Tuber Surface Research Articles

Measuring Behavior of an Acceleration Measuring Unit Implanted in Potatoes

Mechanical harvest and postharvest handling induce numerous mechanical impacts on potato tubers. These impacts may cause damage such as blackspot bruise, resulting in severe economic losses. To obtain reliable data of actual mechanical impacts, a miniaturized triaxial acceleration measuring unit (AMU) was implanted into potato tubers and tested in the laboratory. Tests were carried out with potatoes of two cultivars on several dates during the 2007-2008 season. The potatoes were hand-harvested and stored at 4C. Quasi-static elastic properties of the tubers were determined with a universal testing machine. The dimensions of the AMU were 42 13 13 mm. It was implanted in the tubers by means of a cork borer. A drop simulator was used for free fall tests from heights up to 100 cm. The acquired impact forces closely correlated with the impact acceleration obtained with the AMU. Test samples included both intact tubers and potatoes with the AMU implanted in order to determine the effects of tuber size, position of AMU, tissue thickness between AMU and tuber surface, drop height, and impact material on tissue mechanical properties. The experimental results were compared with data calculated according to Hertz' theory of elastic impact. The implantation procedure caused significant decrease of tuber apparent modulus of elasticity at the location of the drill hole. However, this area comprises less than 5% of the total tuber surface. Impact force and impact acceleration obtained in this study significantly correlated with tuber size, tissue thickness, drop height, and impact material. The dynamic modulus of elasticity of potato tubers calculated from impact force and impact acceleration data declined with increasing impact strength after an intermediate initial increase. This point of decline was similar in intact tubers and in tubers with AMU and may indicate mechanical tissue damage. However, because the AMU was embedded in the cushioning tuber tissue, the AMU peak values of impact were smaller than those obtained with a drop simulator. Furthermore, investigations with the implanted AMU yielded more realistic results of the actual mechanical impacts on potatoes and other susceptible produce than those with comparable electronic fruit.

Colonization and Sporulation of Phytophthora infestans on Volunteer Potatoes Under Western Washington Conditions

Growth, sporulation, and survival of Phytophthora infestans on volunteer potato tubers, was investigated under temperatures representative of winter (4°C, 7°C, and 10°C) and spring (13°C, 16°C, 19°C) soil conditions in western Washington. Inoculated tubers stored at 10°C for 8 days had a significantly (P < 0.05) higher percentage of disease symptoms on tuber surfaces and a higher number of lenticels and eyes with P. infestans sporulation compared to those stored at 4°C or 7°C. Sporulation of P. infestans on cut tuber surfaces was observed following 3-week storage at the three winter soil temperatures. After 12-week storage, tubers inoculated with a US-8 isolate had a significantly higher percentage of late blight on cut surfaces than those inoculated with a US-11 isolate (70% versus 50%, respectively). For spring soil temperature studies, tubers inoculated with the US-8 isolate and held at 19°C had a significantly higher number of lenticels per tuber with P. infestans sporulation than tubers held at 13°C or 16°C. Sporulation of P. infestans on tuber surfaces was detected on infected tubers buried 5-cm deep in potting medium at all tested winter and spring temperatures for 3- or 6-day periods, respectively. The site or depth of tuber inoculation with P. infestans did not influence tuber-to-sprout infection events and whether apical end or stem sprouts become infected. Tubers with late blight that survive the winter in western Washington and support sporulation of P. infestans via lenticels and eyes may enable the transmission of P. infestans from infected tissues to sprouts of volunteer plants. However, the impact of these events on primary inoculum production by P. infestans in the region is probably limited by the mild, winter conditions favoring tuber break-down in soil.

Host resistance and influence of tuber surface on larval performance of potato tuberworm (Lepidoptera: Gelechiidae)

