Plant Height Components and Gibberellic Acid Response of Oat Dwarf Lines

nant dwarfing gene, Dw8, was identified and demonstrated to be distinct genetically from Dw6 and Dw7 The use of oat (Avena sativa L.) dwarfing genes in breeding pro(Milach et al., 1998). This gene has not been used yet grams to improve lodging resistance has been limited, mainly because of decreases in yield and grain quality in many environments. The for cultivar development. objectives of this study were to evaluate the effects of the dominant Yield advantages in oat lines with the Dw6 dwarfing Dw6, Dw7, and Dw8 dwarfing genes on plant height components and gene have been obtained in some Australian environthe gibberellic acid (GA) response of the dwarf lines. Plant height ments (Anderson and McLean, 1989). However, the components including internode length, panicle length, and panicle dwarf phenotype generally limits the use of dwarfing exertion were measured in plants of three nondwarf and nine dwarf genes in oat breeding because of decreases in seed size, lines grown in the field at St. Paul in 1992 and 1993. Five experiments quality, and yield (Brown et al., 1980; Marshall and were performed in growth chambers to assay the response of nondwarf Murphy, 1981; Meyers et al., 1985; Kibite and Clayton, and dwarf oat genotypes to exogenous GA applied at the seedling 2000; Milach and Federizzi, 2001). stage. The Dw6 gene in line OT207 caused a 34 to 37% reduction in Comparison of plant height components of the Dw6 plant height due to the reduction in the length of the three uppermost internodes but not internode number. The 46% reduction in height semidwarf line OT207 with its nondwarf progenitor line caused by the Dw7 gene in line NC2469-3 resulted from decreases OT184 revealed a significant shortening in the Dw6 in both internode number and elongation. The Dw8 gene present in mutant in the length of its three uppermost internodes, derivatives of seven Japanese lines shortened all internodes but did particularly the peduncle (Brown et al., 1980). This renot affect internode number, reducing plant height by about 50%. duction in peduncle elongation has been associated with The dwarf lines that carry these dwarfing loci are responsive to exogethe failure of the panicle to emerge fully from the leaf nously added GA3, GA1 and GA20, and thus the mutations appear sheath, particularly under nonideal growth conditions. not to involve disruptions of the conversion of GA20 to GA1. The Panicle exertion genes introduced or selected for in results indicate that different strategies may be needed to adjust for lines carrying the Dw6 gene have been found to help the different plant height component effects of each of the three ameliorate this problem (Farnham et al., 1990). The dwarfing genes for their use in oat cultivar development. internode constitution of the dwarf lines with the Dw7 gene (in line NC2469-3) or the Dw8 gene in Kanota backcross derivatives has not been previously reported. T development of shorter cultivars with increased This information is important in understanding how resistance to lodging is of interest in oat breeding. these genes affect plant height and in attempting to Major dwarfing genes have been used extensively in adjust for any undesirable effects they might have for developing semidwarf wheat (Triticum aestivum L.) and cultivar development. rice (Oryza sativa L.) high yielding cultivars (Gale and The gibberellic acid (GA) biosynthetic pathway can Youssefian, 1985). Until recently, seven major oat be dissected by means of dwarfing genes (Hedden and dwarfing mutants had been described officially and clasProebsting, 1999). Dwarf mutants that are defective for sified in Avena species (Marshall and Shaner, 1992); different steps in the GA pathway and which respond however, only two of them, the dominant Dw6 and the to the exogenous application of GA have been described semidominant Dw7, are readily available, and only Dw6 in maize (Zea mays L.), rice, and pea (Pisum sativum is being used currently for cultivar development (MarL.) (Phinney, 1984). The early 13-hydroxylation GA shall et al., 1987; Anderson and McLean, 1989; D.D. biosynthetic pathway leading to active GA1 occurs in Stuthman, personal communication, 1998). Potential maize, rice and pea (Phinney, 1984). Intermediates of new sources of dwarfism for oat improvement were this pathway have been identified in oat by gas-chroreported in the hexaploid wild oat A. fatua L. by Morimatographic spectrometry, indicating that the pathway kawa (1989a). Among backcross derivatives of these also occurs in oat (Kaufman et al., 1976). However, dwarfs into the A. sativa cultivar Kanota, a new domiother dwarf mutants have been identified in wheat, rye (Secale cereale L.), maize, and rice that are insensitive S.C.K. Milach, Universidade Federal do Rio Grande do Sul, Faculdade de Agronomia, Departamento de Plantas de Lavoura, Av. Bento to the application of GA (Gale and Youssefian, 1985; Gonçalves, 7712, Cx.P. 776, Porto Alegre, RS 90012-970, Brazil; H.W. Borner, 1991; Harberd and Freeling, 1989; Mitsunaga Rines, USDA-ARS Plant Science Research Unit and Dep. of Agronet al., 1994). In these mutants dwarfism appears to be omy and Plant Genetics, Univ. of Minnesota, 411 Borlaug Hall, 1991 due to causes other than blocks in GA biosynthesis. Upper Buford Circle, St. Paul, MN 55108; R.L. Phillips, Dep. of In wheat, the presence of GA-insensitive dwarfing Agronomy and Plant Genetics and Plant Molecular Genetics Institute, Univ. of Minnesota, St. Paul, MN 55108. Joint contribution of the genes can be identified by a GA response test conducted Minnesota Agric. Exp. Stn. and USDA-ARS. Mention of a trademark at the seedling stage (Yamada, 1990). The genetics of or proprietary product does not constitute a guarantee or warranty the rht1 and rht2 recessive dwarfing genes were not by the USDA-ARS or the Univ. of Minnesota and does not imply clearly resolved until the GA-insensitive response assay approval over other products that also may be suitable. Received 4 June 2001. *Corresponding author ([email protected]). Abbreviations: GA, gibberellic acid; RFLP, restriction fragment length polymorphism. Published in Crop Sci. 42:1147–1154 (2002).