Wheat lines showing high flooding tolerance at reproductive growth stage
Koji Murai
Department of Bioscience, Fukui Prefectural University, Eiheiji-cho, Fukui 910-1195, Japan
Corresponding author: Koji Murai
Department of Bioscience, Fukui Prefectural University,
4-1-1 Matsuoka-kenjojima, Eiheiji-cho, Yoshida-gun, Fukui 910-1195
E-mail. murai@fpu.ac.jp
Abstract
To identify flooding-tolerant wheat lines at reproductive growth stage, ten lines selected by the previous seedling test were grown under flooding condition from seedling to maturing growth stage, and their flooding tolerance was assessed. Among ten wheat lines, U-1339, CNT-1 and #660 exhibited high tolerance with almost normal growth and fertility. These three lines were useful genotypes for developing highly flooding-tolerant as well as waterlogging-tolerant wheat lines.
Wheat (Triticum aestivum L.) is one of the most intolerant crops to soil waterlogging (Thomson et al. 1992). Soil waterlogging is a serious problem especially in central and southern parts of Japan, where wheat plants are cultivated in upland fields converted from rice paddy fields. Varietal difference of waterlogging tolerance was reported among wheat lines (Musgrave 1994), indicating that waterlogging tolerance is genetically controlled trait. From 1986 to 1988 in Japan, the genetic variation of waterlogging tolerance in wheat at seedling stage was examined by large-scale screening in National Agricultural Research Center for Western Region. Among more than 2,000 wheat lines, ten were selected as highly waterlogging-tolerant lines at the seedling stage (unpublished data; personal communication by N. Ishikawa). In this study, to identify highly waterlogging-tolerant lines at reproductive growth stage, ten lines selected by the previous seedling test were grown under flooding condition from seedling to maturing growth stage, and their flooding tolerance was assessed.
Ten wheat lines used in this study are as follows. U-1339 from Nepal, CNT-1 from Paraguay, Tohoku 185 from Japan, and #660 from Italy, which were selected as waterlogging-tolerant lines by the seedling test of 1986. NOVOSADSKA CREVENA, ISKRA and NS-302, all from Yugoslavia, were screened in the seedling test of 1987. Norin 12, Fukuhokomugi and Koyukikomugi, all from Japan, were screened in the seedling test of 1988. In addition to these ten lines, Chinese Spring, a standard line for wheat research, was used in the experiment. Seeds were sprouted in a growth chamber at 23oC, and seedlings were transplanted into soil in 1/5000a Wagner’s pot with a drain hole in a green house at 25oC. One pot was used for one seedling. Soil containing fertilizer for growing rice (Kumiai Lovely Tokotsuchi; N 0.36g, P 0.36g, K 0.36g /kg) was provided from JA Fukui Prefectural Economic Federation of Agricultural Cooperatives, and used in this experiment. For a dry-field condition pot (plot D), a wheat plant was grown in a soil-filled pot with the drain hole open. For a flooding condition pot (plot F), a seedling at the 1-leaf stage was flooded at about 2 cm above the soil surface in a soil-filled pot with the drain hole plugged, and the plant was grown until harvest time under the flooding condition. The following six characters were examined in maturing stage; culm length, tiller number per plant, ear length, spikelet number per ear, grain number per ear, and 1000-grain weight. Culm length, ear length, spikelet number per ear and grain number per ear were measured using the main shoot and its ear of each plant. These characters and tiller number were observed in two to five plants per line in each plot D and F, and the averages were subjected to statistical analysis. The 1000-grain weight was measured for grains from two to five ears per line. The effects of flooding on plant growth were assessed in comparison with plot F with plot D (F/D value: ratio of plot F to plot D).
Table 1 shows the mean values of six agronomic characters in ten wheat lines with high waterlogging tolerance at seedling stage and wheat cv. Chinese Spring grown, under plots D and F. Eleven lines were divided into four classes of flooding tolerance. Tohoku 185, ISKRA and Norin 12 were highly susceptible to flooding, and died during the vegetative growth stage in plot F (class I). NOVOSADSKA CREVENA and NS-302 showed no significant difference in culm length, tiller number, ear length and spikelet number per ear, but were completely sterile (class II). Fukuhokomugi, Koyukikomugi and Chinese Spring showed seed fertility but decreased 1000-grain weight (less than 0.6 in F/D value) (class III). This was due to shriveled kernels found in the plants of plot F (Fig. 1). U-1339, CNT-1 and #660 exhibited high flooding tolerance, with almost normal growth and there are no shriveled kernels in plot F (Fig. 1) (class IV).
This study revealed that ten wheat lines selected as high waterlogging-tolerant lines at seedling stage exhibited different flooding tolerance when they were grown under flooding condition from seedling to maturing growth stage. Wheat lines of class I was highly susceptible to flooding and died during the vegetative growth stage. Class II is intermediate type showing almost normal growth but completely sterility. Class III is also intermediate type showing almost normal growth and fertility, but yielding shriveled kernels. In soybean, Scott et al. (1989) reported that the early reproductive stage is more sensitive to flooding than vegetative stage. The present data suggest that in also wheat reproductive organs were more seriously damaged than vegetative organs by flooding. Based on a field test, Musgrave (1994) reported that yield depression of wheat plants caused by water stress was due to reduced grain number and grain weight. These findings indicate that we have to identify flooding-tolerant lines by the reproductive stage test as well as the seedling test for practical breeding program. Three lines of class IV have high flooding tolerance and show normal growth and fertility. These three cultivars, U-1339, CNT-1 and #660, came from different countries, i.e., Nepal, Paraguay and Italy, respectively, suggesting that different genes may be involved in the flooding adaptability. It is possible that we can develop wheat lines with higher flooding tolerance by pyramiding of these genes. Furthermore, these lines could be useful to study the mechanism of flooding tolerance in wheat.
Acknowledgements
Thanks are due to Dr. N. Ishikawa, National Agricultural Research Center for Western Region for providing wheat materials. Thanks are also due to Dr. A. Oyanagi, National Agricultural Research Center for Tohoku Region for valuable suggestions. This work was supported in part by a Grant-in-Aid for Exploratory Research from the Ministry of Education, Science and Culture of Japan (No. 23401).
References
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