Potato tuberworm (PTW), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is one of the most important pests of potatoes in tropic and subtropic regions. Previous studies suggested that tuber periderm may limit larval penetration and establishment of PTW. Short term influence of parental host plant acclimatization, influence of tuber dormancy and influence of tuber periderm (the outer cork layer of tubers) on aspects of PTW biology were investigated on tubers of a susceptible commercial potato cultivar, cv. Allegany (Solanum tuberosum L.), and a resistant hybrid potato clone, Q174-2 (S. tuberosum × S. berthaultii Hawkes). Short-term parental host plant acclimatization did not affect numbers of PTW larvae on resistant and susceptible tubers. Numbers of larvae produced on tubers of Q174-2, and Allegany, were similar although larval weight was less on Q174-2 than on Allegany. Larval production increased with tuber age on both susceptible and resistant potato clones, suggesting that bud sprouts may enhance fitness by providing food and shelter for first instars prior to tuber entry. Removal of tuber periderm led to a significant increase in larval survival on Allegany and Q174-2, although proportional survival on Allegany and Q174-2 was similar to that on intact tubers, suggesting the involvement of internal rather than external periderm factors in tuber resistance of Q174-2. Weights of larvae reared on Q174-2 were consistently less than those of larvae reared on susceptible potato tubers in both intact and peeled tuber assays. Although the expression of periderm-mediated tuber resistance declines with tuber age, such resistance could significantly reduce preharvest field infestations by PTW and constitute an important component of sustainable PTW management, particularly for fresh market crops and for those potato crops stored for several months or less in the absence of refrigeration.

Assessment of Common Scab-Inducing Pathogen Effects on Potato Underground Organs Via Computed Tomography Scanning

Common scab caused by Streptomyces scabies is a major bacterial disease of potato (Solanum tuberosum). Its best known symptom is superficial lesions on the surface of progeny potato tubers, observed at harvesting. In this study, effects of S. scabies on space occupancy by underground organs and on structural complexity of root systems are investigated during growth via computed tomography (CT) scanning. Two groups of potato plants were grown in a greenhouse in middle-sized plastic pots. Using a high-resolution X-ray CT scanner formerly used for medical applications, their underground organs and surrounding medium (sieved and autoclaved homogeneous sand) were submitted to CT scanning 4, 6, and 8 weeks after planting. For one group, sand was inoculated with the common scab-inducing pathogen (S. scabies EF-35) at potting. Space occupancy by underground organs was estimated via curve fitting applied to histograms of CT scan data, while three-dimensional skeletal images were used for fractal analysis. Root systems of diseased plants were found to be less complex than those of healthy plants 4 weeks after planting, and the relative growth rates derived from space occupancy measures were of different sign between the two groups from week 4 to week 8.

Polyamine Biosynthesis Regulated by StARD Expression Plays an Important Role in Potato Wound Periderm Formation

An acireductone dioxygenase (ARD) gene of potatoes was isolated from the expressed sequence tags (ESTs) of potato post-suberization cDNA libraries. The highest expression levels of the StARD gene and the protein appeared 36 h after suberization. An approximate 9-fold increase in ARD activity was detected at 36 h after wounding. Real-time reverse transcription-PCR (RT-PCR) analysis and immunolocalization studies revealed that StARD transcripts increase at the wound surface of potato tubers. The polyamine (PA) contents increased significantly after wounding at the wound surface. The increased PA content and ARD activity may play an important role in wound periderm formation.

Characterization and Pathogenic Relationships of Rhizoctonia solani Isolates in a Potato–Rice System and their Sensitivity to Fungicides

AbstractPotato is planted after rice in several parts of Punjab in India and both crops are attacked by Rhizoctonia solani Kühn. Potato tubers showing black scurf and rice plants affected by sheath blight were collected from different regions of the state and the isolates of R. solani so obtained were studied to determine their variability and to ascertain their cross‐infectivity and response to fungicides. Potato isolates of R. solani did not infect rice plants but some rice isolates were weakly pathogenic on potato, the sclerotia being less firmly attached on tuber surface, indicating a possible unsuccessful attempt of rice isolates to infect potato. Rice isolates (66.6%) grew faster (&gt;20 mm colony growth per 24 h) than those of the potato isolates (15–20 mm growth rate per 24 h). Hyphal width of isolates from both hosts varied from 7.2 to 12.1 μm. Colony growth of most potato isolates (61.2%) was appressed, whereas that of most rice isolates (53.3%) was fluffy. Rice isolates (73.3%) formed larger sclerotia (1.5–2.0 mm in diameter) than those of the potato isolates (0.5–1.0 mm in diameter). Anastomosis studies indicated that potato isolates belonged to AG‐3 and AG‐5 groups while rice isolates belonged to the AG‐1‐1‐A group. Representative R. solani isolates from the two hosts showed significant variation in response to fungicides (i.e. carbendazim, carboxin, pencycuron, propiconazole and validamycin) based on their ED50 and ED90 values.

