Greenhouse Evaluation of Section Arachis Wild Species for Sclerotinia Blight and Cylindrocladium Black Rot Resistance

ABSTRACT Wild Arachis species from section Arachis have been promoted as sources of resistance to common peanut diseases and insect pests. The objective of our study was to identify wild Arachis species with resistance to Sclerotinia blight and Cylindrocladium black rot (CBR). One hundred and ten accessions/entries from 23 Arachis species including A. hypogaea were evaluated in the greenhouses at North Carolina State University between January and March of 2010 in a 11×10 rectangular lattice experimental design with 4 replications for Sclerotinia blight and 6 replications for CBR. For the Sclerotinia blight test, seeds were planted in 10 cm clay pots and 8-wk-old plants were inoculated in a mist chamber with BEEM capsules containing the fungus inserted on the petioles of the 4th leaf from the apex on the primary branch. Lesion lengths were measured 4, 5, 6, and 7 d after inoculation, and areas under the disease progress curves (AUDPC) were calculated. For the CBR test, seeds were planted in soil mixed with microsclerotia (25/g) in cone-tainers partly immersed in water. Root damage was recorded after 60 d on a 0–5 proportional scale (0 = no decay to 5 = completely decayed). Data analysis indicated significant (p<0.05) variation among and within Arachis species for both diseases. Arachis glandulifera exhibited the highest level of Sclerotinia blight resistance followed by A. correntina, A. herzogii, and A. helodes, although the last three species were not significantly different from A. hypogaea. Overall, low genetic variability for Sclerotinia blight resistance was observed among the wild species accessions. For CBR, A. valida, A. cruziana, A. microsperma, A. williamsii, A. kempff-mercadoi, A. kuhlmannii, A. helodes, A. cardenasii and A. correntina formed the most resistant group with A. hypogaea in the most susceptible group. Overall, significant genetic variability for CBR resistance was found among the different wild species accessions. However, not all accessions within a species were resistant to either disease, and most accessions that were resistant to one disease were susceptible to the other.