Volume 6 Special Issue 1 2012
Potato Pathology

ISBN 978-4-903313-91-7

How to reference: Halterman D, Charkowski A, Verchot J (2012) Potato, Viruses, and Seed Certification in the USA to Provide Healthy Propagated Tubers. In: Daami-Remadi M (Ed) Potato Pathology. Pest Technology 6 (Special Issue 1), 1-14

Guest Editor

Mejda Daami-Remadi

Centre Régional des Recherches en Horticulture et Agriculture Biologique, Chott-Mariem, Tunisia

CONTENTS AND ABSTRACTS

Dennis Halterman, Amy Charkowski, Jeanmarie Verchot (USA) Potato, Viruses, and Seed Certification in the USA to Provide Healthy Propagated Tubers (pp 1-14)

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Invited Review: Potatoes are vegetatively propagated and this can result in the dissemination of pathogens, and viruses in particular, in the tubers. Viruses infecting potato can be categorized by their mechanisms of transmission: aphid transmitted, mechanically transmitted, and soil-borne viruses. The most important viruses in North America include Potato leafroll virus, Potato virus Y, X, A, S, M, Tobacco rattle virus, and Potato mop top virus. The methods for chemical control of virus disease are greatly influenced by their mechanism of spread in the field. However, tubers play an important role in the spread of virus disease and this has led many regions to develop seed certification programs. The use of certified virus-free tubers by growers has been vital for control of disease worldwide. In addition, breeders have identified genetic resistance that can be introgressed into popular cultivated varieties and provides a method of control that is less costly than chemical application. In recent years there has been an emergence of viruses and recombinant virus strains that have posed new challenges to pathologists for seed certification and for breeders. Here we discuss the latest issues and challenges that viruses pose to potato production.

Mejda Daami-Remadi (Tunisia) Potato Fusarium Dry Rot in Tunisia: Current Status and Future Prospects (pp 15-22)

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Invited Review: Fusarium dry rot (FDR) is a postharvest disease of potato tubers of economic importance worldwide. In Tunisia, losses attributed to Fusarium spp. infections may be aggravated in the presence of other tuber rot pathogens. A review of published data indicates that five Fusarium species (F. sambucinum, F. graminearum, F. culmorum, F. oxysporum and F. solani) are involved in a disease complex in Tunisia. These species present a great range of inter- and intra-specific variability in growth, sporulation and aggressiveness. Their level of aggressiveness is variable, depending on storage conditions (mainly temperature) and potato cultivar. Although a large number of cultivars have been assessed, no cultivar was resistant to FDR although potato cultivars exhibited different levels of susceptibility to the disease. The ranking of cultivars with regard to their susceptibility to FDR changed depending on the Fusarium species involved in disease development and on the temperature used for tuber storage. Chemical-based treatments using old and new generations of fungicides tested against Fusarium species have successfully limited dry rot severity and revealed the appearance of benzimidazole-resistant isolates of F. sambucinum. Biological control studies undertaken based on various and complementary experiments in vitro, in vivo and under natural conditions permitted the selection of potentially important microbial agents (fungi and Gram-positive bacteria) for the control of potato FDR. Their mechanisms of action were also elucidated. Other alternatives of disease control which may be a part of an integrated management strategy are also cited. This review highlights the specificity of problems related to FDR in Tunisia, regarding mainly pathogen aggressiveness, genetic resistance and control alternatives and their limits which may be useful for the development of an integrated strategy for FDR management and for better guiding future research on the influence of the Fusarium species complex, potato cultivar, storage conditions and their interactions on the effectiveness of disease control.

