Causal Agent Of Leaf Spot Research Articles

Identification and Characterization ofPseudocercosporaSpecies Causing Grapevine Leaf Spot in China

AbstractPseudocercosporais an important plant pathogenic genus causing leaf spots on grapevine leaves and other hosts worldwide. A survey of vineyards in four provinces of China was carried out to identify the causal agent of Pseudocercospora leaf spot. A phylogenetic analysis based on a combination ofLSU,ITSandACTloci, coupled with morphology, showed thatPseudocercospora vitisis the sole causal agent of this leaf spot disease. This study represents the first attempt to identify and characterize the cercosporoid species causing Pseudocercospora leaf spot in China using morphological and molecular approaches.

Cristulariella depraedans as causal agent of leaf spots of maple and other trees and shrubs

Results of the first studies in Poland on <em>Cristulariella depraedans</em>, the causal agent of necroses on tree and shrub leaves, are presented. The fungus was recorded on <em>Acer platanoides, A. pseudoplatanus</em> and eight other species of trees and shrubs, including <em>Corylus avellana, Fagus sylvatica, Lonicera xylosteum</em> and <em>Padus avium</em> that were not previously known as hosts of the fungus. The disease symptoms, which depend on the host plant species, the size and number of necrotic lesions on leaves, and the morphological features of the fungal propagules were characterized.

Seed transmission of Plectosphaerella cucumerina, causal agent of leaf spot of Diplotaxis tenuifolia in Italy

Plectosphaerella cucumerina has been described recently as the causal agent of a leaf spot on wild rocket (Diplotaxis tenuifolia). Eight seed samples of wild rocket obtained from commercial seed lots used for sowing by farms severely affected by P. cucumerina, were assayed for the presence of the pathogen. Isolations were carried out on subsamples of seeds (400) unwashed or disinfected in 1% sodium hypochloride. The pathogenicity of the isolates of P. cucumerina obtained was tested in two trials carried out on wild rocket; four out of eight samples of rocket seeds were contaminated by P. cucumerina. Eleven isolates of P. cucumerina were obtained from 7,200 not disinfected seeds tested, while none was isolated from an equal number of disinfected seeds. All isolates were pathogenic on wild rocket. The results obtained indicate that rocket seeds are a potential source of inoculum for P. cucumerina. The possibility of isolating the pathogen from seeds, albeit from a low percentage of them, supports the hypothesis that the rapid spread of this new disease of rocket recently observed in Italy is due to the use of infected propagation material. Measures for prevention and control of the disease are discussed.

OCCURRENCE OF ALTERNARIA spp. IN THE SEEDS OF BASIL AND ITS PATHOGENICITY

Eighteen seed samples of basil, belonging to the cultivars most frequently grown in the Piedmont area for pesto production and obtained from farms affected by the disease in Piedmont during the fall of 2010 as well as from experimental lines of basil, were assayed for the presence of Alternaria spp., the causal agent of leaf spot of basil. Isolations were carried out by disinfected and not disinfected seeds. All eighteen tested samples resulted contaminated by Alternaria spp. and the frequency of isolation of Alternaria spp. colonies was higher in the case of not disinfected seeds for all samples tested. In the case of seeds belonging to experimental lines of basil, the frequency of isolation of Alternaria spp. was 1.18% from not disinfected seeds, and 0.43% from disinfected seeds. In the case of seeds belonging to commercial varieties of basil, Alternaria spp. was isolated respectively from 7.29% and 2.62% of not disinfected and disinfected seeds. When twenty-eight isolates of Alternaria spp. obtained from seeds of experimental lines of basil under development were tested for their virulence, 22 were able to infect basil leaves. Twenty of them, obtained from disinfected and not disinfected seeds, showed a good level of virulence, infecting more than 30% of leaves. One hundred eighty one isolates of Alternaria spp. strains were obtained from seeds of commercial varieties, of which 149 from not disinfected seeds and 32 from disinfected seeds. Out of 149 strains obtained from not disinfected seeds, 102 were virulent and 47 were not virulent. Only two isolates of Alternaria spp. out of 32 obtained by disinfected seeds were not virulent when tested on basil. This work provides evidence that Alternaria spp. the causal agent of leaf spot of basil, is seed-transmitted, which suggests that seeds may be important in disseminating the pathogen.

