Incidence Of Scab Research Articles

Relative Susceptibility of Selected Apple Cultivars to Apple Scab Caused by Venturia inaequalis

Apple scab is the most important disease of apples (Malus domestica) in the cool temperate regions where apples are grown. Data were collected over several years from plantings of new apple cultivars and selections established at multiple locations in 1995 (23 entries) and 1999 (24 entries) as part of regional project NE-183. Golden Delicious and McIntosh were the standards in both plantings. Data on incidence of scab on leaves and fruit were collected and analyzed to determine differences due to location and cultivar. None of the analyses indicated significant cultivar differences due to location, likely confirming the diversity of the apple scab fungus in the eastern United States. In general, for scab on leaves, the cultivars Ginger Gold, Orin, Cripps Pink, Silken, and Delblush were as susceptible as McIntosh, a common standard for scab susceptibility in the eastern United States. For scab on fruit, the cultivars Fuji, Cameo, Cripps Pink, Ambrosia, and Silken, and the selection NJ 90, were as susceptible as McIntosh. As expected, the cultivars and selections with genetic resistance to the scab pathogen exhibited the lowest incidences of apple scab on foliage and fruit. Gala Supreme, Sansa, and Honeycrisp, while susceptible to scab, exhibited relatively low levels of the disease. Accepted for publication 2 February 2010. Published 8 April 2010.

Effect of reduced spray programmes on incidences of apple scab, powdery mildew and codling moth damage in environmentally freindly apple production systems

Still a large amount of pesticides and spary applications are used in environmentally friendly fruit production systems; therefore, the aim of our study was first to test the in vitro effeicacy of some fungicides against a key apple disease (apple scab), and secondly to evaulate the effectiveness of reduced spray programmes against apple scab, powdery mildew and coding moth in integrated and organic apple orchards. In vitro efficacy of 7 fungicides (Champion 50 WP, Kocide 2000, Nordox 75 WG, Olajos rézkén, Kumulus S, Rézkén, Rézoxiklorid) and another 6 fungicides (Score 25 EC, Efuzin 500 SC, Systane, Folicur Solo, Zato Plusz, Rovral) approved in organic and integrated production systems, respectively, were tested against apple scab. Altogether four spray programmes were performed i) standard integrated: sprays followed by forecasting systems during the season, ii) reduced integrated: sprays followed by forecasting systems but only 75% of the spray numbers used during the season-long spray programme, iii) standard oragnic: sprays applied every 7–14 days during the season and iv) reduced organic: 60% of the spray numbers used during the season-long spray programme. In vitro results showed that fungicides (with active ingredients of copper and sulphur) applied in organic production showed relatively high percent growth capacity of the apple scab fungus. Rézkén showed the highest and Kumilus S the lowest efficacy against apple scab. Fungicides applied in integrated production showed relatively low percent growth capacity of the apple scab fungus. Score 25 EC showed the highest and Rovral the lowest efficacy against apple scab. Field study showed that reduced spray programmes did not increase significantly scab incidence in the integrated field. However, scab incidence increased significanly (above 30%) in the reduced spray programme for the organic orchard.Mildew incidence was low (below 5%) in both integrated and organic spray programmes. Mildew incidence on both shoots and fruits increased significanly in the reduced spray programme for the organic orchard. Incidence of codling moth damage was affected the most by standard vs. reduced spray programmes. Though incidence remained below 10% in the integrated plots, the incidence was significantly higher in the reduced spray programme compared to the standard programme. Similar results were obtained for organic spary programmes, but the incidence was 10 times higher and the differences among the two programmes were larger.,

Resistance to scab caused by Venturis pirina in interspecific pear (Pyrus spp.) hybrids