Kalthoum Harbaoui (Tunisia), Theo van der Lee (The Netherlands), Walid Hamada (Tunisia) Characterization of the Potato Late Blight Pathogen Phytophthora infestans in Tunisia (pp 23-26)

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Invited Mini-Review: This mini-review focus on summarizing different phenotypic and genotypic analysis recorded on Phytophthora infestans population collected from the Northern area of Tunisia. Here, we demonstrated that mating type distribution plays a primordial role in genetic structure of the pathogen between sampling regions. Also, a probably strong correlation between mating type and metalaxyl resistance could be mentioned. Next to that, we found that the aggressiveness and the virulence patterns were highly effective parameters to outline phenotypic diversity in Tunisian population that showed specific characteristics comparing with Algeria and others countries in the world. Consistently, genotypic diversity based on SSR markers seems to be a very interesting key in the genetic understanding of the pathogen. In fact, we found that P. infestans populations in Tunisia were divided to two major phylogenic groups: a clonal lineage group shared between all sampling regions and a diverse group detected in potato population and specific to two sub-regions. Thus, we could conclude that genotypic diversity confirmed phenotypic diversity and both analysis leaded us to conclude that population structure of P. infestans in Tunisia is very specific either in North African area or all over the world.

Pablo L. Cicore, Patricia A. Suarez, Adriana B. Andreu (Argentina) Phosphites Effect on Late Blight Control and Physiological Parameters in Commercial Potato (Solanum tuberosum L.) in Argentina (pp 27-31)

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Original Research Paper: Phosphite (Phi) has been recommended to enhance plant resistance against spp. The purpose of this study was to evaluate the effect of calcium phosphite (PhiCa) and potassium phosphite (PhiK) under field conditions, taking into account physiological parameters, performance and protection against late blight in the foliage of two potato cultivars, and comparing these results to controlled in vitro experiments. Experimental design was a split plot in randomized complete blocks with four replicates. The main plot comprised two potato cultivars (‘Kennebec’ and ‘Spunta’) and the sub-plots three late blight control treatments: control, PhiCa and PhiK. The interaction between cultivar and treatment on the area under disease progress curve (AUDPC) was determined. In ‘Kennebec’, the PhiK treatment showed a significantly lower AUDPC than control and PhiCa treatments. No differences were detected between treatments on ‘Spunta’. In the detached-leaf tests, there was a significant treatment effect . In both cultivars, PhiK application resulted in a significantly lower damage growth rate (DGR) compared to the control and PhiCa treatments, although there was less difference in ‘Spunta’. Treatments tested had no significant effect on yield. However, PhiK application tended to increase yields by 20.5 and 14.8% in relation to control and PhiCa treatments, respectively. Under experiment conditions, Phi decreased disease severity and increased yields, with differences between cultivars and chemical compounds.

Mejda Daami-Remadi, Inès Dkhili, Hayfa Jabnoun-Khiareddine, Mohamed El Mahjoub (Tunisia) Biological Control of Potato Leak with Antagonistic Fungi Isolated from Compost Teas and Solarized and Non-Solarized Soils (pp 32-40)

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Original Research Paper: Several fungal agents, isolated from compost teas and soil, were tested for their antagonistic activity against Pythium aphanidermatum and P. ultimum causing potato leak in Tunisia depending on the timing of their application. In vitro dual culture experiments showed that Aspergillus spp., Penicillium sp. and Trichoderma sp. isolates had inhibited differently the two Pythium species and that their inhibitory effect was improved when plated 24 h prior pathogen. Tested in vivo for their ability to control leak development, pooled data of antagonistic treatments revealed that all microbial agents had decreased rot incidence and severity compared with the untreated control. Moreover, their preventive application i.e. 24 h prior to pathogen inoculation has contributed by the reduction of leak severity by about 77.28% as compared to simultaneous application. Both Pythium species were differently controlled by the tested fungi. In fact, leak caused by P. aphanidermatum was completely suppressed (100% of inhibition) with all microbial agents applied 24 h before inoculation while for P. ultimum, the percentage of reduction of leak severity ranged between 15.37% and 95.94%.

