Flower Blight Research Articles

Evaluation of phylloplane microorganisms for biological control of camellia flower blight

Microorganisms isolated from camellia blooms were evaluated for their ability to protect camellia flowers against ascospore infection by Ciborinia camelliae. of the 277 isolates tested in camellia petal assays, Bacillus sp. LU1006, Bacillus subtilis LU1007, Pseudomonas sp. A3/B1, Pseudomonas marginalis LU1009, Pseudomonasfluorescens LU1004, Aureobasidium sp. Ch3F3, Cladosporium sp. LU172 and Cladosporium cladosporioides LU174 provided almost total protection against infection. However, when these isolates were suspended in water alone, or with either an organo-silicon surfactant (0.01% Break-Thru) or an ultraviolet protectant sticker-oil (Codacide), and sprayed onto 5-year-old potted Camellia japonica plants, they failed to reduce the incidence of camellia flower blight. Although these microorganisms protected individually sprayed petals from ascospore infection, they were unable to colonise petals on flowers sufficiently well to provide protection against camellia flower blight in field conditions.

First Report of Botrytis cinerea on Pansy Flowers in Buenos Aires.

Pansy (Viola × wittrockiana) is an ornamental annual plant produced as a potted plant in greenhouses around Buenos Aires, Argentina. Flower rot with signs of gray mold was observed on pansy cv. Crown during the autumn of 2003. Diseased tissues were surface sterilized by immersion in 2% NaOCl for 1 min, placed on 2% potato dextrose agar (PDA), and incubated at 22°C. Fungal mycelia were initially white and became gray after 72 h. After 4 days, colonies were 4 cm in diameter and sporulated profusely. Black sclerotia developed after 7 days. Mycelia were septate with dark branched conidiophores bearing unicellular, ellipsoid, hyaline conidia that measured 8 to 12 × 6 to 8 μm in botryose heads. These characteristics agree with Botrytis cinerea Pers.:Fr. (1). Pathogenicity tests were performed by spraying 10 healthy pansy plants during bloom with 3 ml of a conidial suspension (106 conidia per ml) per plant. Controls were treated with sterilized distilled water only. Plants were covered with plastic bags for 2 days and incubated at 18 to 22°C. The flowers developed water-soaked lesions between 4 and 6 days after inoculation. Fifty percent of the flowers were pendulous because flower blight reached the peduncle. The pathogen was reisolated from diseased flowers after superficial sterilization with 2% NaOCl and isolated on PDA. Gray mold has a rapid development during bloom, and the pathogen was able to enter undamaged flower tissues. No disease symptoms were observed on leaves. This report adds pansy as a new host of B. cinerea to a previous list of ornamentals grown in Argentina where gray mold was observed. Reference: (1) M. V. Ellis and J. M. Waller. Sclerotinia fuckeliana (condial state: Botrytis cinerea). No. 431 in: Descriptions of Pathogenic Fungi and Bacteria, CMI, Kew, Surrey, UK, 1974.

Evaluation of Systems for Timing of Fungicide Sprays for Control of Postbloom Fruit Drop of Citrus in Brazil.

Postbloom fruit drop (PFD) of citrus, caused by Colletotrichum acutatum, infects petals of citrus flowers and produces orange-brown lesions that induce the abscission of young fruitlets and the retention of calyces. Proper timing of fungicide applications is essential for good disease control. Different systems for timing of fungicide applications for control of PFD in a major citrus-growing region in southern São Paulo state in Brazil were evaluated from 1999 to 2002. The following programs were compared to an unsprayed control using counts of diseased flowers, persistent calyces, or fruit: (i) a phenology-based program currently recommended in Brazil with one application at early and another at peak bloom; (ii) the Florida PFD model; (iii) the post-bloom fruit drop-fungicide application decision system (PFD-FAD), a new computer-assisted decision method; and (iv) grower's choice. In 1999, no disease developed, sprays applied with the phenology-based program had no effect, and the Florida PFD model saved two sprays compared with the phenology-based program. In 2000, PFD was moderate and the phenology-based and grower's choice treatments had a significantly lower number of persistent calyces and higher fruit numbers than the control, but no differences were found between those treatments and the PFD model. In 2001, PFD was severe with considerable yield loss. The PFD model, the phenology-based program, and the grower's choice reduced flower blight and the number of persistent calyces, and improved fruit yields with two to three applications, but the PFD-FAD achieved comparable yields with only one spray. In 2002, the disease was mild, with no yield loss, and the Florida PFD model and the PFD-FAD saved one spray compared with the other systems. The PFD model and the PFD-FAD were equally effective for timing fungicide applications to control PFD in Brazil. Scouting of trees is simpler with PFD-FAD; therefore, this system is recommended and should eliminate unnecessary sprays and reduce costs for growers.

