Viability Of Urediniospores Research Articles

Urediniospores of Puccinia sorghi: pre- and post-cold storage requirements

The specific pre- and post-cold storage treatments needed to maintain the viability of urediniospores of rust fungi during storage are species dependent. Urediniospore collections are critical to assess pathogen evolution over time, but most importantly, to determine the efficacy of resistance genes in host plants. Puccinia sorghi, the causal agent of common rust of maize, can cause yield losses of up to 40% in susceptible varieties. The purpose of this study was to optimise the pre- and post-cold storage requirements of P. sorghi urediniospores. Here we report that dried urediniospores had an 87% decrease in germination compared with undried spores. Urediniospores of P. sorghi were successfully stored at -80°C for 24 months and remained infectious, and did not require cold shock in liquid nitrogen pre-cold storage, nor a heat shock to revive them from dormancy. Urediniospores removed from storage in a freezer at -80°C germinated readily between 22°C and 55°C.

Effect of pathogen concentrations and period of leaf wetness on orange rust severity in Brazilian sugarcane cultivars

The most important management strategy for orange rust of sugarcane (Puccinia kuehnii) is the use of resistant cultivars. Nevertheless, canes with intermediate resistance are still grown over large areas in the Brazilian sugarcane industry, with varying degrees of disease severity. Factors governing the severity of orange rust in these crops are largely unknown. Therefore, the present work aimed to examine the influence of pathogen concentration, period of leaf wetness, and urediniopore survival on sugarcane residue on disease severity. Thirty-day-old plants of cultivars RB72454, RB855156, RB867515, RB92579, RB935744, RB975201, SP81–3250, and SP89–1115 were inoculated with 50 ml of spore suspension with varying urediniospore concentrations (from 1.101 to 107 spores.ml−1) or period of leaf wetness (12, 24, and 48 h, pathogen concentration 1.106 spores.ml−1). Reaction of cultivars was evaluated by assessing leaf area affected. Survival of urediniospores was examined on sugarcane residues at 0, 10, 15, 20 days after separation from the cane plant. Only RB72454, RB92579, and RB855156, classified as susceptible or intermediate, exhibited higher disease levels as pathogen concentration increased. Extended periods of leaf wetness only influenced susceptible/intermediate cultivars, where higher severity occurred with longer period of leaf wetness. Viability of urediniospores collected in winter always had a greater loss of viability compared to spring but both season harbored viable urediniospores on 20-day-old sugarcane residues, suggesting they potentially could play a role in initiation of disease epidemics.

Preservation of the urediniospores of Phakopsora euvitis, the causal agent of grape leaf rust

Grape leaf rust, caused by Phakopsora euvitis, is an important disease causing considerable damage to vineyards in tropical regions. This study compared different temperatures and dormancy-reversion procedures for the preservation of P. euvitis urediniospores. Urediniospores from inoculated Vitis labrusca cv. Niagara Rosada vine leaves were collected, dehydrated, and compared with non-dehydrated leaves. Both groups of urediniospores were stored at −80 °C, −20 °C, 5 °C, and 25 °C. Urediniospore viability was evaluated by in vitro germination, whereas the severity of grape leaf rust was assessed by inoculation on leaves of ‘Niagara Rosada’ potted plants, performed immediately prior to storage and after 15, 30, 60, 90, 120 and 150 days. The viability of non-dehydrated urediniospores stored at 25 °C was low, while dehydrated urediniospores retained viability up to day 30. Dehydrated urediniospores stored at −80 °C had the best viability values during the 150-day experimental period. Independently of storage conditions, urediniospores germinated in vitro induced symptoms of disease in vine leaves. The severity of the disease had a strong positive correlation with the percentage of preserved urediniospores that germinated (r = 0.88). Combining dehydration and storage at low temperatures is essential to maintain the viability of urediniospores for at least 150 days.

Identification of a Novel Alternaria alternata Strain Able to Hyperparasitize Puccinia striiformis f. sp. tritici, the Causal Agent of Wheat Stripe Rust.

