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Genetic Variability for Seedling Root Numbers in Wild and Domesticated Wheats¹

Genetic variability for seedling root number within the genus Triticum was characterized to determine if this trait could be used in wheat breeding. Average seedling root numbers were determined in the laboratory for 143 accessions of wheat including the diploid species Triticum boeoticum Boiss., T. monococcum L., and T. urartu Tum.; the tetraploid species T. araraticum Jakubz., T. dicoccoides Körn., T. turgidum L. var. dicoccon Schrank and var. durum Desf., and T. timopheevi Zhuk.; the hexaploid species T. aestivum L. var. aestivum, vat. compactum, var. macha, var. spelta, var. sphaerococcum. and var. vavilovii, and T. zhukovskyi Men. & Er. Significantly differently mean root numbers were found within each ploidy level and, in most cases, within each species or variety. The highest mean root number, 6.45, was found in an accession of T. turgidum var. durum, the lowest, 2.50, in accession of T. araraticum. Seed weight was positively correlated with mean root number (r = 0.71) but within each ploidy level accessions having similar seed weights and significantly different mean root numbers were found. Progeny tests of 15 diploid and seven tetraploid accessions showed that seedling root number was stable from one generation to the next. A test of 33 of these accessions and progeny in a greenhouse experiment showed this trait was stable (r = 0.91) across the two environments tested.

Embryos sectioned by hand showed that all accessions tested had about five seminal root primordia present. In general, greater seedling root number may be selected for by selecting for higher seed weight, but exceptions to this rule were observed.

Key Words: Triticum • Drought tolerance • Domestication • Breeding • Selection • Seed morphology • Seed weight

² Former graduate student, associate geneticist, and former post graduate research geneticist (present address: Dep. of Plant Pathology, Kansas State Univ., Manhattan, KS 66502), respectively.

Received for publication November 27, 1978.