Microbial and nematode communities associated with potatoes genetically modified to express the antimicrobial peptide magainin and unmodified potato cultivars

The antimicrobial peptide magainin II has activity against a range of micro-organisms. Tubers harvested from potatoes genetically modified (GM) to express a synthetic magainin gene show improved resistance to the bacterial pathogen Erwinia carotovora. The microbial and nematode communities associated with three magainin-expressing potato lines, their near-isogenic, unmodified parental cultivar (Iwa) and an unrelated cultivar (Karaka) were investigated on field-grown plants. Heterotrophic plate counts were used to enumerate aerobic culturable bacterial and fungal populations, while cultivation-independent analysis of bacterial communities was based on denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from community DNA from phyllosphere, rhizosphere and geocaulosphere (tuber surface) samples. Small but statistically significant differences in the population sizes of culturable bacteria, fungi and yeast were detected among some GM magainin-expressing lines and the unmodified control. However, these differences were typically smaller than the differences between the unmodified parental line control (Iwa) and the unrelated cultivar control (Karaka). Similarly, the difference in the proportion of the nematode population belonging to the fungal feeding trophic group between Iwa and Karaka was greater than that amongst Iwa and its near-isogenic GM lines, and was significantly so for the genus Aphelenchus. The nematode channel ratio (NCR) indicated a more fungal-dominated decomposition channel in soil beneath Karaka compared to Iwa at harvest. In general, eubacterial phylloplane communities were similar for all lines, while the rhizosphere communities associated with two of the three GM lines differed from communities associated with their unmodified parental line control. When roots were senescent, there was no significant difference among potato lines in rhizosphere eubacterial communities or individual trophic groups of the nematode community. Greater diversity was found in geocaulosphere; α-proteobacteria and actinomycete communities of two of the three GM lines differed significantly from their unmodified parental line control and the unrelated cultivar control, while the communities associated with the third GM line were more similar to those of the two control lines. This highlights the importance of testing several GM lines when assessing non-target effects. Results suggest that there is little likelihood of any major sustained non-target effect of genetic modification using a magainin II transgene on plant-associated and soil microflora and function.

Early and Rapid Detection of Potato's Fungal Infection by Fourier Transform Infrared Microscopy

Fungi are considered serious pathogens to many plants and can cause severe economic damage. Early detection of these pathogens is very important and might be critical for their control. The available methods for detection of fungi are time consuming and not always very specific. Fourier transform infrared (FT-IR) microscopy has proved to be a reliable and sensitive method for detection of molecular changes in cells. Fungi pathogens display typical infrared spectra that differ from the spectra of substrate material such as potato. In the present study we used FT-IR microscopy for early and rapid detection of the potato fungal pathogen Colletotrichum coccodes on the surface of potato tubers. Infected potatoes with this fungal pathogen and uninfected potatoes were examined and correctly classified as infected or not infected by FT-IR microscopy at very early stages of infection when no morphological signs of infection could be seen. Unique spectral biomarkers were found in naturally infected potatoes compared to disease-free control potatoes.

The Canon of Potato Science: 45. Brown Centre and Hollow Heart

Brown centre (also referred to as incipient hollow heart, brown heart, or sugar centre) and hollow heart are common physiological disorders of potato. Brown centre and hollow heart are caused by similar conditions, but can occur concurrently or separately in potato tubers. No plant pathogens have been associated with brown centre or hollow heart development and seed tubers afflicted with brown centre or hollow heart commonly produce daughter tubers with no symptoms. Furthermore, tubers afflicted with brown centre or hollow heart show no external signs or symptoms on the tuber and are rarely affected by secondary pathogens. Brown centre can be described by accumulation of brown discolouration of pith tissue which is unique relative to other disorders that cause internal browning. The brown discolouration occurs as a result of cell necrosis caused by cell membrane and organelle damage. Brown centre commonly leads to development of hollow heart under conditions suitable for its development. Conversely, brown centre may not develop into hollow heart or can disappear as the potato plant recovers from conditions and stress that led to its development. Hollow heart is best described by the development of cavities in the pith of the tuber. Hollow heart can occur anywhere along the length of the tuber but always occurs in the central pith. Hollow heart does not occur at the tuber surface. Hollow heart is best described by single or multiple cavities that are traverse or run longitudinal to the pith. Cavities can be a few mm up to 2 or more cm in diameter and can run nearly the entire length of the tuber depending on the severity of the disorder. Cavities are irregularly shaped and can be in the shape of narrow slits or in the form of stars. Potato Research (2007) 50:395–398 DOI 10.1007/s11540-008-9087-0

