Showing papers by "International Potato Center published in 2002"

Reclassification of landrace populations of cultivated potatoes (Solanum sect. Petota)

Abstract: Cultivated potatoes have been classified as species under the International Code of Botanical Nomenclature (ICBN) and as cultivar-groups under the International Code of Nomenclature of Cultivated Plants (ICNCP); both classifications are still widely used. This study examines morphological support for the classification of landrace populations of cultivated potatoes, using representatives of all seven species and most subspecies as outlined in the latest taxonomic treatment. These taxa are S. ajanhuiri, S. chaucha, S. curtilobum, S. juzepczukii, S. phureja subsp. phureja, S. stenotomum subsp. stenotomum, S. stenotomum subsp. goniocalyx, S. tuberosum subsp. andigenum, and S. tuberosum subsp. tuberosum. The results show some phenetic support for S. ajanhuiri, S. chaucha, S. curtilobum, S. juzepczukii, and S. tuberosum subsp. tuberosum, but little support for the other taxa. Most morphological support is by using a suite of characters, all of which are shared with other taxa (polythetic support). These results, combined with their likely hybrid origins, multiple origins, evolutionary dynamics of continuing hybridization, and our classification philosophy, leads us to recognize all landrace populations of cultivated potatoes as a single species, S. tuberosum, with the eight cultivar-groups: Ajanhuiri Group, Andigenum Group, Chaucha Group, Chilotanum Group, Curtilobum Group, Juzepczukii Group, Phureja Group, and Stenotomum Group. We defer classification of modern cultivars, traditionally classified in Tuberosum Group, to a later study.

Conceptualizing integrative, farmer participatory research for sustainable agriculture: from opportunities to impact

Abstract: This paper offers a conceptualmodel for participatory research projects thataim to improve the sustainability ofagriculture and natural resource management.The purpose of the model is to provide asystematic framework that can guide the designof participatory research projects, theiranalysis, and the documentation of results. Inthe model, conceptual boundaries are drawnbetween research and development, developmentand extension and between extension andimplementation. Objectives, activities, andactors associated with each of these realmsneed to be carefully selected, monitored, andevaluated throughout the course of a projectusing well-designed indicators. The depth ofdisciplinary and methodological integration,and quality of participation needed to reachthe desired impact effectively and efficiently,however, needs to be determined on acase-by-case basis depending on the context andissues surrounding each particular project.

Plant defense genes associated with quantitative resistance to potato late blight in Solanum phureja x dihaploid S. tuberosum hybrids.

Abstract: Markers corresponding to 27 plant defense genes were tested for linkage disequilibrium with quantitative resistance to late blight in a diploid potato population that had been used for mapping quantitative trait loci (QTLs) for late blight resistance. Markers were detected by using (i) hybridization probes for plant defense genes, (ii) primer pairs amplifying conserved domains of resistance (R) genes, (iii) primers for defense genes and genes encoding transcriptional regulatory factors, and (iv) primers allowing amplification of sequences flanking plant defense genes by the ligation-mediated polymerase chain reaction. Markers were initially screened by using the most resistant and susceptible individuals of the population, and those markers showing different allele frequencies between the two groups were mapped. Among the 308 segregating bands detected, 24 loci (8%) corresponding to six defense gene families were associated with resistance at chi2 > or = 13, the threshold established using the permutation test at P = 0.05. Loci corresponding to genes related to the phenylpropanoid pathway (phenylalanine ammonium lyase [PAL], chalcone isomerase [CHI], and chalcone synthase [CHS]), loci related to WRKY regulatory genes, and other -defense genes (osmotin and a Phytophthora infestans-induced cytochrome P450) were significantly associated with quantitative disease resistance. A subset of markers was tested on the mapping population of 94 individuals. Ten defense-related markers were clustered at a QTL on chromosome III, and three defense-related markers were located at a broad QTL on chromosome XII. The association of candidate genes with QTLs is a step toward understanding the molecular basis of quantitative resistance to an important plant disease.

