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Author(s):  
Haonan Cui ◽  
Chao Fan ◽  
Zhuo Ding ◽  
Xuezheng Wang ◽  
Lili Tang ◽  
...  

2022 ◽  
Vol 8 (1) ◽  
pp. 46
Author(s):  
Khonesavanh Chittarath ◽  
Chung Huy Nguyen ◽  
Wendy C. Bailey ◽  
Si-Jun Zheng ◽  
Diane Mostert ◽  
...  

Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. cubense (Foc), poses a major threat to global banana production. The tropical race 4 (TR4) variant of Foc is a highly virulent form with a large host range, and severely affects Cavendish bananas. Foc TR4 was recently observed within the Greater Mekong Subregion, after Chinese private companies expanded Cavendish production to the region. In this study, extensive surveys conducted across Laos and Vietnam show that Foc TR4 is still mainly constricted to the northern regions of these countries and is limited to Cavendish cultivation settings. In Laos, Foc TR4 is associated with large-scale Cavendish plantations owned by or involved with Chinese companies through which infected planting material could have been imported. In Vietnam, mostly small-holder Cavendish farmers and backyard gardens were affected by Foc TR4. In Vietnam, no direct link is found with Chinese growers, and it is expected the pathogen mainly spreads through local and regional movement of infected planting materials. Foc TR4 was not recorded on banana cultivars other than Cavendish. The extensively cultivated ‘Pisang Awak’ cultivar was solely infected by VCGs belonging to Foc race 1 and 2, with a high occurrence of VCG 0123 across Laos, and of VCG 0124/5 in Vietnam. Substantial diversity of Foc VCGs was recorded (VCGs 0123, 0124/5, 01218 and 01221) from northern to southern regions in both countries, suggesting that Fusarium wilt is well established in the region. Interviews with farmers indicated that the local knowledge of Fusarium wilt epidemiology and options for disease management was limited. Clear communication efforts on disease epidemiology and management with emphasis on biosecurity practices need to be improved in order to prevent further spread of Foc TR4 to mixed variety smallholder settings.


Plant Disease ◽  
2021 ◽  
Author(s):  
Miryam Valenzuela ◽  
Bastian Fuentes ◽  
Juan Felipe Alfaro ◽  
Eduardo Galvez ◽  
Aldo Salinas ◽  
...  

In Chile, tomato is one of the most widely cultivated vegetables, with around 5,000 ha for fresh market and 8,000 ha for processing industry. During recent years, symptoms of bacterial speck caused by Pseudomonas syringae pv. tomato, have been observed more frequently in tomato plants in different regions of Chile. This pathogen was first identified in Chile in 1987 (Latorre & Lolas, 1988) and the presence of an apparent new variant was reported in 2004 (Besoain et al. 2004). To characterize the pathogen that was affecting this crop, samples of diseased tomato plants were taken in three regions of Chile. The samples were collected in 2016 in Northern Chile in Lluta Valley from the Arica y Parinacota Region, and in Central Chile, in 2014 in Limache from Valparaíso Region and in 2015 in Pichidegua from O´Higgins Region. Affected tomato plants exhibited dark brown to black lesions surrounded by yellow halos in the leaves, and dark brown to black lesions in the stems, pedicels, and peduncles. Plants tissues were macerated, and the suspension was spread on King’s B medium, resulting in fluorescent colonies visualized under 366 nm UV light. LOPAT tests results of three selected isolates from different Regions, were: levan production (+), oxidase reaction (-), potato soft rot (-), arginine dihydrolase production (-), and tobacco hypersensitivity (+) (Lelliot et al. 1966). Molecular identification was carried out by amplification and sequence analysis of housekeeping genes cts, encoding citrate synthase, gyrB, encoding DNA gyrase B, and rpoD, encoding sigma factor 70 (Hwang et al. 2005; Sarkar & Guttmann 2004) (GenBank Accessions No. OK001658-OK001666). BLAST analysis of cts and rpoD genes of the three isolates resulted in a match with a 100% identity (919 bp and 491 bp respectively) with Pseudomonas syringae pv. tomato strain B13-200 (GenBank: CP019871.1). BLAST analysis of gyrB gene of two isolates resulted in a match with a 100% identity (684 bp) and one isolate with 99.85% (683 bp) with Pseudomonas syringae pv. tomato strain B13-200. To identify the race 1, each strain was inoculated in five tomato plants cv. San Pedro, susceptible to both races of P. syringae pv. tomato, and cv. Rio Grande, resistant to race 0. The tomato plants were slightly wounded with a metal sponge and then sprayed with the bacterial suspension (108 CFU mL-1) of each isolate, including the reference strain DC3000 (race 0). Negative controls were sprayed with water. The plants inoculated with Chilean strains in both cv. San Pedro and cv. Rio Grande, showed symptoms of bacterial speck after 7 days. Plants inoculated with DC3000 strain showed symptoms only in cv. San Pedro, whereas control plants remained asymptomatic. Strains were re-isolated from symptomatic plants and identified by gene sequence analyses as Pseudomonas syryngae pv. tomato. This is the first report of Pseudomonas syryngae pv. tomato race 1 in Chile. Race 1 was previously reported in Canada (Lawton and MacNeill. 1986), in Italy (Buonaurio et al. 1996), in California (Arredondo and Davis 2000), in Portugal (Cruz et al. 2010), and in other states in the USA and countries in South America, Europe, Africa, and Australia, becoming the most commonly isolated race today (Cai et al 2011). These results will be the base for future studies of epidemiology, characterization, and virulence in order to explain the outbreak of this disease and the severity of symptoms observed.


