Petal Blight Research Articles

The Preliminary Analysis of Flavonoids in the Petals of Rhododendron delavayi, Rhododendron agastum and Rhododendron irroratum Infected with Neopestalotiopsis clavispora.

The petal blight disease of alpine Rhododendron severely impacts the ornamental and economic values of Rhododendron. Plant secondary metabolites play a crucial role in resisting pathogenic fungi, yet research on metabolites in alpine Rhododendron petals that confer resistance to pathogenic fungi is limited. In the present study, the secondary metabolites in Rhododendron delavayi, R. agastum, and R. irroratum petals with anti-pathogenic activity were screened through disease index analysis, metabolomic detection, the mycelial growth rate, and metabolite spraying experiments. Disease index analysis revealed that R. delavayi petals exhibited the strongest disease resistance, while R. agastum showed the weakest, both under natural and experimental conditions. UHPLC-QTOF-MS/MS analysis identified 355 and 274 putative metabolites in positive and negative ion modes, respectively. The further antifungal analysis of differentially accumulated baicalein, diosmetin, and naringenin showed their half-inhibitory concentrations (IC50) against Neopestalotiopsis clavispora to be 5000 mg/L, 5000 mg/L, and 1000 mg/L, respectively. Spraying exogenous baicalein, diosmetin, and naringenin significantly alleviated petal blight disease caused by N. clavispora infection in alpine Rhododendron petals, with the inhibition rates exceeding 64%. This study suggests that the screened baicalein, diosmetin, and naringenin, particularly naringenin, can be recommended as inhibitory agents for preventing and controlling petal blight disease in alpine Rhododendron.

Early and Late Transcriptomic and Metabolomic Responses of Rhododendron 'Xiaotaohong' Petals to Infection with Alternaria sp.

In recent years, petal blight disease caused by pathogens has become increasingly epidemic in Rhododendron. Breeding disease-resistant rhododendron is considered to be a more environmentally friendly strategy than is the use of chemical reagents. In this study, we aimed to investigate the response mechanisms of rhododendron varieties to petal blight, using transcriptomics and metabolomics analyses. Specifically, we monitored changes in gene expression and metabolite accumulation in Rhododendron 'Xiaotaohong' petals infected with the Alternaria sp. strain (MR-9). The infection of MR-9 led to the development of petal blight and induced significant changes in gene transcription. Differentially expressed genes (DEGs) were predominantly enriched in the plant-pathogen interaction pathway. These DEGs were involved in carrying out stress responses, with genes associated with H2O2 production being up-regulated during the early and late stages of infection. Correspondingly, H2O2 accumulation was detected in the vicinity of the blight lesions. In addition, defense-related genes, including PR and FRK, exhibited significant up-regulated expression during the infection by MR-9. In the late stage of the infection, we also observed significant changes in differentially abundant metabolites (DAMs), including flavonoids, alkaloids, phenols, and terpenes. Notably, the levels of euscaphic acid, ganoderol A, (-)-cinchonidine, and theophylline in infected petals were 21.8, 8.5, 4.5, and 4.3 times higher, respectively, compared to the control. Our results suggest that H2O2, defense-related genes, and DAM accumulation are involved in the complex response mechanisms of Rhododendron 'Xiaotaohong' petals to MR-9 infection. These insights provide a deeper understanding of the pathogenesis of petal blight disease and may have practical implications for developing disease-resistant rhododendron varieties.

Confirmation of Itersonilia perplexans infecting pyrethrum (Tanacetum cinerariifolium) in Australia.