First Report of Petunia Blight Caused by Choanephora cucurbitarum in the United States.

A blight (wet rot) of petunia (Petunia ×hybrida Hort. Vilm.-Andr.) was observed in a wholesale propagation nursery in Baton Rouge, LA in September 2002. The grower reported that plants wilted and then completely rotted. The disease occurred during a period of hot, humid, and cloudy weather. Approximately 100 flats of flowering-age plants of cvs. Rose and White Madness were destroyed. No fungal sporulation was noticed on dead plants, but occasional strands of white mycelium were observed. The grower's use of azoxystrobin, iprodione, and thiophanate methyl plus mancozeb fungicides during current and past outbreaks of this disease did not prevent disease spread, but disease activity stopped after temperature and humidity dropped in early October. A fungus that produced white aerial mycelia that later developed light yellow areas and also black aerial spore masses was consistently isolated from diseased tissue placed on acidified potato dextrose agar (APDA). The fungus was identified as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. on the basis of cultural and morphological characteristics (3). Sporangiola were ellipsoid, pale brown to reddish brown with distinct longitudinal striations and measured 15 to 20 × 9 to 14 μm. Sporangiospores were broadly ellipsoid, pale brown to reddish brown, indistinctly striate with fine, hyaline polar appendages, and measured 16 to 34 × 7 to 12 μm. Spore measurements were within the range previously given for C.cucurbitarum (3). Pathogenicity tests were performed by misting a mixture of sporangiola and sporangiospores (25,000 to 70,000 per ml of water taken from 7- to 10-day-old cultures grown on APDA) on flowering-age petunia plants (cvs. Rose Madness, White Madness, and Dreams Pink). Tests were repeated twice. Inoculated plants and uninoculated control plants (2 to 4 of each treatment in each test) were held in a dew chamber at 28°C for 48 h and then moved to a greenhouse. Within 48 h after inoculation, plants developed water-soaked lesions on flowers, leaves, and stems, then wilted and rotted. Uninoculated plants remained disease free except for several that developed disease symptoms in the first test, apparently from the presence of natural inoculum on healthy-appearing plants that were obtained from the nursery where the disease was found. Koch's postulates were completed by reisolation of the pathogen from diseased inoculated plants. C. cucurbitarum (1) and C. infundibulifera (Curr.) Sacc. (2) have been reported to cause flower blight of petunia in the United States and whole plant blight (wet rot) of petunia in Japan (4). To our knowledge, this is the first report of C. cucurbitarum causing whole plant blight of petunia in the United States.

First Record of Botrytis Flower Blight Caused by Botrytis cinerea on Geraldton Waxflower in South Africa.

