GERMPLASM
Registration of 25 Sheath Blight Disease– Resistant Germplasm Lines of Rice with Good Agronomic Traits M. C. Rush, D. E. Groth,* and X. Sha ABSTRACT Sheath blight (SB; caused by Rhizoctonia solani Kühn AG1–1A [teleomorph: Thanatephorus cucumeris (A. B. Frank) Donk.]) is one of the most important rice diseases in the southern United States. Twenty-five rice (Oryza sativa L.) germplasm lines (Reg. No. GP-115, PI 658312 to Reg. No. GP-139, PI 658336) with high levels of resistance to SB were developed and released by the Department of Plant Pathology and Crop Physiology at the Louisiana State University Agricultural Center, Baton Rouge, LA, and the Rice Research Station, Rayne, LA. The lines were developed from 25 yr of recurrent selections of crosses and backcrosses of various SB-resistant sources and U.S. cultivars. Sources for SB resistance included LSBR-5, LSBR-33, H4/CODF, ‘Taducan’, Rice/Grass, ‘Teqing’, ‘Jasmine 85’, ‘Katy’, ‘Yangdao-6’, and ‘Azmil’, combined with SB resistance sources from previous crosses. Panicle rows tested in 2007 were derived from crosses made in 1997–2004, based on a modified recurrent-selection scheme and inoculated each year with SB inoculum. Short-stature, earlymaturing, high-yielding lines similar to the commercial rice cultivar ‘Cocodrie’ were selected and yield tested in small plots in 2008. Their SB ratings ranged from 3.3 to 5.2 on a scale of 0 to 9, indicating reactions ranging from resistant to moderately resistant, compared with 8.8 and 7.3 for the susceptible cultivars Cocodrie and ‘CL151’, respectively. The lines should be useful for breeders and researchers interested in developing new varieties with resistance to SB.
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heath blight (SB), caused by Rhizoctonia solani Kühn AG1–1A [teleomorph: Thanatephorus cucumeris (A. B. Frank) Donk.], is one of the most important diseases of rice (Oryza sativa L.) in the southern United States (Groth and Lee, 2002). Under conditions favorable for development of the disease, grain yield losses ranging from 1 to 65% have been reported (Marchetti, 1983; Groth, 2005). The severity of the disease is dependent on the amount of inoculum, the crop growth stage at infection, environmental conditions, cultivar resistance, and cultural management (Groth and
M.C. Rush, Dep. of Plant Pathology and Crop Physiology, LSU AgCenter, Baton Rouge, LA 70803; D.E. Groth and X. Sha, Rice Research Station., Louisiana Agric. Exp. Stn., LSU AgCenter, 1373 Caffey Rd., Rayne, LA 70578. Research supported by funds from the Louisiana Rice Research Board. Approved for publication by the director of the Louisiana Agricultural Experiment Station as manuscript no. 2009-266-4025. Registration by CSSA. Received 19 Oct. 2010. *Corresponding author (
[email protected]). Abbreviations: SB, sheath blight. Published in the Journal of Plant Registrations 5:400–402 (2011). doi: 10.3198/jpr2010.10.0601crg Posted online 26 Apr. 2011. © Crop Science Society of America 5585 Guilford 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.
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Lee, 2002). Current U.S. rice cultivars are early-maturing, semidwarf long-grains with good agronomic characteristics, including resistance to lodging, high yield, upright plant type, and high tillering, but they are susceptible or very susceptible to SB. Incorporation of SB resistance into rice cultivars has been a major objective of all rice-breeding programs in the southern United States (Lee and Rush, 1983). Most sources of SB resistance are tall, lodging-susceptible, late-maturing lines that result in higher production costs and low yields (Rush and Lee, 1992). The objective of this project was to develop short-stature, early-maturing, highyielding rice lines similar to current southern U.S. cultivars but with improved levels of SB resistance.
