A standard set of host differentials and unified nomenclature for an international collection of Diplocarpon rosae races

Black spot of rose is distributed throughout the world and is the most serious disease of roses (Rosa spp.) in the outdoor landscape. Resistance breeding has been frustrated by the occurrence of races of the causal pathogen Diplocarpon rosae. Races from Germany, North America and the UK have been characterized and maintained in a pathogenic state. However, these races were characterized using independent sets of host genotypes and are referenced using different nomenclatures. In the present study, a total of 15 D. rosae isolates from these locations, as well as Belgium and Italy, were inoculated to a common set of 15 rose cultivars in replicated, detached leaf trials. Baby Love^TM (cv. Scrivluv) was resistant to all isolates except for one originating from the UK. The rose cultivars Mrs Doreen Pike (Ausdor) and Hansa were resistant to all isolates except for one originating from Minnesota, USA. No rose genotype was universally susceptible. A total of 11 pathogenic races were differentiated based on their unique host ranges and were assigned an international race nomenclature. Nine cultivars are proposed as the first standard set of differential genotypes for characterization of D. rosae races.     

The gene diversity pattern of Diplocarpon rosae populations is shaped by the age,diversity and fungicide treatment of their host populations

Black spot disease caused by the hemibiotrophic ascomycete Diplocarpon rosae is the most devastating disease of field‐grown roses. Although resistance to black spot is an important trait for rose breeding, little information on the diversity of the pathogen is currently available. To date, a number of single‐spore isolates have been characterized based on a set of test genotypes of the host. In this study, six polymorphic simple sequence repeat (SSR) markers for D. rosae were developed and their potential application to single‐spore isolates collected from a wide range of geographic locations within and outside Europe discussed. Populations of the fungus were then analysed in different German rose collections/populations. Gene diversity was highest in older rose collections managed without fungicide application, and lowest in the two‐ to three‐year‐old testing sites of German rose breeders. Additional analyses of a global collection of single samples and populations revealed no unique alleles from any of the locations, indicating that global trading of rose varieties has led to an admixture of the pathogen.     

Interactions of four pathotypes of Diplocarpon rosae with species and hybrids of Rosa

The interactions of four pathotypes of Diplocarpon rosae with 34 species and hybrids of Rosa were compared in an ongoing search for criteria of potential relevance to rose breeding. There were greater similarities in the resistance‐susceptibility interactions of these roses to the pathotypes DA1, CW1 and ZM1, than to a fourth pathotype, DA2. Among the species roses, only those of the section Cinnamomeae were susceptible to DA2 and this susceptibility was transmitted in several cases to hybrid progeny. CW1 had the greatest pathogenicity of the four pathotypes. In a cross between R. rugosa cv. Scabrosa, which was resistant and R. rugosa f. alba, which was susceptible to all pathotypes, the progeny were tested for resistance to pathotypes DA1, CW1 and ZM1. Each of the 20 progeny was susceptible to all three pathotypes. This shows that, unlike the well characterized Rdr1 gene for resistance to D. rosae, the resistance of R. rugosa cv. Scabrosa is not determined by a dominant major gene. The diploid hybrid, R. rugosa cv. Martin Frobisher × cv. Mistress Quickly, was resistant to all four pathotypes, but an induced tetraploid of this hybrid was susceptible to all pathotypes. The relevance of these findings to the breeding of roses for resistance to black spot disease is discussed.     

Genetic diversity and pathogenicity of Sphaceloma rosarum (teleomorph Elsinoë rosarum) causing spot anthracnose on roses

Roses produced or grown in the field, as well as pot‐grown and cut roses, are attacked by different fungal pathogens causing leaf spot diseases. The incorrect identification and scoring of these pathogens and the lack of information about their genetic and pathotype diversity hamper resistance breeding. This is especially true for the hemibiotrophic ascomycete Sphaceloma rosarum, which is often confused with other fungi. Here for the first time, the genetic variability between isolates at both the molecular and morphological level is analysed. Eighty leaf spot samples were collected from different rose genotypes at five different locations, and 15 single conidial isolates established. All of the samples showed high morphological similarities to the reference isolate CBS 213.33 that was obtained from a public repository. By sequencing a part of the large subunit (LSU) of the 28S ribosomal RNA and phylogenetic analysis, high sequence similarities were shown to other Sphaceloma species for 13 of the isolates and the CBS reference. One of the isolates clustered with Septoria species and another clustered with Seimatosporium species. UPGMA clustering with 145 polymorphic AFLP markers resulted in five distinct groups in the majority rule consensus tree for the 14 S. rosarum isolates, including the CBS reference. Jaccard similarities ranged from 0·31 to 0·91. A detached leaf assay using a differential set of five rose genotypes led to the classification of the five tested isolates as five distinct pathotypes. Therefore, grouping depending on the avirulence gene diversity was clearly different from clustering using selectively neutral AFLP markers that were evenly distributed throughout the genome.     

