New Sources of Resistance to Greenbug in Barley

greenbug isolate avirulent to Wintermalt. Subsequent work by Ogecha et al. (1992) confirmed that biotype G Most biotypes of the greenbug [Schizaphis graminum (Rondani)] was less successful in feeding on Wintermalt compared are extremely damaging to barley (Hordeum vulgare L.). However, with other biotypes. When compared with biotypes E greenbug biotype G has been reported to be unable to successfully and H, biotype G spent significantly less time salivating feed on barley, and is described as the first greenbug avirulent to and less time feeding within the phloem, took signifi‘Wintermalt’ barley (which is susceptible to all other greenbug biotypes). The objective of this study was to determine the pest status cantly longer to begin reproduction, and produced fewer of greenbug biotype G in barley by characterizing the response of progeny on Wintermalt (Ogecha et al., 1992). select barley cultivars and germplasm to greenbug biotype G feeding. Biotype G is found throughout the Southern Great Eight barley and four wheat (Triticum aestivum L.) cultivars and Plains of the USA (Anstead et al., 2003), where the germplasm were challenged with biotype G and damage ratings repotential for tapping the alternate use market for barley corded after 22 d of infestation. Barley is indeed a host of biotype G (e.g., bio-based fuels) has generated renewed interest in and genetic diversity exists within barley for reaction to attack by winter barley production. Despite its wide distribution, greenbug biotype G. Three barley cultivars were killed by biotype G, there exists a perception that biotype G is not a pest of while five were resistant to feeding damage. These new sources of barley; given its reported avirulence to Wintermalt, the resistance to greenbug biotype G in barley should prove useful in the susceptible barley check (Puterka et al., 1988). Little is development of new greenbug-resistant barley cultivars. known of its ability to damage barley or the level of genetic diversity within barley for resistance or susceptibility. On the basis of the inability of biotype G to feed T greenbug is an economically important pest of successfully on both resistant and susceptible barley, we barley in the USA (Starks and Webster, 1985). A hypothesized that (i) barley is not an acceptable host, 1942 greenbug outbreak that caused an estimated $38 and therefore greenbug biotype G is not a pest of barley, million yield loss in small grain production precipitated or (ii) Wintermalt is actually resistant to biotype G. The interest in the development of resistant cultivars in the objective of this study was to determine the pest status USA (Atkins and Dahms, 1945). Early work in barley of greenbug biotype G in barley by characterizing the identified a single gene source of resistance to greenbug response of select barley cultivars and germplasm to in PI 87181 (Gardenhire and Chada, 1961). This single greenbug biotype G feeding. dominant gene, Grb, was located on linkage group 1 and on the centromere-bearing segment of chromosome MATERIALS AND METHODS 1 in the T1-6a translocation of ‘Will’ barley (Gardenhire et al., 1973). Will barley was used as a parent to develop Eight barley entries (‘Post 90’, PI 426756, Wintermalt, ‘Ban‘Post’, which has been used extensively as a resistant croft’, ‘Colter’, ‘Crest’, ‘Gus’, and ‘Orca’) and four wheat check in greenbug studies (Puterka et al., 1988). A secentries [Dickinson Selection 28A (DS28A), Amigo, Largo, and GRS1201] were used in this study. Each barley and wheat ond source of resistance to greenbug was discovered entry was tested against biotype G. Reactions of the wheat in PI 426756 (Webster and Starks, 1984) that is also germplasms DS28A, Amigo, Largo, and GRS1201 to greenbug controlled by a single dominant gene (Merkle et al., biotype G are well documented (Porter et al., 1997) and were 1987). Genetic studies showed that this new source of included in this study as either a resistant or susceptible check resistance was nonallelic to Grb, thus the gene symbol to confirm greenbug biotype identity. Post 90 is an improved Rsg2b was assigned to this gene, and Grb was modified selection from ‘Post’ barley that carries the Rsg1a resistance to Rsg1a (Merkle et al., 1987). gene. This resistance gene provides protection against biotype These two resistance genes provide protection against G (Puterka et al., 1988; Ogecha et al., 1992). PI 426756 carries a variety of greenbug biotypes (C, E, F, G, and H) the Rsg2b gene and is also resistant to biotype G (Burd et al., 2003, unpublished data). Post 90 and PI 426756 were in(Webster and Starks, 1984; Puterka et al., 1988) and cluded as resistant checks. Wintermalt, Bancroft, Colter, have been the only sources of resistance reported to Crest, Gus, and Orca were included in this study because of date. However, Puterka et al. (1988) reported that Wintheir divergent reactions to biotype G, as documented during termalt, a barley cultivar previously reported susceptible previous preliminary work (D.R. Porter, 2001, unpublished to all greenbug biotypes, was not damaged by the newly data). detected biotype G. Biotype G was described as the first Five seeds of each entry were planted (1.8 cm deep) in hills spaced 5 cm apart within rows and 4.5 cm between rows (replicated six times) in a flat (35 51 9 cm) containing a USDA-ARS, Plant Sci. Research Laboratory, 1301 N. Western Rd., mixture of sandy loam soil, sand, and peat (1:1:1 ratio). There Stillwater, OK 74075-2714. Received 3 Sept. 2003. *Corresponding was a total of 72 hills per flat (12 entries with 6 replications) author ([email protected]). in a randomized complete block design. Standard greenbug Published in Crop Sci. 44:1245–1247 (2004).  Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: DS28A, Dickinson Selection 28A.