence frequencies to the remaining Yr genes ranged from 2.2% to 89.7%. Population genetic analyses using the GBTS data revealed clear regional differentiations. The Nyingchi population formed a distinct cluster with relatively low genomic diversity despite maintaining considerable virulence diversity, whereas the Lhasa and Shannan populations showed extensive admixture.The Qamdo and Shigatse populations consisted of unique genetic components and exhibited relatively high levels of virulence and genetic diversities. Combined virulence and genomic analyses indicated region-specific epidemiological characteristics and suggested that Qamdo may represent an important center of Pst diversification, whereas Lhasa and Shannan may facilitate pathogen dispersal and gene exchange. This study provides the first comprehensive assessment of Pst populations across Tibet and offers valuable information for disease surveillance, resistance breeding, and integrated management of wheat stripe rust in Tibet and neighboring wheat-growing regions.
Li Geng, Ying Li, Hexin Chen et al.· Plant Disease· 0 citations
Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), threatens food security owing to the pathogen’s high virulence and evolutionary variability, as well as the risk of selecting fungicide-resistant forms. For the first time in Russia, we performed a comparative analysis of virulence and genetic diversity in fungicide-target genes (SdhA–SdhD, Cyp51) in 35 monopustular Pgt isolates collected from regions with contrasting fungicide pressure (Saratov, n = 12; Chelyabinsk, n = 12; Moscow, n = 11). Phenotyping on an extended set of nearly isogenic lines carrying different Sr genes revealed regional specificity in effective resistance genes (Sr13, Sr26, Sr31, Sr32, Sr35), underscoring the vulnerability of genetic protection in Russian commercial cultivars. Targeted amplicon sequencing using the Oxford Nanopore Technologies platform produced 175 amplicons (~38,290 long reads, N50 = 1.06 kb), identifying 87% synonymous SNPs, 12% non-synonymous substitutions, and a single nonsense mutation in SdhA (position 580). The Cyp51 and SdhA genes were the most polymorphic. Recurrent non-synonymous mutations in these genes were detected in Pgt clones from regions with intensive agriculture and high use of chemical plant protection products. These results support the need for predictive breeding of resistant cultivars and adaptation of chemical control within integrated Pgt management in the European part of Russia.
K. Dudnikova, O. Baranova, A. Shingaliev et al.· Journal of Fungi· 0 citations
Fusarium wilt of lettuce, caused by Fusarium oxysporum forma specialis lactucae (FOLac), is an increasing constraint to lettuce production worldwide, particularly because changes in race structure and the emergence of isolates able to overcome host resistance can compromise cultivar-based management. However, information on FOLac race composition and pathogenic variation in Spain remains limited. This study characterized the race structure, molecular diversity, and pathogenic behavior of FOLac isolates collected in Spain between 2019 and 2025. A total of 81 isolates recovered from symptomatic lettuce tissues and soil samples from major lettuce-producing regions were analyzed. Race assignment was performed using race-specific PCR and detection of SIX effector genes, and phylogenetic relationships were inferred from concatenated tef-1α and rpb2 sequences. Pathogenicity assays were conducted with selected race 1 on differential lettuce cultivars to assess aggressiveness and resistance responses. Race 1 was predominant, representing 75.3% of the isolates, and showed broad geographic distribution and temporal persistence. Race 4 was less frequent, representing 9.9% of the isolates, but was detected in southeastern Spain, indicating localized occurrence in a major production area. The remaining 14.8% of the isolates, all recovered from soil samples, were not assigned to FOLac. Phylogenetic analysis separated isolates molecularly assigned to FOLac from non-assigned F. oxysporum isolates but did not resolve races 1 and 4 as distinct groups. Pathogenicity assays revealed variation in aggressiveness among race 1 isolates, including resistance-breaking behavior on `Costa Rica No. 4´ and `Palmos´. These results show that FOLac populations in Spain are epidemiologically and biologically heterogeneous and highlight the need to integrate molecular tools and pathogenicity assays for race surveillance, breeding programs, and disease management.
