Submitted to: Peanut Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2007
Publication Date: 12/15/2007
Citation: Cantonwine, E.G., Culbreath, A.K., Holbrook Jr, C.C., Gorbet, D.W. 2008. Disease Progress of Early Leaf Spot and Components of Resistance to Cercospora Arachidicola and Cercosporidium Personatum in Runner-type Peanut Cultivars. Peanut Science 35:1-10. Interpretive Summary: Early and late leaf spot are important diseases of peanut. Georganic and DP-1 are two new peanut cultivars that have been observed to have field resistance to leaf spot. The objective of this research was to conduct field and greenhouse studies to better understand the disease resistance in these new cultivars. Results indicated that Georganic and DP-1 have resistance to both early and late leaf spot. Results also suggested that the enhance field resistance that has been observed with these cultivars is in part due to lower infection frequencies, smaller lesions, and for DP-1 longer latent periods.
Technical Abstract: The purpose of this study was to assess and compare the components of resistance for three runner-type peanut cultivars to infection by Cercospora arachidicola (CA) and Cercosporidium personatum (CP), the causal organisms of early and late leaf spot, respectively, to disease resistance observed in the field. A field study was carried out to monitor the progression of leaf spot incidence arid severity in peanut cultivars Georgia Green, Georganic, and DP-l. Time of disease onset (TDO) and temporal epidemic rate (rate) was estimated for incidence with the logistic model, and for severity with the linear model. Early leaf spot was the predominant disease in the field. Estimates of TDO were 9 d later for DP than for Georgia Green, based on incidence models, and 6 and 7 d later for Georganic and DP-1 than for Georgia Green, respectively, based on severity models. The rate of incidence progression was highest for Georganic in 2002 and Georgia Green in 2003, while the rate of severity progression was highest for Georgia Green across years. A detached leaf assay was used to determine components of resistance for these genotypes to infections by CA and Cercosporidium personatum (CP), the latter causing late leaf spot. For both pathogens, infection frequency 30 days after inoculation, lesion diameter, and percent necrotic area were greatest for Georgia Green. Besides a 2-d longer latent period for resistant genotypes, no differences of CA reproduction were detected. For CP, latent period was shorter for Georganic than DP-I, and sporulation per unit lesion area was greatest for Georganic. These results suggest that the enhanced field resistance to early and late leaf spot reported for DP-l and Georganic is in part due to lower infection frequencies, smaller lesions, and for DP-l longer latent periods.