Pyrethrum (Tanacetum cinerariifolium (Trevir.) Sch. Bip.) is grown to extract pyrethrins which are active ingredients for insecticides (Greenhill 2007). The Australian pyrethrum industry supplies over 50% of the world market. Surveys of Tasmanian crops in spring 2013, detected the presence of a fungus putatively identified as Itersonilia perplexans Derx. on foliage in 54 of 86 surveyed fields (Hay et al. 2015). This fungus was associated with necrotic leaf tips often spreading to encompass whole leaves. However, pathogenicity to pyrethrum was not confirmed. To isolate, tissue was excised from foliar lesions, surface sterilised using 0.4% NaClO, placed onto 2% water agar and incubated at 20°C for 5 days. Colonies were pure-cultured by hyphal-tip transfer onto potato-dextrose agar. Eleven isolates were cultured onto yeast mold agar (YMA) for 14 days at 15°C in the dark (Horita and Yasuoka 2002). Colonies were slow growing (1.9 to 2.3 mm/day) white to buff on both surfaces, with a darker center visible on lower surfaces. Mycelia were straight and hyaline with clamp connections at the septa. Squares transferred from the edge of YMA colonies onto microscope slides produced ballistoconidia that were aseptate, granular and lunate, kidney or lemon-shaped after 24 h. Ballistoconidia lengths and widths (n = 50/isolate) ranged from 14.6 to 20.4 µm and 10.0 to 13.6 µm. Chlamydospores were not observed. These observations were consistent with descriptions of I. perplexans (Koike and Tjosvold 2001; Liu et al. 2015). All 11 isolates were sequenced across the internal transcribed spacer (ITS) region of rDNA (ITS; primers V9G/ITS4; de Hoog and van den Ende 1998; White et al. 1990), and large (LSU; primers LROR/LR7; Rehner and Samuels 1995), and small (SSU; NS1/NS4; White et al. 1990) subunits of rDNA (Genbank accession nos. KU563626 to KU563658). The ITS (673 bp), SSU (1,047 bp) and LSU (1,318 bp) differed by 3, 1 and 0 bp, respectively, across isolates. Maximum parsimony and maximum likelihood analyses of a concatenated 3 loci alignment with Cystofilobasidiales representatives (Liu et al. 2015) placed all isolates and the I. perplexans ex-neotype strain CBS 363.85 within a single monophyletic clade with 100% bootstrap support. Two representative isolates are stored at the Plant Pathology Herbarium (accession nos. BRIP 57986 and 57987). Leaves of 46-day-old pyrethrum plants (n = 45), generated from surface sterilised seed, were inoculated with a 1.5 × 105 ballistoconidia/ml suspension (equal mix of eight isolates) and maintained between 10 and 22°C under a 12-h photoperiod for 14 days. Brown necrotic leaf tips, consistent with reported field symptoms were observed on 71% of plants and I. perplexans was recovered from 69% of symptomatic plants. For flower inoculations, pyrethrum plants were removed from fields as vegetative plants in spring and maintained in a greenhouse set at 20:14°C and 14:10 h day:night. Open flowers (10 per plant) were dipped into a 1.2 × 104 ballistoconidia/ml suspension mix of three isolates. Brown withered ray florets were observed on 10/12 plants 18 days post-inoculation, matching those described in petal blight of chrysanthemum (McRitchie et al. 1973). I. perplexans was re-isolated from 11/12 inoculated plants and 1 control plant (of 12) which exhibited the same symptoms. In both experiments, I. perplexans was identified based on its distinctive morphology. This confirms the pathogenicity of I. perplexans to both pyrethrum leaves and flowers.

First report of Chaetomium pseudocochliodes causing flower rot disease of Camellia reticulata in Yunnan, China.