The genetics of resistance to Venturia pirina was investigated from 2002 to 2004 on 11 families derived from interspecific crosses between European and Asian pear species. Nearly complete leaf resistance to V. pirina was identified in all progeny of families with at least 50% Asian pear (Pyrus pyrifolia and/or Pyrus × bretschneideri) ancestry, but up to 26% of these trees exhibited fruit scab incidence in any one of three years. However, between 67% and 80% of the scab leaf resistant individuals had fruit russet spotting owing to scab infection in one or more years over the duration of the trial and between 14% and 36% of the leaves were affected by russet spot. The level of affected individuals did not appear to decrease with increasing proportion of Asian parentage for leaves or fruit. In contrast, reference families derived from European pears and many of the families with 12–25% Asian parentage were almost 100% susceptible to scab on both leaves and fruit. In European families, only 2% of these individuals had leaves affected by russet spotting, whereas an average of 23% of fruit were affected. The genetics of non‐host resistance is discussed.

Towards improvement of marker assisted selection of apple scab resistant cultivars: Venturia inaequalis virulence surveys and standardization of molecular marker alleles associated with resistance genes

Molecular breeding for pathogen resistance faces two major problems that delay its widespread adoption, resistance breakdown and difficulties in unambiguously identifying the alleles of the markers associated with specific resistance genes. Since the breakdown of the Rvi6 (Vf) gene in the Northern part of Europe breeders have intensified the search for new resistance sources to be introduced into their breeding programs. Alternative major genes to Rvi6 are available (e.g. Rvi2, Rvi4, Rvi5, Rvi10; Rvi11, Rvi12, Rvi13, and Rvi15, respectively Vh2, Vh4, Vm, Va, Vbj, Vb, Vd, Vr2 according to the old apple scab resistance gene nomenclature) but, with few exceptions (i.e., Rvi4, Rvi5 and, Rvi13), they have so far not been incorporated in commercial varieties. Pyramiding, i.e., combining several of these major resistance genes (R-genes) in individual plants, is one of the most promising strategies currently available to develop apple cultivars with durable apple scab resistance. But, which genes are the best suited to produce such new cultivars? Although the most interesting genes are surely those whose resistance so far has not been broken by the pathogen, genes with resistance that has been overcome coupled with only limited spread of the virulence may also be used in the pyramiding process. However, obtaining information on whether an R-gene is overcome and if so, the extent of the spread of the virulence is difficult and time consuming. Furthermore, often such reports are not up-to-date and the correctness of the data is difficult to verify. To solve these problems, the initiative “Monitoring of Venturia inaequalis virulences” has been proposed. The monitoring is based on a network of orchards of selected differential hosts. Incidence and severity of scab on these genotypes will be collected yearly; and after validation, the data will be published through the homepage of the project (www.vinquest.ch). Here, we present an outline of this initiative. A second major obstacle for broad adoption of marker assisted selection is the lack of tools to align marker analyzes performed in different laboratories to unambiguously identify the alleles linked to specific resistances. The identification of the alleles of the markers in coupling with the resistance genes is often very difficult, if the same genotype used to develop the markers is not simultaneously analyzed. In this paper we present an approach to standardize the size of the alleles in coupling with the resistance genes, using easily accessible cultivars. The proposed procedure has been applied to selected markers for the apple scab resistance genes Rvi2, Rvi4, Rvi5, Rvi6, Rvi11, Rvi12, Rvi13, Rvi14 and Rvi15 (respectively Vh2, Vh4, Vm, Vf, Vbj, Vb, Vd, Rvi14 and Vr2 according to the old nomenclature).

Action Thresholds for Summer Fungicide Sprays and Sequential Classification of Apple Scab Incidence.