The obligate bitrophic fungus Puccinia striiformis f. sp. tritici (Pst) causes stripe (yellow) rust on wheat worldwide. Here, we report a novel fungal strain able to hyperparasitize Pst. The strain was isolated from gray-colored rust pustules, and was identified as Alternaria alternata (Fr.: Fr.) keissler based on a combination of morphological characteristics and multi-locus (ITS, GAPDH, and RPB2) phylogeny. Upon artificial inoculation, the hyperparasite reduced the production and viability of urediniospores, and produced a typical gray-colored rust pustule symptom. Scanning electron microscopy demonstrated that the strain could efficiently penetrate and colonize Pst urediniospores. This study first demonstrates that A. alternata could parasitize Pst and indicates its potential application in the biological control of wheat stripe rust disease.

A novel fungal hyperparasite of Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe rust.

Puccinia striiformis f. sp. tritici (Pst), the causal fungus of wheat stripe rust, was previously reported to be infected by Lecanicillium lecanii, Microdochium nivale and Typhula idahoensis. Here, we report a novel hyperparasite on Pst. This hyperparasitic fungus was identified as Cladosporium cladosporioides (Fresen.) GA de Vries based on morphological characteristics observed by light and scanning electron microscopy together with molecular data. The hyperparasite reduced the production and viability of urediniospores and, therefore, could potentially be used for biological control of wheat stripe rust.

Métodos de preservação in vitro de urediniósporos de Puccinia kuehnii

Com o objetivo de avaliar métodos de preservação de urediniósporos de Puccinia kuehnii, conduziram-se dois bioensaios sendo o primeiro (B1) com diferentes métodos de desidratação e o segundo (B2), com diferentes métodos de reidratação. Em B1 foi adicionado um grânulo de sílica gel para preservação dos urediniósporos nos tubos de microcentrífuga. Foram coletadas folhas com sintomas de ferrugem alaranjada, P. kuehnii, da cultivar de cana-de-açúcar SP89 1115. Os urediniósporos do agente causal de ferugem foram extraídos das folhas com o auxílio de bomba a vácuo. Posteriormente, estes foram acondicionados em tubos de microcentrífuga. Os tratamentos para B1 foram: l- desidratação em sílica gel, liofilização e sem desidratação; ll- temperatura ambiente (20ºC), geladeira (5ºC), congelador (-20ºC) e deep-freezer (-80ºC). Para B2 os tratamentos foram: l- desidratação em sílica gel e sem desidratação; ll- temperatura ambiente (20ºC), geladeira (5ºC), congelador (-20ºC) e deep-freezer (-80ºC); lll- com reidratação e sem reidratação nas avaliações. Para ambos os bioensaios foi realizada a germinação inicial, outras aos 15 e 30 dias de armazenamento e posteriormente a cada 30 dias, até 180 dias. Prepararam-se suspensões de urediniósporos em água e uma alíquota de 0,1 mL foi transferida para placas de Petri contendo meio ágar-água (15g L-1). Essas permaneceram a 20ºC, no escuro. Para a avaliação da viabilidade, procedeu-se a contagem de 200 urediniósporos por placa. Os dados foram submetidos à análise de variância não paramétrica de Kruskal-Wallis e complementadas com o teste de Dunn. Os resultados demonstraram que a viabilidade decresceu em função do tempo, sendo que os melhores tratamentos atingiram 27,6% e 6,6% aos 30 dias, e 12,0% e 1,9% aos 60 dias, para B1 e B2, respectivamente. O método da desidratação em sílica gel seguido do armazenamento a -80ºC foi o único que apresentou urediniósporos viáveis (1,2%) aos 180 dias, para B1. No B2, o melhor método foi preservação com desidratação, armazenados a 5ºC, sem reidratação. Esse método apresentou melhor porcentagem de germinação aos 120 dias (0,4%). Não foi observada influência do fator choque térmico na recuperação de urediniósporos viáveis em B2. A inclusão de grânulo de sílica gel no tubo de microcentrífuga permitiu a recuperação da viabilidade dos urediniósporos aos 180 dias.

