Prevalence of Puroindoline Grain Hardness Genotypes among Historically Significant North American Spring and Winter Wheats

Abstract

Grain hardness (“hard” or “soft” kernel texture) is the single most important trait in determining the utilization and marketing of wheat (Triticum aestivum L.). Puroindoline a and b proteins represent the molecular basis for this trait. This study surveyed the prevalence of puroindoline hardness mutations (alleles) among North American spring and winter wheat varieties with emphasis on those that are historically important. Each variety was assessed for kernel texture using the Single Kernel Characterization System; Hardness alleles were defined by puroindoline gene sequence and the presence or absence of puroindoline a protein on polyacrylamide gels. A total of 90 spring wheats were examined: nine were soft and possessed wild‐type (“soft”) puroindoline sequences, 10 were mixed hardness, and the remaining 71 were uniformly hard. Of these hard spring wheats, 18 carried the Pina‐D1b hardness allele (null for puroindoline a protein), 47 the Pinb‐D1b allele (Gly‐46–Ser‐46), and four the Pinb‐D1c allele (Leu‐60–Pro‐60). Two hard spring wheats possessed a new allele, designated Pinb‐D1e, which involves a single nucleotide change in Trp‐39 to a “stop” codon. Lastly, among the spring wheats, a new hardness allele was found in the hard component of the variety ‘Utac’ which was mixed. This allele, Pinb‐D1f, also involved a single nucleotide change such that Trp‐44 became a “stop” codon. A total of 62 winter wheat varieties were examined, of which five were soft and three were of mixed hardness. Of interest, the three mixed hardness wheats were ‘Turkey’, ‘Kharkof’, and ‘Weston’. The hard component of each carried the Pinb‐D1b allele. Of the 54 remaining wheats, all of which were hard, all but two carried this same Pinb‐D1b allele. ‘Chiefkan’ winter wheat carried the same Pinb‐D1e allele as ‘Canadian Red’ and ‘Gehun’ spring wheats. ‘Andrews’ hard red winter wheat possessed a new allele, designated Pinb‐D1g, which was a single nucleotide change in Cys‐56 to a “stop” codon. In conclusion, hard grain phenotype results from one of various mutations in either of the puroindoline proteins. To‐date, seven hardness alleles have been discovered and characterized in hexapoid wheat. All but one occur in the puroindoline b gene coding sequence and result from single nucleotide changes. These molecular markers are useful in characterizing lineages and analyzing ancestral relationships.