Showing papers by "International Potato Center published in 1998"

Cereal growth, development and yield

Abstract: The objective of the CERES crop simulation models is to predict the duration of growth, the average growth rates, and the amount of assimilate partitioned to the economic yield components of the plant. With such a simulation system, optimizing the use of resources and quantifying risk related to weather variation is possible. The cereal crops included in the DSSAT v3 models are maize, wheat, barley, sorghum, millet and rice. A feature of each model is its capability to include cultivar specific information that make possible prediction of the cultivar variations in plant ontogeny and yield component characteristics and their interactions with weather. Biomass growth is calculated using the radiation use efficiency approach; biomass produced is partitioned between leaves, stems, roots, ears and grains. The proportion partitioned to each growing organ is determined by the stage of development and general growing conditions. The partitioning principles are based on a sink source concept and are modified when deficiencies of water and nutrient supplies occur. Crop yields in the CERES models are determined as a product of the grain numbers per plant times the average kernel weight at physiological maturity. The grain numbers are calculated from the above ground biomass growth during a critical stage in the plant growth cycle for a fixed thermal time before anthesis. The grain weight in all the CERES models is calculated as a function of cultivar specific optimum growth rate multiplied by the duration of grain filling. Grain filling is reduced below the optimum value when there is an insufficient supply of assimilate from either the daily biomass production or from stored mobile biomass in the stem. The CERES models have been tested over a wide range of environments. Although there are improvements that can be made in the simulation procedures, results have shown that when the weather, cultivar and management information is reasonably quantified, the yield results are usually within acceptable limits of ±5% to 15% of measured yields.

Carotenoid contents in fresh, dried and processed sweetpotato products

Abstract: In order to understand the effects of drying and processing sweetpotato storage roots into traditional baked food products on their pro‐vitamin A contents, total carotenoids and s‐carotene were colorimetrically determined. Fresh and cooked storage roots, dried and stored chips, and sweetpotato processed products were used. Flesh colors of the storage roots were white, yellow, cream, orange, and purple. Total carotenoids ranged from trace to above 9 mg s‐carotene equiv./100 g of fresh storage root. Storage roots of high carotenoid content cultivars had consistently orange flesh; those with low to very low carotenoid contents were yellow or white. Hunter “b” values were high and consistent for flours from orange‐ and cream‐fleshed root cultivars, which could easily be used to predict total carotenoid and s‐carotene contents. Drying sweetpotato storage roots at 65°C for 12 h reduced total carotenoid contents by 30%. Storing dried chips in ambient conditions for 11 months induced a 10% loss. Incorporation of ...

A Global Marker Database for Phytophthora infestans.

Abstract: A marker database was compiled for isolates of the potato and tomato late blight pathogen, Phytophthora infestans, originating from 41 locations which include 31 countries plus 10 regions within Mexico. Presently, the database contains information on 1,776 isolates for one or more of the following markers: restriction fragment length polymorphism (RFLP) fingerprint consisting of 23 bands; mating type; dilocus allozyme genotype; mitochondrial DNA haplotype; sensitivity to the fungicide metalaxyl; and virulence. In the database, 305 entries have unique RFLP fingerprints and 258 entries have unique multilocus genotypes based on RFLP fingerprint, dilocus allozyme genotype, and mating type. A nomenclature is described for naming multilocus genotypes based on the International Organization for Standardization (ISO) two-letter country code and a unique number, Forty-two previously published multilocus genotypes are represented in the database with references to publications. As a result of compilation of the database, seven new genotypes were identified and named. Cluster analysis of genotypes from clonally propagated populations worldwide generally confirmed a previously published classification of old and new genotypes. Genotypes from geographically distant countries were frequently clustered, and several old and new genotypes were found in two or more distant countries. The cluster analysis also demonstrated that A2 genotypes from Argentina differed from all others. The database is available via the Internet, and thus can serve as a resource for Phytophthora workers worldwide.

