Showing papers by "International Potato Center published in 2010"

Identification of drought-responsive compounds in potato through a combined transcriptomic and targeted metabolite approach

Abstract: Two potato clones (Solanum tuberosum L.) of the Andean cultivar group, called Sullu and SS2613, with different drought-tolerance phenotypes were exposed to a continuously increasing drought stress in a field trial. At the physiological level, while relative leaf water contents were similar in both clones, osmotic potential was lower in Sullu and declined more strongly during drought compared with SS2613. In the drought-stressed plants, tuber yield was reduced by about 70% compared with control plants in both clones. Potato cDNA microarrays and target metabolite analysis were performed on leaves sampled at several time-points after the onset of drought. At the transcriptomic level, photosynthesis-related genes were already strongly repressed in Sullu after 28 d of withholding irrigation and even more strongly after a longer stress duration, whereas, in SS2613, repression occurred only after 49 d of soil drying; similarly, a strong perturbation of carbohydrate-related genes was observed in Sullu. At the metabolite level, differential accumulation of osmotically active solutes was observed between the two cultivars; indeed, in Sullu, contents of galactose, inositol, galactinol, proline, and proline analogues were higher upon drought stress compared with SS2613. These results point to different drought responses in the cultivars at the leaf level, with, however, similar tuber yield reductions. The previously shown tolerant clone Sullu lost part of its tolerance under the experimental conditions used here; it was, however, able to maintain an absolute yield three times higher than SS2613.

A sweetpotato gene index established by de novo assembly of pyrosequencing and Sanger sequences and mining for gene-based microsatellite markers

Abstract: Background Sweetpotato (Ipomoea batatas (L.) Lam.), a hexaploid outcrossing crop, is an important staple and food security crop in developing countries in Africa and Asia. The availability of genomic resources for sweetpotato is in striking contrast to its importance for human nutrition. Previously existing sequence data were restricted to around 22,000 expressed sequence tag (EST) sequences and ~ 1,500 GenBank sequences. We have used 454 pyrosequencing to augment the available gene sequence information to enhance functional genomics and marker design for this plant species.

Ecogeography of ploidy variation in cultivated potato (Solanum sect. Petota)

Abstract:  Premise of the study : The taxonomy of cultivated potatoes has been highly controversial, with estimates of species numbers ranging from 3 to 17. Ploidy level has been one of the most important taxonomic characters to recognize cultivated potato species, containing diploid (2 n = 2 x = 24), triploid (2 n = 3 x = 36), tetraploid (2 n = 4 x = 48), and pentaploid (2 n = 5 x = 60) cultivars. We tested the environmental associations of different ploidy levels in cultivated potato species that traditionally have been recognized as Linnaean taxa to see whether, in combination with prior morphological, molecular, and crossing data, some of the ploidy variants can be recognized as distinct taxa.  Methods : We summarize 2780 chromosome counts of landrace cultivated potatoes, provide georeferences to 2048 of them, and analyze these data for 20 environmental variables at 10-min resolution using the randomForest algorithm to explore associations with taxa and ploidy variants.  Key results : Except for the S. tuberosum Chilotanum Group and extreme northern and southern range extensions of the Andigenum Group, it is impossible to fidistinct habitats for the ploidy variants of the S. tuberosum Andigenum Group.  Conclusions : Our distributional and ecological data, in combination with prior results from morphology, microsatellites, and crossing data, provide yet additional data to support a major reclassifi cation of cultivated potato species. A rational, stable, and universally accepted taxonomy of this major crop plant will greatly aid all users of wild and cultivated potatoes from breeders to gene bank managers to ecologists and evolutionary biologists.