Optimal sampling strategy and core collection size of Andean tetraploid potato based on isozyme data - a simulation study.

Abstract: Selection of an appropriate sampling strategy is an important prerequisite to establish core collections of appropriate size in order to adequately represent the genetic spectrum and maximally capture the genetic diversity in available crop collections. We developed a simulation approach to identify an optimal sampling strategy and core-collection size, using isozyme data from a CIP germplasm collection on an Andean tetraploid potato. Five sampling strategies, constant (C), proportional (P), logarithmic (L), square-root (S) and random (R), were tested on isozyme data from 9,396 Andean tetraploid potato accessions characterized for nine isozyme loci having a total of 38 alleles. The 9,396 accessions, though comprising 2,379 morphologically distinct accessions, were found to represent 1,910 genetically distinct groups of accessions for the nine isozyme loci using a sort-and-duplicate-search algorithm. From each group, one accession was randomly selected to form a genetically refined entire collection (GREC) of size 1,910. The GREC was used to test the five sampling strategies. To assess the behavior of the results in repeated sampling, k = 1,500 and 5,000 independent random samples (without replacement) of admissible sizes n = 50(50)1,000 for each strategy were drawn from GREC. Allele frequencies (AF) for the 38 alleles and locus heterozygosity (LH) for the nine loci were estimated for each sample. The goodness of fit of samples AF and LH with those from GREC was tested using the χ2 test. A core collection of size n = 600, selected using either the P or the R sampling strategy, was found adequately to represent the GREC for both AF and LH. As similar results were obtained at k = 1,500 and 5,000, it seems adequate to draw 1,500 independent random samples of different sizes to test the behavior of different sampling strategies in order to identify an appropriate sampling approach, as well as to determine an optimal core collection size.

Pesticides and health in highland Ecuadorian potato production: assessing impacts and developing responses.

Abstract: Pesticide use in highland Ecuador is concentrated in the high-risk, commercial production of potatoes. Small farm families experience considerable exposure and adverse health consequences. The authors describe a three-pronged strategy to reduce health impacts: 1) a community-based process of education and provision of personal protective equipment to reduce exposure; 2) farmer field schools to increase agro-ecosystem understanding and to reduce pesticide use; and 3) policy interventions to restructure incentives and to reduce availability of highly toxic insecticides. They discuss the challenges faced by each and the ongoing need for integrated interventions both to reduce adverse pesticide health impacts in the developing world and to promote sustainability of agricultural production in highland ecosystems.

Occurrence and Cytological Mechanism of 2n Pollen Formation in a Tetraploid Accession of Ipomoea batatas (Sweet Potato)

Abstract: We evaluated a 4x accession of Ipomoea batatas (L.) Lam. and four 2x accessions of Ipomoea triloba for 2n pollen production. Approximately 90% of the genotypes of accession 81.2 (I. batatas, 4x) produced 2n pollen with different frequencies. In contrast, none of the genotypes of I. triloba produced 2n pollen. The diameter of the 2n pollen was approximately 30% ((3) sqrt 2) larger than that of the n pollen, making it easy to identify, measure, and quantify. The correlation (r = 0.93**) between the frequency of giant pollen and the frequency of dyads and triads was highly significant, strongly suggesting that the giant pollen grains were 2n pollen. The 2n pollen producers presented either a parallel or tripolar spindle arrangement (Y shaped) at anaphase II instead of the normal 60 degrees crossed spindle orientation. These two abnormal spindle configurations produced dyads and triads, with different frequencies (13-67%), instead of tetrads. Occasionally a metaphase II spindle variation was found with a single fused spindle, which also forms a dyad. The correlation (r = 0.89**) between the frequency of 2n pollen and the frequency of parallel, fused, and tripolar spindle arrangements was also highly significant, suggesting that these abnormal spindle configurations are involved in the production of 2n pollen in I. batatas. When we evaluated the efficiency of 2n pollen in polyploidization using 4x x 4x (2n) crosses, all progenies were 4x, suggesting the existence of barriers to crossability between 4x genotypes and their 2n pollen-producer counterparts.