Geraldton waxflower (Chamelaucium uncinatum Schauer, family Myrtaceae), indigenous to western Australia, is cultivated commercially in South Africa as a cut-flower crop and exported to markets in the Northern Hemisphere. In September 2000, disease symptoms were observed on 4-year-old plants in a commercial orchard of C. uncinatum cv. Ofir in Philippe, in the Western Cape Province. The base of the petals and the calyxes of the waxflowers showed brown necrotic lesions. Eventually the calyx and all the petals turned brown, and the flowers shriveled and abscised. B. cinerea Pers.:Fr was consistently isolated from affected petal and calyx tissues. When placed in a moist chamber, conidia and mycelia formed on the surface of dead and infected tissue. Koch's postulates were confirmed by spraying flower stems of C. uncinatum cv. Ofir with a spore suspension (1 × 106 conidia per ml). Inoculated flower stems were placed in a bottle filled with water and enclosed in transparent plastic bags for 24 h at 21°C. Typical symptoms developed on the petals and calyx within 3 days after inoculation. B. cinerea was reisolated from affected tissues. Botrytis flower blight or gray mold, causing a flower petal disease, has been recorded on C. uncinatum in Australia (1), but this is the first record of Botrytis flower blight of C. uncinatum in South Africa. Because Geraldton waxflower is a major cut-flower crop grown for export, this disease can cause significant losses to the industry, especially under cool, wet growing conditions. Reference: (1) A. Tomas et al. Aust. Plant Pathol. 24:26, 1995.

Efeito de fungicidas em Colletotrichum acutatum e controle da antracnose do morangueiro

Onze fungicidas foram analisados in vitro e seus efeitos testados em campo para o controle de Colletotrichum acutatum, agente da flor-preta do morangueiro (Fragaria X ananassa). Os tratamentos (campo) foram (dosagens de i.a/100 l): iprodione (75 ml), benomil (100 g), tebuconazole (50 ml), tiofanato metílico (70 g), prochloraz (100 ml), propiconazole (50 ml), mancozeb (200 g), folpet (270 g), sulfato de cobre (200 g) e chlorotalonil (200 g), em pulverizações semanais (protetores) e quinzenais (sistêmicos). Foram avaliados a produção de frutos e o número de flores com sintoma de queima. Nos testes de fungitoxicidade in vitro, estudou-se o crescimento micelial, a germinação de conídios e a formação de apressórios. Nos testes in vitro foram utilizadas as concentrações de 1 e 10 ppm de i.a. para todos os fungicidas e posteriormente testadas as concentrações de 0,01, 0,1 e 1 ppm para os mais eficientes, e 10, 50 e 100 ppm para os menos eficazes. Os que resultaram em maior inibição micelial em baixas concentrações foram prochloraz e tebuconazole e os que menos inibiram o crescimento micelial foram sulfato de cobre, clorotalonil e folpet. Para inibir a germinação conidial mostraram-se mais eficientes chlorotalonil, tebuconazole, prochloraz e benomil, e para inibir a formação de apressórios, chlorotalonil e benomil. Os resultados de campo diferiram parcialmente dos testes in vitro: prochloraz e sulfato de cobre apresentaram os menores percentuais de flores doentes (53-55%), enquanto benomil apresentou 100% de ataque. Embora prochloraz, seguido de iprodione, folpet e mancozeb tenham resultado em maiores produções, nenhum fungicida controlou a doença satisfatoriamente.

Proof for the Occurrence of Flower Blight Caused by Ciborinia camelliae in Italy.

Camellia cultivation has a long history in the Lake Maggiore area of Northern Italy where a wide selection of varieties is present. In March to April 2001, a previously unconfirmed flower blight was observed on a collection of camellia varieties grown in a garden. Initial symptoms included the appearance of irregular, small, brown spots on the petals. Under favorable temperature and moisture conditions, the lesions enlarged rapidly and coalesced to form large spots that turned the entire petal brown. When the infection reached the base of the petal, it spread to other petals of the flower and finally caused the entire flower to show symptoms of blight. Eventually, the whole flower became uniformly dull brown and dropped from the plant. At the bases of infected flowers, a white or gray ring of mycelium was seen when the calyx was removed. Fungal pseudoparenchyma in the base of the petals eventually formed sclerotia and microconidia. Large numbers of apothecia and sclerotia were frequently in the soil, below infected plants. Apothecia were nearly sessile or, when buried in soil, had stipes up to 40 mm in length. They also had saucer-like disks of 5 to 20 mm in diameter. Ciborinia camelliae was recovered consistently from infected petals, sclerotia, and spores collected from apothecia, then plated on potato dextrose agar amended with 100 mg of streptomycin sulfate per liter. Pathogenicity of three isolates was confirmed by inoculating flowers of potted camellia plants (cv. Waterhouse), with spores obtained from apothecia. Noninoculated plants served as controls. All plants were kept in a growth chamber at 20°C and kept moist. Inoculated plants developed symptoms within 12 days, whereas control plants remained symptomless. C. camelliae was reisolated from flowers of inoculated plants. Camellia flower blight was first observed in Japan, in 1919, then in the United States (1938), New Zealand (1993), and more recently in several European countries, including Italy (1999) (1). This report confirms the occurrence of camellia flower blight in Italy and apparently is the first report in which C. camelliae was isolated and pathogenicity tests completed. Reference: (1) C. H. Taylor and P. G. Long, NZ J. Crop Hortic. Sci. 28:123, 2000.