The objectives of this study were to establish scab incidence thresholds at which summer fungicide sprays should be initiated and to develop sequential sampling for classification plans to facilitate decision making. The relationship between proportion of scabbed leaves per shoot and percent scabbed fruits at harvest was established based on data collected in both experimental and commercial orchards. Action threshold at which fungicide spray program should be initiated in order to maintain fruit scab at harvest below 2% was established at 0.006 scabbed leaves per shoot; hence incidence thresholds of 0.005 and 0.01 scabbed leaves per shoot were evaluated. Sequential sampling for classification procedures (SSCP), using the Wald's sequential probability ratio test (SPRT), were developed based on a beta-binomial distribution and using parameter estimates of the binary power law. Monte Carlo simulations were used to establish the probability of classifying mean scab incidence as less than the action thresholds (pth = 0.005 and pth = 0.01). Operating characteristic (OC) and average sample number (ASN) curves were established for eight combinations of stop lines and error levels (α and β). Based on the results of the Monte Carlo simulations, four sets of stop lines (two for each pth threshold) were selected for further evaluation. Bootstrap simulations of 50 data sets indicated that both the OC and ASN curves for each of the four pairs of stop lines were similar to OC and ASN values determined by Monte Carlo simulation. When validated with data not used to construct the models, the SSCPs provided the appropriate classification in 98 and 95% of the simulations for the pth = 0.005 and pth = 0.01 (α = 0.05 and β = 0.10), respectively. The sequential sampling plans developed in this study should allow for rapid and accurate classification of the incidence of apple scab on leaves, and aid in sampling for summer scab management decision making.

The relative impacts of elevation and rainy days on the incidence of scab damage of pecan nuts in the southeastern USA

SummaryThe fungus, Fusicladosporium effusum (G. Winters) Partridge & Morgan-Jones, causes scab disease in pecan [Carya illinoinensis (Wangenh.) C. Koch] in the southeastern USA. Infections of the fruit shuck severely reduce nut production and could be minimised with a greater understanding of the ecology of the disease. We investigated the relative impacts of rain and elevation on the incidence of scab, as noted by a decline in nut weight. Data on the suppression of nut growth (weights from sprayed trees – weights from unsprayed trees) due to scab were collected from 18 orchards within ten counties in southern Georgia over 6 years, along with rainfall and elevation data from the National Climatic Data Center. Stepwise multiple regression analyses demonstrated that scab-mediated inhibition of nut growth decreased with elevation, but increased with the maximum rain period in April, June, July, and August (R2 = 0.82). Elevation had twice the effect of rain on the reduction in nut growth due to scab. Substituting total days of rain for the maximum rain period in June, June to July, or June to August, did not improve the relationship. Thus, within the June, June to July, or June to August intervals, scab damage was directly proportional to the single, longest wet period in each period and to orchard elevation. Although damage was most severe in June, the rain effect was cumulative and was greatest from June to August. These results demonstrate the importance of elevation for commercial pecan production, and the susceptibility of the nut to wet periods when the fruit are rapidly elongating and expanding. Spores released from scab lesions on young leaves during the Spring can infect fruit over the Summer, indicating the need for applications of fungicide before flowering.

Estratégias de seleção em progênies de maracujazeiro-amarelo quanto ao vigor e incidência de verrugose

O maracujá-amarelo (Passiflora edulis Sims f. flavicarpa Deg.), originário da América tropical, é cultivado em todo o território nacional, porém as doenças são responsáveis por grandes perdas na cultura. Entre as principais do maracujazeiro, está a verrugose (Cladosporium cladosporioides). Objetivou-se, neste estudo, comparar estratégias de seleção em progênies de maracujazeiro-amarelo quanto ao vigor e incidência de verrugose. Avaliaram-se 75 progênies de meios-irmãos, em novembro de 2006, quanto ao vigor e incidência de verrugose, segundo critério de notas variando de um a cinco. O delineamento experimental foi em blocos ao acaso, com três repetições e quatro plantas por parcela. Simulou-se a seleção para resistência à verrugose e vigor, por três métodos de índices de seleção, envolvendo os dois caracteres. As seleções baseadas em índices de seleção não proporcionaram resultados conjuntos satisfatórios em ganhos, enquanto os ganhos pela seleção combinada foram superiores aos obtidos pela seleção direta e indireta, porém o índice de Pesek & Baker e Mulamba & Mock proporcionaram ganhos totais satisfatórios. A seleção combinada proporcionou ganhos genéticos superiores aos índices de seleção, caracterizando-se como promissora na seleção de progênies com menor incidência de verrugose.