Hybrid origins of cultivated potatoes

Abstract: Solanum section Petota is taxonomically difficult, partly because of interspecific hybridization at both the diploid and polyploid levels. The taxonomy of cultivated potatoes is particularly controversial. Using DNA sequence data of the waxy gene, we here infer relationships among the four species of cultivated potatoes accepted in the latest taxonomic treatment (S. ajanhuiri, S. curtilobum, S. juzepczukii and S. tuberosum, the latter divided into the Andigenum and Chilotanum Cultivar Groups). The data support prior ideas of hybrid origins of S. ajanhuiri from the S. tuberosum Andigenum Group (2x = S. stenotomum) × S. megistacrolobum; S. juzepczukii from the S. tuberosum Andigenum Group (2x = S. stenotomum) × S. acaule; and S. curtilobum from the S. tuberosum Andigenum Group (4x = S. tuberosum subsp. andigenum) × S. juzepczukii. For the tetraploid cultivar-groups of S. tuberosum, hybrid origins are suggested entirely within much more closely related species, except for two of three examined accessions of the S. tuberosum Chilotanum Group that appear to have hybridized with the wild species S. maglia. Hybrid origins of the crop/weed species S. sucrense are more difficult to support and S. vernei is not supported as a wild species progenitor of the S. tuberosum Andigenum Group.

Aflatoxin control and prevention strategies in maize for sub-Saharan Africa.

Abstract: Mycotoxins are secondary fungal metabolites that contaminate agricultural commodities and can cause sickness or death in humans and animals. Risk of mycotoxin contamination of food and feed in Africa is increased due to environmental, agronomic and socio-economic factors. Environmental conditions especially high humidity and temperature favour fungal proliferation. Farming practices in Africa sustain fungal and toxin contamination of food and feed. The socio-economic and food security status of the majority of inhabitants of sub-Saharan Africa leaves them little option in choosing good quality products. Several technologies have been tested in Africa to reduce mycotoxin risk. Field management practices that increase yields may also prevent aflatoxin. They include use of resistant varieties, timely planting, fertilizer application, weed control, insect control and avoiding drought and nutritional stress. Other options to control the toxin causing fungi A. flavus contamination in the field are use of atoxigenic fungi to competitively displace toxigenic fungi, and timely harvest. Post-harvest interventions that reduce mycotoxins are rapid and proper drying, sorting, cleaning, drying, smoking, post harvest insect control, and the use of botanicals or synthetic pesticides as storage protectant. Another approach is to reduce the frequent consumption of ‘high risk’ foods (especially maize and groundnut) by consuming a more varied diet, and diversifying into less risky staples like sorghum and millet. Chemo-preventive measures that can reduce mycotoxin effect include daily consumption of chlorophyllin or oltipraz and by incorporating hydrated sodium calcium aluminosilicates into the diet. Detoxification of aflatoxins is often achieved physically (sorting, physical segregation, flotation etc.), chemically (with calcium hydroxide, ammonia) and microbiologically by incorporating probiotics or lactic acid bacteria into the diet. There is need for efficient monitoring and surveillance with costeffective sampling and anlytical methods. Sustaining public education and awareness can help to reduce aflatoxin contamination. Keywords : Aflatoxin, Sub-Saharan Africa, Control measures

Urban Agriculture in Africa: What Has Been Learned?

Abstract: Though the crisis in world food prices exploded during 2008, the problem of urban food insecurity in Africa has been a fact of life for many low-income urban dwellers for decades, and especially since the period of structural adjustment in the 1980s (Maxwell 1995). It is not that there is no food; it’s that poor urban consumers cannot afford it. This is the stark but simple truth lying behind much of the agriculture that is widespread within and around African cities. What urban households have known and practiced for generations, urban decision-makers have begun to recognize much more recently: urban agriculture is a livelihood strategy.

Phytophthora andina sp nov., a newly identified heterothallic pathogen of solanaceous hosts in the Andean highlands

Abstract: A blight disease on fruits and foliage of wild and cultivated Solanum spp. was found to be associated with a new species of Phytophthora. The proposed novel species is named Phytophthora andina Adler & Flier, sp. nov. based on morphological characteristics, pathogenicity assays, mitochondrial DNA haplotyping, AFLP fingerprinting and nuclear and mitochondrial DNA sequence analyses. Isolates of P. andina (n = 48) from the Andean highland tropics of Ecuador were collected from 1995 to 2006. Phytophothora andina is closely related to P. infestans and has semipapillate, ellipsoidal sporangia borne on sympodially branched sporangiophores. It is heterothallic and produces amphigynous antheridia. The species consists of several clonal lineages, including the EC-2 and EC-3 RFLP lineages, which were described previously as P. infestans. Approximately 75% of isolates react as compatibility type A2 when paired with an A1 compatibility type isolate of P. infestans. However, when A2 isolates from the Anarrhichomenum section of Solanum were paired in all combinations, viable oospores were obtained in several crosses, suggesting that there is a unique compatibility interaction in P. andina that is complementary to that described in P. infestans. Nuclear and mitochondrial sequence analysis supported the species designation of P. andina. This newly identified heterothallic pathogen shares a common ancestor with P. infestans and may have arisen from hybridization events with sister taxa in the Andes.