Evaluation of acibenzolarsmethyl for induction of resistance in camellia flowers to <i>Ciborinia camelliae</i> infection

The synthetic plant defence elicitor acibenzolarSmethyl (CGA245704 50WG Syngenta Crop Protection) was applied to Camellia japonica bushes to induce systemic acquired resistance for protection of flowers against ascospore infection by Ciborinia camelliae Bushes were sprayed weekly at 500 mg/litre either before flowering during flowering or both before and during flowering All untreated and treated flowers became infected with camellia blight to the same degree and produced similar numbers of sclerotia averaging 34 sclerotia/flower Thus acibenzolarSmethyl was not effective in reducing the incidence of camellia flower blight

Alternaria alternata Flower Blight of Zinnia acerosa in Texas.

Zinnia acerosa (D.C.) Gray, is a Southwest native flowering plant frequently observed in the Trans-Pecos desert and desert grasslands of Arizona, Texas, and New Mexico. The plant is valued for producing an abundance of distinctive 2.0 cm diameter white flowers on greenish and sparsely leaved stems. Selections of Z. acerosa from West Texas are under evaluation as a water conserving plant species for use in arid landscapes of the Southwest. During April through June, Z. acerosa plants in TAMU, Dallas field plots were observed with small, brown flower spots that enlarged to include whole petals, causing conspicuous flower blighting. Microscopic examination of lesions from infected flower blossoms demonstrated the presence of short beaked, cylindrical spores near the smaller lesions on flower petals. Isolations from symptomatic flower petals consistently yielded cultures of an Alternaria sp. with long chains of conidia. Typical conidia contained 3 to 5 transverse walls and 1 to 2 longitudinal walls and measured 43 μm length by 15 μm width. The fungus was identified as A. alternata (Fries) Keissler consistent with the description in Ellis (1). Pathogenicity tests were conducted on plants maintained on a greenhouse bench by spraying spore suspensions obtained from 16-day-old A. alternata cultures on potato-dextrose agar. Inoculations produced light brown lesions on blossoms typical of field disease symptoms of the disease. This disease is important as a flower blight, however, infections on the leaves are also apparent but limited. Outbreaks of the disease are frequently observed during periods of rainfall during the summer months. This is the first report of Alternaria alternata causing a floral blight on Z. acerosa.

Infection processes of <i>Ciborinia camelliae</i> on camellia flower tissue

The infection process of Ciborinia camelliae the cause of camellia flower blight was studied using light and confocal microscopy Germination and infection structures of the pathogen on petals were stained with trypan blue in lactophenol and with glutaraldehyde for light and confocal microscopy respectively Within 6 h of inoculation the ascospores germinated and formed short germ tubes The host cuticle was penetrated and within a further 6 to 18 h a large swollen structure formed underneath each penetration From here a hypha grew under the cuticle to the junction between two cells and then developed as intercellular hyphae The mycelium continues to develop intercellularly for the next 72 h but without causing extensive destruction of the host cell walls

Transmission, Field Spread, Cultivar Response, and Impact on Yield in Highbush Blueberry Infected withBlueberry scorch virus