Potential of sexual reproduction among host‐adapted populations of Phytophthora infestans sensu lato in Ecuador

Abstract: To determine the potential of sexual reproduction among host-adapted populations of Phytophthora infestans sensu lato in Ecuador, 13 A1 isolates belonging to clonal lineages US-1, EC-1 and EC-3, and 11 A2 isolates belonging to the clonal lineage EC-2, were paired on agar plates to induce crossing. In the first experiment, six A1 isolates (three US-1, two EC1 and one EC-3) were each crossed with three A2 isolates (total = 18 crosses). Matings involving isolates of the EC-1 lineage produced more oospores of healthy appearance than did matings with isolates of US-1 or EC-3. In the second experiment, the oospores of 35 crosses (21 EC-1 × EC-2; 10 US-1 × EC-2; four EC-3 × EC-2) were dispersed on water agar to assess oospore germination. Overall, germination percentages were low. Only one cross produced enough progeny for evaluation. Twenty-three single-oospore offspring were isolated and evaluated for mating type; electrophoretic patterns of glucose-6-phosphate isomerase ( Gpi ) and peptidase ( Pep ) alloenzyme loci; mitochondrial DNA haplotype; and genomic DNA fingerprint. Multilocus genotype data indicated that all 23 isolates resulted from meiotic recombination. Four progeny with homothallic phenotype appeared to be unstable heterokaryons. Markers at several loci segregated according to simple Mendelian expectations for a diploid organism, but the ratios of three RFLP loci and the Pep locus were not consistent with Mendelian expectations. All progeny were nonpathogenic on hosts of the parental genotypes. Reduced mating success and reduced pathogenic fitness of progeny appear to be postmating mechanisms of reproductive isolation in populations of P. infestans sensu lato in Ecuador.

Protocol for DNA extraction from potato tubers

Abstract: A method to extract high-quality DNA from potato tubers was developed and tested on 3 wild potato species (Solanum raphanifolium, S. megistracrolobum, S. bukasovii) and on the tetraploid B3 bred population, (population number 393228, derived fromS. tuberosum subsp.tuberosum). The average yield of extracted DNA varied from 10–30 μg of DNA per gram of processed tissue. The DNA was pure and suitable for ligation-mediated polymerase chain reaction (LM-PCR) amplification, producing clear, distinctive, and reproducible banding patterns in polyacrylamide gels.

Variabilidade morfológica da coleção de germoplasma de batata-doce da Embrapa-Centro Nacional de Pesquisa de Hortaliças

Abstract: The sweetpotato germplasm collection conserved by Embrapa-Centro Nacional de Pesquisa de Hortalicas was gathered by means of recollection expeditions and the duplication of the collection formerly maintained by Embrapa-Centro Nacional de Pesquisa de Mandioca e Fruticultura. The purpose of this paper was to describe and to analyze the morphological variability maintained in that collection. Three-hundred and twenty-four native accessions were evaluated, using 25 morphological characteristics. It was possible to identify 256 morphological types; 223 accessions presenting unique morphology and 33 groups of morphologically identical accessions. About 20% of the collection were made of duplications. Based on the assessment of the phenotypic diversity maintained in this collection for each descriptor used, it was considered that the collection presents a high level of polymorphism. The results were discussed in relation to their use on the organization of the germplasm collection, on the planning of the in vitro collection, of seed production fields and of the molecular characterization activities and on the management of this genetic resource at national level.

