A Note on a Greenhouse Evaluation of Wild Arachis Species for Resistance to Athelia rolfsii R.S. Bennett*, A.D. Harting, C.E. Simpson, S.P. Tallury, A.B. Pickering, N. Wang, and J.C. Dunne1 ABSTRACT Arachis kempff-mercadoi, Arachis kuhlmannii, Athelia rolfsii (Curzi) C.C. Tu & Kimbr. is the Arachis microsperma, Arachis monticola, one of the most damaging pathogens of cultivated Arachis simpsonii, Arachis williamsii, resis- peanut, causing the soilborne disease known tance assay, Sclerotium rolfsii, Section regionally as white mold, stem rot, or southern Arachis, southern blight, stem rot, white blight. Because the genetic base for cultivated peanut is narrow, wild Arachis species may mold. possess novel sources of disease resistance. We evaluated 18 accessions representing 15 Arachis species (batizocoi, benensis, cardenasii, correntina, Cultivated peanut (Arachis hypogaea L.) is an cruziana, diogoi, duranensis, herzogii, hoehnei, allotetraploid derived from a single recent hybrid- kempff-mercadoi, kuhlmannii, microsperma, mon- ization event between A. duranensis and A. ipaensis ticola, simpsonii, williamsii) in the greenhouse for (Kochert et al., 1996; Moretzsohn et al., 2013; resistance to At. rolfsii. Assays were conducted on Bertioli et al., 2015, 2019). Relative to some intact plants propagated from rooted cuttings inoculated with mycelial plugs, and lesion length domesticated crops such as the common bean, and mycelial growth were measured at 4, 6, 10, Phaseolus vulgaris (Zizumbo-Villarreal et al., 2005), and 12 days after inoculation. For lesion length, peanut cultigens possess little genetic variation Arachis batizocoi (PI 468326 and PI 468327), and (Kochert et al., 1991; Ferguson et al., 2004), even A. kuhlmannii PI 468159 were the most suscepti- those collected from peanut’s center of origin in ble entries with a mean lesion length .50 mm at South America (Halward et al., 1991; Moretzsohn 12 days after inoculation. Arachis microsperma et al., 2004). In contrast to the limited resistance to (PI 666096 and PI 674407) and A. diogoi PI pests and diseases available within the germplasm 468354 had the shortest lesions with mean lengths pool for Arachis hypogaea (Stalker, 2017), many 16 mm at 12 days after inoculation. Arachis wild Arachis species possess high levels of genetic cruziana PI 476003 and the two A. batizocoi PIs diversity, and importantly, resistance to various had the highest mean area under the disease biotic stressors (Stalker et al., 2016; Stalker, 2017). progress curves (AUDPCs), and the lowest Accessions from at least 30 species within Section AUDPC was obtained from the A. microsperma Arachis, the secondary gene pool for cultivated PI 674407. Mycelial growth was correlated with peanut (Krapovickas and Gregory, 2007; Smykal´ lesion length in most species except A. monticola et al., 2015), have demonstrated resistance to PI 497260. These results may be useful to peanut geneticists seeking additional sources of resistance diseases and insects (Stalker, 2017). The U.S. to Athelia rolfsii. National Plant Germplasm System currently has approximately 500 available wild species acces- sions, approximately 200 of which are from Section Arachis. Key Words: Arachis batizocoi, Arachis Despite the potential of wild species for benensis, Arachis cardenasii, Arachis correnti- improving cultivated peanut, most cultivars in the na, Arachis cruziana, Arachis diogoi, Arachis U.S. do not have wild Arachis in their ancestries (Stalker, 2017). Nonetheless, the few examples duranensis, Arachis herzogii, Arachis hoehnei, descended from wild species have had significant impact. All nematode resistance in U.S. cultivars— 1First and second authors: Research Plant Pathologist and i.e., COAN (Simpson and Starr, 2001), NemaTAM Biological Science Technician, USDA-ARS, Wheat, Peanuts and Other Field Crops Research Unit, Stillwater, OK 74075; Third (Simpson et al., 2003), Tifguard (Holbrook et al., author: Professor Emeritus, Department of Soil and Crop Sciences, 2008), Webb (Simpson et al., 2013), Georgia-14N Texas A&M Agrilife, Stephenville, TX 76401; Fourth author: (Branch and Brenneman, 2015), and TifNV-High Geneticist, USDA-ARS, Plant Genetics Resources Conservation Unit, Griffin, GA 30223; Fifth and sixth authors: Undergraduate O/L (Holbrook et al., 2017)—is derived from Student and Professor, Department of Biosystems and Agricultural TxAG-6, a complex interspecific hybrid generated Engineering, Oklahoma State Univ., Stillwater, OK 74078; Seventh from A. cardenasii, A. diogoi (formerly A. cha- author: Assistant Professor, Department of Crop and Soil Sciences, North Carolina State University, Raleigh, NC 27695. coense), and A. batizocoi (Simpson et al., 1993). *Corresponding author’s E-mail: [email protected] Arachis