Two independent sources of the twin-ear expression were identified in 1973. The sources of the progenies that showed the twin-ear expression were an S2 progeny of BS10(FR)C2-2388-10 and an S5 progeny of BSAAo2, an opaque-2 strain of BSAA. Twin-eared plants were selfed to advance to the next generation to verify its expression. Within the selfed progenies, some of the plants had twin ears and were selfed. The selfed progenies were grown in 1975, and the two sources of twin ear were crossed, BS10(FR)C2-2388-10 x BSAAo2. In addition, BS10(FR)C2-2388-10 was crossed to B37o2 and Oh43o2. In 1976, the BS10(FR)C2-2388-10 line and its crosses to BSAAo2S5, B37o2, and Oh43o2 were grown in progeny rows: the frequency of twin-ear expression was 67% (4 of 6 plants) for BS10(FR)C2-2388-10, 5.4% (3 of 56 plants) for its crosses with BSAAo2, 18.2% (2 of 11 plants) for the cross with B37o2, and none (0 of 10 plants) for the cross with Oh43o2. Except for the BS10(FR)C2-2388-10 progeny, the frequency of twin-ear expression was very low, even for the cross between the two cultures that had a frequent expression of twin ears.
The plants that had the twin-ear expression in 1976 were self-pollinated, but they were not grown until 1981. In 1981, 34 self-pollinated ears were planted ear-to-row and those plants that had twin-ear expression were self-pollinated. Twenty-one ears were saved that had the twin-ear expression, and these were planted ear-to-row in 1982. Plants within each progeny row were classified in 1982 to determine the frequency of twin-ear expression: 55 of the 327 plants (16.8%) showed the twin-ear expression. Among the 21 ear-row progenies, the frequency of twin-ear expression ranged from zero (23 plants with no plants having twin ears) to 42.1% (19 plants with 8 plants having twin ears). Fifty-six ears were harvested in 1982 for planting in 1983: 48 ears that were self-pollinated and eight open-pollinated ears were saved. The 56 ears were planted ear-to-row and the plants counted for frequency of twin ears. Of the 889 plants scored, 337 (37.9%) showed the twin-ear expression. Additionally, another 1% (9 of 889) also had the twin ear expression for the ear below the top ear node. The range among progenies was from zero to one progeny in which 17 of 20 plants (85%) showed the twin ear expression. There was not a strong association among families among years for the frequency of twin-ear expression. For example, families 2170, 2177, and 2180 had 9.1, 16.0, and 42.1% twin ears in 1982, whereas their progenies had 35.5% (27 of 76 plants), 36.1% (22 of 61 plants), and 36.8% (21 of 57 plants) twin ears in 1983. For the eight progenies obtained by open pollination, 16.9% (25 of 148 plants) had twin ears.
The twin ears have two separate ears with two separate shanks attached to the same node. It seems the occurrence of the twin ears must depend on some specific timing during the ontogeny of the plant. The occurrence of twin ears does not seem to be predictable, and its expressivity varies among progenies and plants within progenies. In 1983, some plants were observed to have twin ears at the second node below the top ear node, which had one ear. Other plants had twin ears at the top ear node and one ear at the node below the top ear. Additional studies are planned. Multiple pollinations were made on several plants in 1983. Because the twin ears are two separate ears, one ear was selfed and the other crossed with either another twin- or one-eared plant. The self and half-sib progenies will be studied to obtain further information on the twin-ear expression for these two sources.
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