2021 ◽  
Author(s):  
Dominique D. A. Pincot ◽  
Mitchell J. Feldmann ◽  
Michael A. Hardigan ◽  
Mishi V. Vachev ◽  
Peter M. Henry ◽  
...  

Fusarium wilt, a soilborne disease caused by Fusarium oxysporum f. sp. fragariae, poses a significant threat to strawberry (Fragaria × ananassa) production in many parts of the world. This pathogen causes wilting, collapse, and death in susceptible genotypes. We previously identified a dominant gene (FW1) on chromosome 2B that confers resistance to race 1 of the pathogen and hypothesized that gene-for-gene resistance to Fusarium wilt was widespread in strawberry. To explore this, a genetically diverse collection of heirloom and modern cultivars and wild octoploid ecotypes were screened for resistance to Fusarium wilt races 1 and 2. Here we show that resistance to both races is widespread and that resistance to race 1 is mediated by dominant genes (FW1, FW2, FW3, FW4, and FW5) on three non-homoeologous chromosomes (1A, 2B, and 6B). The resistance proteins encoded by these genes are not yet known; however, plausible candidates were identified that encode pattern recognition receptor or other proteins known to mediate gene-for-gene resistance in plants. High-throughput genotyping assays for SNPs in linkage disequilibrium with FW1-FW5 were developed to facilitate marker-assisted selection and accelerate the development of race 1 resistant cultivars. This study laid the foundation for identifying the genes encoded by FW1-FW5, in addition to exploring the genetics of resistance to race 2 and other races of the pathogen, as a precaution to averting a Fusarium wilt pandemic.


2021 ◽  
Vol 39 (4) ◽  
pp. 411-416
Author(s):  
Carlos A Lopes ◽  
Agnaldo DF Carvalho ◽  
Arione S Pereira ◽  
Fernanda Q Azevedo ◽  
Caroline M Castro ◽  
...  