Efeito da temperatura e da luz na germinação de urediniósporos de Phakopsora euvitis

Os objetivos deste trabalho foram analisar o efeito da temperatura e da luz na germinação in vitro de urediniósporos de Phakopsoraeuvitis, assim como avaliar a viabilidade dos urediniósporos armazenados em diferentes temperaturas. Para a determinação do período de incubação foi avaliada a germinação dos urediniósporos em ágar-água 2%, após 2, 4, 6, 8, 10, 12 e 24 h. Para avaliar o efeito da temperatura e da luz na germinação, placas de Petri contendo suspensão de urediniósporos foram mantidas no escuro e sob luz contínua, nas temperaturas de 15, 20, 25 e 30 ºC, por um período de 24 h. No estudo de viabilidade, urediniósporos armazenados em tubos Eppendorf foram mantidos nas temperaturas de -20±2, 5±2, 23±2 e 33±2ºC, no escuro. Verificou-se o aumento contínuo na germinação dos esporos entre as avaliações com 6 a 24 horas de incubação. As temperaturas cardinais (mínima, ótima e máxima) para a germinação de urediniósporos in vitro estimadas foram de 11,6; 21,0 e 30,6 ºC; e 13,1; 21,0 e 30,0 ºC; respectivamente, nas condições de luz contínua e escuro. A viabilidade dos esporos foi reduzida drasticamente no período de 60 dias de armazenamento, verificando-se maior preservação na temperatura de 23±2 ºC.

Sources of primary inoculum ofTranzschelia discolorin Australian almond orchards

Sources of primary inoculum of almond rust (Tranzschelia discolor) were investigated. Retained leaves, fruit not removed during harvest, leaf litter on soil and green or lignified shoots were monitored for viable urediniospores between harvest and the emergence of new leaves. Retained leaves were confirmed as the primary source of overwintering inoculum in almonds with up to 27% of the urediniospores viable at the time of new leaf emergence. Viable urediniospores were also found on symptomless green shoots, retained fruit and lignified shoots. The viability of urediniospores on leaf litter rapidly declined to nil within two months. Inoculation of almond stems and fruit showed that both were capable of producing uredinia, but were less frequently infected compared with leaves. Urediniospores from stem or fruit lesions, symptomless green or lignified shoots, or leaf litter are not considered to play a major role in the epidemiology of almond rust. Inoculation of cherry, peach, nectarine and plum plants with urediniospores collected from almond leaves did not produce disease symptoms indicating that other stone fruit are unlikely to provide an alternative overwintering host for almond rust. Removal of retained leaves in combination with strategic fungicide use may help growers to optimise rust control in almonds.

Latent period and viability of Puccinia jaceae var. solstitialis urediniospores: Implications for biological control of yellow starthistle

Since the introduction of Puccinia jaceae var. solstitialis into California in 2003, multiple urediniospore generations have been observed, along with teliospores and pycnia, on yellow starthistle (Centaurea solstitialis). A field and laboratory study of urediniospore viability was conducted to determine the potential of using infected plant material for redistribution of inoculum into new areas. To better understand the life history of P. j. solstitialis, urediniospore viability was measured during the summer and fall when the host plant is usually senescent. Latent period (time from inoculation to pustule eruption) after field and laboratory inoculations was measured in order to determine the potential number of urediniospore generations that occur per year. Viability of urediniospores stored in the laboratory gradually declined over a period of 10 weeks; spore hydration increased germination. Based on the results obtained in this study, introductions of harvested infected plant material would have to be done quickly to offset losses in urediniospore viability. Urediniospore viability in the field decreased exponentially 86% near the coast and 97% in the Central Valley three weeks after production, and was negligible (0–0.2%) thereafter. Latent period ranged from four to five weeks at cool winter temperatures to two to three weeks at warm summer temperatures in both the laboratory and field. Results of this study suggest that urediniospores are not likely to remain viable through the summer and fall dry season. Teliospores, therefore, serve as the inoculum source when YST seedlings germinate in the winter. Approximately six urediniospore generations can be expected to occur each year in central-northern California under suitable conditions for disease.

Investigations into the use of flame and the herbicide, paraquat, to control peppermint rust in north-east Victoria, Australia

Autumn flaming, spring flaming, and combinations of both were compared with the use of the fungicide propiconazole for their effect on growth, disease levels and oil yields of peppermint growing at the Ovens Research Station near Myrtleford, north-east Victoria in 199415. Spring flaming severely disrupted plant growth, resulting in reduced oil yields despite low levels of disease. Autumn flaming promoted high oil yields, but cannot be recommended to growers due to current legal constraints in Victoria. The contact herbicide, paraquat, is used by peppermint growers in autumn as a clean-up measure; it substantially reduced viability of urediniospores of P. menthae and although not as effective as autumn flaming, its use may help to reduce the level of inoculum carried over into the winter from the previous crop.