The composition of phyllosphere fungal assemblages of European beech (Fagus sylvatica) varies significantly along an elevation gradient

Little is known about the potential effect of climate warming on phyllosphere fungi, despite their important impact on the dynamics and diversity of plant communities. The structure of phyllosphere fungal assemblages along elevation gradients may provide information about this potential effect, because elevation gradients correspond to temperature gradients over short geographic distances. We thus investigated variations in the composition of fungal assemblages inhabiting the phyllosphere of European beech (Fagus sylvatica) at four sites over a gradient of 1000m of elevation in the French Pyrénées Mountains, by using tag-encoded 454 pyrosequencing. Our results show that the composition of fungal assemblages varied significantly between elevation sites, in terms of both the relative abundance and the presence-absence of species, and that the variations in assemblage composition were well correlated with variations in the average temperatures. Our results therefore suggest that climate warming might alter both the incidence and the abundance of phyllosphere fungal species, including potential pathogens. For example, Mycosphaerella punctiformis, a causal agent of leaf spots, showed decreasing abundance with elevation and might therefore shift to higher elevations in response to warming.

Fungos e nematóides fitopatogênicos associados ao cultivo de flores tropicais em São Luís - MA

Considerando a importância do cultivo de flores tropicais no contexto nacional e internacional, buscou-se realizar um levantamento da ocorrência de fungos e nematóides associados às mesmas, em áreas de cultivos de flores tropicais em São Luís - MA. Foram realizadas visitas periódicas, em intervalos bimestrais, nos locais onde a principal atividade era o cultivo de flores tropicais, para o monitoramento e coleta de plantas ou partes de plantas das espécies: Heliconia spp., Alpinia purpurata e Etlingera elatior com sintomatologia típica de doenças. Realizou-se, ainda, o teste de patogenicidade dos principais fungos detectados como agentes causais das manchas foliares. Os resultados obtidos confirmaram a existência de fungos associados aos cultivos de flores tropicais em São Luís, com destaque para Curvularia eragrostides (78 %), Pestalotiopsis sp. (68 %) e Colletotrichum gloeosporioides (47 %) como agentes causais de manchas foliares em espécies da família Heliconiaceae, e Curvularia eragrostides (75 %), Pestalotiopsis sp. (37 %) em espécies da família Zingiberaceae. Foram registrados oito gêneros de nematóides, tanto na família Heliconiaceae, quanto na Zingiberaceae, destacando-se o gênero Meloidogyne.

First Report of Leaf Spot Disease of Peony Caused by Seimatosporium botan in China.

