Localization of Outcrosses within the Panicle of Fertile Sorghum 1

SINCE it is known that Sorghum vulgare Pers. is mostly, but not completely, self-pollinated, a low percent of natural outcrossing must be expected in nursery material. In a breeding program off-type panicles in an otherwise pure line can result in many wasted crosses or undetected erroneous material. To reduce this outcrossing the bloomed portion of panicles used as pollinators could be discarded with the remainder self-pollinated by bagging. This would, however, involve considerable expense and loss of seed set. If sterility or partial fertility exists in an otherwise fertile line, it usually occurs at or near the top of the panicle. Also, from a morphological standpoint the lower flowers should have a better opportunity for self-fertilization, since flowering normally proceeds from top to bottom with only occasional later sectoring. Therefore, it was hypothesized that the greatest amount of outcrossing would be in the upper region of the panicle. To test this assumption, two varieties, Double Dwarf White Feterita and Combine Kafir 60-B, having the recessive condition of white seed, and 3-dwarf height factors, were located within a 1961 nursery population of red seeded strains and 1-dwarf forage sorghum and sudangrass strains. The two varieties were not planted in adjacent rows. Ten randomly selected heads were harvested from each variety. Before threshing, each panicle was separated into an upper 14 and lower %. In 1962, seed from the 2 por-