Comparative effects of temperature and humidity on the activity of three potential antagonists of rose powdery mildew

Three reported antagonists of cucumber powdery mildew,Stephanoascus flocculosus, Stephanoascus rugulosus, andTilletiopsis washingtonensis, were tested and compared under different environmental conditions for their potential for controlling rose powdery mildew, caused bySphaerotheca pannosa var.rosae. Under controlled conditions in vitro, all three fungi induced a rapid collapse of conidia, conidiophores and hyphae ofS. pannosa var.rosae on detached leaflets of miniature roses within 48 h following their application, as observed under a SEM. Both temperature and relative humidity (r.h.) affected the activity of the antagonists differently. The colonization of powdery mildew was maximal at 26 °C, especially forSt. rugulosus andT. washingtonensis. Maximal colonization was achieved at the highest r.h. tested (90%) for all three antagonists but onlySt. flocculosus maintained a colonization of 80% or better under lower r.h. These observations stress the importance of considering environmental conditions when assessing the activity of antagonistic microorganisms.     

Assessment of Partial Resistance to Powdery Mildew (Podosphaera pannosa) in a Tetraploid Rose Population Using a Spore-suspension Inoculation Method

Powdery mildew (Podosphaera pannosa) is the most important fungal disease in greenhouse roses and is in practice controlled by fungicides. The creation of novel cultivars with durable resistance to powdery mildew is highly desirable. To understand the inheritance of mildew resistance, a tetraploid rose population with a size of 181 seedlings was obtained by crossing two tetraploid genotypes each having partial resistance. The population and its parents were tested under greenhouse conditions with two well-defined monospore isolates (2 and F1) using artificial inoculation with spore suspensions. Disease score at 11 days post-inoculation, latent period and rate of symptom development were used to describe seedling resistance. The tests for both isolates exhibited a wide and significant variation among genotypes for resistance. The distribution of the genotypic means of the disease scores was continuous and showed a considerable transgression. Statistical analysis, scatter plot of disease scores for the isolates, and correlation analyses indicated that the two isolates differed in pathogenicity. The outcome of the tests showed that the inoculation assay with spore suspensions was a reliable and effective way to screen large numbers of genotypes under greenhouse conditions for genetic and breeding studies. This is the first report on spore-suspension inoculation to be used successfully in rose.     

Host‐range studies,genetic diversity and evolutionary relationships of ACLSV isolates from ornamental,wild and cultivated Rosaceous species

A large‐scale survey was carried out to study the host range and genetic diversity of Apple chlorotic leaf spot virus (ACLSV) in various Rosaceae species, with a special emphasis on ornamentals and wild shrubs. Samples were tested by DAS‐ELISA using two different antisera, and RT‐PCR amplification of part of the CP gene. There was generally a poor correlation between the results obtained with the two sets of serological reagents and between serological and molecular detection assays. Using a nested RT‐PCR assay developed here, ACLSV was found to be widespread among cultivated, ornamental and wild species of the Rosaceae. The virus was detected for the first time in plum, wild cherry, Crataegus monogyna, Prunus spinosa and Prunus cerasifera in Greece. Sequences of a part of the CP encoding gene and the 3′ untranslated region from ACLSV isolates originating from various wild species and ornamentals were compared to those of isolates from cultivated hosts, showing similar divergence levels. Further phylogenetic analysis using the sequenced region indicated that the isolates from wild or ornamental hosts were not more closely related to each other than to isolates from cultivated hosts. The possible role of different factors in the spread of ACLSV on cultivated, ornamental and wild species is discussed.     

