17. "Alien pollen primacy" detected in rice

Yo-Ichiro Sato

National Institute of Genetics, Misima, 411 Japan


In rice species, partial self-incompatibility has been found in O. longistaminata (Chu et al. 1969), and other mechanisms favoring outcrossing also have been known. The author has found a trend towards selective fertilization in which the stigma prefers alien to its own pollen in a mixed pollination experiment conducted in the summer of 1987.

Four kinds of crosses between two varieties, Taichung 65 (T65, Japonica) and IR36 (Indica) were made as shown in Table 1, where, for instance, T65X(T65+IR36) means that T65's pollen was set on the stigma first, and IR36's pollen was deposited five minutes later on the same stigma. Care was taken to deposit the same amount of the two varieties as far as possible. A mixture of pollen grains was not attempted since the pollen of rice remains fully functional for too short a time to prepare a mixture.

The crossed seeds were sown and examined for gene markers, lg (liguleless) and Sdh-1 (shikimate dehydrogenase) involved in the crosses. In the cross of T65x(T65+IR36), as well as in the cross of IR36x(IR36+T65), resultant sporophytes were nearly equally frequent, even though alien pollen was deposited five minutes later. In other two crosses, sporophytes resulting from fertilization by alien pollen were two to three times as numerous as those resulting from self-fertilization (Table 1).

The present data indicate an obvious advantage of alien pollen in mixed pollinations. A preliminary test indicated that the pollen tube length on the alien stigma was two times as long as that on its own stigma. The author calls this phenomenon "alien pollen primacy". Similar selective fertilization has been reported in maize (Pfahler 1967), raddish (Marshall et al. 1986) and other plants.


Table 1. Successive pollination of pollen grains of T65 and IR36 in different orders resulting in differential rates of fertilization according to the maternal parent

===============================================================================
                     Plants obtained from fertilization by pollen
Cross                ============================================
                      T65lg              IR36              Total
===============================================================================
T65lgX(T65lg+IR36)     39                 42                81
T65lgX(IR36+T65lg)     18                 58                76
IR36X(T65lg+IR36)      38                 19                57
IR36X(IR36+T65lg)      29                 32                61
----------------
T65lg: An isogenic line of T65 with gene lg.
===============================================================================


References

Chu, Y.E., H. Morishima dn H.I. Oka, 1969. Partial self-incompatibility found in Oryza perennis subsp. barthii. Jpn. J. Genet. 44: 225-229.

Marshall, D.L. and N.C. Ellstrand, 1986. Sexual selection in Raphanus sativus: Experimental data on nonrandom fertilization, maternal choise, and consequences on multiple paternity. Amer. Nat. 127: 446-461.

Pfahler, P.L., 1967. Fertilization ability of maize pollen grains, II. Pollen genotype, female sporophyte, and pollen storage interactions. Genetics 57: 513- 521.