Influence of colour type and previous cultivation on secondary metabolites in hypocotyls and leaves of maca (Lepidium meyenii Walpers).

Abstract: BACKGROUND: Maca is an Andean crop of the Brassicaceae family which is mainly known for its fertility-enhancing properties following consumption The hypocotyls display various colours ranging from white to black Each colour has different biological effects The aim of this study was to analyse the concentrations of major secondary metabolites in hypocotyls and leaves of maca in a controlled planting experiment in the Peruvian Andes at 4130 m above sea level The effects of colour type and of previous cultivation of the field were examined RESULTS: In the hypocotyls, the colour type effect was significant for most secondary metabolites; exceptions were β-sitosterol and campesterol The lead-coloured, yellow and violet maca hypocotyls were rich in glucosinolates, macaene and macamides, respectively Previous cultivation affected macaene, campesterol and indole glucosinolate concentrations Effects on metabolite concentrations in the leaves were minor Hypocotyls were richer in macaene, macamides and glucosinolates than were leaves, and were poorer in β-sitosterol and total phenols CONCLUSION: Colour type has to be considered in maca production, as colour associates with variations in concentrations of distinct bioactive metabolites Leaves may be interesting for animal nutrition purposes as they contain essentially the same secondary metabolites as the hypocotyls but in clearly lower concentrations Copyright © 2010 Society of Chemical Industry

Multilevel Agrobiodiversity and Conservation of Andean Potatoes in Central Peru Species, Morphological, Genetic, and Spatial Diversity

Abstract: Botanical species and morphological and genetic diversity represent different yet linked units of conservation. These features, and their spatial distribution in the central Peruvian Andean highlands of Huancavelica, were used as a basis for characterizing and quantifying potato agrobiodiversity at different scales. Results show that individual farm households maintain high levels of cultivar, morphological, and genetic diversity. At the regional level, all cultivated species, with the exception of Solanum ajanhuiri, were found to be present. Tetraploid native potatoes were most abundant, followed by diploids, triploids, and pentaploids. Morphological characterization of 2481 samples belonging to 38 in situ collections resulted in the identification of 557 unique cultivars. Genetic fingerprinting of 989 samples belonging to 8 in situ collections resulted in the identification of 406 unique cultivars. The principal source of genetic variation is found within rather than between geographically dist...

QBOL: a new EU project focusing on DNA barcoding of Quarantine organisms

Abstract: In 2009 a new three year EU funded project (QBOL) started on DNA barcoding of important plant pests. An international consortium of 20 partners (universities, research institutes, and phytosanitary organizations) from around the world, coordinated by Plant Research International (Wageningen, the Netherlands), will collect DNA barcodes from many plant pathogenic quarantine organisms, store these sequences in a database accessible over the internet, develop a DNA bank and train end-users. All these activities should help National Plant Protection Services in the correct identification and detection of plant pathogenic quarantine organisms

Analysis of complete genomic sequences of isolates of the Sweet potato feathery mottle virus strains C and EA: molecular evidence for two distinct potyvirus species and two P1 protein domains

Abstract: The complete nucleotide sequence of the isolate C1 of Sweet potato feathery mottle virus (SPFMV) strain C and the 5′ region of several other strains were determined and analyzed together with the sequences of isolates representing the EA, RC and O strains. This provided molecular evidence for the reclassification of SPFMV strains into two species and the occurrence of a complex recombinant isolate. Analysis also revealed a hypervariable domain in the P1 protein, which separates an N-terminal region unique to SPFMV and members of the ipomovirus species Sweet potato mild mottle virus from the C-terminal protease domain, which is conserved among all potyviruses.

Quantitative resistance to late blight from Solanum berthaultii cosegregates with R(Pi-ber): insights in stability through isolates and environment.