Alternative Bekämpfungsstrategien gegen die Kleine Weiße Rosenschildlaus Aulacaspis rosae (Bouché) (Hemiptera: Diaspididae) an Schnittrosen unter Glas mittels dem Einsatz von Leinöl

The rose scale Aulacaspis rosae has proven to be extremely difficult to control. For some years Hamburg flower producers have reported an increase in infestations in greenhouse grown rose crops. So far no pest management program, including natural, mechanical and chemical methods, have provided effective control. The rose scale feeds on parenchyma plant sap and is mainly found on the woody parts of roses. Under greenhouse conditions several generations may appear in a single year. Contact insecticides do not penetrate the protective covering of the scale insects and are most effective when applied on young larvae stages which are not protected by the shield-like cover yet. However due to long hatching periods the occurance of larvae overlaps with the hatching of the following generation. The outcome of this is a continuous presence of newly emerged larvae on the plants. Resulting in that pesticides need to be frequently applied which is both time consuming and impractical for the gardeners. Another problem is the limited coverage of the infested plant parts when pesticides get sprayed. The scale insects are well protected by both the leafage of the roses and also they tend to crowd together and stack in layers making it harder for contact pesticides to be effective. Systemic insecticides may be effective only on those scales infesting the leaves or those that are actively producing honeydew and showed no sufficient efficacy in practical usage against the rose scale. By searching for an adequate pest management method, linseed oil was tested as an alternative application agent. Linseed oil is a drying oil and polymerizes into a solid form by reacting with oxygen in air. Treatments on permanent rose crops infested by rose scales could decrease the occurance of larvae in a knock-down effect. Newly emerged larvae could be kept sustainably on a low infestation level. The results are showing a promising pest control with good efficacy.     

Screening of rice (Oryza sativa) cultivars for resistance to rice black streaked dwarf virus using quantitative PCR and visual disease assessment

Rice black streaked dwarf virus (RBSDV) causing rice black streaked dwarf disease is transmitted by the small brown planthopper (SBPH, Laodelphax striatellus) in a persistent propagative manner. The disease is considered among the most destructive in rice production in east and southeast Asia. For sustainable control of the disease, planting resistant cultivars is the most economical and efficient method. The virus content in different rice cultivars was quantified using a TaqMan RT‐qPCR assay under greenhouse conditions and the disease was visually assessed in these cultivars in both greenhouse and field conditions. Results revealed significant positive moderate correlation (r = 0.3787; P = 0.0009) between the virus content and visual disease assessment in the greenhouse under forced inoculation. Among 66 rice cultivars, there was no significant difference in RBSDV genome equivalent copies (GEC) in seven cultivars, namely Lian‐dao 9805 (200.2 ± 12), Liangyou 3399 (206.6 ± 28), Ningjing 4 (206.6 ± 28), DaLiang 207 (302.0 ± 61), X 008 (354.0 ± 30), Shengdao 301 (658.4 ± 69) and Liangyou 1129 (679.5 ± 98). These cultivars were also visually assessed as resistant under greenhouse and field conditions. These cultivars could be used in disease management to reduce the likelihood of epidemics.     

Symptom expression and variation of rose mosaic

Three isolates ofPrunus necrotic ringspot virus (PNRV) causing line pattern in rose and one causing yellow mosaic were compared on four greenhouse and on five outdoor rose cultivars with an isolate of the virus causing Stecklenberger disease in morello and with an isolate of apple mosaic virus (AMV) from apple. All PNRV isolates were readily transmissible through budding in rose (up to 100%). AMV was hard to transmit from apple to rose, but as easily from rose to rose as the PNRV isolates. In the greenhouse, first symptoms were produced 28 days after budding. Budding of outdoor roses in early September usually gave first symtoms next spring, but sometimes not until late during the second year after budding. In the course of time symptom production was erratic and often on a few leaves only. Nature and severity of symptoms greatly depended on cultivar and to a lesser extent on the isolate used. Symtomatologically all isolates, including AMV, behaved like members of a continuum, with AMV in certain cultivars causing characteristic rose (yellow) mosaic but usually being more virulent on rose.     