Tree peony (Paeonia suffruticosa Andrews), a perennial ligneous deciduous shrub in the Paeoniaceae family, is known for its beautiful and charming flowers. It is regarded as the flower symbol of China and is cultivated throughout the country. In August 2008, a previously unknown leaf spot was observed on peony cultivated in the Mountain Peony Garden located in the Luoyang area of Henan Province, China. In 2009, the leaf spot disease was observed in some gardens in the city of Luoyang, China. Initial symptoms appeared as small, round or irregular, brown, necrotic lesions in the middle of leaves. These lesions gradually enlarged up to 1 cm in diameter and were circular or irregular, brown to dark brown, and brown on the margins. In a humid atmosphere, black, sessile, discoid acervuli developed on the lesions, and the lesions sometimes became waxy-like, eventually coalesced, and nearly covered the entire leaf. Conidia produced in acervuli had two morphologically different types. One type had a single basal appendage, ellipsoid to fusiform, transversely three septate, 16 to 20 × 5 to 7 μm, smooth, basal cell obconic with a truncate base, subhyaline, 3 to 5 μm long; two central cells subcylindrical to dolioform, brown to dark brown, 8 to 10 μm long, apical cell conical with rounded apex, concolorous with the central cells, 4 to 5 μm long, basal appendage filiform, unbranched, excentric, 4 to 8 μm long. The other type had a single appendage at both ends, fusiform to subcylindrical, transversely three septate, 16 to 20 × 4 to 5 μm, smooth; basal cell obconic with a truncate base, subhyaline, 4 to 5 μm long; two central cells subcylindrical to dolioform, pale brown, 8 to 11 μm long; apical cell conical with an acute apex, hyaline to subhyaline, 4 to 5 μm long; basal appendage filiform, unbranched, excentric, 4 to 8 μm long; apical appendage filiform, unbranched, 4 to 8 μm long. Single conidial isolates of both types of conidia yielded identical colonies, which produced both types of conidia on potato dextrose agar (PDA), thus showing that both types of conidia belonged to the same fungus. Colonies on PDA were slimy in appearance, yellow to villous with an irregular taupe margin; reverse brown to grayish brown. Cultural and conidial characteristics of the isolates were similar to those of Seimatosporium botan (1). The DNA sequence for the fungus showed internal transcribed spacer region (ITS1-5.8S-ITS2) sequences (GenBank Accession No. HM067840) with 93% sequence identity to S. discosioides (Accession Nos. EF600970.1 and EF600969.1). This is the first submission of a S. botan sequence to GenBank. To determine pathogenicity, 20 healthy leaves of P. suffruticosa were inoculated by spraying a conidial suspension of S. botan onto the foliage. Ten leaves were sprayed with sterile water and served as controls. Plants were covered with plastic for 24 h to maintain high relative humidity. After 15 days, the symptoms described above were observed on leaves in all inoculated plants, whereas symptoms did not develop on the control plants. The pathogen was reisolated from inoculated leaves, fulfilling Koch's postulates. On the basis of morphology and ITS region sequences, we conclude that S. botan is the causal agent of leaf spots of P. suffruticosa. There is a report of S. botan on P. suffruticosa stems in Japan (1), but to our knowledge, this is the first report of leaf spot disease of peony caused by S. botan in China.

Isolation and detection of the fungi Alternaria dauci (Kühn) Groves et Skolk and Alternaria radicina Meier, Drechsler et Eddy from carrot seeds

Carrot is among the most important vegetable crops because of its composition and vitamin content. The fungi belonging to genus Alternaria, especially A. dauci (Kuhn) Groves et Skolk, causal agent of leaf spot and blight of carrots, and A. radicina Meier, Drechsler et Eddy, the agent of black root rot, can jeopardize the entire production of carrots. Both types can be found in a high percentage of seeds, carrots, parsley and celery. The method of detection filter paper (blotter method) and the method of isolation on malt agar were recommended by ISTA Rules. The presence of A. dauci (causal agent of leaf spot and blight of carrots) and A. radicina was performed on 12 samples of potentially infected carrot seeds originating from France, as part of laboratory ring tests. The presence of A. dauci and A. radicina using the filter paper method in 12 tested samples ranged from 0% to 21% and from 1% to 30% respectively. On MA medium the respective percentages ranged from 0% to 23% and from 1% to 31%.

First Report of Pilidium concavum on Paeonia suffruticosa in China.