Role of organosilicone surfactant in apple scab control under scab conducive weather conditions

Fungicides of integrated fruit production (dithianon, captan, and diclofluanid) and an organosilicone surfactant were compared in spray schedules from green tip until summer in order to control apple scab caused by Venturia inaequalis and to evaluate their phytotoxicity on fruit. Sixteen sprays of 1.8 kg ha-1captan, 0.41 ha-1 dithianon, and 1.8 kg ha-1 diclolfluanid significantly (P=0.05) reduced the incidence of leaf or fruit scab compared to unsprayed products. All fungicides applied with organosilicone at 0.1% resulted in lower incidence of scab on young and older leaves as well as on harvested fruit, but these were not statistically always better than fungicides applied alone. In case of diclofluanid, the fungicide applied with organosilicone at 0.1% resulted in significantly lower (P = 0.001) incidence of scab on young and older leaves. Diclofluanid applied with organosilicone at 0.1% gave the best scab control on leaf and fruit. Treatments applied with fungicides alone had no significant effect on plant phytotoxicity compared to untreated control. All fungicides applied with organosilicone at 0.1% increased (P = 0.05) fruit damage compared to untreated control or fungicide applied alone, though these were not always significantly different. In case of percentage of fruit russet, treatment of dithianon 0.4 1/ha + 0.1% organosilicone significantly increased fruit russet, while fruit russet index significantly increased in the treatment of diclofluanid 1.8 kg/ha + 0.1% organosilicone compared to untreated control. In sum, application of surfactants can help to increase efficacy of scab fungicides; and consequently, to reduce the risk of fungus infection under high scab disease pressure. This fact may also be helpful in fungicide resistance management and reduced-spray programs with accurate scab warning systems.

The Identification and Detection of Spongospora subterranea and Factors Affecting Infection and Disease

Powdery scab caused by Spongospora subterranea is a serious disease, affecting both the quality and quantity of ware and seed potatoes, particularly in northern Britain where soil conditions are conducive to disease development. To enable accurate quantification of S. subterranea DNA for epidemiological studies, a real-time PCR assay specific to this pathogen was developed. This assay could reliably detect and quantify DNA from sporeballs, zoospores and plasmodia/zoosporangia of S. subterranea. The assay was used to measure the viability of sporeballs in soil, was combined with a tomato bait plant technique in order to study zoospore release and was used to study infection levels in potato under various environmental conditions. Both the incidence and severity of powdery scab were found to be influenced by temperature, soil type and soil moisture regime when tested under controlled conditions. Soil inoculum level did not have a significant effect on infection and disease development and even low levels of inoculum were regularly found to result in severe disease symptoms. Evidence from A GB-wide trial and a five year survey in England and Wales confirmed that there is no simple or consistent relationship between powdery scab inoculum on seed and disease developing on the progeny crop. Disease risk appears to be more related to the relative conduciveness of environmental conditions rather than inoculum level. Integration of control measures is likely to be the most effective way for growers to reduce the impact of the disease.

Powdery Scab of Potato—Occurrence, Life Cycle and Epidemiology

Powdery scab of potato, caused by the zoosporic pathogen Spongospora subterranea f.sp. subterranea (Sss), is an often underestimated disease, which has lead to lack of appropriate control strategies. A new wave of increasing importance of this disease has occurred in the last 30 years in many countries, among them France, Pakistan, Japan, Australia, New Zealand, Costa Rica, USA, and, very recently, Colombia, Korea and China. A consequence is that occurrence of, and research on, powdery scab has shown a cyclic pattern. Additionally to its importance as a pathogen, Sss is a vector of potato mop top virus which itself can cause substantial damage. Factors such as intensification of potato production, increasing use of susceptible cultivars, more frequent irrigation and banning of mercury, previously used as an efficient seed tuber treatment, have all contributed to greater incidence of powdery scab. Since 1842, when Wallroth first described the disease in the scientific literature, many researchers, particularly before 1960, started to work with Sss, mostly because powdery scab became a problem in their respective countries. Today we know many aspects of the biology of the biotrophic protozoan organism that causes powdery scab, but we still lack basic knowledge on the etiology and epidemiology of the disease. We lack sufficient knowledge of the factors that affect survival of the resting structures, potato and alternative host infection and disease development. This knowledge is essential in predicting disease risk and developing effective powdery scab management strategies.

