Genetics Lab., Department of Biology, Wuhan University, Wuchang, Hubei, China
A cross of rice cultivar E-Wan 3 (O. sativa, genome AA, 2n=24)XO. latifolia
(Acc. 100165 from IRRI, genome CCDD, 2n=48) was made, and an F\1\ plant was
obtained by means of embryo rescue, culturing the ovary on a modified MS
medium. The F\1\ plant was an alloploid with genome ACD. It was intermediate
between the parental species morphologically and was completely sterile. It's
primordial panicles, about 1 cm long, were cultured in test tubes to recover
somaclones.
After several cycles of subculture, the SC\1\ plants were obtained which could be classified into two categories: 1) those similar to the F\1\ plant morphologically and sterile, and 2) those showing characteristics of O. sativa and setting seed by self-pollination. Plants of the F\1\ type were propagated by ratooning. The fertile SC\1\ plants produced SC\2\ and SC\3\ progenies through selfing. Observations of these plants are summarized as follows: 1) All fertile plants of SC\1\, SC\2\ and SC\3\ generations had 2n=24 chromosomes. Sterile SC\1\ plants had 2n=36 chromosomes. 2) Isozyme analysis for glutamic oxalo-acetic transaminase indicated that the zymogram of sterile plants was of the F\1\ type, while that of fertile plants was of O. sativa type. This serves as an evidence for the occurrence of segregants of O. sativa type in the somaclones of the alloploid. 3) In the microsporogenesis of the alloploid, abnormalities were observed after the zygotene stage of meiosis. Some pllen mother cells degenerated in prophase I. Unpaired chromosomes, laggards and formation of micronuclei were observed in metaphase I. After meiosis, normal tetrads were rarely formed, and pollen grains were empty or irregularly shaped.