A HAPLOID WHEAT PLANT

Abstract

Hybrid I28, Triticum compactum humboldtii Kcke., is a prolific and popular winter wheat variety of the Pacific Northwest. It normally is diploid, having 42 chromosomes (2I pairs) in somatic cells. A plant was found in I925 in the cereal nursery of the Washington Agricultural Experiment Station at Pullman that had but 2I chromosomes. Examination at sporogenesis showed it to be a haploid plant. This plant was vigorous, tillered well, and could not be distinguished from a normal diploid plant until flowering time, when the spreading of the glumes characteristic of sterility drew attention to it (text fig. I). The seed which produced this haploid plant was supposed to be a cross between Hybrid I28 wheat and Aegilops cylindrica. Seeds from this cross are usually shriveled and weigh from 15 to 25 milligrams, but this kernel was plump and abnormally large, weighing 45 milligrams. Normal seeds of Hybrid I28 weigh from 25 to 35 milligrams, and seeds of Aegilops are much smaller. Evidently the injury to the flower in taking out the anthers or the stimulation of the Aegilops pollen caused this seed to develop without the addition of any male chromatin to the nucleus of the egg which formed the embryo. It is possible that both of the male gamete nuclei fused with the maternal endosperm nuclei, which would account for the giant endosperm. At any rate, the seed germinated and produced a plant resembling Hybrid I28 in every respect. It was marked in the records as it came into head. It is not uncommon in hybridizing wheat to break an anther in the process of emasculating the flower, or to introduce pollen by accident from the pistillate parent, in which case a selfed seed may result. About IO percent of the hybrid seeds obtained in wheat prove to be selfed and produce offspring exactly like the maternal parent in subsequent generations. It was not until the unusual flowering behavior of this haploid plant attracted attention that the notation in the record book was questioned and a cytological study was undertaken. The flowers stood open for 24 to 48 hours, whereas in normal fertilization the time is measured in minutes,