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a USDA-ARS, 1301 N. Western Rd., Stillwater, OK 74075
b USDA-ARS, P.O. Box 307, Aberdeen, ID 83210
* Corresponding author (Do.Mornhinweg{at}ars.usda.gov).
ABSTRACT
STARS 0637B (Reg. No. GP-189, PI 642923), STARS 0638B (Reg. No. GP-190, PI 642924), STARS 0639B (Reg. No. GP-191, PI 642925), STARS 0640B (Reg. No. GP-192, PI 642926), STARS 0641B (Reg. No. GP-193, PI 642927), STARS 0642B (Reg. No. GP-194, PI 642928), and STARS 0643B (Reg. No. GP-195, PI 642929), are spring, two-rowed barley (Hordeum vulgare L.) lines developed cooperatively by the USDA-ARS, in Stillwater, OK, and Aberdeen, ID, as sources of resistance to Russian wheat aphid (RWA) [Diuraphis noxia, (Mordvilko)]. Each resistant line is in one of three, two-rowed, feed barley cultivar backgrounds (‘Bowman’, ‘Hector’, or ‘Otis’). They are comparable to their recurrent parents in yield, test weight, plant height, and heading date in the absence of RWA and superior in grain yield to their recurrent parents in the presence of RWA.
Abbreviations: RCB, randomized complete block • RWA, Russian wheat aphid
Devastating yield losses occurred in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) in the western United States within 2 yr after the first appearance of the Russian wheat aphid [RWA; Diuraphis noxia, (Mordvilko)] in 1986 (Porter et al., 1999). Screening of the entire USDA-ARS National Small Grains Collection of H. vulgare in the greenhouse by the USDA-ARS in Stillwater, OK, resulted in the identification of 109 accessions with resistance to RWA ranging from resistant (1–3) to moderately resistant (4–5) on Webster's scale of 1 to 9 (1 = resistant, 9 = susceptible) (Webster et al., 1991) From these heterogeneous accessions, 109 homogeneous unadapted RWA-resistant germplasm lines were developed by selecting for RWA resistance as well as plant type. Two spring germplasm lines, STARS 9301B and STARS 9577B, were quickly released to breeders in 1993 and 1995, respectively (Mornhinweg et al., 1995, 1999). Although highly resistant to RWA feeding damage, these lines were not well adapted to U.S. feed or malting barley production environments. Breeder concerns about potential negative effects of unadapted germplasm on the agronomic performance and malting quality of elite breeding lines led to the initiation of a backcross-breeding program at Stillwater to develop RWA-resistant germplasm lines in backgrounds adapted to all barley-growing areas of the United States where RWA is a potential threat. All 109 unadapted resistant lines were used in the backcross breeding program. Seven RWA-resistant winter feed barley germplasm lines, STARS 0501B to STARS 0507B, were released in 2005 (Mornhinweg et al., 2006b). Each of the seven lines had a different source of RWA resistance in a ‘Schuyler’ (Jensen, 1972) background. Nineteen RWA-resistant six-rowed spring germplasm lines (STARS 0601B–STARS 0601B) were released in 2006. Each of the 19 lines had a different source of RWA resistance in one of four, six-rowed malting barley backgrounds (Mornhinweg et al., 2007a). Seventeen two-rowed, spring germplasm lines (STARS 0620B–STARS 0636B) were also released in 2006. Each of the 17 lines had a different source of RWA resistance in one of four, two-rowed malting barley backgrounds (Mornhinweg et al., 2007b). Before the release of the lines reported herein, 43 germplasm lines with RWA resistance from a total of 36 different resistant sources in nine different cultivar backgrounds were released.
Genetic diversity for aphid resistance is important because of a very real potential in aphids to develop biotypes capable of damaging previously resistant lines. Four new biotypes of RWA have been reported for wheat in the United States since 2003 (Haley et al., 2004; Burd et al., 2006). All RWA-resistant barley germplasm released by the ARS at Stillwater are resistant to these newly identified RWA aphid biotypes. However, the threat still exists for the development of new biotypes that can overcome resistance in barley.
Seven new spring, two-rowed lines, STARS 0637B (Reg. No. GP-189, PI 642923), STARS 0638B (Reg. No. GP-190, PI 642924), STARS 0639B (Reg. No. GP-191, PI 642925), STARS 0640B (Reg. No. GP-192, PI 642926), STARS 0641B (Reg. No. GP-193, PI 642927), STARS 0642B (Reg. No. GP-194, PI 642928), and STARS 0643B (Reg. No. GP-195, PI 642929), were developed cooperatively by the USDA-ARS, in Stillwater, OK, and Aberdeen, ID, as sources of resistance to Russian wheat aphid (RWA) [Diuraphis noxia, (Mordvilko)]. Each resistant line is in one of three, two-rowed, feed barley cultivar backgrounds (Table 1 ). The resistant sources in STARS 0637B, 0640B, 0642B, and 0643B were collected in Afghanistan, the resistant source in STARS 0641B was collected in the Russian Federation, and the resistant sources in STARS 0638B and STARS 0639B were collected in the United States. Populations have been developed for future determination of the inheritance of resistance in each unadapted line represented in these germplasm lines, as well as, the genetic diversity for RWA resistance among these lines.