The Canon of Potato Science: 43. Skin-set and Wound-healing/Suberization

What is it?The native periderm covering the surface of the potato tuber is composed of phellem,phellogen and phelloderm cell layers. Immature periderm is fragile and susceptible toexcoriation,i.e. skinning injury, at the time of harvest and handling into storage. As theperidermmatures,theskin(phellemcelllayeroftheperiderm)becomestightlyattachedto the underlying cells and thereby resistant to skinning injury. The idiom “skin-set” isusedtoindicatethatthe tuber has becomeresistant toskinninginjury. Some documentsrefertoskinningasfeatheringbecauseofthethinandlightnatureofthephellem afteritis detached from the tuber. Wound-related blemishes, defects, infections and otherquality problems resulting from skinning injury necessitate the development of newapproachesandtechnologiestohastenandenhanceskin-set.However,untilrecentlythedirection for development of new means to improve skin-set was haphazard andseverely hampered because the physiological bases for skin-set and associatedbiological processes were not known. These knowledge gaps were significant and ledto many incorrect assumptions and hypotheses concerning skin-set development andhow the problem should be addressed. For example, one popular and incorrecthypothesis was that skin/phellem thickening was responsible for skin-set development.Another incorrect hypothesis ascribed suberization as the source of skin-set develop-ment.Recentidentificationofthebroadphysiologicalprocessesinvolvedintheskin-setphase of periderm maturation not only refute these hypotheses, but also guide researchin the proper direction for development of approaches to enhance skin-set.The cell walls of the tuber phellem/skin of the native periderm possess a waxycomponent that protects against cell desiccation and a protective suberin biopolymerthat provides a barrier to pathogens and other intrusions. The suberin biopolymer iscomposed of a suberin poly(phenolic) (SPP) domain that protects against bacterialinfections,andasuberinpoly(aliphatic)(SPA)domainthatprotectsagainstinfectionby

First Report of Helminthosporium solani Causing Silver Scurf of Potato in Hebei Province, North China.

Silver scurf disease of potato (Solanum tuberosum) caused by Helminthosporium solani Durieu & Mont. occurs worldwide. Severe occurrence of the disease, the resulting weight loss of stored potatoes, and lower market classes of potato caused by the fungus have been documented in Europe and North America (1). Tubers infected with the pathogen develop tan-to-gray lesions that have a characteristic silvery appearance when moist. In 2005, gray spots with a defined margin and silvery appearance when seen against light were observed on potato tubers of cv. Weishu No. 1. The silver symptoms were distinguished from those of black rot disease of potato caused by Colletotrichum coccodes. The potato tubers were obtained from Weichang County of Hebei Province, North China. Conidia were scraped from the spots with a sterile scalpel and identified primarily as the fungus H. solani on the basis of morphological characters of the spores. The fungus was isolated, purified, and cultured on potato dextrose agar (PDA) amended with penicillin and streptomycin. To produce conidia, the fungus was incubated on V8 juice medium at 20 ± 2°C for 15 days under near-UV light (360 to 400 nm, 12-h light/dark cycles). The culture colony developed slowly and is gray to brown. Conidia form in whorls on conidiophores that are black, unbranched, irregular, and multiseptate. Conidia are appreciably tapered, straight or slightly curved, brown, thick walled, and have two to eight pseudosepta. The size of the conidia ranged from 14 to 70 μm long and 4 to 9 μm wide. The spore suspension was adjusted to 1.5 × 105 spores per ml by using sterile distilled water containing 0.2% Tween 20. Twenty healthy tubers were washed with distilled water and then inoculated by spraying the spore suspension onto the surface with a hand atomizer, while 10 washed tubers were sprayed with distilled water as controls. Inoculated tubers were kept in containers covered with plastic and placed in an incubation chamber at 20°C for 3 weeks. Gray-to-brown blemishes with a silvery appearance as described above were observed on tubers inoculated with the fungus and the tuber surface areas infected were from 1 to 10%, whereas no infection was visible on tubers inoculated with water. The causal agent was reisolated, cultured, and identified microscopically as H. solani. H. solani has been identified from potato tubers in Yunnan Province, Southwest China (2), but to our knowledge, this is the first report of H. solani causing silver scurf of potato in Hebei Province, North China.