The role of agriculture in economic development: visible and invisible surplus transfers

Abstract: The financial surplus of agriculture has been central to theories of the role of agriculture in economic development. Morrisson and Thorbecke (MT) have used a constant‐price social accounting matrix (SAM) framework to measure rigorously the financial surplus of agriculture and decompose the mechanisms of surplus extraction. History and theory have, however, stressed the role of prices as an invisible transfer mechanism in addition to the visible transfers identified in the SAM framework. We extend the MT approach by defining and measuring the real surplus of agriculture and decomposing the mechanisms of surplus extraction between visible and invisible financial transfers. Using an archetype computable general equilibrium model for poor African nations, we trace the generation, transfer, and use of an agricultural surplus created by a productivity gain in agriculture. This shows that prices indeed play an overwhelmingly important role in transferring a surplus from agriculture to the benefit of the rest of...

The incidence of sweet potato virus disease and virus resistance of sweet potato grown in Uganda

Abstract: Summary Sweet potato virus disease (SPVD) was common (25–30% average incidences), and farmers recognised it as an important disease, in sweet potato crops in southern Mpigi, Masaka and Rakai Districts in Uganda, but SPVD was rare in Soroti and Tororo Districts. Whiteflies, which are the vector of sweet potato chlorotic stunt crinivirus (SPCSV) a component cause of SPVD, were correspondingly common on sweet potato crops in Mpigi and rare on crops in Tororo. However, aphids, which are the vectors of sweet potato feathery mottle potyvirus (SPFMV), the other component cause of SPVD, were not found colonising sweet potato crops, and itinerant alate aphids may be the means of transmission. Different sweet potato cultivars were predominant in the different districts surveyed and four local cultivars obtained from Kanoni in S. Mpigi, where whiteflies and SPVD were common, were more resistant to SPVD than four cultivars from Busia in Tororo District, where whiteflies and SPVD were rare. However, nationally released cultivars were even more resistant than the local cultivars from Kanoni. Yield results and interviews with farmers indicated that farmers in S. Mpigi were making compromises in their choice of cultivars to grow, some key factors being SPVD susceptibility, and the yield, taste, and marketability, duration of harvest and in-ground storability of the storage roots. These compromises need to be included in an assessment of yield losses attributable to SPVD.

RAPD variation in sweetpotato (Ipomoea batatas (L.) Lam) cultivars from South America and Papua New Guinea

Abstract: The island of New Guinea is considered a secondary center on diversity for sweetpotato, because of its range of isolated ecological niches and large number of cultivars found within a small area. Information of genetic diversity in Papua New Guinea (PNG) sweetpotato is essential for rationalizing the global sweetpotato germplasm collection. Using random amplified polymorphic DNA (RAPD), we compared the genetic variation and genetic diversity in 18 PNG cultivars versus 18 cultivars from South America. The analysis of molecular variance revealed large genetic diversity in both groups of cultivars. The within-group (among individuals) variation accounted for 90.6% of the total molecular variance. However, the difference between PNG and South American groups is statistically significant, although it explained only 9.4% of the total molecular variance. The PNG cultivars are also less divergent than their South American ancestors as the mean genetic distance in PNG group is significantly smaller than that of South American group. The lower level of genetic diversity in PNG cultivars was also reflected by multidimensional scaling. This study shows that PNG cultivars, after many years of isolated evolution in an unique agro-ecological environment are substantially divergent from their ancestors in South America. The genetic diversity level in PNG cultivars is significantly lower than that in South American cultivars. It thus provides a baseline for continuing studies of genetic diversity in different sweetpotato gene pools.

QTL mapping of foliar glycoalkaloid aglycones in Solanum tuberosum×S. berthaultii potato progenies: quantitative variation and plant secondary metabolism

