Socioeconomic impact of two potato varieties (Cipira and Tubira) released in Cameroon

Deffo V, Njualem D and Demo P. 2003. American Journal of Potato Research 80:151–158.

In 1988, the IRA-CIP potato project was created in Bambui, Cameroon, with the major objective of improving potato production in the country. In 1992, two potato cultivars, Cipira and Tubira, were released by the project. In 1998, a socioeconomic impact study of Cipira and Tubira was carried out in the main potato-producing region of Cameroon to determine the reaction of the farmers, the effect of the new potato cultivars on the farmers’ standard of living, and the level of achievement of the project’s objectives.

Data were collected on-farm using questionnaires and direct observations. An impact survey was carried out in the region with a sample of 297 farmers selected among the potato farmers using stratified random sampling. The survey indicated that 98.6% of the potato farmers were aware of the new cultivars. Their main source of information was other farmers (51.5% of farmers informed). Seventy-eight percent of the farmers were still using Cipira and 62% had adopted it as part of their production system. These farmers (62.6%) reported that the resistance of Cipira to late blight was higher than that of local and European cultivars used in their production system. More than 44% of the farmers believed that their standard of living had improved due to Cipira and Tubira, since they had generated more revenue to improve their family education and nutrition, build more houses, buy more farms, purchase more farm inputs, and open new businesses. In addition, the farmers’ average yearly potato production increased from 1.6 to 3.1 tons during the period when these varieties were being adopted.

Corresponding author: V. Deffo

Email: vdeffo(at)yahoo.fr

Leaf position prevails over plant age and leaf age in reflecting resistance to late blight in potato

Visker M H P W, Keizer L C P, Budding D J, Van Loon L C, Colon L T and Struik P. C. 2003. Phytophthology 93:666–674.

The effects of plant age, leaf age, and leaf position on race-nonspecific resistance against Phytophthora infestans were investigated in a series of field and controlled environment experiments with five different potato (Solanum tuberosum) cultivars. Leaf position proved to be the most significant factor; apical leaves were far more resistant to late blight than basal leaves. Plant age and leaf age had only minor effects; therefore, the resistance of a specific leaf remained about the same during its entire lifetime. The gradual increase in late blight resistance from basal leaves to apical leaves appeared to be a general effect, irrespective of cultivar, growing conditions, or resistance test. Therefore, it is important to consider leaf position in tests for late blight resistance, because contrasts in resistance may be ascribed erroneously to differences between genotypes or treatments, whereas they are actually caused by differences in leaf position.

Corresponding author: M H P W Visker

Email: marleen.visker(at)wur.nl

Resistance to late blight and soft rot in six potato progenies and glycoalkaloid contents in the tubers

Andrivon D, Corbiere R, Lucas J M, Pasco C, Gravoueille J M, Pelle R, Dantec J P and Ellisseche D. 2003. American Journal of Potato Research 80:125–134.

Glycoalkaloids are anti-nutritional compounds commonly found in wild Solanum species used as resistance sources to major potato pathogens. It is therefore important for breeding purposes to know whether selecting for resistance using such species necessarily selects also for high glycoalkaloid contents in the tubers. To test this hypothesis, we used six partial progenies from crosses between Solanum tuberosum and accessions of S. andigena, S. berthaultii, S. phureja, and S. vernei to investigate the possible correlation between resistance to Phytophthora infestans and/or to Erwinia carotovora subsp. atroseptica and the concentration of glycoalkaloids in tubers. Concentrations of -solanine and -chaconine in the tubers segregated in each progeny, as did resistance to each pathogen. Some, but not all, clones from each progeny showed hypersensitive reactions to the isolate of P. infestans used. Furthermore, clones within each progeny also differed for components of partial resistance to P. infestans, suggesting that all four wild species could be used as sources of both race-specific and partial resistance to late blight. With the exception of low, but statistically significant, correlations between concentration of solanine and two late blight resistance components (incubation period and spore production per unit lesion area) in progenies derived from S. vernei, and despite a trend towards higher glycoalkaloid concentrations in the tubers of the clones most resistant to soft rot within progenies derived from S. berthaultii and S. vernei, no consistent relationship between resistance to either disease and concentrations of solanine and/or -chaconine was observed. These results indicate that neither race-specific nor partial resistance to late blight and soft rot in the accessions used as progenitors of resistance depend on high solanine or chaconine concentrations. These resistance sources could thus prove useful in breeding programs for improved behavior against P. infestans and/or E. carotovora.

Corresponding author: D. Andrivon

Email: andrivon(at)rennes.inra.fr

Identification of late blight, colorado potato beetle, and blackleg resistance in three Mexican and two South American wild 2x (1EBN) Solanum species

Chen Q, Kawchuk L M, Lynch DR, Goettel MS and Fujimoto D K. 2003. American ournal of Potato Research 80:9–19.