Abstract: Genetic resistance is a valuable tool in the fight against late blight of potatoes but little is known about the stability and specificity of quantitative resistance including the effect of defeated major resistance genes. In the present study we investigated the effect of different isolates of Phytophthora infestans on the mode of action of RPi-ber, an R-gene originating from Solanum berthaultii. The experiments were conducted on progenies derived from two reciprocal inter-specific backcrosses of Solanum tuberosum and S. berthaultii. The plant–pathogen interaction was tested in diverse environments including field, greenhouse and growth chamber conditions. The RPi-ber gene provided complete resistance against a US8 isolate of P. infestans in all trials. When isolates compatible with RPi-ber were used for inoculation, a smaller, but significant resistance effect was consistently detected in the same map position as the R-gene. This indicates that this R-gene provides a residual resistance effect, and/or that additional resistance loci are located in this genomic region of chromosome X. Additional quantitative resistance loci (QRL) were identified in the analyzed progenies. While some of the QRL (such as those near TG130 on chromosome III) were effective against several isolates of the pathogen, others were isolate specific. With a single exception, the S. berthaultii alleles were associated with a decrease in disease severity. Resistance loci reported in the present study co-locate with previously reported R-genes and QRL to P. infestans and other pathogens.

Secondary Metabolites in Maca as Affected by Hypocotyl Color, Cultivation History, and Site

Abstract: Maca (Lepidium meyenii Walpers) hypocotyls are reported to have a favorable biological activity in man. The presumed bioactive constituents seem to vary among maca hypocotyl color types, but the residual variation is large. This study tested the hypothesis that, apart from color types, environmental factors have a distinct influence on the concentration of characteristic secondary metabolites in maca. In a field experiment at 4100 m altitude (Peru), maca of four hypocotyl color types was evaluated at two sites with different soil types. At each site, experimental areas were either never cultivated or cultivated with maca 2 to 3 yr ago followed by a fallow period. Applying four color replicates per site and area resulted in 64 plots (100 plants plot -1 ). Especially color type largely influenced concentrations of macaene, macamides, β-sitosterol, campesterol, and glucosinolates. Site (also clearly affecting growth yield) was weaker in effect on these metabolites but still significantly influenced concentrations of some constituents, while the effect of cultivation history was widely absent. Macaene, macamides, and β-sitosterol were negatively correlated with glucosinolates. This shows that environmental conditions and color type have to be considered in producing maca with high concentrations of distinct bioactive metabolites.

Evaluating soil rhizobacteria for their ability to enhance plant growth and tuber yield in potato

Abstract: The objectives of this study were to identify promising microorganisms to improve potato productivity in low-input systems of tropical highlands and to compare results from in vitro, greenhouse and field experiments to advance the development of a screening method for rhizobacteria and develop an efficient assessment of their effect on plant growth in field conditions. A total of 150 bacterial strains were screened in vitro, in greenhouse and field trials. The series of experiments confirmed the plant growth-promoting ability of a range of rhizobacteria. Although in vitro and greenhouse results were promising, the field experiment showed variability and the results require further verification. The in vitro tests might have limited value for screening as no correlation could be found between in vitro tests and pot trial results. However, trials in controlled conditions produced insights into the mechanisms causing better plant growth in potato, such as early tuberisation, fast development of leaf area and probably greater photosynthetic rates.

Bemisia afer sensu lato, a Vector of Sweet potato chlorotic stunt virus

Abstract: Bemisia tabaci biotype B is considered to be the primary vector of Sweet potato chlorotic stunt virus (SPCSV, Crinivirus). However, Trialeurodes abutiloneus also has been shown to transmit SPCSV in a semipersistent manner. Mixed infection of SPCSV with the aphid-transmitted Sweet potato feathery mottle virus (SPFMV, Potyvirus) causes sweetpotato (Ipomoea batatas) virus disease (SPVD), the major virus disease affecting this crop. High populations of B. afer sensu lato are seasonally associated with sweetpotato in Peru during times of low B. tabaci incidence. The transmission of SPCSV (in single and double infection with SPFMV) by laboratory-reared B. afer sensu lato and B. tabaci biotype B was investigated. For SPCSV transmission efficiency, individual adult insects were allowed 48 h for acquisition and inoculation access periods at both 20 and 25°C. SPCSV was transmitted by both whiteflies, with similar transmission efficiency when the virus was acquired from plants singly infected by SPCSV or doubly infected with SPCSV and SPFMV, at 20 and 25°C. We conclude that B. afer sensu lato is a newly identified vector of SPCSV. This finding may have important epidemiological significance for the spread of SPCSV and SPVD.