Camellia reticulata is the world-famous ornamental flower (Wang et al. 2021). In February 2021, the infected flowers of C. reticulata 'Shizitou' were collected in Zixi Mountain, Chuxiong city, Yunnan province, China (24°9'95″ N, 101°42'53″ E). Flower rot disease incidence ranged from 40% to 75% in the garden. The infected flowers showed symptoms of varying degrees of yellow-browning, dry or wet rot to the whole flower wilted and even dropped (Figure 1A, B, C). Three symptomatic flowers were randomly collected in the garden. Tissues from the infected flowers (cut to 5×5 mm size) were surface-disinfected by 75% ethyl alcohol for 30s, rinsed in sterile water for 3 times to air dry, and cultured in Potato Dextrose Agar medium (PDA) at 25℃±2 in the normal light for 5-7 days (Fang, 1998). Similar fungal colonies were isolated from 50%-75% of the infected flowers. Three isolates from different flowers showed similar colony morphology. After sub-culturing of hyphal tips on PDA for 5-7 days, the initially yellow colored colonies showed abundant white aerial mycelium, with sporulation (Figure 1E, F). The asci (Figure 1G) sporulation site is 24(-37) ×7(-14) μm, and the stalk length is 17-42 μm, with 8 biseriate acuminate ascospores. The mature ascospores (Figure 1H) are olive-brown or brown, lemon-like, double-pointed, with slightly umbilical protrusions at both ends, flat on both sides, 9(-11.5) × 7(-9) × 5.5(-7) μm in size, with germ holes on the top (Wang et al. 2016). These morphological features are consistent with Chaetomium pseudocochliodes. The genomic DNA was extracted from the isolated strains. To identified this fungal pathogen genetically, sequence analyses were conducted using the ITS1/ITS4 (Henson et al. 1993), NL1/NL4 (Liu et al. 2011), EF1-938F /EF1-2218R (Tan et al. 2016) primers for the internal transcribed spacer (ITS), large ribosomal subunit (LSU), and elongation factor 1-α (EF1-α) genes. The obtained sequences were deposited in GenBank with accession numbers MZ817067 (ITS), MZ817072 (LSU), MZ820167 (EF1-α). The phylogenetic trees (Figure 2) were constructed to determine the phylogenetic relationships based on MEGA 6.0 maximum likelihood method. In order to confirm the pathogenicity, the tests were conducted with fungus plug (5 mm) from a 7-day-old colony placed onto the surface of healthy petals. The sterile water-absorbent cottons place onto healthy petal surface near fungus plug and plastic wraps cover in petri dish were used for moisturizing. A total of 3 replicates in each of 3 groups were included (3 healthy petals for a group, 1 for wounded inoculation, 1 for unwounded inoculation, and 1 for sterile PDA plug). A sterile PDA plug was placed onto the surface of healthy petals as a control. After incubation at room temperature for 5 days (Ren. 2019), 3 replicates in each of 2 groups of treated healthy petals for wounded inoculation showed obvious symptoms (Figure 1D), and no symptoms appeared in the control, and healthy petals unwounded showed symptoms for 7-10 days. The fungus was re-isolated from the lesions of inoculated tissues. The re-isolated fungal colonies showed identical morphology and high sequence similarity with ITS, LSU and EF-1α of the initial isolate. No fungus was isolated from the controls. The first extraction of C. pseudocochliodes was also obtained from the roots of the Panax notoginseng in Wenshan, Yunnan (Wang et al. 2016). To our knowledge, this is the first report of flower rot caused by C. pseudocochliodes on C. reticulata in China.

Untargeted metabolite profiling of petal blight in field-grown Rhododendron agastum using GC-TOF-MS and UHPLC-QTOF-MS/MS

Petal blight caused by fungi is among the most destructive diseases of Rhododendron, especially Rhododendron agastum. Nonetheless, the metabolite changes that occur during petal blight are unknown. We used untargeted gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) and ultra-high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS) to compare the metabolite profiles of healthy and petal blight R. agastum flowers. Using GC-TOF-MS, 571 peaks were extracted, of which 189 metabolites were tentatively identified. On the other hand, 364 and 277 metabolites were tentatively identified in the positive and negative ionization modes of the UHPLC-QTOF-MS/MS, respectively. Principal component analysis (PCA) and orthogonal projections to latent structures-discriminant analysis (OPLS-DA) were able to clearly discriminate between healthy and petal blight flowers. Differentially abundant metabolites were primarily enriched in the biosynthesis of specialized metabolites. 17 accumulated specialized metabolites in petal blight flowers have been reported to have antifungal activity, and literature indicates that 9 of them are unique to plants. 3 metabolites (chlorogenic acid, medicarpin, and apigenin) are reportedly involved in resistance to blight caused by pathogens. We therefore speculate that the accumulation of chlorogenic acid, medicarpin, and apigenin may be involved in the resistance to petal blight. Our results suggest that these metabolites may be used as candidate biocontrol agents for the control fungal petal blight in Rhododendron.

Determining the temporal interaction of Camellia cultivar flowering periods and camellia petal blight disease presence in Auckland, New Zealand

Botanic gardens hold diverse and valuable living collections that provide a number of research, conservation and education opportunities. Auckland Botanic Gardens (ABG) has an internationally significant collection of species and cultivar camellias that have been used for scientific research into understanding which species are susceptible to camellia petal blight. ABG has surveyed all cultivars and species in its collection over multiple years to identify which camellias are affected by petal blight and which avoid it, based on their flowering period. A total of 363 camellias were assessed for petal blight over 6 years of surveying. It was found that 245 cultivars and 6 species were susceptible to the disease, while 68 cultivars and 32 species did not display any visual symptoms. These are important findings, as enthusiasts and breeders alike may use them to inform their respective interests.
 
 

Key Plant, Key Pests: Azalea (Rhododendron spp.)

This series of Key Plant, Key Pests publications are designed for Florida gardeners, horticulturalists, and landscape professionals to help identify common pests associated with common Florida flora. This publication, the sixth in the Key Plant, Key Pests series, helps identify the most common pests found on the Azalea.
 This publication provides information and general management recommendations for the azalea caterpillar, azalea lace bug, azalea leafminer, rhododendron gall midge, azalea gall, cercospora leaf spot, mushroom root rot, ovulinia petal blight, wet root rots, and iron chlorosis.

