TABLE CONTENTS

Heman, and the resistant tomato standard cv. Caramba showed high levels of resistance in the
summer test. In the field, seven rootstocks showed high levels of resistance and one (cv.
Heman) showed intermediate level. In all experimental conditions Beaufort and Maxifort
responded as susceptible to M. javanica (Pf/Pi > 50; RI > 50%). The detection of false
positives for root-knot nematode resistance in cvs. Beaufort and Maxifort was attributed to
their genetic background. The root-knot resistance phenotypic data indicates that Mi23 like
REX-1 is not able to distinguish between resistant and susceptible genotypes in the tomato
hybrid rootstocks.
Changes in Resistance of PI88.788 to Field Populations of Soybean Cyst
Nematode (SCN)
Faghihi, J. (1), V. Ferris (1), P. Donald (2), G. Noel (3) & T. Welacky (4)
(1) Department of Entomology, Purdue University, West Lafayette, IN 47907, USA; (2) USDA ARS, Jackson,
TN 38301, USA; (3) Dept of Crop Science University of Illinois, USDA ARS, Urbana, IL 61801, USA; (4)
Agriculture and Agri-Food Canada, Harrow, ON N0R 1G0, Canada.
PI88.788 has been the major source of resistance to SCN for about three decades, and is
estimated to be present in about 97% of varieties resistant to SCN. Recently, researchers in
the Midwest have observed that varieties with PI88.788 do not seem to be as resistant as they
were formerly. Either the resistant soybean varieties have changed or the field populations of
SCN have themselves changed in response to long exposure to PI88.788. Goals of this
NCSRP funded research were to 1) Determine the current effectiveness of PI88.788 as a
source of resistance to SCN in TN, IL, IN, and Ontario, Canada; and 2) Determine the
reaction to other sources of SCN resistance in areas where PI88.788 may no longer be as
effective. The areas were chosen on the basis of length of time that soybean varieties with
PI88.788 resistance have been widely used. In TN, the area where PI88.788 has been used
the longest, every field population recovered with a high SCN population density was able to
reproduce on PI88.788, and no Hg-Type 0 populations were found. In Ontario, where
varieties with PI88.788 have been used for a shorter period of time, PI88.788 proved to be
resistant to many field populations; but a larger than expected number of Ontario populations
were found to develop on PI548.402 (Peking) and also on PI90.763, two sources of resistance
not generally present in varieties grown in Ontario. While many field populations in IL and
IN were unable to develop on PI88.788, other field populations were capable of reproducing
on PI88.788. PI548.402, PI90.763, and PI437.654 continued to be effective sources of
resistance to such populations. One SCN population from Ontario had a low level of
reproduction on PI437.654, while none of the populations from IN or IL were able to
reproduce on PI437.654.
5 th International Congress of Nematology, 2008 235