Traditional Processing of Black and White Chuño in the Peruvian Andes: Regional Variants and Effect on the Mineral Content of Native Potato Cultivars

Abstract: Traditional Processing of Black and WhiteChunoin the Peruvian Andes: Regional Variants and Effect on the Mineral Content of Native Potato Cultivars. Farmers in the high Andes of central to southern Peru and Bolivia typically freeze-dry potatoes to obtain chuno. Processing of so-called black chuno follows tending, treading, freezing, and drying. The making of white chuno is generally more complex and involves exposure of tubers to water. Regional variants exist for each of these processes, yet their influence on the nutritional composition of native potato cultivars is little known. Tubers belonging to four distinct cultivars and produced in a replicated trial under uniform conditions were processed into four types of chuno following standard traditional procedures (farmer-managed). These regional variants were documented, and the dry matter, iron, zinc, calcium, potassium, phosphorus, magnesium, and sodium content of the four resulting different types of boiled chuno determined at the International Potato Center’s Quality and Nutrition Laboratory (Lima, Peru). Content values were compared with those of boiled (unprocessed) tubers from the same experiment. Regional variants of processing are to a large extent determined by tradition, environmental condition, and market demand. The zinc, potassium, phosphorus, and magnesium content of all types of chuno decreases in comparison with unprocessed tubers. Concentrations of these same minerals decrease more drastically for white as compared to black chuno. The effect of the four regional variants of freeze-drying on the dry matter, iron, calcium, and sodium content of chuno differs by process and/or cultivar.

Restriction of potato and tomato late blight development by sub-phytotoxic concentrations of boron

Abstract: Boron is a microelement required for normal growth and development of plants but its positive effect is restricted to a narrow range of concentrations The gradual increase in use of recycled water, which contains high concentrations of boron for irrigation, has already raised the level of boron in soils and plants in southern Israel This research was conducted to examine the direct effects of sub-phytotoxic boron concentrations on potato late blight epidemics and to explore the mode of action of boron against Phytophthora infestans When boron was applied alone to field grown potato plants it did not affect the epidemic However, together with a reduced rate of the fungicide Melody Duo (propineb + iprovalicarb), boron improved late blight suppression compared to plants treated with the fungicide alone The ED50 of boron against P infestans (256AE 4m g L )1 ) was about 6400 times higher than the ED50 value of the fungicide chlorothalonil (0AE04 mg L )1 ), indicating that boron does not have a direct fungicidal activity that would explain the level of protection seen in the field In greenhouse experiments conducted with potted tomato plants, boron decreased late blight severity in both treated leaves and distant leaves not treated with boron The results suggest that boron is active locally but also may induce systemic acquired resistance against P infestans

Attract‐and‐kill: a new strategy for the management of the potato tuber moths Phthorimaea operculella (Zeller) and Symmetrischema tangolias (Gyen) in potato: laboratory experiments towards optimising pheromone and insecticide concentration

Abstract: BACKGROUND: Sex pheromones of the potato tuber moths Phthorimaea operculella (Zeller) and Symmetrischema tangolias (Gyen) are ideal tools to monitor pest flight activity but are not used as means of control. The aim of the present study was to test the suitability of an attract-and-kill strategy consisting of pure pheromones and the contact insecticide cyfluthrin as the active ingredient, formulated with plant oils and ultraviolet absorbers, and applied in droplet sizes of 100 µL. RESULTS: Cyfluthrin at a concentration of 5 g L−1 resulted in the highest and fastest killing of males after 48 h, with a 100% mortality after 3–4 days. In contrast, control males survived for 13 days. In olfactometer experiments, the pheromone concentration of 0.5 g L−1 was significantly most attractive against eight virgin females. At controlled conditions (20 °C), no reduction in efficacy of the attract-and-kill formulation was observed for a minimum period of 36 days, whereas under natural environmental conditions the efficacy reduced gradually after day 6 of exposure. The longer the droplet was exposed, the longer was the time to reach 100% mortality of males. CONCLUSIONS: Compared with attract-and-kill studies for other pest species, the results are promising as a means of achieving highly effective control of potato tuber moths under field conditions. Copyright © 2010 Society of Chemical Industry

