Daniel Ellissèche

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 Quantitative Trait Loci Originating from Solanum sparsipilum Act Independently on the Sex Ratio of Globodera pallida and Together for Developing a Necrotic Reaction

Plant resistance to nematodes is related to the ability of the host to reduce the development of nematode juveniles into females. Resistance to the potato cyst nematode (PCN) Globodera pallida, originating from the wild species Solanum sparsipilum, was dissected by a quantitative trait loci (QTL) approach. Two QTL explained 89% of the phenotypic variation. The QTL GpaV(s)spl on chromosome V displayed the major effect on the cyst number (coefficient of determination [R2] = 76.6%). It restricted G. pallida development to 16.2% of juveniles, 81.5% of males, and 2.3% of females. The QTL GpaXI(s)spl on chromosome XI displayed a lower effect on the cyst number (R2 = 12.7%). It restricted G. pallida development to 13.8% of juveniles, 35.4% of males, and 50.8% of females. Clones carrying both QTL restricted the nematode development to 58.1% juveniles, 41.1% of males, and 0.8% of females. We demonstrated that potato clones carrying both QTL showed a strong necrotic reaction in roots infected by nematodes, while no such reaction was observed in clones carrying a single QTL. This result underlines the importance to introgress together GpaV(s)spl and GpaXI(s)spl into potato cultivars, in order to reduce the density of this quarantine pest in soil and to decrease the risk of selecting overcoming G. pallida subpopulations.

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.

Chromosome doubling of 2x Solanum species by oryzalin: method development and comparison with spontaneous chromosome doubling in vitro

A potato breeding scheme implies the possibility of ploidy level manipulation either by reducing the chromosome number of cultivars from 48 to 24 to be able to cross them with diploid related species or by doubling diploid material to reach the generally optimal tetraploid level. In vitro spontaneous chromosome doubling is widely used but can lead to somaclonal variation. Since oryzalin has proven to be efficient as a chromosome doubling agent on potato cell suspension cultures, we tried this herbicide on various Solanum species and interspecific diploid hybrids. A 24 h dip in a 28.8 μM aqueous oryzalin solution applied on apical buds was the most efficient treatment in terms of tetraploid plant production (mean = 4.1 tetraploid plants for 10 treated buds over 4 genotypes). However 50–100% of the regenerated tetraploid plants acclimatized after in vitro treatment proved to be chimaeric. Consequently, a selection procedure in the progeny was necessary to obtain real and stable doubled clones and final yields were low. This technique is easy to apply and could be a good alternative to chromosome doubling by spontaneous in vitro regeneration in the case of refractory genotypes especially where somaclonal variation is problematic. Percentage of tetraploids among the regenerated plants varied from 6 to 29% with the oryzalin doubling technique while it varied from 20 to 78% by in vitro spontaneous doubling for five diploid genotypes. An observation of the progeny indicated that chimaeras were more frequent using oryzalin (50–100% of the initially supposed tetraploid plants) than when chromosomes doubled spontaneously (4–67% of the initially supposed tetraploid plants).

Resistance Behaviour of Potato Cultivars and Advanced Breeding Clones to Tuber Soft Rot Caused by Pectobacterium atrosepticum

Genetic resistance is one of the best methods to control bacterial soft rot of potato tubers. However, an extensive description of resistance levels in currently registered cultivars is not available, as the literature contains only scattered reports. Using a half-tuber test, we therefore investigated the resistance to Pectobacterium atrosepticum of 93 potato cultivars registered on the French National List between 1935 and 1987, and 157 candidates for registration between 1987 and 1997. The relative ranking in a set of 11 control cultivars was stable over the 11 test years, with Ackersegen, Daresa and Bintje being the most susceptible and Kerpondy, Sirtéma and Kaptah Vandel being the most resistant. Both registered and candidate cultivars showed a wide distribution of mean rot volumes six days after inoculation, irrespective of cultivar type (ware, starch, or firm-flesh). Mean resistance was significantly higher in recently bred than in older cultivars.

Resistance to the root-knot nematode Meloidogyne fallax in Solanum sparsipilum: analysis of the mechanisms.

The genotype 88S.329.15 of Solanum sparsipilum was studied in order to analyse the genetic basis and the mechanisms of its resistance to Meloidogyne fallax . In infected plants grown at 20°C, juveniles invaded the root system with a clear delay and a lower infection rate in comparison to the susceptible S. tuberosum genotype BF15 H1. No defence reaction occurred during root invasion and migration toward the vascular cylinder. The juveniles induced development of feeding sites usually composed of several giant cells, which contained condensed cytoplasm, only small vacuoles, enlarged nuclei with pronounced nucleoli and almost no endoplasmic reticulum. Abundant necrosis of surrounding parenchymatous vascular cylinder cells lead to the degeneration of the giant cells. More than 90% of the invading juveniles failed to develop. The others developed as males. The resistance inheritance was analysed on 128 F1 hybrids obtained using the susceptible line BF15 H1 as the female parent and 88S.329.15 as the male parent. Among the progenies, 68 genotypes produced a necrotic reaction to nematode infection and 60 produced no necrosis. This 1 : 1 segregation pattern suggests a monogenic control of this defence reaction. Unlike the resistant parent 88S.329.15, some M. fallax females developed in the roots of necrotically responding hybrids. There was a normal distribution of mean numbers of adult females found in the roots of these genotypes. This result suggests that the ability of the resistant genotype 88S.329.15 to suppress development of females is quantitatively inherited and likely to be controlled by more than one locus. These data indicate that the mechanism of resistance is different from the resistance to Meloidogyne incognita conferred by the Mi gene of tomato.

Guidelines for evaluating disease resistance in potato cultivars. Foliage blight resistance (field test)Phytophthora infestans (Mont.) de Bary

Objective : To determine, by means of official tests, the resistance to foliage blight under field conditions of advanced clones and new potato cultivars which may be included on a National List or The Common Catalogue of Varieties of Agricultural Plant Species.

Conséquences du stress hydrique chez huit cultivars de Pomme de terre (Solanum tuberosum L.)

Abstract The objective is to identify, in the greenhouse conditions, genotypes of Potato, which are well adapted to climate of Sahel, characterised by almost permanent water deficit. Désirée and Sahel present the best yield in terms of the number of tubers obtained per plant, with 5.6 and 5.4 tubers/plant respectively. The best weight of tuber yield is obtained from Sahel (124.2 g/plant), Claustar (110.2 g/plant) and Aïda (104.4 g/plant). Claustar, Sahel and Atlas are the most resistant to water stress, with yield reduction estimated at 80, 68 and 62% respectively. Best results on the ratio plant growth/tuber yield are obtained with cv Claustar and Sahel in the conditions of water stress. The mean values of tuber yield parameters converge on the index rate of susceptibility to drought according to Acevedo (1991).