Effect of Integrating Planting Time, Fungicide Application and Host Resistance on Potato Late Blight Development in South‐western Uganda

Abstract: The presence of inocula all year round poses a daunting challenge to the management of late blight [causal agent Phytophthora infestans (Mont.) De Bary] of Solanum potato in the highlands of eastern Africa. Commercial production depends heavily on use of fungicides and, to some extent, host resistance. In this study, integration of host resistance and fungicide application reduced late blight severity by more than 50% and resulted in yield gains of more than 30% when compared with the untreated control. The study demonstrated that susceptible varieties can be successfully grown in the region if well-timed fungicide sprays are administered. Under high late blight pressure, fungicide application was necessary but integration of resistant cultivars in late blight management assisted in reducing the amount and frequency of fungicide applications. However, integration of timely planting (early planting) is difficult due to limitations in weather monitoring and the subsistence nature of the farming system in the eastern African highlands.

Poverty And The Deterioration Of Natural Soil Capital In The Peruvian Altiplano

Abstract: The most severe challenges to sustainable development occur where many poor people struggle to eke out a living from marginal lands. In some cases, high human populations on fragile lands have led agricultural productivity to deteriorate (Garcia-Barrios and Garcia-Barrios, 1990, Mink, 1993, Zimmerer, 1993), but likewise intensification in some locales has led to sustainable productivity increases (Boserup, 1965, Tiffen, et al., 1994). These mixed results beg closer inquiry, in order to understand how contrary outcomes can come about. For the context of Peru's chilly high plain surrounding Lake Titicaca, this paper examines changes in the stock of natural capital in agricultural soils, how that came about, and what policy tools might contribute to sustaining this key natural capital stock and the agricultural productivity that it enables.

Hierarchical and factorial mating designs for quantitative genetic analysis in tetrasomic potato.

Abstract: Plant breeders need to quantify additive and non-additive components of genetic variance in order to determine appropriate selection methods to improve quantitative characteristics. Hierarchical and factorial mating designs (also known as North Carolina mating designs I and II, respectively) allow one to determine these variance components. The relative advantages of these two designs in the quantitative genetics of tuber yield in tetrasomic potato were investigated. Likewise, the number of female parents to include in design I was also investigated. Data were collected from two independent experiments at two contrasting Peruvian locations: La Molina in the dry coast and San Ramon in the humid mid-altitude. In the first experiment, although design I gave a negative digenic variance (sigma(2)(D)), this design provided almost the same estimate of narrow-sense heritability (h(2)) for tuber yield as that obtained in design II (0.291 and 0.260, respectively). Therefore, design I appears to be appropriate for quantitative genetics research in tetrasomic potato, a crop in which some clones are male sterile. The easy handling of crosses (distinct random females included in the crossing scheme) is another advantage of design I relative to design II. In the second experiment, 12 males were crossed with either two or four females following a design-I mating scheme. The additive genetic variance (sigma(2)(A)) was zero (or negative) when two females per male were included but was positive with four females. These results suggest that two females per male may not be enough for design I in tetrasomic potato. Four females per male are preferable to determine sigma(2)(A) in design I for this tetrasomic crop.

Inbreeding and true seed in tetrasomic potato. III. Early selection for seedling vigor in open-pollinated populations

Abstract: Tuber yield in open-pollinated (OP) offspring of potato cultivars appears to be correlated with the proportion of hybrids within each population. OP true potato seed (TPS) from ten selected clones was tested in an experiment at two Peruvian locations, San Ramon (mid-altitude warm tropics) and Huancayo (highland cool tropics), to investigate the early selection effect on OP populations. Another experiment in La Molina (dry coast) was included to confirm the results from these other two locations. The results clearly showed that plant survival, tuber yield and berry number can be increased by a strong early selection. Likewise, the results suggested that the most-promising OP offspring for TPS production could be derived from tetraploid clones with a high rate of outcrossing. This experiment demonstrates that high tuber yield may be obtained in OP TPS cultivars with little effort, using early selection for seedling vigor in the nursery. Genetic interpretation of this response to early selection indicates that both the intensity of selection and non-additive genetic variation for tuber yield account for these observed gains.