Moisés de León, Daniel Palmero, Laura Gálvez· Plant Disease· 0 citations
Rhizoctonia solani AG-3 is a major pathogen of solanaceous crops, with subgroups PT, TB, and TM causing potato black scurf and tobacco target spot in China, yet their population structures remain unexplored. Here, we used microsatellite markers to genotype 160 PT isolates from Northeast China, 189 TB and 124 TM isolates from tobacco-growing areas nationwide, and assessed their baseline sensitivity to fludioxonil. The three subgroups exhibited contrasting structures. PT showed high gene diversity (Hexp = 0.634) but significant linkage disequilibrium and low differentiation (FST = 0.008-0.033) without isolation-by-distance, suggesting clonal reproduction and dispersal via contaminated seed tubers. TB displayed moderate diversity (Hexp = 0.385), linkage equilibrium, and significant isolation-by-distance, indicating sexual reproduction with gene flow constrained by geography. The Yunnan population may represent a diversity center. TM showed the lowest gene diversity (mean Hexp = 0.273), low differentiation (FST = 0.005-0.051), and a mixed reproductive mode: Liaoning populations exhibited linkage equilibrium (P > 0.05), while Heilongjiang and Jilin populations showed significant disequilibrium (P < 0.01). High genetic differentiation (FST = 0.269-0.549) confirmed PT, TB, and TM as distinct lineages, with PT and TM most closely related. Fludioxonil effectively inhibited all subgroups (mean EC50 = 0.054-0.090 mg·L-1), with six resistant isolates detected. Sensitivity was independent of origin or genetic background. This study reveals contrasting population structures among AG-3 subgroups, and provides a foundation for subgroup-specific disease management and resistance monitoring.
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Lettuce Downy Mildew (LDM), caused by Bremia lactucae, is a major disease during the winter, particularly under prolonged wetness periods. Pathogen populations are dynamic and evolve through the emergence of new virulence phenotypes (v-phenotypes). Breeding programs focus on identifying resistance genes that confer broad and durable resistance, particularly against highly virulent populations such as those commonly reported Europe, and USA. Private breeding companies, on the other hand, are engaged to identify resistance genes (R-genes) that offer useful resistance to LDM. Continuous monitoring of B. lactucae population is crucial to aid the development and deployment of LDM-resistant cultivars. This study aimed to monitor the v-phenotypes of B. lactucae in major lettuce production regions in Brazil. A differential set of lettuce genotypes was used to determine the sextet codes corresponding to the v-phenotypes of isolates collected in 2020-2022. The most prevalent v-phenotypes were 31-00-00, 51-00-00, and 31-00-02. The R-genes found in ‘Balesta’, ‘Kibrille’, ‘Bartoli’, and ‘RYZ910457’ provided resistance against most of the isolates collected. The R-gene present in ‘Balesta’ is particularly effective for LDM, breeding programs should aim to improve lettuce similar to this cultivar for the Brazilian market. V-phenotypes corresponding to European (Bl:16EU, Bl:18EU, Bl:20EU, Bl:23EU, Bl:24EU, Bl:25EU, Bl:26EU), and USA (Bl: 8US) Bremia races were identified. Unique v-phenotypes of B. lactucae were found in Brazil, along with the detection of several common to Europe, suggesting that new lettuce cultivars tested for resistance to these European v-phenotypes, are likely to exhibit some degree of resistance in these Brazilian regions.
Izabella Garbeline Okuma, Pablo Forlan Vargas, C. Franco et al.· PhytoFrontiers™· 0 citations
Spot blotch caused by fungal pathogen Bipolaris sorokiniana (Sacc.) Shoemaker is an important fungal disease in warm and humid wheat growing condition. Study on pathogenic variability of B. sorokinianana isolates is limited in Nepal. Information based on host × pathogen interaction is a useful tool to devise the disease management strategy. Therefore, aggressiveness of total 36 single spore isolates of B. sorokiniana (27 isolates from terai, 7 isolates from mid hill and 2 isolates from high hill) of Nepal were evaluated on 14 days old seedling of RR-21 (susceptible check), Guatam (moderate resistant) and Chirya 3 (resistant check) under polyhouse condition. Results revealed highly significant isolate-by-variety interaction (P<0.001) for all the disease development traits, suggesting substantial variability in the pathogenicity of the isolates. Moreover, days to disease appearance, number of lesions per leaf and disease severity was highly correlated to Area Under Disease Progress Curve (AUDPC), illustrating those traits as an important indicator of disease development and pathogen aggressiveness. RR-21 exhibited susceptible to overall isolates response followed by Gautam and Chirya 3. On the basis of AUDPC value, top ten aggressive isolates were identified (N-BS24, N-BS7, N-BS28, N-BS36, N-BS27, N-BS37, N-BS15, N-BS38, N-BS19 and N-BS16). Among them, N-BS24 and N-BS28 were able to show high disease against resistant check Chirya 3, so aggressiveness of these two isolates can be further validated through adult plant screening and genetic study and utilize it for resistant breeding program in Nepal.
L. Aryal, S. Shrestha, H. Manandhar et al.· Nepal Agriculture Research J...· 0 citations
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