It is known that normal seeds can develop by pollination of maize haploids by pollen of diploid plants. We observed this phenomenon in haploids of parthenogenetic line AT-1. The frequency of haploidy varied from 1 to 26 seeds on an ear. In 1986, 60 haploids of AT-1 line were pollinated by Mangelsdorf's tester pollen. 840 seeds were produced. Among them 72 matroclinous haploids, one androgenic haploid and 16 twins were discovered. 10 twins were of 2n-n type, 6 of n-n type. One twin of n-n type had both matroclinous and androgenic seedlings. Next year, in 1987, 390 seeds were produced from 40 haploids, developed from haploids. 48 matroclinous haploids and 9 twins were discovered among them. In 1988-1990 we continued to discover haploids formed on haploids of previous generations. The frequency of haploidy reached 10-20%.

So, during 5 generations, monoploid individuals served as sporophyte. This can be considered as an experimental system of seed reproduction on the haploid level. By a comparatively small number of plants (50-100) it can be maintained for a long time.

Later (1990-1996) we pollinated by diploid pollen haploids of another line, AT-3, which regularly appeared in the field. Haploids similarly developed on them. Subsequently haploid level was maintained during 2-3 generations by presence of 5-8 plants only.

We suppose, that development of haploids on haploids can be a diagnostic trait of parthenogenesis. This work was supported in part by a grant from the Russian Foundation for Basic Research. 

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