Abstract: Glycoalkaloids are quantitatively inherited in Solanum, and in high concentrations they can be toxic to humans. The increased use of wild potato germplasm to improve the pest resistance, yield, and quality characteristics of cultivated potato may elevate or introduce new, more toxic glycoalkaloids into the cultivated gene pool. Therefore, it is important to increase our understanding of their inheritance, accumulation, and biosynthesis. Glycoalkaloids have two basic constituents – a glycosidic grouping and a steroid alkaloid skeleton. Steroid alkaloids are classified as solanidanes and spirosolanes, of which solanidine and solasodine are, respectively, representatives. RFLP-mapped, diploid, reciprocal backcross potato progenies involving the parents S. tuberosum and S. berthaultii, which produce solanidine and solasodine, respectively, were analyzed for segregation of the glycoalkaloids solanine, chaconine, solasodine and solamargine to identify quantitative trait loci (QTLs) for the production of the aglycones solanidine and solasodine. The F1 clone M200-30 exhibited low to nondetectable levels of solasodine and solanidine, suggesting that expression was controlled by recessive genes. In a backcross to berthaultii (BCB) and backcross to tuberosum (BCT), several QTLs for the accumulation of solasodine and solanidine were identified. Three QTLs explaining approximately 20% of the variation in solasodine were identified in BCB on chromosomes 4, 6, and 12. Similarly, three QTLs were identified in BCT on chromosomes 4, 8 and 11, but these accounted for only 10% of the variation observed in solasodine accumulation. Two QTLs for solanidine were identified in BCT on chromosomes 1 and 4. The QTL located on chromosome 1 was highly significant, accounting for 17% and 22% of the variation in solanidine accumulation in 1994 and 1995, respectively. This same QTL was also detected in BCB. The QTLs detected in this study probably represent structural and/or regulatory genes controlling the accumulation of solasodine and solanidine. Results are discussed in the context of steroid alkaloid accumulation and biosynthesis.

Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid

Abstract: Fungicides applied to potato can enhance green peach aphid,Myzus persicae (Sulzer), outbreaks by interference with entomopathogenic fungi. (Order Entomophthorales). Late season aphid numbers were highest in potatoes sprayed with metalaxyl + mancozeb, captafol, or mancozeb, and lowest in potatoes sprayed with benomyl, triphenyltin hydroxide, chlorothalonil, or copper hydroxide. In field-collected aphids,Pandora (= Ernyia) neoaphidis (Remaudiere et Hennebert) andEntomophthora planchoniana Cornu (F. Entomophthtoraceae) were the predominant cause of mycoses, 66.7% and 22.3%, respectively.Conidiobolus obscurus (Hall and Dunn) Remaudiee and Keller (F. Ancylistaceae) accounted for 8.5% of mycoses. In the laboratory, fungicides were shown to have direct effects on these entomopathogens. Metalaxyl + mancozeb, mancozeb and captafol were strongly inhibitory of germination of conidia, copper hydroxide was intermediate, and chlorothalonil had little effect. Triphenyltin hydroxide, benomyl, metalaxyl + mancozeb, and mancozeb were strongly inhibitory of growth of mycelia, copper hydroxide was intermediate, and chlorothalonil and copper hydroxide had least effect. Benomyl was highly toxic to green peach aphid, copper hydroxide and chlorothalonil intermediate, and captafol, mancozeb, and metalaxyl + mancozeb least toxic. Possible interference of potato fungicides with aphid pathogens is now an important consideration because of the intensity of spraying required to protect the crop from infection by metalaxyl-resistant strains of the late blight pathogen,Phytophthora infestans (Mont.) de Bary. Minnesota potato growers reported high green peach pressure in both 1995 and 1996, years of intensive fungicide spraying. Concomitantly, there was a marked increased in the incidence of PLRV in seed lots entered for winter testing.

Oil content in fried processed sweetpotato products

Abstract: Ninety-four different sweetpotato cultivars with various dry matter contents were used to process crisps and the end product was analyzed to determine the oil content. A linear relationship between dry matter content in raw sweetpotato storage roots and the level of oil uptake in crisps was determined. Sweetpotato storage roots with 23-25% (fwb) dry matter content gave crisps containing between 21% and 32% of oil, while the fat contents of crisps from potatoes having a similar dry matter content were 36% and more. Consequently, storage roots from Kemb 10 sweetpotato cultivar having a high dry matter content of 32.9% (fwb), either in boiled and mashed, raw and grated, or flour form, were used to partially substitute wheat flour in processing fried products. It has been found that boiled and mashed sweetpotato lessens oil uptake in mixtures of fried products such as "mandazis" (doughnuts).

