Submitted to: American Peanut Research and Education Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2003
Publication Date: 12/15/2003
Citation: Dong, W.B., Holbrook Jr, C.C., Timper, P., Noe, J.P. 2003. Comparison of inoculation methods to more rapidly identify peanut genotypes with resistance to meloidogyne arenaria. Proc. Amer. Peanut Res. and Educ. Soc. 35:82. Interpretive Summary: not required
Technical Abstract: Developing and utilizing resistant peanut cultivars is a desirable approach to manage peanut root-knot nematode disease, caused by Meloidogyne arenaria. Greenhouse screening techniques to identify peanuts with resistance to M. arenaria are available, however, the standard protocol can take up to 10 weeks before results are available. The objective of this study was to evaluate more rapid techniques for assessing resistance to M. arenaria in peanut. During 2002-2003, two pot trails were conducted in Tifton, Georgia to determine the appropriate screening protocol for identifying resistant genotypes under greenhouse conditions. Two levels of egg suspension inoculum and two levels of second-stage juveniles (J2) inoculum were used to inoculate four peanut genotypes with different resistance to M. arenaria. Galling index values and gall numbers were evaluated 2 and 4 weeks after inoculation (WAI); while galling index values, gall numbers, egg mass index and egg number per gram fresh were evaluated 6 and l0 WAI to determine the most suitable inoculum and harvest date for identifying resistance. The results indicated that all of the tested inoculum levels, 2000 J2, 4000 J2, 8000 eggs, and 16000 eggs would be suitable to inoculate the peanut plants. It took 3-5 days to collect enough J2 for inoculating a trial, however, using J2 as inoculum did not show any advantages, compared to using eggs. The peanut genotypes with different resistance to the nematode can be identified correctly two weeks (around 150 degree days) after inoculation based on the 0-5 scale galling index values. Dependable resistance can be identified 6 WAI (about 520 degree days) as well as 10 WAI, based on egg mass index or egg number per gram fresh root. Pearson's correlation coefficients were calculated to compare galling index, gall number, egg mass index, and egg number per gram fresh root for every harvest. Significantly positive correlations (P<0.01) were observed among galling index, gall number, egg mass index, and egg number per gram root. We propose a two-stage greenhouse screening protocol to identify peanut genotypes with resistance to the root-knot nematode. A preliminary screen would first be used to eliminate susceptible genotypes based on the 0-5 galling index values assessed 14 days (150 degree days) after inoculation with 8000 eggs. The selected genotypes should then be assessed for egg mass index or egg number per gram fresh root at 6 weeks (520 degree days) after inoculation with 8000 eggs to verify the resistance.