Paeonia suffruticosa Andrews, a deciduous perennial shrub, is known for its beautiful and charming flowers. It is regarded as the flower symbol of China and cultivated throughout the country. Since 2006, large, brown necrotic spots have been observed on numerous P. suffruticosa plants in gardens in Luoyang, China. Spots appeared each year and were observed on more than 50% of the plants, sometimes affecting more than half of the leaf. Initial symptoms appeared as small, round, water-soaked lesions in the middle or on the margin of leaves. These areas enlarged up to 1 to 3 cm in diameter and were circular or irregular, brown to dark brown, and pale brown on the margins. In a humid atmosphere, black, sessile, discoid conidiomata developed on the spots and exuded a pink spore mass that turned brown with age. Conidiophores were hyaline, unicellular, cylindrical, and fusiform and 5.0 to 8.0 μm long and 1.4 to 2.0 μm wide. Pure cultures were obtained by plating the spores on potato dextrose agar (PDA) medium. In culture, the fungus produced a gray-to-brown colony with whitish aerial mycelium. The morphology and size of conidia were comparable with previous descriptions of Pilidium concavum (Desm.) Höhn. (1). The ITS1-5.8S-ITS2 region of the isolate was amplified by PCR with primers ITS1 and ITS4 and sequenced. The 472-nt sequence was 100% identical to that of the Pilidium concavum specimen voucher BPI 1107275 (GenBank Accession No. AY487094). To validate Koch's postulates, pathogenicity was tested by inoculating 10 leaves of P. suffruticosa with mycelia plugs from a colony growing on PDA; leaves inoculated with the plugs of PDA medium only served as the control. Leaves were covered with plastic for 24 h to maintain high relative humidity. After 7 days, 100% of the mycelium-inoculated leaves showed symptoms identical to those observed on P. suffruticosa leaves affected in the field, whereas all leaves inoculated with PDA medium only remained free of symptoms. Reisolation of the fungus from leaf lesions confirmed that the causal agent was Pilidium concavum. Thus, we concluded that Pilidium concavum is the causal agent of leaf spots of P. suffruticosa. This disease has been reported to be frequently occurring on P. suffruticosa stems imported from Japan (1), but to our knowledge, this is the first report of Pilidium concavum on P. suffruticosa in China.

Etiologia de Bipolaris incurvata, agente causal da mancha foliar do coqueiro

Summary: In Sococo farm, located in the municipality of Moju, Para, between the years 2000 to 2002, more than 14,000 coconut trees died due to the occurrence of a leaf spot disease nicknamed the coconut. Aiming to diagnose the etiologic agent of this disease, were collected in the same property, between August 2003 and April 2004 samples in the field with the typical symptoms of stain and laboratory isolates were proceeded in PDA culture medium. after analyzes morphological in crops with seven days old, three fungi were identified: Cylindrocladium pteridis, Bipolaris incurvata and Pestalotiopsis sp. After pathogenicity in plants and detached leaves of the hybrid PB121 tests, it was found that only the fungus Bipolaris incurvata was able to induce the disease. In inoculations with injuries, macroscopic symptoms were observed after two days, while in inoculations made without injury symptoms were observed at eight days after inoculation, indicating that Bipolaris incurvata is the causal agent of leaf spot of coconut.

Severe Outbreak of Crown Rot and Root Rot Caused by Cylindrocladium pauciramosum on Strawberry Tree in Italy.