Three-dimensional Stochastic Shape Modelling for Potato Tubers

Tuber shape is a genetically determined, important varietal characteristic that is also influenced by environmental factors. In this study, the overall dimensions of tubers of two potato cultivars (Van Gogh and Yukon Gold) were determined using a triaxial ellipsoid model that was found to encompass the main varietal differences. The more detailed surface features were captured using a spherical-harmonics series representation for the residual undulation. The method was then applied to four additional cultivars (Bellona, Lady Rosetta, Pito, and Sabina). Modelling the undulation of tuber surface in addition to the overall dimensions indicated that cultivars differed in the global shape and, in specific cases, also in the surface undulation of tubers. The new, improved method for modelling tuber shapes can thus capture and distinguish the overall three-dimensional shape and irregularities caused by growth conditions and other factors. It is envisaged to be useful for quantitative genetics approaches aiming to resolve the relative impact of different genes on tuber shape, as well as for various machine vision and other applications.

First Report of Potato Tuber Sprout Rot Caused by Fusarium sambucinum in Michigan.

Fusarium dry rot is one of the most important diseases of potato (Solanum tuberosum L.), affecting tubers in storage and whole seed or seed pieces after planting (2). Fusarium sambucinum Fuckel (teleomorph Giberella pulicaris) is the most common pathogen causing dry rot of stored tubers in North America. (4). Cut seed potato tubers of cvs. FL1879 and Pike with severe sprout rot were collected in Michigan during May 2006. As well as having rotted sprouts, all diseased tubers had dry rot. When diseased sprouts were cut in half, brown, necrotic lesions could be seen spreading down the center of the sprout in vascular tissue and at the base of the sprout in tuber tissue. Pathogen isolations were made from both infected tuber tissue and diseased sprouts on potato dextrose agar (PDA). In both cases, only F. sambucinum was isolated from diseased sprout and tuber tissue. Identification of the pathogen was based on colony and conidial morphology. This included white, fluffy mycelium on the surface and crimson coloration of the colonies viewed from the underside of PDA plates and large distinctive macroconidia (3). Identification was confirmed by comparison of ITS (internal transcribed spacer) sequence data with reference isolates. The ITS region of rDNA was amplified by polymerase chain reaction (PCR) with primers ITS1/ITS4 and sequenced. BLASTn analysis (1) of the sequence obtained showed a 100% homology with F. sambucinum Fuckel. For inoculum production, isolates were grown on PDA at 8°C for 14 days prior to inoculation. Pathogenicity was tested in potato tubers of cv. FL1879 with a single isolate collected from diseased sprouts. Whole seed tubers with 4 mm long sprouts were cut in half longitudinally with a sterile knife to ensure that seed pieces had viable sprouts. The cut surfaces of seed pieces were spray inoculated with 200 ml of conidial suspension (1 × 104 conidia ml-1) over the entire cut surface to give a final dosage of approximately 1 ml per seed piece. Care was taken to limit inoculum spray to the cut surface so that sprouts were not inoculated. Seed pieces (40 per replicate × 4 replicates) were then placed in plastic boxes (30 × 15 × 10 cm) and incubated in the dark at 18°C and 95% relative humidity for 30 days in a controlled environment chamber. As a control, cut seed pieces were spayed with sterile distilled water and incubated as above. All tubers inoculated with the pathogen developed typical Fusarium dry rot symptoms consisting of a brown, dry decay of tuber tissue with mycelial lined cavities. Sprouts on inoculated tubers developed symptoms that were observed in the initially collected seed pieces, and F. sambucinum was reisolated from all infected sprouts. The noninoculated control tubers did not develop any symptoms of dry rot. The results of the pathogenicity tests indicate that F. sambucinum caused sprout rot on potato seed pieces. Since only the cut surfaces of tubers were inoculated, it is assumed that infection of sprouts is systemic through the tuber. To our knowledge, this is the first report of F. sambucinum causing a sprout rot of developing sprouts on seed tubers in the United States.