cardenasii is also in the heritage of Bailey Peanut Science (2021) 48:40–48 40 RESISTANCE TO ATHELIA ROLFSII IN WILD ARACHIS 41 (Isleib et al., 2011), the popular Virginia cultivar alone, an estimated $91.4M was lost in yield and with some resistance to early and late leaf spots, control costs from At. rolfsii in 2017 (Little, 2017). Sclerotinia blight, Cylindrocladium black rot, Disease-resistant peanut cultivars developed from tomato spotted wilt virus, and Athelia rolfsii resistant wild species would save growers millions (Curzi) C.C. Tu & Kimbr. GP-NC WS 13, a North of dollars and mitigate health impacts by reducing Carolina State University (NCSU) germplasm fungicide applications (Fisher et al., 2018). release generated from A. hypogaea and A. cardenasii (Stalker et al., 2002), is two breeding cycles removed from Bailey. The International Materials and Methods Crops Research Institute for the Semi-Arid Tropics A total of 18 PIs from the U.S. National Plant (ICRISAT) has also released several cultivars Germplasm System representing 15 section Arachis developed from interspecific crosses containing A. species (batizocoi, benensis, cardenasii, correntina, batizocoi, A. cardenasii, A. duranensis, A. steno- cruziana, diogoi, duranensis, herzogii, hoehnei, sperma, and A. villosa with resistances to peanut kempff-mercadoi, kuhlmannii, microsperma, monti- rust, late leaf spot, and viruses (Gowda et al., 2002; cola, simpsonii, williamsii) were screened in the Singh et al., 2003; Stalker, 2017). greenhouse for resistance to At. rolfsii (Table 1). Multiple studies have evaluated wild Arachis Resistant and susceptible reference genotypes, the species for resistance to early and late leaf spots, runner cv. Georgia-03L (Branch, 2004), U.S. mini- rust, viruses, and nematodes (Subrahmanyam et core accessions CC650 (PI 478819), CC038 (PI al., 1983b; a, 1985, 2001; Nelson et al., 1989; Holbrook and Noe, 1990; Reddy et al., 2000; 493581), and CC041 (PI 493631)(Bennett and Pande and Rao, 2001; Sharma et al., 2017; Stalker, Chamberlin, 2020) were included to compare the 2017). However, considerably less attention has greenhouse system to a previous-used growth been paid to soilborne disease resistance. An chamber system (Bennett, 2020). The susceptible expansive evaluation by Tallury et al. (2013) Virginia cv. NC-V11 (Wynne et al., 1991), rated evaluated 110 accessions from 23 Arachis species ‘‘30’’ for white mold resistance by Peanut Rx for resistance to Cylindrocladium black rot (CBR) (Culbreath et al., 2010) was also included. and Sclerotinia blight. Considerable variation in Plant Preparation. resistance was found for CBR, but only A. Because of limited seed and inconsistent germi- glandulifera exhibited significantly more resistance nation of most wild Arachis accessions, they were than A. hypogaea for Sclerotinia blight (Tallury et vegetatively propagated from May to September al., 2013). Pande et al. (1994) included one each of 2019 to obtain plants for the experiments. Mother A. chacoense (¼ diogoi, PI 276235), monticola (PI plants were maintained in pots (33-cm-top diam., 497260), A. stenosperma (PI 497579), and an 20-cm-bottom diam., 15-cm tall) filled with the interspecific hybrid of A. hypogaea and A. carde- soilless mix BM7-35 (Berger). Greenhouse temper- nasii in a greenhouse resistance assay for At. rolfsii. atures were set at 22 to 32 C. A small amount of Bera et al. (2016) at the Indian Council of Rhizobium inoculant (Guard-N; Verdesian Life Agricultural Research Directorate of Groundnut Sciences) was applied by dipping the seed into the Research (ICAR-DGR) evaluated a total of 25 inoculant powder immediately before planting or 3 accessions of 11 species from four sections of by placing ca. 3 mm of the inoculant into the Arachis for resistance to At. rolfsii. The most planting hole. resistant accessions, A. pusilla DGR 12047 and A. Cuttings were taken from branches with 3 to 4 appressipila ICG 8945, had 13 and 14% mortality, nodes, and leaves, pegs, and flowers were removed respectively. Researchers at ICAR-DGR also from the lowermost 1 to 2 nodes. The bottom developed NRCG CS85, a multiple disease-resis- nodes were dipped in rooting powder (Garden Safe tant genotype derived from A. kretschmeri,to TakeRoot; Spectrum Brands Holdings) before create a mapping population (Dodia et al., 2019) placing in 9.5-diam. pots filled with a soilless and to investigate mechanisms of resistance to propagation mix (Sunshine Redi-Earth Plug and southern blight (Bosamia et al., 2020). Seedling; Sungro). Rhizobium inoculant was ap- The objective of this study was to evaluate a plied to the planting hole as previously described small subset of accessions within the Section before cuttings were inserted into the potting mix. Arachis