New Zealand Plant Protection Society Research Scholarship

The necrotrophic fungus Ciborinia camelliae Kohn causes a disease known as camellia petal blight that has been disfiguring camellia flowers (Fig. 1) since it was first found in New Zealand in 1993. This blight has severally impacted the camellia seed oil industry, floriculture industry, and has been a great frustration to keen camellia growers over the last 25 years but no viable control methods for camellia petal blight have been discovered so far. The Camellia Memorial Trust has helped fund a research team at Massey University to study the interaction between
 camellia plants and this pathogen. Hannah McCarthy, recipient of the 2017/2018 New Zealand Plant Protection Society Research Scholarship, is part of this team. Ciborinia camellia is host and tissue specific, which restricts its infection capability to flowers of the Camellia genus. This disease spreads by ascospores, which after landing on a susceptible Camellia spp. bloom, germinate to grow hyphae and cause necrosis and death of the petal tissues. The flower then falls prematurely to the ground, where the fungus survives as hardened sclerotium until the next flowering season.
 Most plant pathogens utilise a range of proteins to promote infection using mechanisms that include the suppression of plant immunity, degradation of cell walls, or the manipulation of the host’s immunity to their own advantage. These proteins are known as ‘effectors’ and identification of these complex molecules has led to a better understanding of disease and new disease-control strategies for other plants. The aim of Hannah’s MSc research is to identify effectors in Ciborinia camelliae, and she has been focusing on a protein family that shares characteristics (such as high cysteine content and the size of protein sequences) with known effectors from other fungi. This protein family is called Ciborinia camelliae-like small secreted proteins (CCL-SSPs). There are 73 unique protein sequences in Ciborinia camelliae but of the ten tested for necrotic ability by recombinant expression and infiltration into camellia petals, none were found to induce cell death. However, a protein found in the closely related fungus Sclerotinia sclerotiorum, was found to induce very rapid cell death, which was visible just two hours after infiltration. This protein from Sclerotinia sclerotiorum has high sequence similarity to CCL- SSPs. To identify the function of this protein family, Hannah is performing region swaps between the S. sclerotiorum protein and a Ciborinia camelliae CCL-SSP. By the end of
 this project, the research team hopes to have: (a) identified the region of the S. sclerotiorum protein responsible for its necrotic activity; (b) compared this region with sequences of Ciborinia camelliae CCL-SSPs; and (c) deduced the likely function of this protein family, and its role in camellia petal blight.

Controlling Botrytis elliptica Leaf Blight on Hybrid Lilies through the Application of Convergent Chemical X-ray Irradiation.

X-ray irradiation with convergent chemicals such as nano-silver particles or sodium dichloroisocyanurate (NaDCC) has been used to control leaf blight on cut lilies. The oriental hybrid lily cultivars Siberia, Le Reve, and Sorbonne were irradiated five times by 200 Gy of X-rays in 2014. In 2015, Siberia and Sorbonne were irradiated three times by 150 Gy of X-rays. After artificial infection with Botrytis elliptica on the leaves and petals of cut lilies, this study used convergent chemical X-ray irradiation of 200 Gy or 150 Gy. Leaf and petal blight was measured in terms of incidence and severity at 8 days after infection using total 552 cuttings. Results indicate that the treatments of X-ray irradiation and NaDCC in 2014 and 2015 slightly decreased the severity of petal blight on Siberia and Sorbonne. However, the results were not significant and severity did not decrease as NaDCC concentration increased. Vase-life was observed separately after X-ray irradiation of 270 cut lilies in 2014 and 108 cut lilies in 2015. Chlorophyll content was not affected by either 200 Gy or 150 Gy of X-rays. The number of days of fully opened flowers at Siberia of 150 Gy and Le Revu of 200 Gy increased by 1–2 days. In addition, the relative fresh weights of the X-rayed flowers were 10% drier than the non-irradiated controls. Overall, leaf blight control by X-ray was inferior to the control by gamma rays, and petal color was bleached in Sorbonne and Le Reve cvs. by 150 Gy of X-rays.