Boutheina Mejdoub-Trabelsi, Hayfa Jabnoun-Khiareddine, Mejda Daami-Remadi (Tunisia) Effect of Fusarium Species and Temperature of Storage on the Susceptibility Ranking of Potato Cultivars to Tuber Dry Rot (pp 41-46)

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Original Research Paper: The relative susceptibility of 11 potato cultivars to Fusarium solani, F. oxysporum f. sp. tuberosi, F. sambucinum, and F. graminearum was assessed under different temperatures of storage. Obtained results revealed that these Fusarium species showed variable aggressiveness upon the 11 tested potato cultivars. In fact, F. sambucinum was the most aggressive on the majority of cultivars. F. graminearum showed comparable aggressiveness as F. sambucinum only on some cultivars. F. oxysporum f. sp. tuberosi and F. solani caused a relatively less severe dry rot on the cultivars tested. After 21 days of incubation at 15, 20, 25 and 30°C, none of the cultivars tested was completely resistant to all Fusarium species and only some of them showed lesser susceptibility to at the most one species. This is the case of ‘Spunta’, ‘Mondial’ and ‘Nicola’, the most cultivated in Tunisia, which tolerated at least one species of Fusarium: F. oxysporum f. sp. tuberosi for the two first cultivars and F. solani for the second. The rank order of susceptibility levels to Fusarium dry rot varied depending on Fusarium species and temperature of storage. When tubers were inoculated with F. sambucinum (the most aggressive species), cultivars placed in the less susceptible group at 30°C were classified as highly susceptible at 15°C. However, when tubers were inoculated with F. oxysporum f. sp. tuberosi (the least aggressive), cultivars placed on category of less susceptible were almost the same at all tested temperatures.

Mejda Daami-Remadi, Rafik Bouallègue, Hayfa Jabnoun-Khiareddine, Mohamed El Mahjoub (Tunisia) Effect of the Level of Seed Tuber Infection by Colletotrichum coccodes at Planting on Potato Growth, Black Dot Severity and Subsequent Yield Reduction (pp 47-53)

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Original Research Paper: A great deal of attentionhas been giventotuber infections of Colletotrichum coccodes as skin blemishes depreciate the tuber’s commercial value and serve as means of pathogen spread into new productions areas. This study was carried out on cv. ‘Spunta’ potato plants to compare, quantitatively, the relative impact of different tuber-borne inoculum levels on black dot severity, plant growth and expected yield loss. Black dot severity recorded 60 (pot experiment) or 90 days post-planting (field experiment) on the below-ground plant parts varied significantly depending on inoculum levels tested. The severest symptoms were induced by the highest seed tubers infections corresponding to more than 50% of the seed tuber surface area covered with black dot lesions. The recorded disease severity was found to be highly and positively correlated with the level of seeds contamination. The aerial part fresh weight noted 60 DPP was reduced, compared to plants grown from the symptomless seed tubers, by 24 and 42% when heavily infested seeds were planted. This growth parameter was also negatively correlated with black dot severity on seed tubers and on the below-ground plant parts. In the pot experiment, tuber weight was reduced by about 14-21% on plants grown from extremely infected seeds as compared with the non infested control plants. Yield decrease, subsequent to the planting of diseased seeds, varied between 15 and 27% when C. coccodes inoculum levels ranged between 1 and 5. The field study revealed the existence of significant and negative correlations between the tuber yield, the level of seed-borne inoculum and disease severity on the below-ground stems, roots and stolons.

Mejda Daami-Remadi, Hayfa Jabnoun-Khiareddine, Abir Sdiri, Mohamed El Mahjoub (Tunisia) Comparative Reaction of Potato Cultivars to Sclerotium rolfsii Assessed by Stem Rot and Tuber Decay Severity (pp 54-59)

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Original Research Paper: Experiments were conducted to evaluate the relative susceptibility of 11 local potato cultivars to Sclerotium rolfsii by using several stem and tuber disease parameters. Based on stem rot severity, noted three weeks post-inoculation, pathogen penetration, and percentage of rotten tissue, recorded after 8 days of incubation at 30°C, none of the cultivars tested was resistant to S. rolfsii. However, there was a variable degree of susceptibility in which cultivar ‘Tango’ was found to be the most susceptible whilst ‘Daisy’ was the most tolerant to the disease. The most severe stem rot attributed to pathogen inoculation was observed, three weeks post-inoculation, on ‘Tango’ and ‘Spunta’ plants. For all cultivars combined, the percentage of rotten tuber tissue was related to the lesion diameter formed on the tuber surface and to the pathogen penetration.

