C06-12-0793 Murphy.indd

Crown freezing tolerance is the most important factor conferring oat (Avena spp.) winter hardiness. The objective of this study was to identify quantitative trait loci (QTL) for crown freezing tolerance in the ‘Kanota’ × ‘Ogle’ recombinant inbred line (RIL) mapping population and to examine their relationship with other winter hardiness traits. One hundred thirty-fi ve RILs were evaluated for crown freezing tolerance in a controlled environment. Previously published molecular marker and linkage map information was used for QTL detection. Seven QTL and four complementary epistatic interactions were identifi ed that accounted for 56% of the phenotypic variation. Ogle contributed alleles for increased crown freezing tolerance at three loci, while Kanota contributed alleles for increased crown freezing tolerance at four loci. All loci where Kanota alleles increased crown freezing tolerance showed complementary epistasis for decreased crown freezing tolerance with the QTL near UMN13. Two of the major QTL identifi ed were in the linkage groups (LG) associated with a reciprocal translocation between chromosomes 7C and 17, which was previously associated with spring growth habit in oat. The results confi rm the importance of the chromosomes involved in the reciprocal 7C-17 translocation in controlling winter hardiness component traits. D.R. Wooten and J.P. Murphy, Dep. of Crop Science, Box 7629, North Carolina State Univ., Raleigh, NC 27695-7629; D.P. Livingston III, USDA-ARS and Dep. of Crop Science, North Carolina State Univ., 840 Method Rd. Unit 3, Raleigh NC 27695; J.B. Holland, USDAARS and Dep. of Crop Science, North Carolina State Univ., Box 7629 Williams Hall, Raleigh, NC 27695; D.S. Marshall, USDA-ARS and Dep. of Plant Pathology, North Carolina State Univ., 1419 Gardner Hall, Raleigh NC 27695. Received 13 Dec. 2006. *Corresponding author ([email protected]). Abbreviations: LG, linkage group; MIM, multiple interval mapping; QTL, quantitative trait loci; RIL, recombinant inbred line. Published in Crop Sci. 48:149–157 (2008). doi: 10.2135/cropsci2006.12.0793 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA 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. R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 150 WWW.CROPS.ORG CROP SCIENCE, VOL. 48, JANUARY–FEBRUARY 2008 An intergenomic reciprocal translocation associated with winter fi eld survival and crown freezing tolerance has been identifi ed (Santos et al., 2006; Wooten et al., 2007). This work indicated chromosomes where crown freezing tolerance genes were located, but more specifi c chromosomal regions have yet to be identifi ed in oat. This contrasts with other winter cereals because quantitative trait loci (QTL) or genes for freezing tolerance have been identifi ed in diploid wheat (Triticum monococcum L.) (Vagujfalvi et al., 2003), bread wheat (T. aestivum L.) (Limin and Fowler, 2002; Toth et al., 2003; Fowler and Limin, 2004; Kobayashi et al., 2005), and barley (Hordeum vulgare L.) (Hayes et al., 1993; Pan et al., 1994; Francia et al., 2004). Almost all of these QTL for freezing tolerance are also linked to QTL for other winter hardiness component traits, such as vernalization response or heading date. The ‘Kanota’ × ‘Ogle’ recombinant inbred line (RIL) population has been studied by several researchers in oat (Siripoonwiwat et al., 1996; Holland et al., 1997; BarbosaNeto et al., 2000; Wight et al., 2003). Kanota is a facultative winter type released in the early 1920s (Salmon and Parker, 1921). It does not have the 7C-17 translocation as is typical of A. byzantina C. Koch winter oat (Zhou et al., 1999; Jellen and Beard 2000). Ogle is an improved spring oat cultivar released in Illinois in 1980 (Brown and Jedlinski, 1983). Ogle has poor freezing tolerance and has the 7C-17 translocation typical of A. sativa L. spring oat ( Jellen and Beard 2000). The diff erence in freezing tolerance between the parents and the large quantity of molecular marker and related QTL data accumulated in previous research make this population useful for identifying QTL for crown freezing tolerance. Identifi cation of crown freezing tolerance QTL would provide a tool for improving winter hardiness through marker-assisted selection. This approach is particularly suitable for a low heritability trait that can be measured only under certain environmental conditions. An additional benefi t would be enhanced understanding of the relationships among different winter hardiness traits. The objective of this study was to identify QTL for crown freezing tolerance in the Kanota × Ogle RIL mapping population. MATERIALS AND METHODS Phenotypic Evaluation Seed of 135 RILs from the cross between the cultivars Kanota and Ogle were provided by Dr. Howard Rines of the USDAARS in St. Paul, MN. Crown freezing tolerance data were collected on all 135 RILs, but fi ve lines were dropped from the subsequent QTL analysis based on questions as to their legitimacy (Wight et al., 2003). A sets within replications experimental design with four replications was utilized. In each replication, the full complement of 135 RILs plus seven entries of one parent and eight entries of the alternate parent were assigned at random to 15 sets of 10 entries each. Five plants