Performance of Garden Roses in North-central Texas under Minimal Input Conditions

One hundred sixteen rose (Rosa spp.) cultivars were evaluated under minimal input conditions in north-central Texas for 3 years. Plant quality data included overall plant performance, number of flowers, percentage of bloom coverage, final vigor, and survival. Disease ratings for black spot (Diplocarpon rosae), petal blight (Alternaria alternata), powdery mildew (Sphaerotheca pannosa), and aphid (Myzus spp.) infestations were previously reported. Of the original 116 cultivars, 25 had 50% or higher mortality during the trial. Own-root cultivars performed significantly better than the grafted cultivars and had significantly better survival (P = 0.001). As a class, the Polyantha cultivars exhibited the best overall performance, mean bloom percentage, final vigor and survival, while cultivars in the Hybrid Tea class had the worst performance in all measures. Foliar nutrient content, bloom number, and mean percentage of bloom were not good predictors of overall performance. Of the diseases monitored, black spot was the most severe and was closely correlated to overall performance and final vigor, but was not the only factor determining overall performance. The top five cultivars in mean overall performance were RADrazz (Knock Out™), Caldwell Pink, Sea Foam, Perle d'Or, and The Fairy, in descending order.

Host Range of Itersonilia perplexans and Management of Itersonilia Petal Blight of China Aster

Isolates of Itersonilia perplexans were tested for pathogenicity on 14 different plant species. Isolates from China aster and sunflower were each pathogenic to the other host and both isolates were pathogenic to chrysanthemum and gerbera, causing moderate to high incidences of flower or seedling blight in these hosts. China aster and sunflower isolates were not pathogenic to burdock, but an isolate from burdock was pathogenic to florists' chrysanthemum and gerbera. In a survey of weed species near a cut-flower production facility in southwest Florida, I. perplexans was found in only one weed species, Emilia fosbergii. However, two isolates from this weed host produced severe petal blight symptoms when inoculated onto China aster. Myclobutanil, potassium bicarbonate, and propiconazole were highly effective in reducing disease severity of petal blight in China aster, while azoxystrobin reduced disease moderately in fungicide evaluation trials. Accepted for publication 28 July 2006. Published 18 October 2006.

PERFORMANCE OF GARDEN ROSES UNDER MINIMAL INPUT CONDITIONS IN NORTH-CENTRAL TEXAS

To enlarge the palette of environmentally-responsible landscape plants, 117 garden rose cultivars were evaluated under minimal input conditions. Other than mulching and irrigation, no other inputs were provided, including no fertilization and no pesticide applications. Plants were established in completely randomized blocks with four reps in the spring of 1998 with data collection beginning in 2000 and continued through 2002. Data on overall performance (an index comprised of flower number, percent of plant covered with flowers and plant growth) and relative chlorophyll content were collected the first and third week of each month from April through October. Disease ratings or incidence ratings were collected for Diplocarpon rosae Wolf (black spot), Alternaria sp. (petal blight) and Sphaerotheca pannosa (powdery mildew). Statistical analysis was performed on the mean data for all dates. `Knockout' was the top rose for overall quality with little or no disease observed, high foliage quality, and continuous flowers from spring until late in the fall. `Knockout' also ranked among the top rose cultivars in terms of overall nutrient concentrations (N, P, K, and Fe) in new growth tissue. Most of the hybrid tea roses such as `Peace' and `Double Delight' died in at least three blocks due to disease and a lack of vigor.

LANDSCAPE PLANT OBSERVATIONS FROM THE LSU AGCENTER, 2004

Performance evaluations of numerous annual and perennial herbaceous ornamentals were conducted in landscape settings in 2004 at the LSU AgCenter in Baton Rouge. A mid-summer through fall evaluation of Kong coleus found no difference in flowering performance and visual quality ratings of the five available cultivars. In a sun/shade study, Kong coleus cultivars in 60% shade were about 50% shorter than those in sun. Other impressive coleus have been Aurora Black Cherry and Mississippi Summer Sun. The Stained Glassworks series of coleus have been average performers. The Son series of lantanas (Sonrise, Sonset, Samson, Sonshine) have been top performers in terms of visual quality and continual bloom. All-America daylilies most prevalent to rust symptoms have included Judith, Leebea Orange Crush, Starstruck, Lady Lucille, and Chorus Line. Some rust has also been noted on Plum Perfect and Frankly Scarlet. Profusion Apricot and Profusion White have been less susceptible to Xanthomonas bacterial petal blight than Profusion Fire, Profusion Cherry, and Profusion Orange. Earth Kind roses, being promoted by Texas A&M, are being evaluated for landscape performance along with black spot and powdery mildew susceptibility. Most problematic cultivars thus far have included Georgetown Tea, Clotilde Soupert, Nacogdoches, Reve d'Or, New Dawn, Souvenir de St. Anne's, Spice, Lamarque, Puerto Rico, Sarah Jones, Ducher, and Louis Philippe. Lady Bird cosmos have been good late summer/early fall landscape performers.