Mohamed Ali Triki, Ines Hammami, Samira Krid Hadj-Taieb, Mejda Daami-Remadi, Aymen Mseddi, Mohamed El Mahjoub, Radhouane Gdoura, Nouri Khammassy (Tunisia) Biological Control of Atypical Pink Rot Disease of Potato in Tunisia (pp 60-64)

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Original Research Paper: In order to biologically manage the atypical pink rot disease of potato, various indigenous antagonistic bacteria were tested against Pythium aphanidermatum. In vitro tests showed that Achromobacter xylosoxidans (B₄),Pseudomonas putida (B₇) and P. fluorescens (B₁₀)isolates resulted in significant decreases in the mycelial growth of P. aphanidermatum ranging from 50 to 88%. Therefore, they were further evaluated for their abilityto produce diffusible metabolites in culture filtrates. P. fluorescens was shown to be the most efficient by exhibiting the highest inhibitory activity in vitro. Total inhibition of P. aphanidermatum growth was achieved with the culture filtrates of this antagonistic agent applied at a 1/2 (v/v) ratio. The biological treatments of inoculated potato (Solanum tuberosum L.) tubers cv. ‘Spunta’ by the bacterial culture filtrates were also efficient in reducing the rotting severity by more than 90% with P. fluorescens as compared to the untreated and inoculated tubers.Thus, the management of natural potato infection in storage and in the field by applying some antagonistic bacteria should be investigated.

Heba Mahfouze, Khalid El-Dougdoug, Badawi Othman, Mostafa Gomaa (Egypt) Inhibition of Potato Virus Y by Ribosome Inactivating Proteins (RIPs) (pp 65-69)

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Original Research Paper: Antiviral proteins (AVPs), also referred to as ribosome inactivating proteins (RIPs), are an extended, fairly heterogeneous group of plant proteins which confer resistance against different viruses when applied exogenously or expressed in transgenic lines. These have been identified in a number of plant species such as pokeweed(Phytolacca americana, P. acinosa), and “the marvel of Peru” (Mirabilis jalapa). The primary objective of this study was the development of an easily adaptable technology for controlling Potato virus Y (PVY^NTN) by the pre-inoculation application of Phytolacca sp. and M. jalapa extracts on five potato(Solanum tuberosum L.) cultivars (‘Selan’, ‘Spunta’, ‘Cara’, ‘Diamond’, and ‘Nicola’). In addition, we aimed to investigate the functional expression of PVY^NTN resistance in these potato cultivars by comparing protein composition using SDS-PAGE and polyphenol oxidase and peroxidase isozymes. Leaf extracts from Phytolacca sp. and M. jalapa leaves were blended and diluted (1: 5, w/v) in distilled water and sprayed on the five potato cultivars before virus inoculation, inhibiting infection by almost 100%, as corroborated by DAS-ELISA. SDS-PAGE was used to detect antiviral proteins in P. americana, P. acinosa and M. jalapa, in addition to studying genetic variability among healthy, resistant and susceptible potato cultivars through the quantitative and qualitative determination of total proteins. Monomorphic bands with molecular weights 11 and 28.5 KDa appeared in AVP-treated leaves in addition to another common band at 28.5 KDa induced in AVP-treated tubers and disappeared in non-AVP-pretreated potato plants and the control. On the other hand, polyphenol oxidase isozyme activity in the non-AVP-pretreated potato cultivars (PVY-infected) was higher than in AVP-pretreated cultivars. In addition, one unique peroxidase marker appeared at an Rf value 0.280 in all the potato cultivars except for ‘Spunta’. Also, in non-AVP-pretreated potato plants a monomorphic band appeared at an Rf value 0.945 in all five potato cultivars.

