Broad spectrum late blight resistance in potato differential set plants MaR8 and MaR9 is conferred by multiple stacked R genes

Abstract

Phytophthora infestans is the causal agent of late blight in potato. The Mexican species Solanum demissum is well known as a good resistance source. Among the 11 R gene differentials, which were introgressed from S. demissum, especially R8 and R9 differentials showed broad spectrum resistance both under laboratory and under field conditions. In order to gather more information about the resistance of the R8 and R9 differentials, F1 and BC1 populations were made by crossing Mastenbroek (Ma) R8 and R9 clones to susceptible plants. Parents and offspring plants were examined for their pathogen recognition specificities using agroinfiltration with known Avr genes, detached leaf assays (DLA) with selected isolates, and gene-specific markers. An important observation was the discrepancy between DLA and field trial results for Pi isolate IPO-C in all F1 and BC1 populations, so therefore also field trial results were included in our characterization. It was shown that in MaR8 and MaR9, respectively, at least four (R3a, R3b, R4, and R8) and seven (R1, Rpi-abpt1, R3a, R3b, R4, R8, R9) R genes were present. Analysis of MaR8 and MaR9 offspring plants, that contained different combinations of multiple resistance genes, showed that R gene stacking contributed to the Pi recognition spectrum. Also, using a Pi virulence monitoring system in the field, it was shown that stacking of multiple R genes strongly delayed the onset of late blight symptoms. The contribution of R8 to this delay was remarkable since a plant that contained only the R8 resistance gene still conferred a delay similar to plants with multiple resistance genes, like, e.g., cv Sarpo Mira. Using this “de-stacking” approach, many R gene combinations can be made and tested in order to select broad spectrum R gene stacks that potentially provide enhanced durability for future application in new late blight resistant varieties.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-011-1757-7) contains supplementary material, which is available to authorized users.

DNA Markers for Selection of Late Blight Resistant Potato Breeding Lines

“…The presence of major resistance (R) genes has been shown to increase resistance to foliar late blight infection in many potato cultivars [6] [26]. To assess this relationship in the breeding progeny analyzed in this study, the levels of resistance to tuber rot were also evaluated.…”

“…Since these clones showed various levels of susceptibility to late blight in both leaves and in tubers, we can assume that the presence of both genes is required for a clone to possess high levels of resistance to late blight. The need for multiple potato R genes to achieve strong resistance against several strains of P. infestans was suggested or demonstrated in several other studies [6] [26] [27] [28].…”

“…Also, while some studies suggested that some R genes in potato have the ability to confer both foliar and tuber resistance [32] [33] [34] [35], other studies suggested the opposite [36] [37]. Clearly, as mentioned before, multiple R genes are essential for strong and durable resistance against late blight and this can be achieved only by obtaining, through classic breeding or by transgenic approaches, potato cultivars that harbor three or more such R genes [6] [26] [27] [28].…”

Agroinfiltration and PVX Agroinfection in Potato and <em>Nicotiana benthamiana</em>

“…A mixture of the Agrobacterium strain AGL1(pVirG) 23 containing pBINplus-R3a and pK7WG2-AVR3a was used as positive control 24,25 , while AGL1(pVirG) was used as negative control. Figures 1A and 1B show good examples of agroinfiltration in the potato genotype MaR8 (Mastenbroek R8) 26 and N. benthamiana, respectively, which are very amenable for agroinfiltration. There is confluent cell death in the leaf panel coinfiltrated with positive control, while no cell death response occurs with negative control or pBINplus-R3a.…”

ANTICIPATORY BREEDING: MOLECULAR MARKERS AS A TOOL IN DEVELOPING DONORS OF POTATO (Solanum tuberosum L.) LATE BLIGHT RESISTANCE FROM COMPLEX INTERSPECIFIC HYBRIDS

“…These differential races only identify 11 R genes of S. demissum (not all of which are cloned) and do not recognize other genes which may be present in Solanum species. Some of these differential plants have more than one R gene [19]. Avirulence gene ipiO, identifying RB/Rpi-blb1 gene in potato, which is common to S. bulbocastanum and absent in S. demissum [20], is represented by two classes in P. infestans differential races.…”