Timing of first and final sprays against apple scab combined with leaf removal and pruning in organic apple production

The aim of this two-crop season study was to evaluate scab development and scab control efficacy in integrated approaches of (i) three sanitation treatments (fallen leaf removal combined with winter pruning and non-sanitized control), (ii) three onsets of first fungicide sprays (dormant bud, early tight cluster and pink bud stage) and (iii) three final dates for finishing fungicide programmes (mid-July, mid-August and mid-September). The study was performed in a Hungarian commercial organic apple orchard on a scab-resistant cultivar Prima and a moderately scab-susceptible apple cultivar, Jonathan. Final scab incidence of cultivar Prima was low on both leaves (below 3%) and fruits (below 1%) at harvest in all treatments, and delaying the first spray and/or omitting final sprays did not significantly affect fruit scab development on this cultivar. Results on cultivar Prima indicated that sprays against scab could be omitted before pink bud stage and after mid-July if the cultivar is not susceptible to summer fruit diseases and fruit scab incidence remains below 1% by harvest. On cultivar Jonathan, a delay in the onset of the first spray until pink bud stage resulted in higher scab incidences on both leaves (16.6–20.6%) and fruits (13.1–15.3%) compared with the non-delayed (dormant bud) spray treatments (5.2–8.3% and 6.7–9.4%, respectively). Final leaf and fruit scab incidence of cultivar Jonathan increased significantly when sprays were omitted after mid-July compared with spray treatments finished at mid-August or mid-September. Treatments of combining leaf removal with winter pruning resulted in lower scab incidence (5.2–11.8%) compared with treatments of non-sanitized plots (6.7–14.7%) when spray treatments were finished at mid-August or mid-September. Results on cultivar Jonathan suggested that sprays against scab could only be omitted before early tight cluster stage and after mid-August if removal of fallen leaves combined with pruning was applied and if the cultivar expressed <15% leaf scab incidence at harvest.

Doses de aplicação de nitrogênio e potássio em relação à podridão parda e sarna em ameixeira 'Reubennel' na região de Araucária, Paraná

O estado nutricional do hospedeiro pode influenciar na severidade de varias doencas de plantas, embora exista pouca informacao relacionando nutricao mineral com podridao parda e sarna em ameixeira. O objetivo do presente trabalho foi avaliar durante tres safras o efeito da adubacao nitrogenada e potassica, aplicada ao solo, na incidencia da podridao parda e na incidencia e severidade da sarna para ameixeira 'Reubennel', em pomar comercial no Municipio de Araucaria PR. Os tratamentos consistiam de cinco doses de nitrogenio (40, 80, 120, 160 e 200 kg ha-1 ano-1) aplicado na forma de ureia, e duas de K (55 e 110 kg ha-1 ano-1), aplicado na forma de cloreto de potassio. A incidencia de podridao parda foi avaliada na colheita determinando-se a incidencia em todos os frutos produzidos. A incidencia de sarna foi avaliada em amostra de 100 frutos, 20 desses considerados para avaliacao da severidade. A maior incidencia de podridao parda foi obtida na maior dose de K de 110 kg ha-1 ano-1 e nas maiores doses de N de 160 e 200 kg ha-1 ano-1 comparado com as outras doses utilizadas. O potassio na dose de 110 kg ha-1 ano-1 reduziu a severidade de sarna nos fruto em 21,2% para a safra de 2003/04. Ao contrario, a maior dose de N aumentou a severidade de sarna para a safra de 2004/05. A incidencia de sarna nao apresentou diferenca em funcao da adubacao nitrogenada utilizada. Nao houve interacao entre as doses de nitrogenio e o potassio na incidencia ou severidade de sarna e podridao parda.