From 2006 to 2009, a new disease was noticed in several commercial nurseries in Sicily (Italy) on ~13,000 potted plants of strawberry tree (Arbutus unedo L.) ranging from 3 months to 4 years old. Symptomatic plants showed a crown and root rot and internal brown discoloration of the basal stem. No leaf spots were detected. The percentage of symptomatic plants was variable in the different stocks (1 to 28%). A Cylindrocladium sp. was isolated consistently from symptomatic tissues on potato dextrose agar (PDA). Although many crown rots are caused by Phytophthora or Rhizoctonia spp., plating small pieces of diseased tissue from rotten roots and crowns onto corn meal agar or PDA yielded these pathogens sporadically. Twenty Cylindrocladium isolates obtained from infected basal stems, crowns, and roots were selected and subsequently cultured on carnation leaf agar (CLA). Macroconidiophores consisted of a stipe, a penicillate arrangement of fertile branches, and stipe extension terminating in an obpyriform-to-ellipsoidal vesicle (6 to 10 μm in diameter). Conidia cylindrical, straight, and 1-septate ranged from 40 to 60 × 4 to 5 μm. All single-conidial isolates were mated with tester strains DISTEF-G87 (MAT1-1) and DISTEF-G128 (MAT1-2) of Cylindrocladium pauciramosum (3) on CLA and produced fertile perithecia after 2 months. Perithecia were solitary or in groups, orange to red-brown, subglobose to ovoid, and ranged from 260 to 400 × 180 to 290 μm in diameter. On the basis of the combination of morphological and perithecial characters and mating type the isolates were identified as C. pauciramosum C.L. Schoch & Crous, teleomorph Calonectria pauciramosa C.L. Schoch & Crous (1,4). One representative isolate was deposited at Centraalbureau voor Schimmelcultures (CBS; No. 123918) open fungi collection. Pathogenicity tests were performed by adding sterile water to CLA cultures of C. pauciramosum from a single-conidial isolate and incorporating the resulting spore suspension (105 conidia per ml) on the soil surface of 20 3-month-old strawberry tree potted plants. The same number of plants served as a control. After inoculation, plants were maintained in a growth chamber at 25 ± 1°C and 90 to 95% relative humidity. All inoculated plants developed crown and root rot identical to one observed in the nursery 2 months after inoculation. Control plants remained symptomless. C. pauciramosum was always reisolated from infected plants. This fungus represents a serious threat for ornamental nurseries in Europe. Diseases related to infection of C. pauciramosum are different in relationship to the host tissues and the affected species. On strawberry tree, C. pauciramosum was previously detected in Italy as causal agent of leaf spots (2). To our knowledge, this is the first record of crown and root rot of strawberry tree caused by C. pauciramosum. In contrast with leaf spots, this report could indicate an important limiting factor for cultivation of strawberry tree potted plants in nurseries. The knowledge of the susceptibility of this host to crown and root rot caused by C. pauciramosum can help growers apply specific control strategies in nurseries.

Screening siderophore producing bacteria as potential biological control agent for fungal rice pathogens in Thailand

Rice (Oryza sativa) is a staple food in Thailand and, in addition, feeds around one half of the world’s population. Therefore, diseases of rice are of special concern. Rice is destroyed by 2 main pathogens, Fusarium oxysporum and Pyricularia oryzae the causative agents of root rot and blast in rice respectively. These pathogens result in low grain yield in Thailand and other Southeast Asian countries. Soil samples were taken from paddy fields in Northern Thailand and bacteria were isolated using the soil dilution plate method on Nutrient agar. Isolation yielded 216 bacterial isolates which were subsequently tested for their siderophore production and effectiveness in inhibiting mycelial growth in vitro of the rice pathogenic fungi; Alternaria sp., Fusarium oxysporum, Pyricularia oryzae and Sclerotium sp., the causal agent of leaf spot, root rot, blast and stem rot in rice. It was found that 23% of the bacteria isolated produced siderophore on solid plating medium and liquid medium, In dual culture technique, the siderophore producing rhizobacteria showed a strong antagonistic effect against the Alternaria (35.4%), Fusarium oxysporum (37.5%), Pyricularia oryzae (31.2%) and Sclerotium sp. (10.4%) strains tested. Streptomyces sp. strain A 130 and Pseudomonas sp. strain MW 2.6 in particular showed a significant higher antagonistic effect against Alternaria sp. while Ochrobactrum anthropi D 5.2 exhibited a good antagonistic effect against F. oxysporum. Bacillus firmus D 4.1 inhibited P. oryzae and Kocuria rhizophila 4(2.1.1) strongly inhibited Sclerotium sp. P. aureofaciens AR 1 was the best siderophore producer overall and secreted hydroxamate type siderophore. This strain exhibits an in vitro antagonistic effect against Alternaria sp., F. oxysporum and P. oryzae. Siderophore production in this isolate was maximal after 15 days and at an optimal temperature of 30°C, yielding 99.96 ± 0.46 μg ml−1 of siderophore. The most effective isolates were identified by biochemical tests and molecular techniques as members of the Genus Bacillus, Pseudomonas and Kocuria including B. firmus D 4.1, P. aureofaciens AR1 and Kocuria rhizophila 4(2.1.1). The study demonstrated antagonistic activity towards the target pathogens discussed and are thus potential agents for biocontrol of soil borne diseases of rice in Thailand and other countries.