Host Specialization not Detected Among Isolates of the EC-1 Lineage of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> Attacking Wild and Cultivated Potatoes in Peru

To determine whether populations of Phytophthora infestans attacking wild and cultivated potatoes in the highlands of Peru are specialized on their hosts of origin, we characterized isolates using several neutral markers, metalaxyl resistance and for aggressiveness in a detached leaf assay. One hundred and fifty-three isolates were collected from the northern and central highlands of Peru from different potato cultivars (both modern and native cultivars) and from different species of wild, tuber-bearing potatoes. All the isolates analyzed belonged to one of four clonal lineages that had been described previously in Peru: EC-1, US-1, PE-3 and PE-7. The EC-1 lineage (n = 133) was dominant and present in similar frequencies on wild and cultivated potatoes. PE-3 (n = 14) was found primarily on cultivated potatoes, with only one isolate coming from a wild host. US-1 (n = 2) and PE-7 (n = 4) were rare; all but one (PE-7) occurred on wild potatoes. Isolates from the EC-1 lineage from modern cultivars were compared in three separate detached leaf inoculation assays with EC-1 isolates from the wild potato species S. sogarandinum, S. bill-hookerii or S. huancabambense, respectively. No significant interactions between isolate type (from wild or cultivated potato) and host type (wild or cultivated) were measured for any assay. It appears that the pathogen genotypes in the EC-1 lineage indiscriminately attack both wild and cultivated tuber-bearing solanaceous hosts in Peru, and breeders should be able to select for resistance using the common EC-1 lineage.     

New Leaf Spot Disease of Cymbidium Species Caused by Fusarium subglutinans and Fusarium proliferatum

Fusarium species were consistently isolated from yellow, swollen spots with reddishbrown centers and small black spots on leaves of Cymbidium plants in the greenhouse. Fusarium subglutinans caused the yellow spots and Fusarium proliferatum caused either the yellow or the black spots. We propose the name “yellow spot” for the new disease. To denote differences in their pathogenicity to orchid plants, we designate the population causing yellow spot as race Y and that causing black spot as race B of F. proliferatum. Received 29 October 1999/ Accepted in revised form 10 March 2000     

Use of wild Setaria viridis (L.) Beauv. to improve triazine resistance in cultivated S. italica (L.) by hybridization

Interspecific hybrids were obtained between two triazine-resistant forms of the wild species Setaria viridis and the triazine-susceptible cultivated foxtail millet (Setaria italica). The main agronomic characteristics of the hybrids were generally intermediate between the parental forms, except for fertility which was low. Some differences were observed according to the wild parent used. Progeny analysis confirmed the cytoplasmic inheritance of the resistance. The creation of resistant cultivars would allow the use of triazines in foxtail millet cultivation.     

Susceptibility of wild carrot (Daucus carota ssp. carota) to Sclerotinia sclerotiorum

Sclerotinia soft rot, caused by Sclerotinia sclerotiorum, is a severe disease of cultivated carrots (Daucus carota ssp. sativus) in storage. It is not known whether Sclerotinia soft rot also affects wild carrots (D. carota ssp. carota), which hybridise and exchange genes, among them resistance genes, with the cultivated carrot. We investigated the susceptibility of wild carrots to S. sclerotiorum isolates from cultivated carrot under controlled and outdoor conditions. Inoculated roots from both wild and cultivated plants produced sclerotia and soft rot in a growth chamber test. Two isolates differed significantly in the ability to produce lesions and sclerotia on roots of both wild carrots and cv. Bolero. Flowering stems of wild carrots produced dry, pale lesions after inoculation with the pathogen, and above-ground plant weight was significantly reduced 4 weeks after inoculation in a greenhouse test. Wild and cultivar rosette plants died earlier and fewer plants survived when inoculated with the pathogen under outdoor test conditions. Cultivar plants died earlier than wild plants, but survived as frequently. Plants inoculated in the crown died earlier and at a lower frequency than plants inoculated on leaves. Wild carrots may thus serve as a host of S. sclerotiorum and thus eventually benefit from any uptake of resistance genes, among them transgenes, via introgression from cultivated carrots.     