Classification of apple cultivar reactions to scab in integrated and organic production systems

In a 7-year Hungarian study, 27 apple cultivars (9 scab resistant, 9 commercial, and 9 old) were evaluated for scab resistance in high-density integrated and organic apple orchards; classified into five susceptibility categories (low, low to middle, middle, middle to high, and high) based on their season-long leaf and fruit scab development; and the temporal progress of scab in each classification category was analyzed. Mean final scab incidence was considerably higher in the organic than in the integrated production system except for the resistant cultivars, which had no fruit scab symptoms. Fruit of all cultivars was protected in the integrated production system (final fruit scab was below 1.1%), but most commercial cultivars (‘Idared’, ‘Jonagold’, ‘Jonathan’, ‘Jonica’, ‘Mutsu’, and ‘Royal Gala’) were moderately or highly infected by harvest in the organic production system. Categorization of cultivar susceptibility indicated that season-long leaf and fruit scab development was low for the majority of resistant cultivars and moderate to high or high for most commercial cultivars. The resistance of old cultivars to scab ranged from low to moderate to high. Temporal scab progress of each classification category was analyzed by (i) calculating standardized area under the disease progress curves (AUDPCS); (ii) fitting a three-parameter logistic function to the disease progress data; and (iii) estimating upper asymptote (y f), relative rate parameter, and the inflection point from the fitted function. Results demonstrated that y f and AUDPCS showed significant differences (P < 0.05) among each scab classification category of leaf and fruit in both production systems; therefore, y f and AUDPCS can be used to differentiate the relative resistance of apple genotypes. Classification categories can assist in the selection of the most appropriate cultivars for planting in integrated or organic apple orchards.

Organic apple growing using sanitation treatments against apple scab

Effects or sanitation practices were evaluated on primary and autumn infection by Venturia inaequalis in an organic apple orchard at Eperjeske on the moderately scab-susceptible apple cultivar Jonathan in 2005 and 2006. Evaluated sanitation practices were: i) collection of fallen leaves in autumn; ii) destroying fallen leaves by disc cultivation in autumn; iii) spraying fallen leaves with 2% lime sulphur in autumn; iv) spraying fallen leaves with 2% lime sulphur in autumn and then collection of fallen leaves in autumn; and v) untreated control. In both years, most sanitation practices reduced significantly (P&lt; 0.05) scab incidence in the primary infection periods compared to untreated control. The highest leaf scab incidence was observed in the untreated plots (26:2 and 24.3% in 2005 and 2006, respectively), while the lowest was in the treatments of spraying fallen leaves with 2% lime sulphur combined with collection of fallen leaves (11.7 and 12.3% in 2005 and 2006, respectively).

Micronised and non‐micronised sulphur applications control peach scab equally well with negligible differences in fruit quality

AbstractIn a 2‐year study, micronised (finely ground) and non‐micronised sulphur spray programmes were investigated for peach scab control and influence on peach fruit quality variables including fruit colouration, soluble solids content and flesh firmness. Both sulphur programmes, applied six or 11 times at 15 kg ha−1, controlled scab equally well in both years on cultivars (cvs) Contender and Cresthaven. Six applications of a half dosage of both micronised and non‐micronised sulphur programmes were significantly less effective (P &lt; 0.05) compared with all other programmes when scab incidence was &gt;90% on cv. Contender. None of the sulphur programmes influenced significantly (P &lt; 0.05) colouration and flesh firmness of harvested fruits compared with the industry standard (a chlorothalonil–captan programme). Only soluble solids concentrations showed significant differences among fungicide programmes (P &lt; 0.05), but these differences were not consistent with either particle sizes of sulphur fungicide or reduced application fungicide programmes. In conclusion, our study showed that (a) micronised sulphur did not control peach scab more effectively compared to non‐micronised sulphur; (b) six applications of sulphur were sufficient to control peach scab when disease pressure was low to medium; and (c) neither six nor 11 applications of sulphur‐based products applied at 15 kg ha−1 had commercially relevant negative impacts on important peach fruit quality variables.