Heba Mahfouze, Khalid El-Dougdoug, Badawi Othman, Mostafa Gomaa (Egypt) Molecular Markers in Potato Cultivars Treated with Ribosome-Inactivating Proteins (pp 70-74)

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Original Research Paper: Most plants produce ribosome-inactivating proteins (RIPs) that inhibit protein synthesis through modification of RNA. In this report we studied the inheritance of resistance to Potato virus Y (PVY) in five potato cultivars treated with RIPs using ISSR-PCR since genetic information on this topic is limited. Leaf extracts from pokeweed (Phytolacca americana and P. acinosa and the marvel of Peru (Mirabilis jalapa) were sprayed on five potato cultivars (‘Selan’, ‘Spunta’, ‘Cara’, ‘Diamond’ and ‘Nicola’) before virus inoculation, inhibiting infection by almost 100%, corroborated by DAS-ELISA. Changes in DNA (relative to PVY^NTN-infected plants and the healthy control) in potato cultivars pretreated with 100 μg/ml AVP resulted in genetic variations detected by ISSR-PCR analysis, which was performed using five primers. A total of 63 scorable amplified DNA fragments ranging from 9 0 to 1105 bp were observed using these primers, 43 of which were polymorphic while the others were monomorphic. The five primers showed a mean polymorphic percentage of 68.25%, the highest percentage derived from primer ISSR-1 (87.50%). The AVP-pretreated potato cultivars varied considerably in banding patterns using the five ISSR-PCR primers. ‘Nicola’ had the highest number of unique markers (9), followed by ‘Selan’ (8), ‘Spunta’ (5), ‘Dimond’ (1) and ‘Cara’ (0). Leaf extracts from P. americana, P. acinosa and M. jalapa could be used in simple crop-protection agricultural systems by spraying these extracts on leaves of various crops to prevent or control viral infection.

Lobna El Hajji, Najet Horrigue-Raouani (Tunisia) Efficiency of Solarization and Incorporation of Cattle Manure in Management of Meloidogyne javanica (Treub.) Chitwood and Globodera pallida (Stone) Behrens Associated with Potato (pp 75-78)

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Original Research Paper: Potato is a strategic crop in Tunisia but is susceptible to many pests and diseases. Nematodesof the genera Meloidogyne and Globodera are important pests that cause yield losses and depreciation of tuber quality. A trial was carried out in a plot where the soil was naturally infested with M. javanica and G. pallida. Three soil treatments were tested and compared. Soil solarization (SS) and incorporation of cattle manure (70 T/ha), applied alone or in combination, were assessed for their impact on potato crop. SS alone improved potato growth by 13.56% and yield by 26.53%. Compared to the control, SS combined with cattle manure decreased the multiplication rate of M. javanica by 38.14% and enhanced plant height (29.47%), fresh root and shoot weight (47.89 and 59.53%, respectively) and yield (26.40%).

V. Prathap Reddy, N. Narasimha Rao, P. S. Vimala Devi, M. Lakshmi Narasu, V. Dinesh Kumar (India) PCR-Based Detection of cry Genes in Local Bacillus thuringiensis DOR Bt-1 Isolate (pp 79-82)

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Original Research Paper: A sporulating culture of Bacillus thuringiensis ssp. kurstaki strain DOR Bt-1 was isolated from castor semilooper (Achaea janata L.) cadavers from a castor bean (Ricinus communis L.) field at Kothakota mandal of Mahaboobnagar district, Andhra Pradesh, India. This strain has shown high toxicity against many insect pests and the wettable power formulation of this strain obtained through solid-state fermentation has been registered with the Central Insecticides Board (CIB), India under section 9 (3b). Based on the bioassay results and the efficacy of the formulation on different Lepidopteran insects, it was concluded that the strain must be carrying diverse cry genes. Therefore, to understand the cry gene profile of this strain, a PCR-based assay was carried out. Genomic PCR analysis of the DOR Bt-1 isolate with universal primers specific to cry gene classes indicated the presence of both cry1 and cry2 class-specific genes. Further, PCR analysis with cry gene-specific primers revealed the presence of cry1Aa, cry1Ab, cry1Ac, cry2Aa and cry2Ab genes. Thus, DOR Bt-1 isolate harbors a combination of different cry genes, such as Lepidoptera-active cry1Aa, cry1Ab and cry1Ac, and Lepidoptera-Diptera-active cry2Aa and cry2Ab genes, indicating that this isolate has the potential to be effective against both Lepidopteran and Dipteran insect pests.