Black Streak of Edible Burdock Caused by Itersonilia perplexans in Japan

Black streak disease of edible burdock (Arctium lappa L.) has been observed periodically in Hokkaido Prefecture, Japan since 1988. Symptoms appeared initially as small, dark brown to black spots on the leaf veins and petioles. The necrotic spots developed longitudinally along the leaf veins or petioles. Diseased leaf veins or petioles occasionally snapped off at the necrotic lesions. An Itersonilia sp. was isolated from rotting leaf veins and petioles. Laboratory inoculations of edible burdock seedlings using ballistospore suspensions produced typical symptoms observed in nature. The fungus had a feathery mycelium and developed a white to pale cream colony color. The mycelium was composed primarily of branched hyphae with clamp connections at the septa. Ballistospores, formed at the apex of inflated cells, were lunate, ovoid to pyriform. The fungus occasionally produced appressoria, chlamydospores and yeast cells. Based on the morphological characteristics, the causal agent was identified as Itersonilia perplexans Derx. Edible burdock strains were also pathogenic to chrysanthemum and caused petal blight. This report is the first of a foliar disease of edible burdock caused by I. perplexans in Japan.

Westcott's Plant Disease Handbook, Sixth Edition

Westcott's Plant Disease Handbook, Sixth Edition. Revised by R.K. Horst . 16 × 24 cm , 1028 pp. Dordrecht, the Netherlands : Kluwer Academic Publishers ( www.kap.nl ), 2001 . £210 . ISBN 07923 8663 9 (hardback ). This thousand-page handbook – for plant pathologists with big hands and deep pockets – starts with a short introduction on plant disease control, followed by two principal sections: the main types of disease classified by symptom, from anthracnose to wilt, and an A–Z of plant genera with their most common diseases. There are no diagnostic keys, but the A–Z and a comprehensive index allow diseases to be tracked fairly easily. The emphasis is on practical disease management. There is plenty of advice on fungicides, but the selection exemplifies the problem with this book for European readers: it is an American book. Of the long list of products, some are no longer available even in the USA, and very few indeed are sold on the UK amateur market. The USA legal background to pesticide use is given very clearly, but things are different over here and the crucial constraint (at least for UK users) – that the target diseases and hosts are specified explicitly in the statutory part of the label – is not discussed. The book is written for gardeners, and reassuringly advises ‘Don’t let all the scientific names worry you’, but I think these names should have worried the editors a bit more, as errors are rather frequent. Neem, for example, is Azadirachta indica, not Melis (sic) azedarach. The updating has not been very consistent, various editions of the Dictionary of the Fungi (see Plant Pathology51, 255) as far back as 1961 are cited. I checked Westcott's entry for camellia petal blight, a disease of current interest in the UK. It is listed as Sclerotinia camelliae in the host A–Z, and appears under Sclerotinia in the Blights section, but as ‘Ciberinia (sic) camelliae (formerly Sclerotinia camelliae)’. The genus Ciborinia is listed separately under Blights, but it does not yet include C. camelliae. Perhaps it will get there by the next edition. I also checked Dutch Elm Disease, where Ophiostoma ulmi and O. novo-ulmi are both listed as pathogens. There is much detail on the introduction of O. ulmi from Europe in infested elm wood and the devastation it caused in the USA, but there is no other mention of O. novo-ulmi, the cause of the current epidemic in the USA and Europe, which arrived in the UK in infested North American elm wood! A proposed control strategy for DED mentions insecticide spraying during the dormant season, something never seriously countenanced in the UK. Environmental problems with massive DDT spraying are noted, but no substitute is suggested. There are line drawings of symptoms and also fungal microstructure, although the latter are microscopic characters inaccessible to most gardeners. The many black and white photographs are more useful, and there are also eight colour plates. The illustrations are often nowhere near the text that they illustrate, and the cross-referencing is from text to picture, but not vice versa. If I worked as a plant diagnostician in the USA, I should expect my employer to buy this book. Despite the rather erratic updating it is undoubtedly a uniquely useful resource. It is not a book for amateur gardeners, but it would be very useful for professional horticulturalists and also extension workers, who are almost extinct in UK but still survive in North America. If you are a keen UK gardener, Buczacki S & Harris K 1998. Collins Photoguide to Pests, Diseases and Disorders of Garden Plants. London, UK: HarperCollins, will serve your needs better, with pests and disorders thrown in for good measure and leaving you about £190 richer. Those working in the professional sector will buy Alford DV (ed.) 2000. Pest and Disease Management Handbook. Oxford, UK: Blackwell Science, for the same reasons, and also be much better off. A few European diagnosticians and plant health professionals will probably want Westcott as a source of information on North American plant diseases, but the price is ludicrous. I would make the purchase of the excellent American Phytopathological Society's compendia (www.scisoc.org) a higher priority.

