Submitted to: American Peanut Research and Education Society Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 4/15/2008
Publication Date: 1/15/2009
Citation: Culbreath, A.K., Brenneman, T.B., Branch, W.D., Holbrook Jr, C.C. 2008. Resistance to Cercosporidium personatum in medium-maturity runner-type peanut cultivars. In: Proceedings of American Peanut Research and Education Society, July 15-18, 2008, Oklahoma City, Oklahoma. p. 67-68. Interpretive Summary: not required
Technical Abstract: Several peanut (Arachis hypogaea) cultivars have been released with moderate resistance to Cercospora arachidicola (early leaf spot) and/or Cercosporidium personatum (late leaf spot). However, in the southeastern U.S., resistance to these pathogens in runner-type cultivars has typically been limited to cultivars that mature 2 to 3 weeks later than the standard runner-type cultivar Georgia Green. Multiple field experiments were conducted in 2005-2007 in which disease progress and/or final disease severity of late leaf spot were compared for medium-maturity runner-type cultivars (ca. 135 days to maturity) Georgia Green, Georgia-03L, and Tifguard (tested as C724-19-15) grown using no fungicides or reduced fungicide regimes. In 2005, in an experiment in which plots received three early season applications of chlorothalonil for leaf spot control, final leaf spot (Florida 1-10 scale) ratings were 6.8 for Georgia Green and 5.1 for Tifguard (LSD = 1.1). Aven~ged across similar experiments conducted in 2006 and 2007, final leaf spot ratings were 5.6, 3.9, and 3.3 (LSD = 0.9) for Georgia Green, Georgia-03L, and Tifguard, respectively. In a field experiment in 2005, factorial combinations of Georgia Green, Georgia-03L, C-99R, and Georgia-01R with applications of 0, 2, 3, and 6 fungicide sprays of regimes that included pyraclostrobin, tebuconazole, and chlorothalonil were evaluated for control of late leaf spot. In the nontreated plots of that experiment, disease progress of late leaf spot was suppressed in Georgia-03L compared to Georgia Green, and was comparable to that of C-99R and Georgia-01R during the period when all were in the field. A similar experiment was conducted in 2006, but leaf spot epidemics developed much later. However, averaged across fungicide treatments, final leaf spot severity was lower in Georgia-03L than in Georgia Green. In 2007, Georgia Green, Georgia-03L, Tifguard, Georgia-01R, and York were compared in a field experiment in which cultivars were factorially arranged with 0, 3, 4, and 6 applications of fungicides that included pyraclostrobin, mixtures of prothioconazole + tebuconazole, or prothioconazole + tebuconazole + chlorothalonil, and chlorothalonil. In nontreated plots, disease progress of late leaf spot was suppressed in Georgia-03L and Tifguard, compared to Georgia Green, with standardized area under the disease progress curve values of 4.0, 3.8 and 5.4(LSD = 0.3) respectively for the three cultivars. Disease progress was similar for Georgia-03L, Tifguard, Georgia-01R, and York, for the time in which all were in the field. However, both Georgia-03L and Tifguard had final leaf spot severity ratings that were lower than final ratings for Georgia-01R and York that remained in the field 14 days longer. Georgia-03L is the first medium-maturity runner-type cultivar with appreciable resistance to either leaf spot pathogen. The recently released cultivar Tifguard has a similar level of resistance. The components of resistance responsible for the suppression of epidemics have not been determined for either cultivar. The combination of moderate levels of leaf spot resistance in Georgia-03L and Tifguard, which have shorter time to maturity than other leaf spot resistant cultivars, could allow production of either of these cultivars with greatly reduced fungicide inputs for leaf spot control compared to requirements for susceptible cultivars.