Wild potatoes are important sources of genes for resistance to disease and insect pests. A collection of wild Mexican and South American Solanum species from the US potato Genebank was evaluated under laboratory and/or field conditions for their reaction to late blight (Phytophthora infestans), Colorado potato beetle (CPB, Leptinotarsa decemlineata Say), and blackleg (Erwinia carotovora subsp. atroseptica (van Hall) Dye) in order to identify individual genotypes with multiple resistance genes. Late blight inoculations using aggressive isolates (US-8/A2 and US-11/Al mating types) of P. infestans revealed a wide range of variation for resistance between and within the accessions of the wild species tested. For late blight, susceptible as well as moderately to highly resistant genotypes were observed in all the species tested. However, at least one accession from the three Mexican and one South American wild diploid species tested showed a relatively uniform high level of resistance to P. infestans. These included S. bulbocastanum, S. pinnatisectum, S. cardiophyllum, and S. circaeifolium. Two accessions from South American species S. commersonii were highly susceptible to late blight. For the Colorado potato beetle test, only one species, S. pinnatisectum appeared uniformly resistant to CPB under field conditions. Results of screening for blackleg resistance showed that there were major differences between genotypes in the wild species. Accessions of S. circaefolium P1498119 and S. bulbocastanum P1 243504 were identified as having significantly higher blackleg resistance than cultivated potato and the other wild species tested. However, genotypes from these two accessions were more susceptible to late blight and CPB. Characterization of the P. infestans isolate P18O1C.16 used for late blight evaluation and multilocus isolate tests using US-8/A2 and US-11/Al races revealed that the resistance in S. pinnatisectum genotypes tested corresponded to a race-non-specific genetic system, which was different from any existing R genes. Solanum pinnatisectum genotypes with both high levels of late blight and CPB resistance as well as blackleg resistance genotypes identified in the present study represent a diverse gene pool that may be useful for development of new potato cultivars with multiple disease and insect resistance. The potential utilization of these valuable sources for improvement of cultivated potato is discussed.

Corresponding author: Q Chen

Email: chenqi(at)agr.gc.ca

Expression of a fungal glucose oxidase gene in three potato cultivars with different susceptibility to late blight (Phytophthora infestans Mont. de Bary)

Felcher K J, Douches D S, Kirk W W, Hammerschmidt R and Li W. 2003. Journal of the American Society for Horticultural Science 128:238–245.

Research was done to determine if enhanced resistance to potato (Solanum tuberosum L.) late blight could be obtained by combining host plant resistance and engineered resistance. Late blight susceptible cultivars, Atlantic, and Spunta and the partially resistant cultivar Libertas were transformed with a fungal glucose oxidase gene, resulting in lines, which ranged in transgene copy number from 1 to 8. Glucose oxidase enzyme activity ranged from 0.00 to 96.74 × 10 units/mg plant tissue. There was no correlation between copy number and level of transgene mRNA, level of transgene mRNA and enzyme activity, or between level of enzyme activity and disease resistance. Field and growth chamber evaluation of late blight response demonstrated little to no effect of the glucose oxidase transgene in either late blight susceptible or partially late blight resistant cultivars. However, enzyme activity levels were much lower than levels reported in previous research, which may account for the lack of effect of glucose oxidase against Phytophthora infestans. Twenty-one percent of the transgenic lines were phenotypically off-type compared to nontransgenic controls. Most of the off-type transgenic lines (four out of seven) were derived from ‘Libertas’. Because several off-type lines did not express the glucose oxidase protein, this phenomenon could not be attributed solely to the glucose oxidase transgene. Based on these results, transgenic lines produced for this study do not increase resistance to P. infestans even in combination with moderate host plant resistance. However, production of greater numbers of transgenic lines with the current construct or, production of transgenic lines in which a different constitutive promoter drives the expression of the glucose oxidase gene might result in greater disease resistance. However, the usefulness of any small increase in resistance would need to be evaluated against the time and cost required for development of transgenic potato cultivars and the potential for off-type tubers and plants.

Corresponding author: D Douches

Email: douchesd(at)msu.edu

Thermal properties of overwintered piles of cull potatoes

Kirk W W. 2003. American Journal of Potato Research 80:145–149.

Annual epidemics of late blight of potato have lead to debate as to the relative importance of overwintering sources of inoculum. Host availability is a key factor for overwinter survival of Phytophthora infestans and the initiation of epidemics of potato late blight. Temperature within discarded piles of cull potatoes may influence tuber tissue temperature and therefore affect survival of meristematic tissue. Consequently the risk of initiation of an epidemic of late blight from cull piles is closely related to the thermal experience of overwintered potato culls. Temperature monitoring of cull piles over two years indicated that temperature was stable in the interior of the piles regardless of cull pile size (1-15 ton) or year. The possible use of ambient temperature information gathered during winter months in potato-growing regions may not help estimate the risk (If an epidemic of late blight initiated from cull piles as, although highly correlated with the surface temperature of cull piles, ambient temperature was not correlated with the temperature within the cull piles. The presence of cull piles in excess of 1 ton may enhance the survival of the host and thus the development of P. infestans from infected tubers.

Corresponding author: W W Kirk

Email: kirkw(at)msu.edu

Relative performance of five forecasting schemes for potato late blight (Phytophthora infestans). I: Accuracy of infection warnings and reduction of unnecessary, theoretical, fungicide applications

Taylor M C, Hardwick N V, Bradshaw N J and Hall A M. 2003. Crop Protection 22:275–283. © Elsevier Science Ltd 2002.

The Smith Period, Negative Prognosis, Blitecast, Sparks and NegFry forecasting schemes for potato late blight were evaluated over a 6-year period at five locations representing a range of blight risk situations. Frequent measurements were made by in-field meteorological stations and untreated, blight susceptible, potatoes in small plots were regularly assessed for symptoms of the disease. Although the Smith Period was the most reliable scheme (warnings rarely in error) it often gave too long an advanced warning of an eventual disease outbreak; NegFry was the most accurate scheme assuming an ideal warning of 10 days was required by growers.

Corresponding author: M. C. Taylor

Email: moray.taylor(at)csl.gov.uk

These abstracts were reprinted with the kind permission of the Potato Association of America (www.ume.maine.edu/PAA), the American Phytopathological Society (www.apsnet.org), the American Society for Horticultural Science (www.ashs.org) and Elsevier Science (http://www.elsevier.com).