Scorch disease caused by Blueberry scorch virus (BlSV) spreads rapidly and radially from foci of infection. Healthy potted blueberry plants became infected when placed next to diseased field bushes from early May through mid-August. The aphid Fimbriaphis fimbriata, collected from infected field bushes, transmitted BlSV to healthy blueberry plants in controlled tests and was regarded as the most important means by which bushes in commercial fields became infected. The rate of spread in the symp-tomless cv. Stanley appears to be the same as the rate of spread in the cv. Pemberton, which exhibits blight and dieback. Most field bushes showed symptoms during the year following inoculation, but a few did not show symptoms until the second or third year. Many (30 out of 59) cultivars and selections infected with BlSV exhibited severe blighting of flowers and young leaves and dieback of twigs. Three cultivars showed only chlorosis of leaf margins. The virus was also detected in numerous cultivars (26 out of 59) that exhibited no symptoms, and they were considered tolerant of BlSV. The virus had no effect on germination of pollen from several cultivars. BlSV reduced yield in 'Pemberton', with the loss being related to the number of years bushes displayed symptoms. Yield was reduced by more than 85% in the third year of symptom expression. The virus did not significantly reduce the yield of six tolerant cultivars that were infected with the virus but displayed no symptoms.

New Diseases and Records of Flowering Potted Plants Caused by Phytophthora species in Taiwan

Phytophthora diseases of flowering potted plants were investigated from 1989 to 1999. A total of 16 new diseases, which have not been formally reported in Taiwan, were found and described in the study. An atypical type of Phytophthora capsici was found to cause wilt and death of azalea. P. citrophthora attacked was detected from the infected diseased tissues of seven species of plants including Aphelandra sp. (whole plant wilt), bougainvillea (leaf and flower blight), hibiscus (root rot), flame vine (leaf and flower blight), desert rose (young tissue and stem blight), chincherinchees(wilt and blight of whole plants), and Aeschynanthus sp. (wilt). While P. palmivora caused flower blight of curcuma and wilt of garden petunia. Besides, P. cinnamomi was isolated from the rotted basal stem tissues of begonia, P. citricola from the blighted leaves of Taiwan pleione, and P. cryptogea from the diseased root tissues of sweet alyssum. Disease symptoms similar to those occurring in natural conditions were reproduced when each host was inoculated with zoospore suspension of their respective isolates of Phytophthora species in pathogenicity. Same species of Phytophthora was reisolated from all artificially infected tissues. Among these new diseases, P. capsici on azalea, P. cinnamomi on begonia, P. citricola on Taiwan pleione, P. citrophthora on anthurium, P. cryptogea on sweet alyssum, P. parasitica on Aeschynanthus sp., chincherinchees, flame vine and desert rose, and P. palmivora on curcuma have not been described in any other places previously.

First Report of Azalea Petal Blight Caused by Pestalotiopsis guepini in Argentina.

The most important azalea (Rhododendron spp.) growing area in Argentina is located in the outskirts of Buenos Aires. A disease of the azalea flower was detected during surveys conducted during September 1998. Irregular brown spots were uniformly distributed on petals and resulted in a flower blight that did not lead to abscission of petals. Pieces of infected petals were surface-sterilized for 1 min in 2% NaOCl, plated on potato dextrose agar, and incubated at 24 ± 2°C. Pure cultures were identified as Pestalotiopsis guepini (Desmaz.) Steyaert (synamorph P. guepini Desmaz.) based on morphological characteristics (1,2). Inoculation for pathogenicity testing was carried out by spraying a conidial suspension (1 × 106 conidia per ml) on plants with previously punctured petals. Inoculated plants with unwounded flowers, as well as noninoculated controls, were included. Plants were incubated in moist chambers at 24°C. Symptoms appeared on all punctured flowers within 4 to 5 days. Petals were blighted by 9 days after inoculation and were covered with black acervuli by 12 days after inoculation. Unwounded and noninoculated controls remained symptomless. The pathogen was reisolated from inoculated flowers, completing Koch's postulates. Pathogenicity of P. guepini on azalea leaves in Argentina was reported in 1991. This is the first report of P. guepini causing disease on azalea flowers in Argentina.

1998 survey shows Camellia flower blight is widespread in New Zealand

1998 survey shows Camellia flower blight is widespread in New Zealand

Screening for resistance to camellia flower blight

Screening for resistance to camellia flower blight

First Report of Blossom Blight of Strawberry Caused by Xanthomonas fragariae and Cladosporium cladosporioides in California.