Inbreeding and true seed in tetrasomic potato. IV. Synthetic cultivars.

Abstract: A true potato seed (TPS) synthetic cultivar from open pollination may broaden the genetic base in potato. A synthetic cultivar can also reduce the effect of inbreeding and maintain the productivity from generation to generation. Selected tetraploid parental genotypes, based on combining-ability tests, were chosen for isolated polycrosses to obtain tetraploid offspring. A series of experiments were undertaken to investigate the development of these TPS synthetic populations in two Peruvian locations: San Ramon, a rainfed, humid, mid-altitude environment, and La Molina, an arid, coastal environment under irrigation. Natural open-pollinated synthetics or control-mixture synthetics, involving two to six parents, had a similar tuber set but plant survival and tuber weight were higher in control synthetics including two or six parents. The results suggest that two-parent open-pollinated TPS synthetics may be a feasible option by selecting the right parents for the base population. A subsequent experiment showed that four-parent control synthetics (i.e. double crosses) were the best for tuber weight and size, followed by the two-parent control synthetics. Synthetic breeding populations could be shared with other breeders, who in cooperation with their local farmers may select promising genotypes for further cultivar release.

Identification and sequence analysis of Potato yellow vein virus capsid protein minor gene

Abstract: Potato yellow vein virus (PYVV) is a whitefly-transmitted (Trialeurodes vaporariorum) closterovirus (WTC) with an as yet unidentified genome composition. PYVV dsRNA preparations consist of three high molecular weight dsRNA species (dsRNAs 1, 2 and 3) 8.0, 5.5 and 4.0 kbp in size respectively, as well as two low molecular weight dsRNA species of 2.0 and 1.8 kbp (denoted x and y). The PYVV capsid protein minor (CPm) gene was identified on the dsRNA 3 species, and was subsequently cloned and sequenced. The PYVV CPm gene is 2022 nucleotides long and putatively encodes a protein with estimated size 77.5 kDa. The PYVV CPm gene product is considerably larger than the equivalent proteins encoded by the bipartite criniviruses, Lettuce infectious yellows virus (LIYV) and Cucurbit yellow stunting disorder virus (CYSDV) (52 and 53 kDa, respectively). The PYVV CPm possesses a centralized domain which is absent from both the LIYV and CYSDV CPm counterparts. Pairwise comparisons as well as phylogenetic analysis based on the available amino acid sequences of the CPm of various WTCs, showed that PYVV is closely related to LIYV, CYSDV and also Beet pseudo-yellows virus.

Quinoa (Chenopodium quinoa Willd.), a potential new crop for Pakistan

Abstract: Quinoa (Chenopodium quinoa Willd.) is one of the main food crops of the Andean mountains, where it has been a staple crop for thousands of years. It is characterized by an outstanding protein quality and a high content of a range of vitamins and minerals, and for that reason it has been selected by FAO as one of the crops destined to offer food security in this century. The genetic variability of quinoa is huge, with cultivars being adapted to growth from sea level to 4000 masl, from 40 °S to 2 °N, and from cold, highland climates to subtropical conditions, which makes it possible to select, adapt and breed cultivars for growth under Asian conditions. The nutritional characteristics, its modest requirements, its wide adaptability, and its multiple uses, explain the interest in the crop in South America and outside. Demand for quinoa is increasing, but the supply from the quinoa producing countries of South America is insufficient. Production and productivity of quinoa could be increased within the Andean region, and additionally by sowing in new sites outside the Andes, for instance some of those identified as suitable in the American and European Test of Quinoa, organized by FAO and the Quinoa Project CIPDANIDA, where Pakistan and other Asian countries are participating. Quinoa could be an important new crop for Pakistani agriculture, providing highly nutritive and versatile food products for the population, and a new raw material for the industry. In particular, it could be cultivated in many of the marginal environments afflicted by drought or salinity stress, which currently suffer from very low productivity.