ABSTRACT Bacterial wilt (BW), or brown rot, caused by the soil and seed borne bacterium Ralstonia solanacearum, is one of the most devastating diseases of potatoes cultivated in warmer regions of the world. There are no potato cultivars with a desirable level of BW resistance, although it has been recognized that resistance can be an outstanding component for disease management. However, the sources of resistance available lack agronomic traits required by potato growers, therefore being of little interest to breeders. The objective of this work was to evaluate the performance of 11 clones selected for BW resistance and improved for tuber traits upon selection in the last two decades. The clones under test were compared with susceptible and resistant clones and cultivars, in a completely randomized blocks design with three replications of single lines of 10 plants, in a field naturally infested with race 1, biovar 1, phylotype II of R. solanacearum. BW incidence was assessed 60-70 days after planting and total tuber yield in each plot was recorded 110 days after planting. All the evaluated clones presented higher levels of resistance to BW compared with the commercial varieties, not differing from the resistant, not commercial, controls. In a next step, these clones will be characterized for other desirable traits and those which combine high level of resistance and commercial characteristics will be recommended for breeders for enriching the genotypic background in the search for commercial varieties. We also confirmed that the cultivar BRSIPR Bel displays an intermediate level of resistance, what makes it an interesting genitor for its good agronomic characteristics. The findings of this work demonstrate that the improved potato clones selected under tropical conditions in the Embrapa’s pre-breeding project possess high and stable levels of resistance to bacterial wilt, being a valuable resource for breeders.


2021 ◽  
Vol 15 (11) ◽  
pp. 277-287
Author(s):  
Oyesigye Elias ◽  
Tinzara William ◽  
Karamura Georgina ◽  
Cosmas Wacal

HortScience ◽  
2021 ◽  
pp. 1-13
Author(s):  
Jesse J. Murray ◽  
Gulnoz Hisamutdinova ◽  
Germán V. Sandoya ◽  
Richard N. Raid ◽  
Stephanie Slinski

Fusarium wilt of lettuce is caused by the pathogen Fusarium oxysporum f. sp. lactucae (Fol) and is a growing threat to global lettuce production. Fol was first detected in Florida in 2017 and was subsequently confirmed as race 1. Management strategies for this long-persisting soil pathogen are limited, time-consuming and expensive, and they may lack efficacy. Identifying diverse sources of genetic resistance is imperative for breeding adapted cultivars with durable resistance. The objectives of this study were to identify sources of resistance against a race 1 isolate of Fol in Florida, delineate the relationship between foliar and taproot symptoms, and investigate the inheritance of resistance and partial resistance in two F2 populations. Thirteen experiments were conducted in greenhouse and field locations to characterize the diversity of genetic resistance in the genus Lactuca. Leaf cultivars Dark Lollo Rossa and Galactic; romaine breeding lines 43007, 60182, and C1145; and iceberg breeding line 47083 consistently exhibited low foliar and taproot disease symptoms. Resistance was not identified among the wildtype Lactuca or primitive plant introductions (PI) in this study based on taproot symptoms. An additional test was conducted to study the segregation pattern of Fol resistance between one resistant and one susceptible accession (R × S) and one partial resistant and one susceptible accession (PR × S). The F2 population from ‘60182 × PI 358001-1’ fit the expected segregation ratio for a single recessive locus model, whereas the ratio for ‘Dark Lollo Rossa × PI 358001-1’ did not fit either recessive or dominant single locus models. These sources of resistance are potential candidates for developing commercial cultivars with multiple resistance loci against Fol race 1, especially for the Florida lettuce production system.


2021 ◽  
Author(s):  
◽  
Barry Victor Sneddon

<p>The taxonomy of Microseris subgenus Monermos (Hook. f.) Chambers (Compositae) is investigated. Two species are recognized, namely M. scapigera (sol. ex A. Cunn.) Sch.-Bip. and M. lanceolata (Walp.) Sch.-Bip., which are confined to New Zealand and Australia respectively. In M. scapigera, taxonomic subdivision was not practicable, the formae of Allan (1961) not being upheld. Microseris lanceolata is subdivided into three groups which are described informally as races. The races are viewed as probable subspecies but need further study before this status can be confirmed. The two species are described and illustrated and details are given for each on typification, synonymy, chromosome number, distribution, ecology and geographical variation. Strong self-incompatibility is prevalent in both M. scapigera and M. lanceolata. The only exceptions in the populations examined were in M. scapigera, in which two populations were only moderately self incompatible, and another was substantially self-compatible. The last population appeared to have morphological and behavioural adaptations to promote autogamy. Artificial hybridizations were made within and between the two species. Microseris scapigera and M. lanceolata were freely or poorly intercrossable according to the populations used, and formed semi-fertile or sterile hybrids. Semi-fertile hybrids were virtually blocked from forming a F2 generation (fruit set was very low and no fruits germinated) but they cold be backcrossed. Fertility in BC1 hybrids was mostly higher than in the F1, but was not restored to normal. Microseris scapigera and M. lanceolata race 1 appear to have largely homologous chromosomes. Attempts to cross the species of subgenus Monermos with M. borealis (subgenus Apargidium) were unsuccessful</p>