In the spring of 1996, severe blossom blight occurred in some strawberry fruit production fields in the Watsonville area. The symptoms, in addition to blighting of entire flowers, were as follows: on the lower surface of the calyx, watersoaked lesions that appeared dark green under reflected light and translucent under transmitted light; necrotic calyces of seemingly healthy green and ripe fruits; watersoaking of the base of the calyx that extended into the pedicel; green-gray sporulation on dead anthers; and presence of flower clusters with small and irregularly shaped fruits. Yellow bacterial colonies were consistently isolated from water-soaked and necrotic lesions on calyces and pedicels. These colonies were entire, circular, raised, glistening, mucoid, and slow growing, characteristics typical of Xanthomonas fragariae on nutrient agar-glucose-yeast extract medium. The bacterial isolate was also identified by rep-polymerase chain reaction as X. fragariae. In addition to the yellow bacteria, a fungus was also frequently isolated from infected anthers, sepals, petals, and pistils, and was identified as Cladosporium cladosporioides. On potato dextrose agar, the fungus had velvetlike colonies colored olivaceous-green to olivaceous-brown, apically and laterally branched conidiophores, and lemon-shaped conidia that were usually smooth but sometimes textured. Blossoms of greenhouse-grown strawberry plants cv. Selva were inoculated with either or both organisms. Blossoms inoculated with X. fragariae developed symptoms distinct from those inoculated with C. cladosporioides. The most prominent visible symptoms caused by X. fragariae were watersoaked lesions on calyces that later became necrotic, watersoaking of the calyx that extended into the pedicel, and blighting of flowers and developing fruits as a result of girdling of the pedicel. Infection by C. cladosporioides was characterized by necrosis of flower parts or the entire flower, presence of green-gray sporulation on dead anthers, and production of small and malformed or misshapen fruits. Inoculation with both organisms produced all the symptoms described above in different flowers of a plant. Infection with both organisms aggravated disease severity, but each organism was capable of inducing blossom blight independently. Both organisms were reisolated from artificially inoculated strawberry flowers, fulfilling Koch's postulate for proof of pathogenicity. This is the first report of the two organisms causing blossom blight of strawberry in California. This is also the first report that C. cladosporioides is a pathogen of strawberry.

Occurrence of Colletotrichum acutatum, Causal Organism of Strawberry Anthracnose in Southwestern Spain.

A wilting disease of strawberry (Fragaria × ananassa Duchesne 'Oso Grande') was observed in production fields in Huelva, southwestern Andalucía, Spain. Crowns of wilted plants developed a reddish brown, firm rot. Longitudinal sections of roots of diseased plants showed a black coloration of the cortex. Symptons also included blighting of flowers due to floral infection and rotting of green and ripening fruits. On the fruit, the round, firm sunken lesions were covered with masses of salmon-colored spores. Lesions on the leaves were round, ranged in diameter from 5 to 10 mm, and were light brown with purple edges. Infected tissues were surface disinfected in 20% sodium hypoclorite, blotted dry, and plated on water agar. Dishes were incubated at 25°C; hyphal tips made of fungi growing from lesions were transferred to potato dextrose agar (PDA) and incubated under cool-white fluorescent light at 25°C. One fungus was isolated consistently from lesions on different tissues. It was identified as Colletotrichum acutatum by morphological characteristics (2) and enzyme-linked immunosorbent assay (1). On PDA, the mycelium of the fungus was white to gray and covered with salmon spore masses. Colony diameters on PDA averaged 45 mm after 7 days at 25°C. Hyaline, aseptate conidia were cylindrical, fusiform, and intermediate in shape and averaged 12.8 × 4.2 μm in size. The fungus produced setae on infected fruit. Inoculations of strawberry cvs. Oso Grande and Chandler with conidial suspensions (106 conidia per ml) of C. acutatum produced lesions on the fruit, petioles, and crowns, and caused wilt. The pathogen was reisolated from lesions on the inoculated plants. This is the first report of C. acutatum causing strawberry anthracnose in Huelva.

