Submitted to: Journal of Peanut Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2006
Publication Date: 4/1/2006
Citation: Dong, W., Shi, Y., Holbrook Jr, C. C., Timper, P., and Noe, J. P. Evaluation of assessment methods to rapidly identify resistance to Meloidogyne arenaria in greenhouse screening of peanut. J. of Peanut Sci. 33:(3):5-9. 2004. Interpretive Summary: The purpose of this study was to develop a more rapid method for identifying peanut that are resistant to nematodes. Two greenhouse trials were conducted to evaluate different nematode inoculation systems, and different resistance rating systems. Based on the results of this study, we propose a two-stage greenhouse screening to identify peanut genotypes with nematode resistance. A preliminary screen would first be used to eliminate susceptible genotypes based on egg number 14 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 after inoculation to verify the resistance.
Technical Abstract: Reliably and rapidly identifying resistance is one of the critical techniques for developing peanut cultivars with resistance to the root-knot nematode (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 objectives of this study were to evaluate several methods and develop the more rapid techniques for assessing resistance to M arenaria in peanut under greenhouse environments. 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. Two systems galling index and gall number were evaluated 2 and 4 weeks after inoculation (WAI); while galling indexes, gall number, egg mass index and egg number per gram fresh root were evaluated 6 and 10 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 could be used, however, 8000-egg inoculum was more suitable to inoculate the peanut plants in greenhouse screening test than the other three inocula. Egg number can be used to substitute the galling indexes to separate the different resistance in peanut two weeks (around 150 degree days) after inoculation. Dependable reductions in nematode reproductions 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 the galling index systems, gall number, egg mass index, and egg number per gram fresh root for every harvest. Significantly positive correlations (P<0.0 1) were observed among galling index systems, 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 egg number 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 to verify the resistance.