Response of potato (Solarium tuberosum) tuber yield components to gel‐polymer soil amendments and irrigation regimes

Two field experiments were conducted to investigate the effects of two gel‐polymer formulations (pure and fertiliser‐fused) and moisture stress on yield and quality of potato (Solanum tuberosum). The experiments were carried out at the Hatfield Experimental Farm of the University of Pretoria, South Africa. Six gel‐polymer rates, consisting of pure gel polymer at 1.5kg/m3 of soil, with 85% and 70% fertiliser rate of the control, and fertiliser‐fused gel polymer at 1.5, 2, and 3kg/m3 soil, and control (without gel polymer) were assigned to the subplots. Four maximum allowable moisture depletion (MAD) levels, 25%, 40%, 55%, and 70% of the plant available soil moisture, were allocated to the main plots. Rate of phosphorus (P) was the same for all treatments (168kg/ha). Total nitrogen (N) and potassium (K) budget for the treatments (except one pure gel‐polymer treatment received 85%) were balanced to 70% of the control. The fertiliser‐fused gel polymer showed no substantial improvement in tuber yield parameters for all rates. The pure gel polymer, especially at higher fertiliser rate, improved total and marketable tuber yield. Marketable tuber number and yield, and total tuber mass showed declining trend with an increase in MAD. Significant reduction in tuber fresh and dry mass was observed at the 55% and 70% MAD irrigation levels. Both high and low soil moisture levels reduced tuber specific gravity. Incidence of common scab was inversely related to the irrigation frequency.

Seven-year orchard performance of eleven new apple cultivars from Holovousy in comparison with some commonly grown ones

&amp;nbsp;In an orchard trial that was established in the spring of 1999 on M 9 rootstock at the spacing of 4 &amp;times; 1 m, eleven new apple cultivars bred in Holovousy (Angold, Julia, Nabella, Primadela, Produkta, Resista, Rubinstep, Rucla, Selena, Vysočina and Zuzana) were evaluated in comparison with three standard varieties (Gala, Golden Delicious and Jonagold) and another two with resistance to scab (Rosana and Topaz). In the first three years, the incidence of scab and mildew was evaluated under limited chemical protection. In 2000&amp;ndash;2005 on each of 10 randomly selected trees of each cultivar, the time of flowering and optimum harvest ripening were recorded, flower set and fruit sets were rated, yield per tree and weight of 10 fruit samples were measured. Trunk diameter was measured between 2002 and 2005. The early summer apple Julia had the healthiest state and it was recommended for organic growing. Selena was the most precocious, the least vigorous and had the highest crop efficiency. The highest annual yields per tree were recorded with Produkta, but this cultivar had the highest proportion of trees with biennial bearing. Primadela achieved the highest cumulative yields, whereas Angold brought the largest fruits on average. With the obtained results, the evaluated cultivars were characterised by some important features or recommendations for growers. &amp;nbsp;

Induction of polyphenol gene expression in apple (Malus x domestica) after the application of a dioxygenase inhibitor

A comprehensive study of the complex polyphenol biosynthesis in developing leaves of apple (Malus domestica) was performed comprising gene expression, enzyme activities and polyphenol composition. During leaf development, an early increase in gene expression was observed for phenylalanine ammonia lyase (PAL, EC 4.3.1.5), chalcone synthase (CHS, EC 2.3.1.74), flavanone 3‐hydroxylase (FHT, EC 1.14.11.9) and dihydroflavonol 4‐reductase/flavanone 4‐reductase (DFR/FNR, EC 1.1.1.219). Their enzyme activities showed a corresponding trend during the time course. A parallel set of experiments was carried out with leaves treated with prohexadione‐Ca (ProCa), which is an enzyme inhibitor of 2‐oxoglutarate dependent dioxygenases (2‐ODDs). ProCa is known to induce changes in polyphenol biosynthesis, which are accompanied by a reduced incidence of fire blight and scab, the two major pome fruit diseases. The application of ProCa led to an increase in activities of PAL, CHS, FHT and DFR/FNR, which was based on an enhanced gene expression. In contrast, an inhibition of gene expression was detected for anthocyanidin synthase (EC 1.14.11.19). These effects are interpreted as a feedback regulation by changed polyphenol levels. Because of the inhibition of the 2‐ODDs FHT and flavonol synthase (EC 1.14.11.23), some pronounced changes in polyphenol composition were observed. Eriodictyol, the substrate of FHT, accumulated as eriodictyol‐7‐O‐glucoside and 6″‐O‐trans‐p‐coumaroyleriodictyol 3′‐O‐glucoside. In addition, the 3‐deoxycatechin luteoliflavan was formed which is not present in untreated apple leaves. Hence, beyond the redirection of polyphenol biosynthesis by the enzyme inhibitor, changed polyphenol levels obviously cause a distinct induction of gene expression by feedback regulation.