A Blight Disease of Dill in California Caused by Itersonilia perplexans.

In 2000, a foliar disease was observed in commercial field plantings of dill (Anethum graveolens) in coastal California. Initial symptoms consisted of a gray-green discoloration and wilting of the tips of dill leaves. As disease developed, many of the leaves discolored and collapsed, which gave the foliage a blighted appearance and made the leaves unsuitable for harvest. A fungus was consistently isolated from symptomatic leaves. Slow growing colonies were cream-colored, velutinous, and flat with minimal aerial mycelium. Mycelium was hyaline and had clamp connections. Ovoid to subglobose sporogenous cells were abundant and measured 11 to 14 × 12 to 16 μm. Spores were ballistospores that were bilaterally symmetrical, lunate, 16 to 18 × 12 to 13 μm, and germinated with hyphae or secondary ballistospores. The fungus was identified as Itersonilia perplexans Derx (1,2). Pathogenicity was tested by preparing spore suspensions (1 × 104) and spray-inoculating potted dill plants. Plants were placed in a dew chamber for 24 h and then maintained in a greenhouse (23 to 25°C). After 10 days, leaves showed symptoms similar to those observed in the field and the same fungus was reisolated. Control plants sprayed with water did not develop symptoms. Inoculations were repeated and the results were the same. In another experiment, sets of dill plants and flowers of five cultivars of potted florist's chrysanthemum (Dendranthema × grandiflorum [= Chrysanthemum × morifolium]) and one cultivar of Leucanthemum paludosum (= C. paludosum) were spray-inoculated with several dill isolates and incubated as described previously. Dill plants developed symptoms and the fungus was reisolated. However, flowers of the six chrysanthemum cultivars did not develop any petal blight symptoms. Inoculations were repeated and the results were the same. These findings are consistent with previous studies that indicate I. perplexans consists of pathogenic forms that are host-specific to either chrysanthemum and closely related Compositae or to Apiaceae plants such as dill, carrot (Daucus carota subsp. sativus), parsley (Petroselinum crispum), and parsnip (Pastinaca sativa) (1,2,3). To our knowledge, this is the first report of I. perplexans on dill in California, and also appears to be the first record of this disease in North America.

Petal Blight of Sunflower Caused by Itersonilia perplexans.

In February 1999, a cut-flower grower from Florida reported post-harvest losses of approximately 25% in Helianthus annuus (sunflower) cvs. Sunrich Orange and Sunbright. Symptoms began as small, pinpoint brown lesions on the petals, which enlarged and coalesced, leading to necrosis of the entire blossom. Symptomatic petals were surface disinfested for 30 sec with 0.5% NaOCl and suspended over plates containing acidified 25% potato-dextrose agar. Petals adhered to lids of the petri dishes by the surface tension of the water on the petals. Itersonilia perplexans Derx was consistently isolated. Inoculation of sunflower with I. perplexans was achieved using three detached, mature blossoms of the cv. Sundance Kid with their pedicels placed in sterile water. Each blossom was inoculated with 3.5 ml of a spore suspension (1 × 105 spores/ml) applied as a spray. Three noninoculated control blossoms were sprayed with sterile, distilled water. Blossoms were incubated in a controlled environment chamber at near 100% RH, a constant temperature of 18°C, and a 12-h photoperiod. Three days following inoculation all of the inoculated blossoms were symptomatic, with necrosis ranging from 50 to 100% on individual petals. I. perplexans was recovered from all of the inoculated blossoms. Noninoculated controls remained symptomless, and I. perplexans was not recovered. I. perplexans has been reported to cause lesions on the cotyledons, first true leaves, and the hypocotyl region of sunflower seedlings in Canada and Uruguay (1,2). However, this is the first report of post-harvest petal blight in sunflower caused by I. perplexans and the first report in the United States of infection of sunflower by I. perplexans.