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.

Digital imaging for evaluation of potato after‐cooking darkening and its comparison with other methods

SummaryAfter‐cooking darkening (ACD) phenomenon occurs when potato tubers develop greyish dark colour after boiling, frying, or steaming. The pigment responsible for ACD is a complex of chlorogenic acid and iron, which is formed during cooking and oxidised during cooling. The evaluation of ACD is thus based either on the amount of chlorogenic acid in raw tubers or the greyish colour intensity on cooked tuber surfaces. This study introduced a new method, the digital imaging method, for evaluation of potato ACD. The comparison of this new method with visual evaluation and the measurement of chlorogenic acid using HPLC were also presented. The digital imaging method is based on the direct measurement of the degree of dark colour on cut tuber surfaces, expressed by pixel levels. The new method is faster, more reliable and simpler when compared with any methods presently used. It is particularly applicable to handling large sample numbers.

Limonius californicus

<i>Limonius californicus</i>

Diferenciação de estirpes de Potato virus Y (PVY) por RT-PCR

O Potato virus Y (PVY) tornou-se o maior problema nas áreas de produção de batata semente do Brasil. Somente as estirpes comum (PVYº) e necrótica (PVY N) eram detectadas infectando batata no Brasil. Esta situação mudou drasticamente a partir de 1997 quando um surto epidêmico de uma variante da estirpe necrótica de PVY causando arcos e anéis necróticos na superfície do tubérculo (PVY NTN) foi observado no país. Este estudo visou avaliar e validar uma metodologia de diferenciação de estirpes que causam necrose em tubérculos, proposta por Weilguny e Singh (1998). Vinte e oito isolados de PVY originários de tubérculos infectados de batata, provenientes de quatro estados brasileiros, foram analisados em sua reação em plantas de fumo, por Elisa, utilizando anti-soro policlonal e pelo método 3-primer RT-PCR. Quatro isolados induziram clareamento de nervuras e manchas peroladas em folhas de Nicotiana tabacum conforme esperado para a estirpe comum. Os 24 isolados restantes induziram necrose de nervuras neste hospedeiro portanto, classificados como da estirpe necrótica. Todos os 28 isolados de PVY reagiram positivamente contra o anti-soro policlonal de PVY por Elisa. Três métodos de extração de RNA foram testados, sendo que o método de hidrocloreto de guanidina mostrou-se o mais eficiente e de menor custo. Dos 28 isolados submetidos ao RT-PCR, um isolado de Santa Catarina e três do Rio Grande do Sul foram diferenciados como PVYº, confirmando os resultados do teste biológico. Um isolado de PVY N foi detectado no Estado de Santa Catarina e quatro no Rio Grande do Sul. O PVY NTN foi detectado em Minas Gerais (seis isolados), Santa Catarina (três isolados) e São Paulo (dez isolados). Estes resultados confirmam a presença dessa variante necrótica, PVY NTN, nas principais regiões produtoras de batata do Brasil.

First Report of the Occurrence of Potato Wart Disease Caused by Synchytrium endobioticum in Turkey.

