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Studies of Inbreeding Depression, Breeding Behavior, and Heterosis with Inbred Lines of Buckwheat¹

Homomorphic, self-fertile inbred lines of buckwheat (Fagopyrum esculentum Moench) are a recent development, and little is known about their potential for improvement of the crop. My objectives were to determine the breeding behavior of several inbred lines and to measure the effects of inbreeding depression and heterosis on several characteristics of buckwheat.

In polycross blocks during 2 years, all inbreds had reduced gross size, plant height, seed yield, and seed weight relative to an open-pollinated parent. The percentage of hybrid plants in the polycross populations ranged from 0 to 93. All polycross hybrids exhibited heterosis for plant height and dry weight at the early blossoming stage compared to their seed parent and to all the possible inbred pollen parents. During 2 years, populations with the highest percentages of hybrids were the highest yielding, but none exceeded the yield of an open-pollinated check strain.

The four inbred lines with the least selfing in the polycross trials were paired in enclosed areas to produce single-cross populations. ‘Kasho’, a cultivar with both compatible and incompatible pollen, also was paired with each of the inbreds. The percentage of hybrid plants in the inbred line combinations ranged from 5 to 72. Differences were found between reciprocal crosses for some combinations. When Kasho was the pollen parent, the percentage of hybrid plants ranged from 28 to 97. Regardless of the pollen parent, an inbred with the shortest style (0.58 vs. up to 1.16 mm) provided the fewest hybrids. The higher percentages of hybrids from Kasho pollinations apparently resulted from a differential rate of pollen tube growth that favored compatible pollen from thrum flowers. Differential pollen tube growth could provide pollen control to produce hybrid cultivars if thrum-flowered inbred lines can be developed.

Heterosis was studied in 10 of the single-cross populations. Relative to the high inbred parent, all single-crosses showed heterosis for plant height and total dry matter yield, eight showed heterosis for seed yield, and five showed heterosis for seed weight.

Key Words: Fagopyrum esculentum Moench • Self-incompatibility • Polycross populations • Single-cross populations • Hybrids • Self-fertility

² Research agronomist, SEA-USDA and professor of plant breeding, The Pennsylvania State Univ., University Park, PA 16802.

Received for publication November 9, 1977.