First Report of Hainesia lythri Causing Leaf Spots of Paeonia suffruticosa in China.

Tree peony (Paeonia suffruticosa) is known as "the king of flowers" for its beautiful and showy flowers. It is regarded as the symbol flower of China and is cultivated throughout the country. During the summer of 2006, a leaf spot was observed on tree peony cultivated in the Zhengzhou area of Henan Province, and in 2007, the leaf spot was observed in the Luoyang area. In some gardens, the leaf spot affected more than 50% of the plants. Early symptoms appeared as small, round, water-soaked lesions on the leaves. Lesions expanded into 5 to 35-mm-diameter spots that were circular or irregular, brown to dark brown, with pale brown margins. Later, the center of some lesions dropped out. Signs of the suspected pathogen were usually seen on the leaf spots after an abundant rainfall. Lesions contained numerous, pale brown, cupulate conidiomata with salmon-colored spore masses. Conidiophores (70 × 1 to 2 μm) were hyaline, branched, septate, and filiform. Conidia (5.5 to 7.5 × 1.5 to 2 μm) were hyaline, aseptate, and cymbiform to allantoid. The pathogen was identified as Hainesia lythri on the basis of the morphology. This fungus infects a wide variety of hosts including P. suffruticosa, Acer pseudoplatanus, Calluna sp., Dissotis paucistellata, Epilobium angustifolium, and Eucalyptus saligna (3). The fungus was isolated on potato dextrose agar (PDA) medium using conidia from conidiomata found on symptomatic leaf tissue; the fungus produced gray-to-brown colonies. Pathogenicity was tested by inoculating 10 leaves on one 5-year-old tree with a mycelia plug from the colony (0.5 cm in diameter); leaves inoculated with plugs of PDA medium served as controls. Inoculated leaves were covered with plastic for 24 h to maintain high relative humidity and incubated at 25 to 28°C. After 5 days, 100% of the inoculated leaves showed symptoms identical to those observed on leaves from P. suffruticosa infected in the field while controls remained symptom free. Reisolation of the fungus from lesions on inoculated leaves confirmed that the causal agent was H. lythri. Thus, we concluded that H. lythri is the causal agent of leaf spots of P. suffruticosa. To our knowledge, this is the first report of H. lythri infecting P. suffruticosa in China. H. lythri has been previously reported on Paeonia in Japan and Korea (1,2).

Características culturais e severidade da mancha foliar de Quambalaria eucalypti sob diferentes regimes de temperatura, luz e período de molhamento foliar

Quambalaria eucalypti foi recentemente relatado como agente etiológico da mancha foliar e do anelamento da haste de Eucalyptus spp., no Brasil. Em vista do pouco conhecimento disponível sobre este patossistema, procurou-se, neste trabalho, avaliar o crescimento micelial e a esporulação do fungo em diferentes meios de cultura, determinar "in vitro" a temperatura ótima para o crescimento micelial, esporulação e a germinação de conídios, avaliar a influência do regime de luz sobre a germinação de conídios e determinar a influência do binômio temperatura - tempo de câmara úmida sobre a severidade da doença. As temperaturas de 25, 13 e 37 ºC foram respectivamente, ótima, mínima e máxima, para o crescimento. A temperatura ótima para esporulação foi de 25 ºC. A interação entre meios de cultura e isolados foi significativa, sendo que os meios de batata-dextrose-ágar (BDA), V8-ágar (V8) e caldo de vegetais-ágar foram os mais favoráveis ao crescimento micelial, seguidos de caseína hidrolizada ágar e ágar água. Todavia, para a esporulação, a interação entre meios de cultura e isolados não foi significativa e o meio de BDA foi o mais favorável à esporulação do patógeno. A temperatura e o regime de luz não afetaram significativamente a germinação de conídios, com uma taxa média de 85 % de germinação. A interação entre temperatura e tempo de permanência em câmara úmida não foi significativa para severidade da doença. O modelo quadrático foi o que melhor representou a severidade em função da temperatura, com ponto ótimo estimado igual a 27 ºC. O modelo exponencial foi o que melhor representou a severidade em função do tempo de câmara úmida.

