No abstract

Harvesting and threshing are crucial processes that influence the quantity, quality, and economic efficiency of rice production. Therefore, the threshability of rice varieties is an important agronomic trait for breeding programs. However, selection for threshability is hardly standardized. With the application of an improved threshing meter, the threshability of four local temperate japonica rice varieties was determined during the ripening phase (DAF 37–60) in three consecutive years. Panicle threshing force (TF in N) was measured parallel with seed moisture content (MC) to describe differences in ripening habits of the genotypes. Shapes of the separation pilei were observed and the relationship with the different types of grain shattering was found. The different threshability patterns of the genotypes were found as quite stable along these periods. Moreover, correlation among TF, MC, and 5-day averages of meteorological parameters during the ripening phase was determined. Precipitation, Tmean, Tmax, and relative humidity had a significant influence on the MC. Based on our results, the MC had a low but significant positive correlation with the TF (0.312 *).

Doubled haploid (DH) plant production, such as anther culture (AC), is an effective tool used in modern rice breeding programs. The improved efficient protocols applied can shorten the process of breeding. The effect of combinations of plant growth regulators (2.5 mg/L NAA, 1 mg/L 2,4-D and 0.5 mg/L kinetin; 2 mg/L 2,4-D and 0.5 mg/L BAP) in the induction medium were compared in AC for five rice breeding materials and combinations. Induction of calli ranged from 264.6 ± 67.07 to 468.8 ± 123.2 calli/100 anthers in AC of rice genotypes. Two basal media (MS and N6) and two combinations of growth regulators (1 mg/L NAA, 1 mg/L BAP and 1 mg/L kinetin; 1.5 mg/L BAP, 0.5 mg/L NAA and 0.5 mg/L kinetin) were used as regeneration media. The in vitro green plant production was the highest with the application of the N6NDK induction medium (NAA, 2,4-D and kinetin) and the MS-based regeneration medium (1 mg/L NAA, 1 mg/BAP and 1 mg/L kinetin) in anther culture of the ‘1009’ genotype (95.2 green plantlets/100 anthers). The mean of five genotypes was 24.48 green plantlets/100 anthers for the best treatment. Flow cytometric analyses conducted identified the microspore origin of the haploid calli produced in AC, while the uniformity of spontaneous DH plants was checked in the DH1 and DH2 generations. Spontaneous chromosome doubling ranged from 38.1% to 57.9% (mean 42.1%), depending on the breeding source. The generated and selected DH lines were tested in micro- and small-plot field experiments to identify promising lines for a pedigree breeding program. The improved AC method was integrated in a Hungarian temperate rice pedigree breeding program.