Identification and Characterization of Near-Isogenic Hard and Soft Hexaploid Wheats

1974; Barlow et al., 1973; Rogers et al., 1993; Giroux and Morris, 1997, 1998; Bergman et al., 1998; Morris et A complete understanding of the physical–chemical mechanism al., 1999). and underlying genetic control of wheat (Triticum aestivum L.) endosperm texture will contribute to defining optimal grain utilization Regarding the underlying molecular basis of grain while assisting the breeding and development of new cultivars. World hardness, Greenwell and Schofield (1986) reported that trade in wheat grain primarily is based on the two main market classes, the presence of the starch surface protein friabilin was “soft” and “hard,” which are mostly determined by the expression associated with grain softness. The occurrence of friaof the puroindoline genes at the Hardness (Ha ) locus. Here we idenbilin was inherited additively (Bettge et al., 1995) and tify and characterize new genetic stocks (near isogenic lines, NILs) mediated by bound polar lipids (Greenblatt et al., 1995). in four different genetic backgrounds (20 NILs total, nine hard and Friabilin proved to be identical to the Triton X-114 11 soft). Methods included identifying homogenous or mixed texture soluble proteins, puroindolines a and b (Blochet et al., lines by Single Kernel Characterization System and Near-Infrared 1993; Jolly et al., 1993; Morris et al., 1994; Gautier et Reflectance Spectroscopy. Puroindoline genes and Ha alleles were al., 1994). Recent studies revealed that as many as four determined through nucleic acid sequence analysis. The four different genetic sources for NILs were (i) accessions of ‘Gamenya’ cultivar specific mutations in the puroindoline genes confer which were physical mixtures of hard and soft types, (ii) existing nearwheat grain hardness (as opposed to soft which is the isogenic lines from the cultivars Heron and Falcon, (iii) advancedwild-type allele). The first mutation involves a complete generation backcross lines involving ‘Paha’ and ‘Early Blackhull,’ and absence of puroindoline a mRNA and protein (Giroux (iv) ‘Nugaines’ and ‘Early Blackhull Derivative’. The NILs reported and Morris, 1998), whereas the second involves a single here provide new genetic materials for the study of wheat grain texture nucleotide change in puroindoline b such that the Glyand the effect of puroindolines and the Hardness gene on end-use 46 residue of the protein is altered to a Ser-46 (Giroux quality. Two of the four sets of NILs possess the Gly-46 to Ser-46 and Morris, 1997). The third and fourth mutations are Pinb-D1b hardness allele which has not been previously available in also single-nucleotide changes such that Leu-60 is NILs. The results corroborate a model of wheat grain texture that changed to Pro-60, and Trp-44 is changed to Arg-44, identifies two major hardness classes, as opposed to one that accommodates intermediate texture classes such as “semi-hard” and “merespectively (Lillemo and Morris, 2000). To date, a surdium-soft.” A direct role of the puroindoline proteins in conferring vey of several hundred hard wheats indicates that all soft grain phenotype is supported; conversely, no genetic basis for ha (hard) alleles are attributable to specific changes in intermediate hardness was found. Rather, intermediate hardness rethese puroindoline proteins. sulted from mixtures of the soft and hard classes. An issue related to wheat grain hardness, utilization, and the breeding of improved cultivars is the existence of what is commonly referred to as “semi-soft” or “semihard” wheats. We have been keen to better understand K hardness (texture) is arguably the single and elucidate the genetic basis for such wheats as they do most important determinant of wheat grain quality not apparently fit the current genetic model of hardness and utilization (Pomeranz and Williams, 1990; Morris, described above. One such semi-soft cultivar is Ga1992; Morris and Rose, 1996; Campbell et al., 1999). menya (Crosbie, 1989). A second example of possible The majority of phenotypic variation among cultivars semi-soft genotypes occurred among the set of ‘Falcon’ and individual grain lots for kernel texture can be attriband ‘Heron’ hard and soft NILs (Symes, 1965; Giroux uted to the Ha gene, located on the short arm of chromoand Morris, 1998). However, the two lines that exhibited some 5D (Mattern et al., 1973; Law et al., 1978; Symes, intermediate levels of grain hardness were found to be 1965; Baker, 1977). Defined genetic stocks that differ mixtures of hard and soft types (Giroux and Morris, in either the presence or absence of the hardness gene, 1998). To date, the set of Falcon and Heron NILs has or differ in their allelic state (Ha, soft vs. ha, hard) are been one of the primary genetic materials for studying valuable in studying the biochemical and genetic bases the effects of Ha (Rogers et al., 1993). The recombinant of wheat grain hardness and provide material to cominbred lines derived from ‘Clark’s Cream’ and ‘NY6432pare the effect(s) of this gene on wheat and flour proc18’ represent another (Campbell et al., 1999). Campbell essing and end-use quality (Symes, 1969; Simmonds, et al. (1999) showed how the hardness gene was an often overwhelming contributor to variation in end-use C.F. Morris and R.E. Allan (retired), USDA-ARS, Pullman, WA quality among those Clark’s Cream X NY6432-18 lines. 99164; G.E. King, Dep. Food Sci. & Human Nutrition and M.C. During the course of our studies on Gamenya, we Simeone, Dep. Crop & Soil Sciences, Washington St. Univ., Pullman, WA 99164. Mention of trademark or proprietary products does not found that the semi-soft character of some earlier types constitute a guarantee or warranty of a product by the U.S. Departof this cultivar appear to have resulted from mixtures ment of Agriculture and does not imply its approval to the exclusion of hard and soft types. Sibling lines have been isolated of other products that may also be suitable. This article is in the public domain and not copyrightable. Received 8 March 2000. *CorrespondAbbreviations: NIL, near-isogenic line; NIR, near-infrared reflectance ing author ([email protected]). spectroscopy; NSGC, National Small Grains Collection; PCR, polymerase chain reaction; SKCS, Single Kernel Characterization System. Published in Crop Sci. 41:211–217 (2001).