Land use and potato genetic resources in Huancavelica, central Peru

Abstract: Three specific dimensions of potato land use were researched to gain insights into possible contemporary changes affecting the in situ conservation of potato genetic resources: land use tendencies, rotation designs and their intensity, and sectoral fallowing systems. The main research method involved participatory cartography combined with in-depth consultation through interviews and focus group meetings with members of eight Andean highland communities. Land use tendencies between 1995 and 2005 show that the total cropping area dedicated to improved cultivars has grown fast whereas the area reserved for native-floury and native-bitter cultivars has remained more or less stable. Reduced fallow periods for existing fields and the gradual incorporating of high-altitude virgin pasture lands sustain areal growth. Although areas of improved cultivars are proportionally growing fastest at extremely high altitudes between 3900 and 4350 m, overall cropping intensity or fallowing rates are inversely related to alt...

Comparison of transcript profiles in late blight-challenged Solanum cajamarquense and B3C1 potato clones.

Abstract: Two Solanum genotypes, a wild relative of cultivated potato S. cajamarquense (Cjm) and an advanced tetraploid clone B3C1 (B3), were inoculated with two Phytophthora infestans isolates and leaves were sampled at 72 and 96 h after inoculation. Gene expression in the inoculated versus noninoculated samples was monitored using the Institute of Genomic Research (TIGR) 10K potato array and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The current experiment is study number 83 of the TIGR expression profiling service project, and all data are publicly available in the Solanaceae Gene Expression Database (SGED) at ftp://ftp.tigr.org/pub/data/s_tuberosum/SGED. Differentially regulated cDNA clones were selected separately for each isolate-time point interaction by significant analysis of microarray (SAM), and differentially regulated clones were classified into functional categories by MapMan. The results show that the genes activated in B3 and Cjm have largely the same biological functions and are commonly activated when plants respond to pathogen attack. The genes activated within biological function categories were considerably different between the genotypes studied, suggesting that the defence pathways activated in B3 and Cjm during the tested conditions may involve unique genes. However, as indicated by real-time RT-PCR, some of the genes thought to be genotype specific may be activated across genotypes at other time points during disease development.

Influence of day-length and isolates of Phytophthora infestans on field resistance to late blight of potato

Abstract: Main and interaction effects of day-length and pathogen isolate on the reaction and expression of field resistance to Phytophthora infestans were analyzed in a sample of standard clones for partial resistance to potato late blight, and in the BCT mapping population derived from a backcross of Solanum berthaultii to Solanum tuberosum. Detached leaves from plants grown in field plots exposed to short- and long day-length conditions were independently inoculated with two P. infestans isolates and incubated in chambers under short- and long photoperiods, respectively. Lesion growth rate (LGR) was used for resistance assessment. Analysis of variance revealed a significant contribution of genotype × isolate × day-length interaction to variation in LGR indicating that field resistance of genotypes to foliar late blight under a given day-length depended on the infecting isolate. An allele segregating from S. berthaultii with opposite effects on foliar resistance to late blight under long- and short day-lengths, respectively, was identified at a quantitative trait locus (QTL) that mapped on chromosome 1. This allele was associated with positive (decreased resistance) and negative (increased resistance) additive effects on LGR, under short- and long day-length conditions, respectively. Disease progress on whole plants inoculated with the same isolate under field conditions validated the direction of its effect in short day-length regimes. The present study suggests the occurrence of an isolate-specific QTL that displays interaction with isolate behavior under contrasting environments, such as those with different day-lengths. This study highlights the importance of exposing genotypes to a highly variable population of the pathogen under contrasting environments when stability to late blight resistance is to be assessed or marker-assisted selection is attempted for the manipulation of quantitative resistance to late blight.

