Norihiko Tamaru1 and Toshiro Kinoshita 2
1)Agricultural Laboratory, Kushiro College, Hokkaido University of Education, Kushiro, 085 Japan; 2) Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan
Genetic male sterile mutants were induced in a cultivar 'Nihonmasari' by three mutagenic treatments, namely, chronic gamma-ray irradiation, see irradiation, and ethylen-imine treatment (Hiraiwa and Tanaka 1980). The present authors made cyto-histological observations of microsporogenesis and tapetal abnormalities of the above-mentioned materials. The following seven types of abnormalities of microspores and tapetum were observed in the 29 male sterile mutants.
1) Abnormality at PMC stage: PMC stage was prolonged to the stage of 4 mm lemma length. There was no pollen in the anthers which were shorter in length.
2) Abnormality at tetrad or early microspore stage: Just after the tetrad stage, various abnormalities of microspores such as inhibition of exine formation and giant pollen grains containing several nuclei were observed at the anthesis, most of the mutant lines had no pollen, except ms-5 in which giant pollen grains having abnormally thickened exine were mixed with various kinds of other abortive pollen grains.
3) Tapetal abnormality: Various types of tapetal abnormalities were observed in most of the mutant lines, without pollen. ms-10 and ms-12 sometimes produced a small amount of fertile pollen.
4) Abnormality at microspore stage: No abnormality was seen in the tapetum of anther locules. However, only a trace of degenerated pollen grains were attached to the anther wall at the anthesis. In ms-20, pollen grains developed nearly normally in some spikelets.
5) Abortive young pollen: The tapetum was basically normal, but most of the anthers contained aborted pollen grains characterized by thin exine. Various amounts of fertile pollen grains existed in several mutant lines.
6) Abnormal binucleate pollen: There were a plenty of binucleate pollen grains in the anther locules just before the anthesis. Mixture of aborted and normal pollen grains were seen in the anthers at maturity.
7) Stainable pollen: Normal pollen grains stainable by potassum iodide were abundant. There was no apparent abnormality in the tapetal disintegration and microspore development. Partial seed setting occurred in some lines having normal pollen grains.
As shown in Fig. 1, the 29 male sterile lines were classified into seven types according to the developmental stage of microspores at which anomaly occurred.
According to Hockett (1985), 34 different loci for genic male sterility were identified in barley by allelism tests. Therefore, it is probable that different genes for male sterility are responsible for the different types of pollen abortion in the induced genetic male sterile mutants.
Fig. 1. Diagrams illustrating normal microsporogenesis and the relationship between auricle distance and average diameter of pollen grains. The growth of lemma length measured in the spikelets at 4th location of uppermost primary branch are shown in the dashed line. The 29 ms-lines were classified into the seven types due to the stages of microspore breakdown.
Hiraiwa, S. and S. Tanaka, 1980. Induction of male sterile mutation in rice. Gamma Field Symposia No. 19, 103-115.
Hockett, E.A., 1984. Coordinator's report: the genetic male sterile barley collection. BGN 14: 70-75.