Late Blight of Tomato - Translational Genomics for Crop Breeding: Biotic Stress - page 262

and only in the presence of other lines with single
gene resistance in the same plantings (Scott and
Gardner 2007). In contrast, under severe LB
infestation in multiple locations in Pennsylva-
nia, we have observed that the resistance con-
ferred by the combination of Ph-2 and Ph-3 held
very well. Nonetheless, there exists a possibil-
ity for breakdown of the resistance conferred
by the combination of Ph-2 and Ph-3 , and thus
the continued search for identification and sub-
sequent introduction of additional LB-resistance
genes in tomato remains of crucial importance.
Fortunately, research in this direction is under-
way, which will provide opportunities for pyra-
miding multiple resistance genes and develop-
ing tomatoes with stronger and more durable
resistance against LB. This is a strategy that
only will gain more significance, since predict-
ing the extent to which an R -gene will continue
providing resistance against a highly-variable
pathogen remains problematic. Another promis-
ing research area is to combine single resis-
tance genes with QTLs that may confer moderate
but more broad-spectrum field resistance against
tomato LB. Similar to work in potato, consider-
able efforts have been made in tomato to identify
QTLs for LB resistance in different wild species,
and the findings may prove to be useful for devel-
opment of tomatoes with more durable resistance
against LB. Furthermore, as exemplified by the
fast progress in potato research and conserva-
tion of LB-signaling pathways between potato
and tomato, detailed knowledge of the pathogen
effectors, in combination with high-throughput
genomics, may significantly contribute to identi-
fication and deployment of tomato LB-resistance
sources.

ture and Pennsylvania Vegetable Growers Asso-
ciation. The authors are indebted to Dr. D. M.
Tappenden (Michigan State University) for skill-
ful editorial handling and critical reading of the
manuscript.

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Acknowledgments

LB-related research conducted by M. Nowicki
and E. U. Kozik is supported by the Polish
Ministry of Agriculture and Rural Development
grant #DHOR 95/2011. LB research conducted
by M. R. Foolad has been supported by grants
from the Pennsylvania Department of Agricul-