Phenotypic Expression of Resistance to Phytophthora infestans in Processing Potatoes in Argentina

Abstract: Ten potato cultivars were evaluated in Argentina for foliage and tuber susceptibility to Phytophthora infestans, the oomycete pathogen causing late blight. Pathogen isolates collected from two major potato production regions in the country were polymorphic for specific virulence and isozyme banding patterns, although diversity was found among and not within specific locations. Four of the cultivars were found to be highly resistant in foliage, having little disease in the field and greenhouse and race-specific resistance is suspected. One of these is Russet Burbank, which is highly susceptible in the United States. Cultivar Shepody was the most susceptible and was assigned a value of 8, which was used together with area under disease progress curve values to calculate scale values of the other cultivars on a 1 to 9 susceptibility scale (where 9 is highly susceptible). Cultivar Ranger Russet had values of about 2.5 and resistance could be race-non-specific. The other cultivars for which race incompatibility did not appear to be a problem had susceptibility values between 4 and 8. Foliage susceptibility values for greenhouse and field were correlated. Foliage and tuber susceptibility were also correlated, although with exceptions and only one cultivar, Innovator, was highly resistant in tubers. The two isolates chosen for assessment of foliage susceptibility in the greenhouse differed for aggressiveness in separate tests where components were measured; however, no cultivar-by-isolate interaction was measured. Cultivars with high levels of putative race-specific foliage resistance should be used with constant monitoring in Argentina.

Priming of pioneer tree Guazuma ulmifolia (Malvaceae) seeds evaluated by an automated computer image analysis

Abstract: Direct seeding is one of the most promising methods in restoration ecology, but low field seedling emergence from pioneer tree seeds still reduces its large scale applicability. The aim of this research was to evaluate seed priming for the pioneer tree species Guazuma ulmifolia. Priming treatments were selected based on seed hydration curves in water and in PEG 8000 solution. Seeds were primed in water for 16 h and in Polyethylene glycol - PEG 8000 (-0.8 MPa for 56 and 88 h) at 20°C to reach approximately 30% water content. Half of the seed sample of each treatment was dried back to the initial moisture content (7.2%); both dried and non-dried primed seeds as well as the unprimed seeds (control) were tested for germination (percentage and rate) and vigor (electrical conductivity of seed leachates). Seedling emergence percentage and rate were evaluated under greenhouse conditions, while seedling length and uniformity of seedling development were estimated using the automated image analysis software SVIS®. Primed seeds showed the highest physiological potential, which was mainly demonstrated by image analysis. Fresh or dried primed seeds in water for 16 h and in PEG (-0.8 MPa) for 56 h, and fresh primed seeds in PEG for 88 h, improved G. ulmifolia germination performance. It is suggested that these treatments were promising to enhance efficiency of stand establishment of this species by direct seeding in restoration ecology programs.

Comparative assessment of pest management practices in potato production at Farmer Field Schools

Abstract: Farmer field schools (FFS) and other participatory approaches are useful methods for rapid delivery of agricultural technologies, knowledge, and information in resource-constrained agro-ecosystems. Cultivar selection, weekly fungicide applications and integrated disease management (IDM) based on a disease monitoring strategy were evaluated at FFS for late blight control. Farmers’ knowledge and perceptions of pest management and agronomic practices were also assessed for both FFS participants and non-participants from 1999–2002. Late blight development and tuber yield varied among field schools, but cultivars had significant effects on late blight severity and yield over a range of disease management options relative to the untreated check. FFS participants and non-participants used diverse sources of pest management information, but differed significantly (P < 0.05) in their use of management methods and practices. Cultivar resistance and fungicides were ranked as major components of pest control by 18%–85% and 7%–30% of FFS participants and non-participants, respectively. Differences in knowledge of cropping practices and pest biology, causal agents, disease symptoms, factors favoring disease development and cultural management of insects and storage pests were recorded. Participatory field experiments, access to resistant cultivars, disease management and use of various agronomic practices learnt at FFS can greatly improve pest control and potato production.