Dasylirion serratifolium as a New Host of Botrytis cinerea, the Causal Agent of Leaf Spots and Blight in Italy.

Sandpaper sotol (Dasylirion serratifolium Zucc.), native to Mexico, has green leaves with margins highlighted by whitish yellow prickles like a fine sandpaper. During the spring of 2004 and 2005, necrotic lesions were observed in the middle of leaf blades and near prickles on 2- to 5-year-old, container-grown sandpaper sotol plants from two nurseries in eastern Sicily (Italy). Symptoms were detected on 20 to 30% of plants and consisted of reddish lesions that developed a reddish brown stripe surrounded by a yellow halo. As lesions enlarged, the center turned yellow and expanded rapidly causing blight of young leaves. Occasionally, symptomatic tissues had masses of gray fungal conidia and/or sclerotia. Botrytis cinerea was isolated consistently from infected tissues disinfected for 1 min in 1% NaOCl and rinsed in sterile distilled water and grown on potato dextrose agar (PDA). Hyaline, ovoid conidia (average 6.4 × 9.7 μm) and conidiophores were similar to those described of B. cinerea, and 5- to 8-day-old cultures developed black sclerotia that were round or irregular in shape (average 1.55 × 1.02 mm) that is typical of gray mold (1). Koch's postulates were performed by spraying 6-week-old sandpaper sotol plants grown in 12-cm pots with a spore suspension (1 × 106 CFU per ml) obtained from 12-day-old cultures grown on PDA. Eight plants were naturally wounded by scratching leaf blades among themselves and were subsequently inoculated, while eight plants were inoculated without wounding. An equal number of noninoculated plants sprayed with sterile water served as controls. All plants were maintained in high humidity conditions (90 to 95% relative humidity) at 20 ± 2°C. Leaf spots similar to the ones observed in nurseries were evident on all naturally wounded and nonwounded plants within 2 to 3 weeks after inoculation. Noninoculated control plants were symptomless. B. cinerea was reisolated from affected tissues. The pathogen has reduced commercial value of sandpaper sotol plants and may represent a limiting factor for the cultivation of this plant in eastern Sicily. To our knowledge, this is the first report in the world of leaf spot and blight caused by B. cinerea on D. serratifolium. Reference: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CAB International Mycological Institute, Kew, Surrey, England, 1971.

Leaf spot of cultivated and wildAlstroemeriaspp. caused byAsperisporium alstroemeriae

Asperisporium alstroemeriae (Allesch.) Maubl., the causal agent of leaf spot on Alstroemeria spp., is recorded for the first time in Argentina on commercial hybrids and on the native species A. psittacina. It appears that cultivated hybrids of Alstroemeria spp. and A. psittacina are new hosts for this pathogen. Disease symptoms and fungal description are provided.

