Evaluation of Resistance to Cylindrocladium Parasiticum of Runner-Type Peanut in The Greenhouse and Field

Abstract

Identification and utilization of peanut cultivars with resistance to Cylindrocladium black rot (CBR) is a desirable approach to manage this disease. The objectives of this study were to improve greenhouse and field screening techniques for resistance to CBR, and to evaluate the reaction of selected runner-type peanut genotypes. Georgia-02C (moderately resistant to CBR) and C-99R (CBR-susceptible) were used in comparing the effectiveness of different inoculation methods in the greenhouse. Disease development was affected by both size and density of microsclerotia in soil. Use of microsclerotia at a size of ≥150 to <250 µm and a density of 1 to 5 microsclerotia/g soil provided the best separation the CBR-resistant cultivar Georgia-02C and the susceptible C-99R based on root rot severity. Genotypes with varying resistance to CBR were evaluated by growth in a naturally infested field, and by inoculating plants in the field and greenhouse. Disease incidence and severity at harvest were the most effective parameters for evaluating CBR resistance in the field and greenhouse, respectively. The cultivars Georgia-02C and Georganic had the lowest disease incidence, whereas C-99R and DP-1 had the highest disease incidence in a naturally infested field in 2005 and 2006. Incidence of CBR was moderate for Georgia-01R in both years, but was inconsistent for C34-24-85. Georgia-02C and Georganic also showed partial resistance to CBR in greenhouse tests. Inoculated plants in the field had similar reaction with Georgia-02C and Georganic showing higher CBR resistance than C-99R and DP-1 in both 2006 and 2007. The root rot severities for genotypes Georgia-02C and Georganic were lower than those for C-99R and DP-1. Incidence of CBR in the naturally infested field was significantly correlated with CBR incidence in the inoculated plants in the field (r = 0.84, P ≤ 0.01), but neither was correlated with disease ratings for greenhouse experiments. Peanut genotypes are most reliably screened by inoculating plants in the field or using uniformly infested fields. Further study is needed to improve greenhouse screening procedures.

Influence of Planting Pattern on Pest Management in Virginia Market Type Peanut (Arachis hypogaea L.)

“…However, differences in plant condition rating associated with CBR were noted for cultivars (p 5 0.0038), with VA 98R expressing more disease than Perry (12% versus 5%, data not shown in tables). The cultivar VA 98R is more susceptible to CBR than the cultivar Perry (Dong et al, 2008;Isleib et al, 2003;Mozingo, 2000).…”

Effect of Container Size, Inoculum Density, and Test Duration on Detecting Resistance to Cylindrocladium Black Rot of Peanut

“…Effect of container size (CN), Cylindrocladium parasiticum inoculum density (DN) (microsclerotia/g soil (ms)), and week (WK) of sampling on resistant (NC 3033 = R) and susceptible (NC 7 = S) peanut genotypes for each disease assessment method in trial II. disregarded potential violations of assumptions and analyzed data using analysis of variance rather than employing non-parametric tests (Dong et al, 2008;Hollowell et al, 2008). Our research demonstrates that taproot necrosis measurements are a valid alternative to root rot ratings.…”

“…However, there was still variability in severity from trial to trial. The variability between trials is likely due to the different sizes of sclerotia that are counted or not counted due to a continuum of microsclerotia sized (Dong, 2008) and/or changes in isolate aggressiveness between trials. Pataky et al (1983) suggested that pronounced differences in the response of Florigiant to increasing inoculum densities between trials were a result of changes due to long term storage of C. parasiticum cultures.…”

“…As a result of these problems, some breeding programs are utilizing greenhouse screening to augment field trials. However, there are examples of poor correlation between greenhouse and field screening results (Dong et al, 2008;Lemay, 1999;Pataky et al, 1983). Hollowell et al (2008) found that their greenhouse technique correlated well with field studies (r 5 0.83) when the field studies were repeated over 4 years, but not with single year field studies.…”

“…Some factors that affect greenhouse assays include isolate virulence (Rowe and Beute, 1975) and density and size of microscloertia (Dong et al, 2008). Additional factors that may influence the effectiveness of greenhouse assays are container size, duration of the test, and method of evaluating symptoms.…”