of each of the 150 entries were grown for 5 wk in a 9 m2 growth chamber in the Southeastern Plant Environment Laboratory at North Carolina State University. The chamber was illuminated for a 12-h photoperiod with photosynthetic photon fl ux density of 300 mmol m–2 s–1 with a day temperature of 13°C and night temperature of 10°C. Seeds of each entry were planted 1.5 cm deep in fi ve adjacent 20-cm-long nursery tubes held in racks of 100 tubes. Plants were grown in Metromix 200 (Scotts-Sierra Horticultural Products Co., Marysville, OH) and lightly watered daily with a complete nutrient solution (Livingston, 1991). At approximately the fi ve-leaf stage, plants were transferred to a hardening growth chamber for a 3-wk cold hardening treatment. The hardening chamber held a constant 2°C with a 12-h photoperiod of photosynthetic photon fl ux density of 300 mmol m–2 s–1. Plants were watered with a complete nutrient solution three times per week, and watered with tap water on alternate days. After hardening, plants were removed from the nursery tubes and soil was washed off the roots with ice water. Roots were trimmed to 0.5 cm in length and crowns were trimmed to 5 cm in length. The crowns were placed in slits in cold, slightly-moist sponges. The crowns and sponges were sprinkled with crushed ice to prevent super cooling and sealed in plastic bags. The sealed unit was placed on a steel plumbing fl ange to provide thermal and structural stabilization. The prepared units were then placed in a freezer at −1.5°C for 36 h to induce second phase cold hardening (Livingston, 1996). Subsequently, the freezer temperature was decreased to −5°C at a rate of −1°C per hour. The freezer was held at −5°C for 3 h and then raised to 2°C at a rate of 2°C per hour. Within each replication the entries were assigned to 15 sets of 10 entries each. Each set was represented by fi ve sponges. One of the fi ve plants representing each of the 10 entries in the set was placed in each of the fi ve sponges. Thus each sponge contained 10 plants each representing a diff erent entry. The fi ve sponges representing each 10-entry group were placed on fi ve diff erent shelves in the freezer. This modifi cation to the Marshall (1965) protocol permitted more precise estimates of entry means by modeling the variation caused by the diff erent sponges within each replication. After the crowns and sponges thawed, the roots were removed from the crowns by trimming with scissors, and the crowns were planted in 50by 30-cm plastic fl ats fi lled 5 cm deep with moist Metromix 200. The fl ats were returned to the growth chamber in the Southeastern Plant Environment Laboratory where environmental conditions were the same as those provided prehardening. After 3 wk of regrowth, recovery for each crown was visually measured on a scale of 0 to 10 (0 = dead, 10 = no freezing damage). Phenotypic estimates of crown freezing tolerance for each entry were based on a mean of 20 crowns, fi ve crowns per replication. The data were analyzed using the MIXED procedure of SAS (Littell et al., 1996) with the Satterthwaite option for calculating degrees of freedom. Narrow-sense heritability was estimated for the population excluding parental checks using an all random eff ects (entry, replication, set, and sponge) model following the method described by Holland et al. (2003, table 2.1 section 10), but adjusted for the diff erences in experimental design. Entries (including parents) were then considered R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . R e p ro d u c e d fr o m C ro p S c ie n c e . P u b lis h e d b y C ro p S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . CROP SCIENCE, VOL. 48, JANUARY–FEBRUARY 2008 WWW.CROPS.ORG 151 the alleles from the same parent at both fl anking loci, the genotype at locus UMN433 was not predicted. The GLM procedure was used to model the additive terms and the orthogonal epistatic interaction, and the LSMEANS statement with the PDIFF option was used to estimate and compare the means of the four diff erent marker combination classes. Four marker combination classes are expected at two distinct loci with homozygous lines. Marker class means suggested possible complementary gene action, so duplicate or complementary gene action between each pair of loci was further evaluated using ANOVA with a coded dummy variable. If an RIL had the Kanota allele at UMN13 and the Ogle allele at the other locus (UMN433, BCD1968B, BCD1230B, or UMN5485) then it was coded 0, otherwise it was coded 1. For each pair of markers, crown freezing tolerance was modeled in the MIXED procedure using three potential models: (i) a simple linear model with the two markers (modeling simple additive gene action); (ii) a linear model with interaction (a typical test for epistasis); (iii) a model consisting of the coded variable (modeling duplicate or complementary gene action). These models were compared using the Akaike information criterion (Akaike, 1969) calculated with the MIXED procedure to identify the regression model that best fi t the gene action (Rawlings et al., 1998). Finally QTL estimates were re-estimated using MIM including the epistatic interaction terms between QTL near UMN13 and each of the four other QTL near UMN433, BCD1968B, BCD1230B, or UMN5485.