Camellia flower blight in New Zealand

Camellia flower blight is caused by Ciborinia camelliae. Originating in Japan, the disease spread to the USA in 1938 and was first found in New Zealand in Wellington in 1993. In 1996, the disease was found in Waikanae and Wanganui. A survey carried out from September to November 1997 showed that the disease had spread up the west coast of the North Island as far as New Plymouth. It had also spread over the Rimutakas to the Wairarapa as far as Pahiatua. The disease had spread north from Wellington almost to Taihape and there were two isolated outbreaks, one in Turangi and one at Hatepe near Lake Taupo. The distribution suggests that dispersal of the disease has been primarily by windborne spores, but there is potential for future dispersal from nurseries.

First Report of Choanephora Flower Spot and Blight of Periwinkle

Periwinkle or vinca (Catharanthus roseus (L.) G. Don) is widely planted as a flowering annual in home and business landscapes in hardiness zones 9 and 10 and the southernmost portions of zone 8. Many improved selections, such as those in the Pacifica, Tropicana, and Cooler cultivar series, are currently available. Dark gray flower spots that often coalesced and led to blighting of flowers under conditions of high humidity, were observed on all of 18 periwinkle cultivars in a variety trial at Burden Research Plantation in September 1997. The disease affected only the flowers and was also observed on periwinkle in commercial landscape plantings around Baton Rouge. Fungi were isolated from flower spots by plating necrotic tissue on acidified potato dextrose agar (PDA). Fungal isolates were maintained on PDA and 20% V8 juice agar under continuous fluorescent light. A fungus that produced cottony, white mycelium and black spore masses was consistently isolated from diseased tissue. Pathogenicity tests were conducted by misting a spore suspension (70,000 per ml produced on V8 juice agar) onto detached flowers held in a moist chamber and to flowers on intact plants. Inoculated plants were held for 24 h in a dew chamber at 25°C. Typical irregular dark spots appeared on attached and detached flowers within 18 h after inoculation and flowers held for longer periods under high humidity developed a soft rot. Koch's postulates were fulfilled by reisolating the fungal pathogen, which was identified as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. (1). This is the first report of the occurrence of C. cucurbitarum on periwinkle. Reference: (1) P. M. Kirk. Mycol. Pap. 152:1, 1984.

RESISTÊNCIA DE Colletotrichum fragariae E C. acutatum AO BENOMYL NA CULTURA DO MORANGO NO ESTADO DE SÃO PAULO

O fungicida benomyl, utilizado intensivamente na cultura do morango a partir do final da década de 60, tem sido ineficiente para o controle da flor preta, causada por Colletotrichum acutatum, devido ao aparecimento de formas resistentes ao fungicida, já detectadas desde 1984. Para C. fragariae, no entanto, não há registro de ocorrência de resistência no Estado de São Paulo, embora venha se observando há alguns anos que o produto não tem apresentado resultados satisfatórios para o controle da podridão do rizoma ("chocolate"). Para verificar a ocorrência de resistência em C. fragariae foram testados 22 isolados, coletados em diversas regiões produtoras de morango do Estado de São Paulo, e 22 isolados de C. acutatum, para comparação. Todos os isolados de C. acutatum foram resistentes, mesmo na concentração de 1000 ppm. Dos 22 isolados de C. fragariae, 10 comportaram-se como resistentes, crescendo em todas as concentrações testadas. Os demais só se desenvolveram até 1 ppm, sendo considerados sensíveis. As porcentagens de inibição do crescimento dos isolados de C. fragariae resistentes variaram de 50,0 a 88,8 (1 ppm), 54,5 a 89,8 (10 ppm), 63,6 a 78,7 (50 ppm), 67,3 a 80,3 (100 ppm), 74,4 a 82,0 (500 ppm) e 76,4 a 86,0 (1000 ppm). Inoculando-se isolados resistentes e sensíveis de C. fragariae em plantas da cultivar IAC-Campinas, observou-se que todos foram igualmente patogênicos.