The use of gene ig in sterile-counterpart production of corn lines
--Shatskaya, OA; Zabirova, ER; Shcherbak, VS

Gene ig (indeterminate gametophyte) was used as a source of high androgenetic haploid frequency for production of male-sterile counterparts of corn lines. Three types of stocks were included in the research work: stocks of ig/+ R-nj type from the genetic collection (USA), transferred into S and C cytoplasms (Chumak, 1977) stocks with different cytoplasms (Vg, CA, ME, SD, S, C) received from Kindiger, which have gene ig in a homozygous state due to B-A translocation, and hybrid stocks partly adapted to Krasnodar climatic conditions. From published data ig/+ R-nj stocks increase the frequency of androgenetic haploids to 2% (Kermicle, 1969) and ig/ig TB-3Ld stocks to 9% (Kindiger, 1992).

The aim of this investigation was to show the possibility of practical use of these stocks for male-sterile counterpart production. Stocks with gene ig were used as females, and several Krasnodar inbreds as males. Haploid kernels were selected from hybrid ears for endosperm and embryo coloration. Supposed haploids were planted in the field, where supplementary selection was done for phenotype. Matroclinous haploids and hybrids were excluded from further investigation. The selected androgenetic haploids were pollinated by corresponding lines -- sterility maintainers. Natural female fertility of androgenetic haploids was high enough that there was no need for colchicine treatment for chromosome doubling. We obtained 67 androgenetic haploid seedlings in 1996 (Table 1). Ten of 67 haploid seedlings were identified among polyembryonic kernels: two (n:n), five (2n:n), one (2n:n:n), and two (2n:2n:n). In addition, in one (n:n) kernel one haploid proved androgenetic and the other maternal.

Frequency of androgenetic haploids appeared to be significantly lower than described by Kermicle and Kindiger. It is necessary to note that we did not count the chromosome numbers of supposed haploids, and selection was done only on phenotypic traits. Some haploids, perhaps, were left in defective and aborted kernels. Only viable haploid plants have particular value for us.

Despite higher haploid frequency, cms ig/ig TB-3Ld R-nj stocks are less suitable for breeding practice against cms ig/+ R-nj stocks for some reasons. Their plants are not vigorous enough, the ears are small, endosperm and embryo coloration is not well enough developed, and their vegetation period is too long. Hybrid stocks appeared to be more suitable due to better plant phenotype.

All studied stocks will be convenient for practice after adaptation, and after increase of viable haploid frequency to at least 0.1%.

Sterile counterparts of Kr710Vg, Kr710CA, Kr726CA, Kr752ME, Kr752Vg, Kr10811S, RP-8C and Lu7C lines were obtained through these investigations.

Table 1. Frequencies of androgenesis in crosses of several inbred lines as male to ig female stocks.
 

					Comp. with cms ig/+ R-nj
Stocks	Ears	Kernels	Haploid Seedlings	Freq. of haploidy, %	X2	P
cms ig/+/R-nj	626	142,39 9	17	0.012	-	-
cms ig/ig TB-3Ld R-nj	127	29,111	12	0.041	10.58	0.001
Hybrid stocks
cms ig/ig TB-3Ld R-nj/N ig/+ R-nj	361	86078	38	0.044	21.80	0.001

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