Potencial de rendimento de grãos e outras características agronômicas e tecnológicas de novos genótipos de trigo

Estudou-se o comportamento de17 novos genótipos de trigo (Triticum aestivum L.) tendo como testemunha as cultivares IAC 370, IAC 289 e IAC 350 em experimentos semeados em dois sistemas de cultivo, sequeiro: Capão Bonito e Itapeva, e com irrigação por aspersão: Paranapanema, Ribeirão Preto e Mococa, no período de 2001 a 2002, no Estado de São Paulo. Avaliaram-se os rendimentos de grãos de cada genótipo em relação às diferentes condições de cultivo, tolerância ao alumínio com o emprego de soluções nutritivas, reação às principais doenças fúngicas e a qualidade tecnológica da farinha. Destacaram-se, na média geral, quanto ao rendimento de grãos os genótipos ALD/CEP76630//CEP73234/PF7219/3/BUC"S"/BYJ"S" e MARNG/BUC"S"//BLO"S" /PSN"S"/3/BUC/PVN"S", em cultivo de sequeiro e com irrigação por aspersão, respectivamente. Os genótipos CNO79/PRL"S'//IAC 227 e RAC 646/BH 1146 foram tão tolerantes à toxicidade de Al3+ quanto a cultivar tolerante BH 1146. A incidência da ferrugem-da-folha não foi constatada nos genótipos CHAT"S"/CEP7780//PRL"S"/ BOW"S'", SABUF, WG 3070/2*WEAVER e ALDAN"S"/IAS 58//IAC 60 que foram imunes à doença, no biênio em estudo, em ambos os sistemas de cultivo. Todos os genótipos foram suscetíveis aos agentes causais das manchas foliares. A qualidade tecnológica das amostras de farinhas procedentes de Capão Bonito, Região Sudoeste, foram superiores às obtidas em Ribeirão Preto, Região Central do Estado São Paulo.

Identification of the Causal Agent of Leaf Spot of Betelnut and in vitro Evaluation of Fungicides and Plant Extracts Against it

Identification of the Causal Agent of Leaf Spot of Betelnut and in vitro Evaluation of Fungicides and Plant Extracts Against it

First Report of Alternaria alternata Causing Leaf Spot on English Walnut.

A foliar disease of English walnut (Juglans regia L.) was observed in 1998 in an orchard in northern Italy. Symptoms consisted of circular, necrotic spots bordered with concentric zones of darker tissue. Average lesion diameter was 20 mm, although lesions could extend to half of the leaflet lamina. A fungus identified as Alternaria alternata (Fr.:Fr.) Keissl. (1) was observed on the necrotic tissue and was consistently isolated from the margins of the necrosis. Conidia from leaves were brown, ellipsoid to ovoid (primary conidia 28 to 60 × 8 to 15 μm; secondary conidia 10 to 30 × 7 to 13 μm), with walls often ornamented, 1 to 6 transversely septate and 0 to 3 longitudinally septate. For pathogenicity tests, three isolates were grown on potato dextrose agar for 2 weeks. Inoculations were performed on detached, surface-sterilized, healthy J. regia leaflets. Four drops (5 μl each) of a sterile water suspension of 1 × 105 conidia per ml were placed on each leaflet; three leaves per isolate were used. Leaves were incubated in a moist chamber. After 10 days, leaf spots similar to the original symptoms developed on all the inoculated points for all three isolates, and the pathogen was reisolated. Control leaflets inoculated with sterile, distilled water remained symptomless. The experiment was performed three times and the results were similar. Alternaria alternata is a well-known pathogen on many crops but a few records report this fungus as a causal agent of leaf spot on deciduous trees. This is the first report of A. alternata on English walnut. Reference: (1) E. G. Simmons. Mycotaxon 37:79, 1990.

Gene disruption and biochemical characterisation of 3‐isopropylmalate dehydrogenase from Stagonospora nodorum

This summary reports work with auxotrophs of the pathogenic fungus Stagonospora nodorum, the causal agent of leaf spot and glume blotch in wheat and barley, with a view to investigating the biochemical basis of pathogenicity. Biosynthetic enzymes may serve as targets for novel fungicides and genetic target validation can identify new candidates for a biochemical approach to fungicide discovery. © 1999 Society of Chemical Industry