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Genetic Diversity and Heterosis of Spring Wheat Crosses

Pioneer Hi-Bred International, Inc., 30263 Country Highway 1, Redwood Falls, MN 56283
Plant Science Res. Unit, USDA-ARS, 411 Borlaug Hall, Univ. of Minnesota, St. Paul, MN 55108

Khalil Khan and Linda Huckle

Dep. of Cereal Science, Harris Hall, North Dakota State Univ., Fargo, ND

^* Corresponding author (busch005{at}maroon.tc.umn.edu).

Genetic diversity between parents may contribute positively to both heterosis and transgressive segregation. The objectives of this study were to determine (i) whether genetic diversity in spring wheat (Triticum aestivum L.) affected F₂ bulk heterosis and (ii) whether genetic diversity affected the amount of transgressive segregation among progeny from a cross. Genetic diversity was measured by pedigrees, morphology, and gliadin seed proteins. Heterosis was evaluated for 137 F₂ bulks tested at two Minnesota locations in 1993 and three locations in 1994. These bulks were developed from crosses among 91 cultivars. No linear relationship between genetic distance and F₂ bulk heterosis was detected. However, when crosses were divided into related and unrelated groups, crosses with parents unrelated by pedigree or morphology expressed greater heterosis than crosses with related parents. Bulks of crosses between cultivars that were classified as unrelated by two or more of the distance measures showed more heterosis than related crosses. Thus, part of heterosis seems to be due to parental diversity, though not in a linear fashion. Expression of greater-than-average heterosis by the highest yielding bulks, without an increase in genetic distance, suggested additional factors were influencing the expression of heterosis. Transgressive segregation was evaluated for six of the 137 crosses; 30 to 40 inbred lines from each of the crosses was evaluated in three environments. Data for these populations were consistent with an additive genetic model. The expression of heterosis was due in part to genetic diversity but was unpredictable and also depended on factors not elucidated by this study.

Received for publication June 25, 1997.

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