Conservation and Cardamom Cultivation in Nature Reserve Buffer Zones in the East Usambara Mountains, Tanzania

Abstract: Forest destruction continues to be a major threat to the unique biological diversity of the East Usambara Mountains in Northeast Tanzania. One of the most serious current pressures comes from the widespread cultivation of cardamom (Elettaria cardamomum) and other spices under the diminishing forest canopy. In this research, we studied the cultivation methods of cardamom farmers in the buffer zone of Amani Nature Reserve and the proposed Derema Wildlife Corridor, the importance of cardamom for income generation, and farmers' responses to expanding conservation activities, with the aim of proposing locally appropriate solutions based on these practices. Interviews, questionnaires, field experiments, and farm visits were used in data collection. Our results suggest that sustainable cultivation of cardamom is possible, and that some farmers have already adopted ecologically sound intensification practices in home gardens using agroforestry systems. However, some factors hinder broader adoption of such practic...

Variations in resistance against Phthorimaea operculella in wild potato tubers

Abstract: Tuber resistance can contribute to current management strategies against the potato tuber moth, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), in field and stored potatoes. Wild potatoes represent a potential source of novel resistance traits against the moth. We assessed resistance in three wild potato species, Solanum multiinterruptum Bitt., Solanum sparsipilum (Bitt.) Juz. & Buk., and Solanum wittmackii Bitt. against neonate and developing tuber moth larvae. All three species had high levels of resistance but accessions of S. sparsipilum and S. wittmackii were significantly more resistant. Resistance in S. multiinterruptum was generally concentrated in the tuber periderm, whereas in S. sparsipilum and S. wittmackii resistance was mainly cortex-based. Unidentified cortex-resistance factors in all three species reduced survival and increased larval and pupal development times, but had no apparent effects on the pupal weights of survivors. A high proportion of larvae abandoned or died within tubers of S. wittmackii, which has particularly high levels of unidentified cortex-based defenses. Resistance decreased in S. multiinterruptum and S. sparsipilum as tubers sprouted but was more stable in S. wittmackii. Periderm-based resistance was more stable than cortex-based resistance in S. multiinterruptum during sprouting. In contrast, cortex-based resistance was stable in tubers of S. wittmackii as these sprouted, and resistance may have increased on some older sprouting tubers. Solanum multiinterruptum and S. sparsipilum are proposed as potential sources of resistance against the potato tuber moth.

Comparison of “Remote” Versus “Easy” In Situ Collection Locations for USA Wild Solanum (potato) Germplasm

Abstract: A basic question in germplasm collecting is whether the in situ genetic diversity in a given geographic range has been adequately sampled. While one would ideally sample all diverse sites with appropriate habitat, there is usually a practical bias against visiting relatively inaccessible sites. For wild potato in the USA, mountain habitats often include easy access locations (near roads, usually at lower altitudes), and relatively remote locations (usually high altitude crests that can be accessed only by trail hiking and camping). This work used AFLP markers to compare three southeastern Arizona mountain ranges for which multiple "easy" and "remote" Solanum fendleri populations had been collected. Of the total markers detected, 24%, 6% and 3% were unique to the "remote" locations, and 3%, 21% and 34% were unique to "easy" locations. This case study demonstrates that populations at such locations are not identical, but the most unique alleles are sometimes captured at the remote location, sometimes at the easy. The practical conclusion is that both locations need to be sampled and compared empirically in the lab for unique allele richness to identify locations with highest priority for additional collecting.

Control microbiano de la palomilla de la papa Phthorimaea operculella (Lepidoptera: Gelechiidae)

Abstract: The natural occurrence of specific pathogens and biopesticides applied in an inundative fashion can contribute significantly to control of the potato tuber moth, Phthorimaea operculella. Most of the research conducted and practices used for control of P. operculella use one species of granulovirus and the bacterium Bacillus thuringiensis (Bt). The P. operculella granulovirus (PhopGV) has the potential to play a significant role in the integrated management of the pest in stored tubers as well as in field crops. At the same time, Bt has been used successfully against P. operculella infestations in the field and in stored tubers. PhopGV and Bt are safe for application personnel and for the food products; in addition, they do not affect beneficial insects and other nontarget organisms. Other natural insecticides are the biofumigant fungus Muscodor albus, botanicals, sex pheromones and physical measures for P. operculella control in stored tubers. The implementation of biopesticides will ultimately depend on an increased awareness of their attributes by growers and the public, who will be the main drivers for their use and commercialization.