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Each of the seven germplasm lines, STARS 0637B through STARS 0643B, was developed with three backcrosses of an unadapted RWA-resistant germplasm donor line as the male to a two-rowed feed cultivar female recurrent parent (Table 1). Backcross progeny were screened in each generation (BC1 and BC2), and only resistant plants were used in the next backcross. BC3F1 were advanced to BC3F2 in the greenhouse and BC3F2 populations were screened for RWA resistance. Approximately 100 RWA-resistant BC3F2 individuals from each cross were increased in the greenhouse and harvested individually as BC3F2:3. Progeny from individual plants were screened with RWA, and remnant seed from homozygous resistant BC3F2:3 were grown in the field as plant rows at Aberdeen, ID, and evaluated for agronomic performance in comparison to the susceptible recurrent parent. Selected lines from each resistant source and their recurrent parents were grown in replicated yield trials from 2000 through 2005. STARS 0637B, 0638B, 0640B, 0641B, ‘Bowman’, and ‘Hector’ were evaluated in dryland and irrigated yield trails in a randomized complete block (RCB) design with 4 replications in the absence of aphids for 2 yr at four locations in Idaho. STARS 0639B and Bowman were evaluated in dryland and irrigated yield trials in a RCB design with 2 replications for 1 yr at two locations in Idaho. STARS 0642B, 0643B, ‘Otis’, and Otis treated with Gaucho insecticide (a.i. imidacloprid seed treatment, Bayer Agricultural Products, Kansas City, MO) were evaluated in dryland yield trials in an RCB design with four replications for 4 yr at four locations in eastern Colorado and one location in western Nebraska. The locations in Colorado and Nebraska were extremely moisture limiting in three of the four years, and RWA was present naturally or artificially infested at many locations and years. One line from each resistant source was selected for release (Table 1). BC3F6 seed from each of these seven lines was screened in the greenhouse in Stillwater for homogeneous resistance to RWA. If a selection was not homogeneous for resistance, resistant plants were rescued, increased in the greenhouse, and screened again. Homogeneous resistant plants were then increased in the greenhouse and field and bulked for release.
Data from replicated trials were analyzed with a mixed model analysis of variance with fixed effects of line, location, and line x location. Linear contrasts were made for line x recurrent parent using SAS PROC MIXED (2005, SAS Institute, Cary, NC), and significance was determined by a t test with p = 0.10.
Characteristics
STARS 0637B, STARS 0638B, STARS 0639B, STARS 0640B, STARS 0641B, STARS 0642B, and STARS 0643B were the best agronomic performers in each of three, two-rowed feed barley backgrounds, ‘Bowman’ (Franckowiak et al., 1985), ‘Hector’ (developed by Agriculture Canada and released in 1973), and ‘Otis’ (Robertson, 1965).
All seven of these lines had a high level of resistance to RWA when seedlings were screened in the greenhouse with greenhouse-reared RWA colonies (Table 1). Greenhouse seedling screening resistance ratings have been shown to accurately predict field resistance (Mornhinweg et al., 2006a; Bregitzer et al., 2003). The major component of resistance in these lines is tolerance. Even while supporting high RWA populations, leaves of tolerant germplasm lines do not roll or streak. Therefore, yield reductions resulting from head trapping and chlorosis, as seen in susceptible cultivars, does not occur in these lines (Bregitzer et al., 2003).
Analysis of variance over all locations, lines, and years indicated a significant location x line interaction for heading date, height, test weight, and grain yield (Table 2 ). Years varied greatly for moisture, and locations varied greatly for moisture, irrigated vs. dryland, and the presence and absence of RWA. Further analysis was conducted on locations separately.
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Lines reported herein either were not significantly different from their recurrent parent or outperformed their recurrent parent for heading date, height, test weight, and grain yield in the absence of RWA. When RWA were present, germplasm lines outperformed their recurrent parent in grain yield and, often, test weight.
STARS 0637B and STARS 0642B have a common source of resistance, as do STARS 0640B and STARS 0643B. STARS 0642B and STARS 0643B, with Otis as recurrent parent, were developed and selected for adaptation to the high dry plains of eastern Colorado and western Nebraska. This area of the United States is historically drought prone and a perfect environment for RWA, which is a persistent and serious pest. Otis performs well in this area of extreme moisture stress and, often, high heat conditions. During the four years the Otis-derived lines were tested in Colorado and Nebraska, moisture and therefore yields varied greatly. In 2002, when grain yields were the lowest, Otis and Otis-derived lines were the only lines that survived to maturity. Other cultivars and lines in the test did not survive to heading. Because of their drought hardiness, STARS 0642B and STARS 0643B are unique RWA-resistant germplasm lines.
Availability
Seed of these germplasm lines are deposited in the National Plant Germplasm System where they are available for research purposes, including development and commercialization of new materials. It is requested that appropriate recognition of the source be given when these germplasm lines contribute to research or the development of an improved line, cultivar, or hybrid. Seed of resistant STARS lines will be distributed on request to breeders and geneticists in lots of 5 g. Requests for seed should be sent to the corresponding author.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication December 31, 2007.
References
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