Progress in Breeding Sclerotinia Blight-Resistant Runner-Type Peanut1

Abstract

Field screening tests were conducted in 1991, 1992, and 1993 to identify Sclerotinia blight-resistant runner-type peanuts. Selections were made from three populations, “backcross to runner,” “backcross to Tamspan 90,” and “single cross.” Runner parents were chosen for agronomic qualities and resistance to other pathogens. Resistant (Spanish) parents used were cultivar Tamspan 90 and TxAG-5 germplasm. Families within populations were planted as single row 3 × 0.9-m plots. Repeated plant-by-plant inspections (PBPI) were made for assessment of sequence of infection and subsequent calculation of an area under the disease progress curve (AUDPC). Most families in the backcross to Tamspan 90 population consistently had a disease reaction close to or lower than Tamspan 90 but also retained undesirable plant forms (i.e., upright). By 1993, the F2:5 backcross to runner population had the highest percentage of runner-type families (88%) and a mean disease reaction close to Tamspan 90. Whole plot evaluation of Sclerotinia blight severity was compared with PBPI for effectiveness on a segregating population containing a total of 298 F4:7 single cross and F2:5 backcross entries. The whole plot system used a scale of 0 = no visible plot infection to 5 ≥80% infection in the plot. Correlation between area under disease progress curve values of both methods was high (>.85). Remnant seed of selections screened for resistance in the greenhouse were planted in the field and evaluated for resistance. Chi-square test for independence indicated a significant (α = .012) relationship between greenhouse and field performance. Field screening and limited greenhouse screening appears to be an effective way to develop resistant runner-type peanut lines.

Reaction of the Core Collection of Peanut Germplasm to Sclerotinia Blight and Pepper Spot1

“…Both Tamspan 90 and Southwest Runner are consistently among the most resistant cultivars in field evaluations. Ratings from assays designed to identify physiologic resistance on whole or detached plant parts are generally not well correlated with field screenings (1,15,20,21) Tamspan 90 was grown on nearly all of the problem fields in Oklahoma during the 1990's, but susceptibility to web blotch (caused by Phoma arachidicola Marassas, G.D. Pauer & Boerema) and reduced demand for spanish peanut have contributed to the increase in acreage planted to runner cultivars. While Southwest Runner is partially resistant to Sclerotinia blight, it was never accepted by the shelling industry because of its small seed size.…”

“…Partial resistance in these market types has two forms. Physiologic resistance is expressed as reduced lesion expansion over time as measured on inoculated seedlings or detached plant parts following incubation under artificial conditions favorable for disease development (1,4,15,20,21). Architectural or morphological resistance is expressed in some genotypes with an erect growth habit and sparse plant canopy that results in reduced contact of main and lateral stems with mycelium from the germinating sclerotia or adjacent infections; and/or reduced periods of microclimate favorable for disease development compared to spreading genotypes with a dense canopy (1,4,6).…”

Three Inoculation Methods for Evaluating Sclerotinia Blight Resistance in Peanut

“…The assay was particularly useful in identifying susceptible entries: plants that were susceptible in the assay had an 87% chance of being susceptible in the field. However, plants identified as being resistant in the laboratory assay had only a 33% chance of being resistant in the field (Goldman et al, 1995). In Australia, Cruickshank et al (2002) also reported a significant correlation between one year of field results and an assay similar to the one used by Goldman et al In contrast, Hollowell et al (2008) did not find that intact plant assays correlated well with four years of field data, but the correlation improved significantly when field data from a year with low disease pressure was removed from the analysis.…”

“…Some assays used main stems and lateral branches of whole, intact plants (Goldman et al, 1995;Cruickshank et al, 2002;Woodward et al, 2006;Hollowell et al, 2008). Goldman et al (1995) inoculated non-detached main stems of six-week-old plants with S. minor and found a significant relationship using a chisquare test between three years of field results and the laboratory assays. The assay was particularly useful in identifying susceptible entries: plants that were susceptible in the assay had an 87% chance of being susceptible in the field.…”

Three Inoculation Methods for Evaluating Sclerotinia Blight Resistance in Peanut

“…The assay was particularly 54 useful in identifying susceptible entries: plants that were susceptible in the assay had an 87% 55 chance of being susceptible in the field. However, plants identified as being resistant in the 56 laboratory assay had only a 33% chance of being resistant in the field (Goldman et al, 1995). 57…”