Materials and Methods
The sources for SB resistance, which have SB ratings between 2 and 5, included the somaculture-derived SBresistant germplasm lines LSBR-5 and LSBR-33 (Xie et al., 1992), H4/CODF (a semidwarf mutant developed through cobalt irradiation of the Sri Lanka cultivar H4), the Philippine introductions ‘Taducan’ and ‘Azmil’, the Chinese cultivars ‘Teqing’ and ‘Yangdao-6’, ‘Jasmine 85’ (Marchetti et al., 1998), ‘Katy’ (Moldenhauer et al., 1990), a rice/grass cross from China, ‘Starbonnet’ (Johnston et al., 1968), and ‘Nortai’. The SB-susceptible U.S. long-grain rice cultivars used as semidwarf elite trait sources included ‘Cocodrie’ (Linscombe et al., 2000), ‘Cypress’ (Linscombe et al., 1993), ‘Jodon’ (Linscombe et al., 1995), ‘Lemont’ (Bollich et al., 1985), ‘Maybelle’ (Bollich et al., 1991), ‘Priscilla’, and
Journal of Plant Registrations, Vol. 5, No. 3, September 2011
‘Rosemont’ (Bollich et al., 1993). Over the years, resistant germplasm was crossed with these elite U.S. long-grain genotypes, which possess good agronomic characteristics and adaptation. Pedigree selection was conducted under artificial inoculation on segregating progenies. Isolate LR 172 of Rhizoctonia solani was grown on a mixture of moist rice hulls and grain and spread by hand onto each row at the rate of 10–20 or 100 mL/yield plot. Selection criteria include, in order of importance, high levels of SB resistance, semidwarf plant height, early maturity, typical long-grain shape, and good plant type. To introgress and enhance the SB resistance of different sources, pedigree-selected SB resistance lines were further crossed among themselves or to cultivars from 1997 to 2004. All F1 seed was germinated in the greenhouse and later transplanted into the field. The F1 plants of each cross were bulk harvested, and the resulting seeds were grown as a F2 population. All F2 populations, as well as the subsequent panicle rows (1.8 m with 0.2 m spacing), were planted in the field of the Rice Research Station near Crowley, LA, and inoculated for SB (Groth, 2005). Various numbers of F2 panicles were selected from each F2 population that had acceptable plant height, optimum maturity, and the typical long-grain shape similar to current commercial cultivars such as Cocodrie. The panicles were individually threshed and planted as 2.1-m F2:3 rows in the following year. From those, superior rows were visually selected, individually threshed, and planted as F2:4 rows. Such selection or reselection was repeated over the years until the panicle rows became reasonably uniform enough to be advanced to the replicated yield trials. The SB-resistant germplasm lines were initiated from bulks of individual F2:4 –F2:9 panicle rows harvested in 2007. Yield trials were conducted in 2008 in 1.2- × 4.9-m plots using standard agricultural practices and inoculation with R. solani (LR 172) (Groth, 2005). Plots were arranged in a randomized complete block design with four replications. Data on disease severity, extended-head plant height, days from emergence to 50% heading, and rough rice yield were collected. Twenty-five lines and two commercial cultivars Cocodrie and ‘CL151’ (unpublished registration) checks were tested (Table 1). Sheath blight resistance levels and absence of offtypes were confirmed in 2009 in SB inoculated rows from 2008 harvested seed.
Characteristics
The long-grain germplasm lines (Reg. No. GP-115, PI 658312 to Reg. No. GP-139, PI 658336) ranged from 0.84 to 1.04 m in height compared with 0.88 m for Cocodrie and 0.94 m for CL151 (Table 1). The germplasm lines ranged from 84 to 95 d from planting to 50% heading compared with 80 d for Cocodrie and 83 d for CL151. The lines had a 3-yraverage SB rating ranging from 3.3 to 5.1 on a 0–9 rating scale (Groth, 2005), where 0 = immunity, and 9 = very susceptible, compared with 8.3 and 7.3 ratings for the very susceptible cultivars Cocodrie and CL151, respectively. The 25 long-grain germplasm lines, which were developed through crossing with adapted southern U.S. cultivars and recurrent selection, have moderate levels of resistance to SB, semidwarf plant height, early maturity, and high yield characteristics similar to Cocodrie and CL151. With Journal of Plant Registrations, Vol. 5, No. 3, September 2011
general agronomic characteristics similar to those of commercial cultivars and improved disease resistance to SB from several different sources, these lines will become useful parental lines for rice improvement programs. It is strongly suggested that SB resistance screening should be a part of the selection process beginning in early generations since resistance from these sources are polygenic and can easily be lost without selection.
Availability
These 25 lines were released 8 Oct. 2009 by the Louisiana Agricultural Experiment Station of the Louisiana State University Agricultural Center. Amounts of germplasm seeds
