Resistance to Soybean Aphid in Early Maturing Soybean Germplasm

yellow, and even drop. Other symptoms of direct feeding damage include plant stunting, poor pod fill, reduced Since 2000, the soybean aphid (Aphis glycines Matsumura) has pod and seed counts, smaller seed size, and nutrient become a major pest of soybean [Glycine max (L.) Merr.] in North America. In the USA, there are currently no commercial soybean deficiencies resulting in overall yield and quality reduccultivars with aphid resistance and there are no reported resistance tion (DiFonzo and Hines, 2002). Significant yield loss sources in early maturing soybean germplasm. The objectives of this (8–25%) occurs when the soybean plants are heavily study were to identify sources and types of resistance to soybean aphid infested by the aphid during the early reproductive stage from early maturing soybean germplasm. Over a 2-yr period, 2147 (DiFonzo and Hines, 2002). Honeydew, a sticky subsoybean accessions from maturity group (MG) 0 to III, originally stance excreted by soybean aphids onto the leaves, leads from northern China, were evaluated for aphid resistance in a greento the development of sooty mold, which affects photohouse and in field cages. The plants were hand-inoculated and aphid synthesis and results in yield loss (Baute, 2004). During populations were evaluated 10 d after inoculation. A damage index the feeding process, soybean aphids are capable of trans(0–100%) was calculated for each accession. After 2 yr of evaluation mitting viruses including Alfalfa mosaic virus, Soybean and confirmation in choice tests, four MG III accessions from Shandong province, PI 567543C, PI 567597C, PI 567541B, and PI 567598B, mosaic virus, and Bean yellow mosaic virus. These viwere found to be resistant to the soybean aphid. Two of these accesruses commonly occur together and form a disease comsions, PI 567541B and PI 567598B, possessed antibiosis resistance, plex that leads to plant stunting, leaf distortion and preventing the aphids from reproducing on the plants in a no-choice mottling, reduced pod numbers, and seed discoloration study. PI 567543C and PI 567597C possessed antixenosis resistance. (Glogoza, 2002). These resistant sources can be used to develop commercial cultivars In the USA, soybean aphid research is still in its early with aphid resistance for the North Central states. stages. The aphid was first found in 2000 and annual infestations have been unpredictable (Steffey and Gray, 2004). Insecticides are the only available method of conS is the leading oilseed crop produced and controlling soybean aphids in the USA. Although the use sumed worldwide (Wilcox, 2004). In the past half of insecticides can be a quick and easy way to control century, the USA has been the world’s leading producer. aphids, the ideal time to spray is not well defined. InsecIn 2003, the USA produced 35% (65.8 million Mg) of ticides also have many adverse effects such as killing the world’s total soybean (FAOSTAT, 2004). Soybean beneficial insects, environmental contamination, and inhas many insect pests limiting its production, including creased production costs (Sun et al., 2000). Aphid poputhe soybean aphid. A native to eastern Asia, the soybean lations may resurge when applications of insecticides aphid was not reported in the USA before July 2000. are poorly timed or applied. Developing soybean varieSince then, the insect has rapidly spread to the major ties that are resistant to the aphid is a long-term solution soybean production areas in the USA and Canada to the aphid problem. (Plant Health Initiative, 2004). Outbreaks have been To develop aphid resistant varieties, sources of resissevere in the northern part of the midwestern USA and tance must be identified. Sources of resistance to the in Ontario, particularly in 2001 and 2003. soybean aphid are reported in China. In the late 1980s, Several factors affect soybean aphid outbreaks, intwo highly resistant varieties were found among 181 variecluding environmental conditions, over-wintering sucties evaluated (Fan, 1988). In 1991, resistance was also cess, cultural practices, natural enemies, and the synreported in soybean germplasm in China (Sun et al., 1991). chronization of soybean and aphid development (Wu The type of resistance, antixenosis or antibiosis, was not et al., 1999). The soybean aphid is the only aphid in indicated in these studies. Antixenosis is nonpreference North America that develops large colonies on soybean. of insects for a host plant (Kogan and Ortman, 1978). Plant damage occurs when large numbers of aphids reAntibiosis includes all adverse effects on an insect’s life move significant amounts of water and nutrients as they history after a resistant host plant has been used for feed on leaves and stems, causing leaves to wilt, curl, food (Painter, 1951). Knowing the type of resistance is important to fully understand and utilize resistant accesC. Mensah and D. Wang, Dep. of Crop and Soil Science, Michigan sions in a breeding program. Hill et al. (2004) recently State Univ., East Lansing, MI 48824; C. DiFonzo, Dep. of Entomology, reported three lines with resistance to soybean aphid. Michigan State Univ., East Lansing, MI 48824; R.L. Nelson, USDAPI 71506 (MG IV) has antixenosis and the cultivars ARS, Soybean/Maize Germplasm, Pathology, and Genetics Research Dowling (MG VIII) and Jackson (MG VII) are reported Unit, Dep. of Crop Sciences, 1101 W. Peabody Dr., Univ. of Illinois, Urbana, IL 61801. Received 27 Nov. 2004. *Corresponding author to have antibiosis resistance. ([email protected]). In 2002, when this research was initiated, there were no known sources of host plant resistance to soybean Published in Crop Sci. 45:2228–2233 (2005). aphid in the USA. The objectives of this study were to: Crop Breeding, Genetics & Cytology doi:10.2135/cropsci2004.0680 © Crop Science Society of America Abbreviations: DI, Damage Index; MG, Maturity Group; PI, Plant Introduction. 677 S. Segoe Rd., Madison, WI 53711 USA 2228 Published online September 23, 2005