云南省玉米白斑病病原菌鉴定与品种田间抗性评价

为明确近年来云南省严重发生的玉米白斑病病原菌及不同玉米品种对玉米白斑病的抗性差异,2021年于云南省昆明市阿子营乡和曲靖市罗平县九龙镇采集病样,进行病斑组织分离纯化,通过形态学特征和分子生物学方法对病原菌进行鉴定,并在云南省曲靖市罗平县九龙镇采用田间自然发病方法对622份玉米品种的抗性进行鉴定。从2个采样地点的病叶中各分离出5株和9株菌株,经柯赫氏法则验证,确定了菌株WS-1、WS-191为白斑病致病菌;经形态学观察以及基于ITS、rpb2、tub2和LSU基因序列构建的系统发育树分析结果确定其分类学种名为宽颈附球菌Epicoccum latusicollum。田间抗病性试验结果表明,在622份区域试验品种中对白斑病表现高抗、抗病、中抗、感病和高感的品种分别为4、184、216、186和32份,分别占品种总数的0.64%、29.58%、34.73%、29.90%和5.14%。     

Flower Quality in Roses (Rosa Hybrida) Sprayed with Ascorbic Acid

Colombia is a country recognized for its variety of fresh flowers for export, among which roses represent a significant quantity. However, cut flowers must meet some quality requirements imposed by the international market. Ascorbic acid in living organisms has an extensive function as a free radical scavenger; therefore, it reduces the negative effects of oxidative stress. It is also involved in the biosynthesis of several hormones, has many functions in chloroplasts, and is a fundamental compound for the correct functioning of the photosynthetic apparatus. The exogenous application of ascorbic acid improves the quality and nutritional value of agricultural products and induces stress resistance in plants. A greenhouse study was carried out in Cota, Colombia, with the objective of improving the quality of rose flowers by spraying ascorbic acid in concentrations of 0.0 (control), 600, and 1200?mg?L^?1 in the Escimo, Latin Beauty, and Freedom cultivars. In response to the spraying, an increase in stem length and stem thickness was observed in all cultivars which was directly proportional to the concentration of ascorbic acid applied. There was no clear trend found in the response of cultivars to ascorbate regarding head size and chlorophyll content (SPAD) since in some cultivars, the values of these variables increased or decreased with statistically significant differences. As a result, spraying with ascorbic acid significantly improves some components of the quality of rose cut flowers, even though the response is highly dependent on the cultivar.

     

Evaluation of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis>) cultivars grown in Eastern Europe and progress in breeding for resistance to angular leaf spot (<Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">lachrymans</Emphasis>)

Increased occurrence of cucumber angular leaf spot, Pseudomonas syringae pv. lachrymans, has caused significant losses in cucumber, Cucumis sativus, yield in Poland in recent years. These losses necessitated evaluation of the level of resistance in cucumber cultivars of mainly Polish breeding, cultivated in Eastern Europe, and initiation of a breeding programme for resistance to this disease. Screening for resistance was performed on 84 cucumber accessions under growth chamber conditions using a highly aggressive strain of P. syringae pv. lachrymans. Most of the screened accessions were either susceptible or displayed intermediate resistance. The screening resulted in the identification of five F₁ hybrid cultivars moderately resistant to angular leaf spot. The identified F₁ hybrids were self-pollinated up to the F₄ generation. Individuals resistant to angular leaf spot were identified. These individuals can be used as a source of resistance to angular leaf spot in future breeding efforts.     

The relative tolerances of wild and cultivated oats to infection byErysiphe graminisf.sp.avenae: I. The effects of infection on vegetative growth and yield

The effects of infection by the powdery mildew fungusErysiphe graminisf.spavenaewere studied in one line of wild oat (Avena fatua), and two cultivars, Lustre and Peniarth, of cultivated oat (A. sativa) to determine if the wild oat was more tolerant of infection than the two cultivated oats. Seven weeks after inoculation, when the plants were 10-weeks-old with fully expanded flag leaves, the fungus had colonized approx. 40% of the leaf surfaces of wild oat and cv. Lustre but only about 30% of the leaf surfaces of cv. Peniarth. The lower leaves of cv. Peniarth were at least as susceptible, if not more so, than those of the other two lines but the upper leaves, including the flag leaf, were much more resistant. Although cv. Peniarth supported the production of about half the number of mildew conidia as the wild oat and cv. Lustre its total dry weight and grain yield were reduced to the greatest extent. The wild oat was clearly much more tolerant of mildew infection than cv. Peniarth and slightly more tolerant than cv. Lustre. The greater tolerances of the wild oat and cv. Lustre compared to cv. Peniarth appeared to be due to the lower sensitivities of their metabolism to the activities of the mildew fungus.