2021 ◽  
Author(s):  
◽  
Barry Victor Sneddon

<p>The taxonomy of Microseris subgenus Monermos (Hook. f.) Chambers (Compositae) is investigated. Two species are recognized, namely M. scapigera (sol. ex A. Cunn.) Sch.-Bip. and M. lanceolata (Walp.) Sch.-Bip., which are confined to New Zealand and Australia respectively. In M. scapigera, taxonomic subdivision was not practicable, the formae of Allan (1961) not being upheld. Microseris lanceolata is subdivided into three groups which are described informally as races. The races are viewed as probable subspecies but need further study before this status can be confirmed. The two species are described and illustrated and details are given for each on typification, synonymy, chromosome number, distribution, ecology and geographical variation. Strong self-incompatibility is prevalent in both M. scapigera and M. lanceolata. The only exceptions in the populations examined were in M. scapigera, in which two populations were only moderately self incompatible, and another was substantially self-compatible. The last population appeared to have morphological and behavioural adaptations to promote autogamy. Artificial hybridizations were made within and between the two species. Microseris scapigera and M. lanceolata were freely or poorly intercrossable according to the populations used, and formed semi-fertile or sterile hybrids. Semi-fertile hybrids were virtually blocked from forming a F2 generation (fruit set was very low and no fruits germinated) but they cold be backcrossed. Fertility in BC1 hybrids was mostly higher than in the F1, but was not restored to normal. Microseris scapigera and M. lanceolata race 1 appear to have largely homologous chromosomes. Attempts to cross the species of subgenus Monermos with M. borealis (subgenus Apargidium) were unsuccessful</p>


Plant Disease ◽  
2021 ◽  
Author(s):  
Jing Jin ◽  
Kestrel Lannon McCorkle ◽  
Vicki Cornish ◽  
Ignazio Carbone ◽  
Ramsey Lewis ◽  
...  

Host resistance is an important tool in the management of black shank disease of tobacco. While race development leads to rapid loss of single-gene resistance, the adaptation by Phytophthora nicotianae to sources of partial resistance from Beinhart 1000, Florida 301, and the Wz gene region introgressed from Nicotiana rustica is poorly characterized. In greenhouse environments, host genotypes with QTLs conferring resistance from multiple sources were initially inoculated with an aggressive isolate of race 0 or race 1 of P. nicotianae. The most aggressive isolate was selected after each of six host generations to inoculate the next generation of plants. The race 0 isolate demonstrated a continuous gradual increase in disease severity and percent root rot on all sources of resistance except the genotype K 326 Wz/--, where a large increase in both was observed between generations two and three. Adaptation by the race 0 isolate on Beinhart 1000 represents the first report of adaptation to this genotype by P. nicotianae. The race 1 isolate did not exhibit significant increases in aggressiveness over generations, but also exhibited a large increase in aggressiveness on K 326 Wz/-- between generations 3 and 4. Molecular characterization of isolates recovered during selection was completed using ddRADseq, but no polymorphisms were associated with the observed changes in aggressiveness. The rapid adaptation to Wz resistance and the gradual adaptation to other QTLs highlights the need to study the nature of Wz resistance and for conducting field studies on efficacy of resistance-gene rotation for disease management.


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