Reaction of potato varieties toPotato mop-top virus infection in the andes

The unexpected detection ofPotato mop-top virus (PMTV) in potatoes growing at several locations in the U.S.A. and Canada in 2002 has led to the realization that this soil-borne virus may be widespread throughout the potato-producing regions of both countries. A lack of information concerning the response of U.S. cultivars to PMTV infection caused us to examine the effects of PMTV on field-grown plants at three locations in the Peruvian Andes where the virus and its fungal vector,Spongospora subterranea, are endemic. All 21 U.S. cultivars tested proved susceptible to PMTV infection, especially at La Victoria where the overall incidence of both PMTV and powdery scab was high. Symptom expression in the foliage proved to be an unreliable indicator of virus infection, and thus, more reliable serological (NCM-ELISA) and nucleic acid-based techniques (NASH and RT-PCR) were used to monitor tuber tissue for the presence of PMTV. As much as 25% of field-grown tubers of cvs Kennebec, Monona, and Norland were infected with PMTV, but no correlation between virus infection and either the incidence or severity of powdery scab for any variety was apparent. Although PMTV infection did not result in the appearance of spraing or other internal necrotic reactions resembling those reported from many North American and European locations, a disproportionate proportion of infected tubers did exhibit a reticulate surface cracking. In hydroponic culture, the proportion of cracked tubers increased dramatically when the nutrient solution was seeded with virus-infestedS. subterranea. Comparatively few tubers of cvs Monona and Russet Burbank exhibited this surface cracking, suggesting that these two varieties may be somewhat tolerant to PMTV infection.

Effect of a combination of chlorine dioxide and thiophanate-methyl pre-planting seed tuber treatment on the control of black scurf of potatoes

The pre-planting seed tuber treatments of chlorine dioxide (ClO 2), thiophanate-methyl (TPM), and a combination treatment of ClO 2, followed by TPM, were evaluated for control of stem canker and black scurf ( Rhizoctonia solani), and storage rots; black scurf, common scab ( Streptomyces scabies), dry rot ( Fusarium spp.) and silver scurf ( Helminthosporium solani) on potato ( Solanum tuberosum L.) cv. Kennebec. Field experiments were conducted in two consecutive years, 1999 and 2000, at the Agriculture and Agri-Food Canada Research Farm in Harrington, Prince Edward Island (PEI), Canada. The combination treatment of ClO 2 (200 μg g −1) and TPM (50 g active ingredient100 kg −1 of tubers) significantly ( P = 0.05 ) reduced stem canker and black scurf on progeny tubers at harvest and after storage. The low incidence of scab and dry rot in untreated controls hindered the evaluation of the efficacy of the combination treatment and also showed that conditions were not favourable for disease development during this period at Harrington. The combination treatment was not effective on silver scurf in storage. A comparison among control, ClO 2, TPM, and the combination treatment indicates that pre-planting ClO 2 treatment may have killed the majority of the black scurf sclerotia on the tuber surface and that the combination of TPM fungicide treatment following ClO 2 treatment gave protection to progeny tuber by suppressing the growth of the R. solani. A higher marketable yield was observed in the combination treatment as compared with the untreated control. Phytotoxicity was not observed in tubers treated with the combination treatment.