Petal Blight of Callistephus chinensis Caused by Itersonilia perplexans

From November 1997 to March 1998, a cut-flower grower in southwest Florida reported post-harvest losses due to a petal blight of 10 and 50%, respectively, in China aster (Callistephus chinensis (L.) Nees) cultivars Rainbow Mix and Matsumoto Lavender. Initial symptoms observed included pinpoint, bleached lesions on petals. Enlargement of lesions resulted in bleached streaks on ray flowers and eventually necrosis of entire blossoms. Symptomatic petals were surface disinfested in 0.5% NaOCl and suspended on the lids of plastic culture plates over acidified potato dextrose agar (APDA). Itersonilia perplexans Derx was isolated consistently from diseased petals but not from symptomless controls. Confirmation of the pathogenicity of I. perplexans used three detached, mature flowers of China aster cv. Matsumoto Rose and seven mature flowers of Bidens bipinnata L., a common composite found near the production site. The pedicels of flowers were placed in sterile, deionized water, and 1 ml of a spore suspension (1.2 × 104 spores per ml) of I. per-plexans was sprayed on aster flowers, and 0.5 ml was applied to flowers of B. bipinnata. An equal number of noninoculated control flowers were sprayed with sterile, deionized water only. The flowers were incubated in a controlled environment chamber at near 100% relative humidity, a constant temperature of 18°C, and a 12-h photoperiod. Bleached spots were detected on the petals of Matsumoto Rose flowers 10 days after inoculation, and the fungus was reisolated on APDA. Control asters remained symptomless, and were negative for I. perplexans. Brown blotches appeared on the petals of B. bipinnata flowers 12 days after inoculation, and infection by I. perplexans was confirmed by reisolation. The fungus was not detected in noninoculated B. bipinnata flowers, including some that exhibited brown discoloration. A survey was conducted in early March 1998 to examine the incidence of Itersonilia petal blight in China aster and the occurrence of the fungus in B. bipinnata. Fifty flowers of each of four China aster cultivars were collected at random without regard to symptoms. Approximately 20 flowers of B. bipinnata exhibiting brown spots were also collected near this site. The fungus was isolated at incidences of 18, 6, 8, and 6% in flowers from aster cultivars Rainbow Mix, Matsumoto Blue, Matsumoto Pink, and Matsumoto Scarlet, respectively. I. perplexans was not detected in B. bipinnata flowers collected from the field during this period. I. perplexans previously was detected in florists' chrysanthemum (Chrysanthemum × morifolium Ramat.) at the same cut-flower production site in January 1973 during a period of uncharacteristically cool weather (2). The weather during the recent outbreak of Itersonilia petal blight in aster was also unusually cool and rainy and resulted from the “El Niño” weather pattern prevalent during the period. I. perplexans has been found to over-season on many weeds in Great Britain, particularly on those in the Compositae (1). Experimental transmission of I. perplexans to B. bipinnata suggests that it and other wild composites may serve as reservoirs of the fungus in Florida.

Alternaria alternata causes petal blight and flower drop in harvested Geraldton waxflower

Six isolates of Altemaria alternata were tested and shown to be pathogenic on detached flowers of Geraldton waxflower cv. Alba. The fungus caused petal blight and abscission ofthe pedicel from inoculated flowers. This finding strengthens the hypothesis that fungal infection of Geraldton waxflower flowers commonly leads to premature flower drop. Furthermore, it shows that, in addition to Bohytis cinerea, which has been shown previously to cause flower abscission, A. alternata can also cause flower abscission.

Stemphylium lycopersici . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Stemphylium lycopersici . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Lycopersicon most commonly but also found on Allium, Carthamus, Gladiolus and other plants. DISEASE: Stemphylium leaf blight of tomato, petal blight of carnation. The fungus forms necrotic lesions, closely resembling those of grey leaf spot ( S. solani ), on foliage and floral parts in which conidia are borne in later stages of infection. Relatively severe attacks have been recorded on chrysanthemum in Canada (41, 309; 46, 3384) and tomato in Israel (53, 2683). GEOGRAPHICAL DISTRIBUTION: Asia (Arabia, Israel, Malaysia (W. and Sarawak), India, Hong Kong, Yemen); Africa (Kenya); N. America (USA, Canada); S. America (Venezuela); Central America and W. Indies (Cuba); Australasia and Oceania (Tahiti). TRANSMISSION: By air-borne conidia. Conidia have been shown to survive in dried plant refuse for 4 months and in dried agar culture for 8 months (Hannon & Weber, 1955).