CHISINAU, MOLDOVA
Institute of Genetics and Physiology

The influence of ear age on the frequency of maternal haploids produced by a

haploid-inducing line

-- Rotarenco, VA, Mihailov, ME

Large-scale production of haploids in maize became possible when an ability to induce maternal haploids was revealed in Stock 6 line. Stock 6 line and its derivatives have a wide distribution among maize breeders, which, besides using haploids for breeding work, try to improve the haploid-inducing ability and explain the nature of this phenomenon.

Producing haploids every year by applying the same inducer – MHI (Chalyk, MNL-73, 1999), we have noticed that their frequency significantly varies: depending on the way of pollination – artificial or natural (Rotarenco, MNL-76, 2002), in different maternal genotypes and even within one ear (Chalyk, MNL-73, 1999).

It is known from the literature that delayed pollination increases the frequency of haploids (Randolph, 1946; Seaney, 1954; Chase, 1969). However, the opposite results have been obtained in our experiments.

The main purpose of our work was to estimate the influence of delayed pollination on the percentage of kernels with haploid embryo when a haploid-inducing line was used.

A number of hybrids and inbred lines have been crossed with the MHI inducer line by hand pollination. Plants have been divided into four groups within one maternal genotype – with two-day, four-day, seven-day and ten-day ears. The start day of the ear-age recording was the day of silk emergence and such ears were considered one-day ears. When the ears reached the needed age, they were pollinated with the inducer.

After harvesting, those genotypes that had rather good seed set and the best expression of the R1-nj gene (marker gene allowing kernels with haploid embryo to be identified) were selected. Thus, four inbred lines and four hybrids were used for the experiment (Table 1).

The number of ears in the each ear-age group varied from 10 to 15. Therefore, the total number of analyzed ears for the each genotype exceeded 40. In the lines MK01 and Мо17 the total number of plants was less than 40 that were divided into three and two groups, respectively. In the Mo17xB73 hybrid there were 37 plants and they were divided into two groups.

In all the genotypes the delay of pollination has caused a decrease of frequency of kernels with haploid embryo (Table 1) According to the coefficients of correlation, this decrease was statistically significant for the most genotypes. Additionally, a significant difference has been revealed between averaged percent of haploids in the inbred lines (6.2) and the hybrids (4.3). The average number of haploid kernels per ear has not changed significantly, except for the МК01 line (Table 2).

Table 1.

Frequencies of haploid inducing (%) in the four groups of ears and in general for the each genotype, coefficients of correlation

Maternal genotype	Day of pollination after silk emergence				General average	Coefficient of correlation, r
Inbred lines	2 days	4 days	7 days	10 days
A464	7.3	5.6	3.9	4.6	5.4	-0.45**
A619	7.1	6.1	4.8	5.3	5.8	-0.34*
MK01	10.3	6.2	6.2	-	7.6	-0.56**
Mo17	6.82	5.4	-	-	6.11	-0.27
On average for lines					6.2***
Hybrids
Modavian450	6.2	4.4	4.0	3.8	4.5	-0.39*
Porumbeni295	4.3	2.9	4.5	3.3	3.7	-0.15
Porumbeni359	7.0	4.2	2.6	2.9	4.1	-0.61**
Mo17xB73	5.5	4.2	-	-	4.8	-0.43*
On average for hybrids					4.3

*, **, *** significant at 5%, 1% and 0.1% level, respectively.

Table 2.

Average number of haploid kernels per ear in the four groups of ears and in general for the each genotype, coefficients of correlation

Maternal genotype	Day of pollination after silk emergence				General average	Coefficient of correlation, r
Inbred lines	2 days	4 days	7 days	10 days
A464	7.8	7.2	7.8	5.1	7.0	-0.18
A619	10.4	13.8	10.1	8.2	10.6	-0.17
MK01	16.1	9.4	10.7	-	12.1	-0.37*
Mo17	11.2	7.5	-	-	9.3	-0.31
On average for lines					9.7
Hybrids
Modavian450	9.4	8.8	10.0	9.6	9.4	0.01
Porumbeni295	11.4	10.6	14.5	9.8	11.6	-0.04
Porumbeni359	11.4	11.2	6.3	6.4	8.8	-0.36
Mo17xB73	14.7	15.0	-	-