Roland Pellé

Adaptation of Phytophthora infestans to Partial Resistance in Potato: Evidence from French and Moroccan Populations.

ABSTRACT The use of partially resistant cultivars should become an essential component of a sustainable management strategy of potato late blight, caused by Phytophthora infestans. It is therefore important to determine to what extent P. infestans populations can be selected for increased aggressiveness by potato cultivars with different levels of partial resistance. To this end, we sampled P. infestans populations from France and Morocco, chosen as locations where late blight occurs regularly but which differ in the distribution of potato cultivars. Cross-inoculation experiments were used to determine the aggressiveness of all populations to potato cvs. Bintje (prevalent in France but not grown in Morocco) and Désirée (popular in Morocco but cultivated to a very small extent in France). French populations were more aggressive on cv. Bintje than on cv. Désirée, irrespective of the site they were sampled from. Their aggressiveness increased between early and late samplings, suggesting that both cultivars selected for increased aggressiveness during epidemics. By contrast, Moroccan populations were more aggressive on Désirée, regarded as partially resistant in Europe, than on Bintje, highly susceptible under European conditions. These data indicate that P. infestans populations adapt to locally dominant cultivars, irrespective of their resistance levels, and can therefore overcome polygenic, partial resistance. This adaptive pattern may render partial resistance nondurable if not properly managed.

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

Glycoalkaloids are anti-nutritional compounds commonly found in wildSolanum 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 betweenSolanum tuberosum and accessions ofS. andigena, S. berthaultii, S. phureja, andS. vernei to investigate the possible correlation between resistance toPhytophthora infestans and/or toErwinia carotovora subsp.atroseptica and the concentration of glycoalkaloids in tubers. Concentrations of α-solanine and α-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 ofP. infestans used. Furthermore, clones within each progeny also differed for components of partial resistance toP. 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 α-solanine and two late blight resistance components (incubation period and spore production per unit lesion area) in progenies derived fromS. vernei, and despite a trend towards higher glycoalkaloid concentrations in the tubers of the clones most resistant to soft rot within progenies derived fromS. berthaultii andS. vernei, no consistent relationship between resistance to either disease and concentrations of α-solanine and/or α-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 behaviour againstP. infestans and/orE. carotovora.ResumenLos glicoalcaloides son compuestos antinutricionales que se encuentran presentes en las especies silvestres deSolanum usadas como fuentes de resistencia a los principales patógenos. Es por lo tanto importante con fines de mejoramiento, conocer si la selección hecha para obtener resistencia utilizando tales especies selecciona también necesariamente para contenidos altos de glicoalcaloides en los tubérculos. Para probar esta hipótesis, hemos utilizado seis progenies parciales provenientes de cruzamientos entreSolanum tuberosum y accesiones deS. andigena, S. berthaultii, S. phureja yS. vernei, con el objeto de investigar la existencia de una posible correlación entre la resistencia aPhytophthora infestans y/o aErwinia carotovora subsp.atroseptica y la concentración de glicoalcaloides en los tubérculos. Las concentraciones de α-solanina y α-chaconina en los tubérculos segregaron en cada progenie, asi como la resistencia a cada uno de los patógenos mencionados. Algunos, aunque no todos los clones en cada progenie mostraron reacciones de hipersensibilidad al aislamiento utilizado deP. infestans. Más aun, los clones dentro de cada progenie también mostraron diferencias en los componentes de la resistencia parcial aP. infestans, lo que sugiere que las cuatro especies de papa silvestre antes mencionadas pueden ser utilizadas como fuentes tanto para resistencia específica como para resistencia parcial aP. infestans. Con excepción de una reducida pero estadísticamente significativa correlación entre concentración de α-sblanina y dos componentes de resistencia al tizón tardío (periodo de incubación y producción de esporas por unidad de área de lesión) en progenies derivadas deS. vernei, y a pesar de una tendencia hacia altas concentraciones de glicoalcaloides en los tubérculos de los clones más resistentes a la pudrición blanda dentro de las progenies derivadas deS. berthaultii yS. vernei, no se ha observado una relación consistente en la resistencia a ambas enfermedades y la concentracios de α-solanina y/o α-chaconina. Estos resultados indican que ni la resistencia especifica, ni la resistencia parcial al tizón tardío y a la pudrición blanda en las accesiones utilizadas como progenitores de resistencia depende de la presencia de altas concentraciónes de solanina o de chaconina. Estas fuentes de resistencia pueden así ser de utilidad en los programas de mejoramiento para una mejor respuesta contraP. infestans y/oE. carotovora.

Major-effect QTLs for stem and foliage resistance to late blight in the wild potato relatives Solanum sparsipilum and S. spegazzinii are mapped to chromosome X

To find out new resistance sources to late blight in the wild germplasm for potato breeding, we examined the polygenic resistance of Solanum sparsipilum and S. spegazzinii by a quantitative trait locus (QTL) analysis. We performed stem and foliage tests under controlled conditions in two diploid mapping progenies. Four traits were selected for QTL detection. A total of 30 QTLs were mapped, with a large-effect QTL region on chromosome X detected in both potato relatives. The mapping of literature-derived markers highlighted colinearities with published late blight QTLs or R-genes. Results showed (a) the resistance potential of S. sparsipilum and S. spegazzinii for late blight control, and (b) the efficacy of the stem test as a complement to the foliage test to break down the complex late blight resistance into elementary components. The relationships of late blight resistance QTLs with R-genes and maturity QTLs are discussed.

Modeling of yield losses caused by potato late blight on eight cultivars with different levels of resistance to phytophthora infestans

The Shtienberg model for predicting yield loss caused by Phytophthora infestans in potato was developed and parameterized in the 1990s in North America. The predictive quality of this model was evaluated in France for a wide range of epidemics under different soil and weather conditions and on cultivars different than those used to estimate its parameters. A field experiment was carried out in 2006, 2007, 2008, and 2009 in Brittany, western France to assess late blight severity and yield losses. The dynamics of late blight were monitored on eight cultivars with varying types and levels of resistance. The model correctly predicted relative yield losses (efficiency = 0.80, root mean square error of prediction = 13.25%, and bias = -0.36%) as a function of weather and the observed disease dynamics for a wide range of late blight epidemics. In addition to the evaluation of the predictive quality of the model, this article provides a dataset that describes the development of various late blight epidemics on potato as a function of weather conditions, fungicide regimes, and cultivar susceptibility. Following this evaluation, the Shtienberg model can be used with confidence in research and development programs to better manage potato late blight in France.