Potato wart caused by Synchytrium endobioticum (Schilberszky) Pervical was observed in Turkey on different cultivars (Agria, Granola, Marabel, Marfona, Russet Burbank and Van Gogh) during the 2004 harvest season in the Misli (Bud) Plain where approximately 40,000 ha of potatoes are grown. This plain, lying between Nigde and Nevsehir provinces in the central-eastern Anatolia Region, has a predominance of sandy soils (60 to 80% sand) and climatic conditions suitable for production that has been a long-term monoculture using heavy fertilization with nitrogen (500 to 1,500 kg of N per ha) and phosphorus (200 to 500 kg of P2O5 per ha). The wart symptoms were observed on tubers but not on roots and stems. The warts were white, almost spherical, and softer in texture than the tuber tissue. Resting sporangia, observed within the fresh wart tissue using light microscopy, were light brown, spherical to ovoid and 50 to 70 μm in diameter. Soil surveys confirmed that resting sporangia were present in the fields where wart was observed. Resting sporangia were isolated from infected tubers and surrounding soil (2). An average of <1 sporangium per gram of soil was detected in the infested fields. Pathogenicity of the causal agent was demonstrated on 10 tubers of potato cv. Granola. Sprouts on the tubers were cut off at 2 mm above the tuber surface, the eye fields were ringed with warm vaseline using a sterile syringe without a needle and then inoculated by placing fresh cauliflower-like warts containing summer sporangia in the vaseline wells. The tubers were first incubated at 8 to 12°C for 48 h in the dark and after removing the wart tissue, placed in moist peat at 18°C and kept in an 8-h lighting period per day as described by Glynne-Lemmarzalh (1). Sporangia were reisolated from the white, fresh wart tissues observed 8 to 10 weeks later on the inoculated tubers. Two tubers inoculated with sterile tap water did not develop warts. Koch's postulates were fulfilled. Currently, approximately 20,000 ha of the Misli Plain are under official quarantine due to the finding of potato wart. Because of the large-scale occurrence in 2004, it is suspected that the pathogen entered Turkey 3 to 4 years earlier through importation of seed potato tubers from European countries. To our knowledge, this is the first report of the occurrence of wart on potatoes grown in Turkey. The importance of this occurrence in the middle of an area where 50% of Turkey potatoes are produced is duly noted.

TX1523-1Ru/Y a.k.a Sierra Gold™: An early maturing, yellow-fleshed ruseet cultivar for the specialty/gourmet market

TX1523-1Ru/Y, a unique specialty cultivar with deep-yellow flesh color and an attractive russet skin, was released in 2003 by the Texas Agricultural Experiment Station. The smaller, immature tubers are round, but take on an oval shape as they mature. Eyes are shallow and the tuber surface is smooth. Tuber size tends to be medium (113.4–283.5 g; 4–10 oz). Total and marketable yield varies with year and location, but tends to be comparable to ‘Yukon Gold’, with percent marketable yield slightly higher. Vines are semi-prostrate, with medium vigor and size, and relatively early maturity. Specific gravity is about the same or slightly less than Yukon Gold, but generally greater than ‘Russet Norkotah’. TX1523-1Ru/Y has good culinary qualities, with resistance to after-cooking-darkening, and can be chipped, boiled, baked, or microwaved. It has been reported to be excellent to superior as a microwave product. Unlike Yukon Gold, TX1523-1Ru/Y is resistant to hollow heart, brown centers, and internal discoloration. It tends to be less susceptible to tuber infection by late blight (Phytopthora infestans) than Yukon Gold, has greater resistance to common scab (Streptomyces scabies), and is less susceptible to black scurf (Rhizoctonia solani). TX1523-1Ru/Y is believed to be the first yellow-fleshed resset-skin cultivar released in the United States.

Resistance of potato genotypes to common and netted scab‐causing species of Streptomyces

Common and netted scabs are two disfiguring bacterial diseases of potato tubers, caused by various groups of Streptomyces species. Common scab, caused primarily by Streptomyces scabies and Streptomyces europaeiscabiei, is characterized by more or less deep pustules on the tuber surface, while symptoms of netted scab, caused mainly by Streptomyces reticuliscabiei, are superficial, corky alterations of the tuber periderm. Some isolates of S. europaeiscabiei are able to induce both common and netted scab symptoms, and therefore constitute a third pathogenicity group. Like most bacterial diseases, potato scabs would be best controlled by using resistant cultivars. Repeated experiments with soil artificially infested with isolates of three species representative of the three pathogenicity groups showed the level and stability of cultivar resistance, as well as the existence of a range of aggressiveness among different isolates. The distribution of scab severity indexes recorded on a collection of 16 potato cultivars and 27 breeding clones grown in soil infested with common scab‐inducing isolates was continuous, suggesting isolate nonspecific quantitative resistance. Least susceptible cultivars were Nicola, BF15, Sirtéma, and Charlotte, while Urgenta, Désirée, Ondine and Bintje were very susceptible. The same genotypes proved either highly susceptible (e.g. cvs Bintje, Désirée or Carmine) or highly resistant (e.g. cvs Charlotte, Sirtéma, Monalisa, BF15 or Belle de Fontenay) to isolates forming netted scab symptoms, suggesting isolate‐specific qualitative resistance. The ability was confirmed of some isolates of S. europaeiscabiei to induce one or the other type of symptoms depending on cultivar and soil temperature.