Segregation analysis of heading time and its related traits in wheat F₂ populations between two Nepal landraces and a Japanese cultivar Shiroganekomugi

Shigeo Takumi

Laboratory of Plant Genetics, Graduate School of Agricultural Science, Kobe University, Nada-ku, Kobe 657-8501, Japan

Corresponding author: Shigeo Takumi

E-mail: takumi@kobe-u.ac.jp

Heading time is one of the most important traits for wheat improvement. Especially in Japan, rainy season is overlapped with wheat harvesting, resulting in occurrence of pre-harvest sprouting and Fusarium damage, and reduction of grain quality. Genetic control of heading time, therefore, is critical for wheat breeding in Japan. Landraces collected in Nepal, Bhutan and China abundantly provide natural variation (Kihara and Yamashita 1956; Redaelli et al. 1997; Ward et al. 1998).

To study the genetic variation of days to heading, seeds of 41 accessions listed in Table 1 were sown in 19th November 2005 (two seeds per accession) and plants grown under field conditions at Kobe University. Heading time of the landraces and a Japanese cultivar ‘Shiroganekomugi’ of common wheat (Triticum aestivum L.) was scored using the first column of the individual plants. Shiroganekomugi is a standard line for early flowering in Japan. Heading time among the 41 landraces varied from 141 to 160 days (mean = 153 days, SD = 2.8) (Table 1; Fig. 1). Two Nepal varieties, KU-4770 and KU-180, showed the earliest flowering in the examined accessions.

Next, KU-4770 and KU-180 were crossed to Shiroganekomugi, and heading and flowering time of the F₁ plants was compared with those of the parental lines in 2007-2008. Heading and flowering of the F₁ plants were as early as those of their parental landraces. Spike maturation time was estimated as the date to become completely yellowish peduncle after flowering. The maturation time of KU-4770 and KU-180 were earlier than that of Shiroganekomugi, and days to maturation of the F₁ plants were the middle of the days of parents (Fig. 2).

Seeds of the 51 and 52 F₂ plants, which were respectively selfed progeny of the KU-4770- and KU-180-crossed F₁ plants, were sown in 8th December 2007 and plants grown under field conditions. As a control, F₂ population with 104 plants between common wheat cultivar ‘S-615’ and ‘Chinese Spring’ (CS) was additionally used. Three field traits, i.e., heading, flowering and spike maturation dates, were scored in the three F₂ populations. In the F2 populations between Shiroganekomugi and Nepal landraces, much earlier- and later-heading plants were transgressively segregated compared with their parental accessions (Fig. 3A, B). On the other hand, heading and flowering dates of most F₂ plants ranged within the dates of their parental lines in the F₂ population of S-615 and CS (Fig. 3C). Some early- and late-matured F₂ plants were transgressively segregated, but the numbers of transgressive segregants were limited in the three F₂ populations (Fig. 3D-F). Days from flowering to spike maturation of most F₂ plants ranged in the middle of those of their parental accessions in the three populations (Fig. 3G-I).

Correlation coefficients among the examined traits were calculated in the three F₂ populations (Fig. 4). In all populations, days to heading, flowering and spike maturation were significantly correlated to each other. Correlations between heading and flowering times and days from flowering to maturation were negative in the F₂ population of Shiroganekomugi and KU-4770, which was not significant in the other populations. Days from flowering to spike maturation were significantly correlated with days to maturation in the F₂ populations between Shiroganekomugi and KU-180 and between S-615 and CS.

These results indicated that genes associated with early-flowering in KU-180 and KU-4770 were different from early-flowering genes in Shiroganekomugi. It is well known that heading time is genetically determined by vernalization requirement, photoperiodic sensitivity and narrow-sense earliness (Yasuda and Shimoyama 1965; Kato and Yamagata 1988). The early-flowering genes in the Nepal landraces might be associated with narrow-sense earliness and useful for breeding of earlier-flowering Japanese cultivars. Genetic mapping of the early-flowering genes in the Nepal landraces should be required for the breeding in the further study. Probably landraces in Nepal and Bhutan provide a lot of agronomically important genes for wheat breeding. Natural variation analyses of these landraces are efficient to identify the useful genes.

Acknowledgement

I thank Drs. T. Kawahara (Kyoto Univ.) and R. Ward (Michigan State Univ.) for the landrace seeds.

References

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