Inbreeding and true seed in tetrasomic potato. I. Selfing and open pollination in Andean landraces (Solanum tuberosum Gp. Andigena)

Abstract: True potato seed (TPS) may be an alternative method of potato production in developing countries. A breeding method for the sexual propagation of this vegetatively propagated crop should consider the development of parental lines and the type of cultivar to be released. Open-pollinated (OP) cultivars seem to be an inexpensive procedure to produce potato from true seed. However, OP progenies are the result of selfing and outcrossing in male-fertile tetraploid potatoes. The aim of the present research was to establish the effect of inbreeding and open pollination in TPS. Ten Andigena clones were used as parental material to derive hybrid (S0), inbred (S1 and S2), and open-pollinated (OP1 and OP2) generations. Significant differences among generations were found for pollen production, pollen viability (as determined by its stainability with aceto-carmine glycerol), number of flowers and berries plant-1, number of seeds berry-1, weight of 1000 seeds, and tuber yield plant-1. The parental populations were significantly different for most of the traits, but not for flower production and berry weight. The interaction of population ×generation was significant for pollen and seed production as well as for weight for 1000 seeds. All the traits evaluated except seed weight showed a strong inbreeding depression, while the OP progenies had intermediate values between the S0 and the S1. This demonstrates that open pollination in potatoes is not exclusively the product of selfing; it also results from outcrossing.

The simulation of cropping sequences using DSSAT

Abstract: The crop models that are distributed with DSSAT version 3 permit the simulation of long-term cropping sequences. This added capability enhances the value of crop growth models as a tool for analyzing the long-term consequences of management practices on a site-specific basis. The models can be used to predict changes and detect trends in biophysical indicators such as crop yield, nitrogen uptake, soil carbon levels, and nitrate leaching. In this way, management practices that are potentially sustainable or unsustainable can be identified. In the systems approach to research, simulation tools remain in constant need of critical evaluation and refinement. The models, which currently provide reasonable simulation of single-season processes, require a better understanding of long-term soil processes and how these processes are affected by management.

Inbreeding and true seed in tetrasomic potato. II. Selfing and sib-mating in heterogeneous hybrid populations of Solanum tuberosum

Abstract: Inbreeding depression may affect the performance of consecutive generations of potatoes propagated by true potato seed (TPS). The effect of inbreeding was established using selfed and sib-mated generations of five TPS families. Correlation coefficients were calculated between the level of inbreeding and different traits. Inbreeding depression was expressed mainly by pollen viability, as measured by its stainability (r=−0.912, P<0.01), and tuber yield (r=−0.837, 0.01

Germplasm conservation of oca (Oxalis tuberosa Mol.) through botanical seed. Seed formation under a system of polymorphic incompatibility

Abstract: Seven clonal accessions representing all three stylar morphs of tristylous oca were intercrossed and selfed in a complete diallelic crossing design The four traits total capsule production, total number of seeds/capsule, total number of seeds containing an embryo/capsule, and percent seeds containing an embryo of all seeds per capsule were recorded Both capsule and seed production were highest in the legitimate pollinations (in which styles are pollinated with pollen of the corresponding anther level), but also in illegitimate pollinations of mid-styled seed parents with long-level anther pollen of short-styled accessions All 18 types of pollination, consisting of 6 legitimate, 6 illegitimate intermorph, and 6 illegitimate intramorph pollinations, expressed gradually different levels of capsule and seed production Intramorph pollinations and selfs of mid-styled seed parents were less incompatible than intramorph pollinations and selfs of the long- and short-styled morphs All accessions studied expressed an intact system of heteromorphic stylar incompatibility despite their exclusive clonal propagation for millennia A maximum of 16,3 seeds/capsule containing an embryo was obtained in an individual legitimate cross of two accessions, although an average of 25 ovules are present in a flower of O tuberosa The results are discussed in relation to the establishment of a genebank based on botanical seed of this clonally propagated, valuable Andean tuber crop

Relationship between ineffective R-genes and expansion rate of lesions on potato leaves, caused by Phytophthora infestans

Abstract: Progenies from eight tetraploid potato crosses were assessed for the association between ineffective R-genes and lesion expansion rate (LER) in mm per day on detached leaves that had been inoculated with Phytophthora infestans. In two of the progenies, a significant association between ineffective R-genes and LER was measured, which could be an indication of residual effects. No association was found in the other progenies. These results and other corroborative evidence do not support an approach to plant breeding based on the stacking of R-genes to accumulate residual resistance effects. Using the same detached-leaf test, differences in aggressiveness between two isolates of P. infestans could be measured in all eight progenies. LER values were consistent with previously published ranges and were distributed continuously and unimodally in all progenies, suggesting that differences in relative aggressiveness of isolates were probably not affected by R-genes.