Survival ofPuccinia reconditaandP. graminisUrediniospores Exposed to Temperatures from Subfreezing to 35 C

Viable urediniospores and dormant mycelial infections are the principal inoculum sources that contribute to the establishment and development of destructive wheat rust epidemics in the central Great Plains. Viability of urediniospores of Puccinia recondita and P. graminis was measured by exposure in environmental chambers set at constant temperatures ranging from −6 to 35 C. Exposure of P. recondita and P. graminis urediniospores for up to 120 h to constant temperatures of 5-35 C did not significantly (P ≤ 0.05) affect spore viability among isolates. However, P. recondita and P. graminis urediniospore viability as measured by germination observed after exposure to constant temperatures of -6, −4, −2, 0, 5, 10, 20, 25, 30, or 35 C for 24, 48, 72, 96, or 120 h indicated significant differences in viability among temperature treatment means (P ≤ 0.05). Urediniospores remained viable up to 864 h at constant temperatures between 10 and 30 C and up to 504 h at constant temperatures of 5 and 35 C. Viability of urediniospores exposed at temperatures ranging from −2 to 0 C decreased rapidly after the first 4 h of exposure. At below-freezing temperatures, viability of spores declined rapidly after 1-2 h of exposure. Viability of urediniospores exposed to freezing or below-freezing temperatures was not restored by heat shocking at temperatures typically encountered in the field during an epidemic. Infectivity of P. recondita and P. graminis urediniospores exposed at 5-35 C for 120 h was not significantly different from infectivity of unexposed urediniospores; an average of 58% of the viable urediniospores produced appressoria

Detection, Viability, and Possible Sources of Urediniospores of Puccinia recondita f. sp. tritici in Louisiana

The number and viability of spores trapped was maximum during the active epidemic period between February and May and was least during the summer. Viability of the urediniospores was significantly inversely correlated with ambient maximum temperature. Rusts from Hordeum pusillum and Lolium multiflorum failed to infect wheat and vice versa. Surveys during mid-December 1986 and 1987, at Alexandria and Baton Rouge, showed uniform distribution of leaf rust over a large area, indicating the possibility of a major exodemic origin of inoculum for winter wheat in Louisiana for these years

Effect of temperature on germination and viability of urediniospores of four races of Puccinia striiformis from barley

Urediniospores of cultures of four barley isolates of Puccinia striiformis had an optimum temperature for germination of around 10 °C and a maximum of around 25°, resembling most other British races of P. striiformis . There was no evidence of the existence of any high temperature strains. Spores of one isolate of race 24 germinated more slowly than those of the other isolates of races 23 and 24. Duration of spore survival at high temperatures became less as the temperature rose, declining from 24 h at 28° to less than half that at 30°. Since spores survived for at least 48 h at 25°, lack of infection on wheat cultivars at that temperature is probably due to high temperature resistance in the host.

Effect of Cladosporium aecidiicola Thum. on the viability of urediniospores of Melampsora medusae Thum. in storage

The viability of urediniospores of Melampsora medusae decreased markedly when stored in mixture with the conidia of Cladosporium aecidiicola. The rate of decrease was more rapid in samples stored at 16°C with high concentration of Cladosporium (ratio of urediniospores to conidia 10:1 by weight) than at −12°C and low concentration (20:1 by weight).

Germination of Aeciospores, Urediniospores, and Teliospores of Puccinia coronata

1. Aeciospores from herbarium specimens of Rhamnus were not viable after a period of 167 days from date of collection. 2. Urediniospores from herbarium specimens of Avena sativa proved to be viable as long as 87 days after date of collection. 3. Unprotected urediniospores lost their viability within 22 days, with a minimum temperature, during this period, of -27°F. and a maximum of 42°F. 4. When afforded protection with a temperature range similar to the unprotected, these spores remained viable as long as 44 days. 5. Exposed to light, viability of urediniospores was lost within 23 days, during which period the maximum temperature was 86°F. and the minimum 29°F. 6. Kept in the dark, urediniospores at similar temperatures to those exposed to light, remained viable as long as 79 days. 7. Urediniospores germinated at a temperature as low as 7°C., with an optimum of 18°C., and a maximum of 32°C. 8. Teliospores developed on oat seedlings in the greenhouse and not afforded a period of overwintering did not germinate. 9. Previous to overwintering and as late in the spring as May 2, teliospores developed in the field were incapable of germination.