Ecogeography and breeding potential of the wild Peruvian tuber-bearing species ofSolanum

Abstract: About 225 wild tuber-bearing species of Solanum occur on the American continent. Seventy-five percent of these are distributed in South America, with the largest concentration (approximately 100 species) occurring in Peru. Located on the western side of South America, Peru has five main regions: the Pacific Ocean Territory, the Coast, the Sierra, the Ceja de Selva, and the Selva. Wild potatoes are found only along the Coast, the Sierra, and the Ceja de Selva. The Coast (Fig. 1), a vast desert territory 2500 km long and 150 km wide, varies in elevation from sea level to 1000 m. The central and southern part of this region is usually covered with low clouds from April or May until October or November. When these clouds touch the mountains to the east, they produce a very fine condensation or mist called garua. This mist gives rise to a special ephemeral plant formation called the loma, which is notably lacking in species diversity. Within this coastal fog zone, the precipitation is extremely low, ranging from 4 to 80 mm of rainfall per year. Temperatures range from 13 to 23?C, and the humidity varies from 65 to 95 percent. During the winter season, some tuber-bearing species of Solanum occur in the lomas formation, including S. immite, S. medians, S. mochiquense, S. chancayense, S. neoweberbaueri and S. wittmackii. Not only are these species remarkable for their drought tolerance, but some are also quite resistant to viruses, fungi and bacteria. Solanum immite, for example, the first tuber-bearing species described for Peru by Dunal in 1852, is resistant to the spindle tuber viroid (PSTVd) and to the fungal wilt caused by a Verticillium species. Solanum medians, a coastal mountain species, has perhaps the widest distribution in the loma formations of the Peruvian coast. It is found from the Lomas de Manchay (350 m asl.) near La Molina, Lima (12?05' S and 76056' W) all along the southern Peruvian coast to the Lomas de Ilo (400 m asl.) and the Lomas de Sama (550 m asl.) in the departments of Moquegua and Tacna (or approximately 17?48' S and 70030' W). At Manchay-La Molina, the average annual precipitation is only 18 mm, while at Sama Grande it is 40 mm. The monthly median temperature for both places is 24?C and the minimum is nearly 13.5?C. Solanum medians represents a valuable source of genes for potato breeding programs. It is resistant to the attack of several potato viruses, including potato virus X (PVX), leaf roll (PLRV), potato viruses S (PVS) and M (PVM) and the potato spindle tuber viroid (PSTVd). It is also resistant to the tuber canker fungus, Synchytrium endobioticum; to the potato ring rot disease caused by the bacterium, Corynebacterium; the cyst nematode Globodera rostochiensis; and the tuber moth, Phthorimaea operculella. The most northern loma formation along the Peruvian coast is found at Cerro Campana (400 m asl.) in the vicinity of Trujillo (08005' S and 79?06' W). Here, thrives Solanum mochiquense, a species resistant to the potato black leg bacterium, Erwinia carotovora; the fungal organism, Synchytrium endobioticum; potato viruses PVS, and PVM; and, the nematode Meloidogyne. The Sierra divides the Coast from the Selva

The Role of Agriculture in Economic Development: Visible and Invisible Surplus Transfers

Abstract: The financial surplus of agriculture has been central to theories of the role of agriculture in economic development. Morrisson and Thorbecke (MT) have used a constant‐price social accounting matrix (SAM) framework to measure rigorously the financial surplus of agriculture and decompose the mechanisms of surplus extraction. History and theory have, however, stressed the role of prices as an invisible transfer mechanism in addition to the visible transfers identified in the SAM framework. We extend the MT approach by defining and measuring the real surplus of agriculture and decomposing the mechanisms of surplus extraction between visible and invisible financial transfers. Using an archetype computable general equilibrium model for poor African nations, we trace the generation, transfer, and use of an agricultural surplus created by a productivity gain in agriculture. This shows that prices indeed play an overwhelmingly important role in transferring a surplus from agriculture to the benefit of the rest of...