Wheat Generation Adding in Xundian County of Yunnan Province in Summer

Kong Zhi-you, Liu Ye-ju, and Qin Peng

1 College of Resources and Environment, Baoshan University, Baoshan 678000, Yunnan, China

2 Postgraduate Administration Off i ces, Yunnan Agricultural University, Kunming 650201, China

3 College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming 650201, China

Introduction

Crossbreeding is the most important and most eff i cient method of the developing new wheat cultivars(Triticum aestivum L.). However, the process of the crossbreeding requires plenty of the time (eight to ten years without reproduction. Developing new wheat cultivars to reduce the time are desirable and necessary for both producers and research institutions. Formerly,most of the wheat were sown in China from October to November and harvested from May to June, with only one generation obtained per year. Currently,two generations of the wheat can be cultivated per year through summer reproduction. The special climatic conditions of the specific locations greatly influence spike number, the amount of the grain per spike, thousand kernel weight, and wheat yield of the summer reproduction. It is very important to master the sowing time of the local ecological and climatic conditions, as well as the regulation of the growth and development, and to take the appropriate scientific measurements to improve the propagation coeff i cient of the wheat in summer reproduction.

Wheat go through heading and filling after vernalization after being sown in autumn. Vernalization is controlled by two nonallelic genes, Vrn1 and Vrn2, which are different in expression. Phosphodiesterase, zearalenone, cytokinin, and gibberellin are involved in the vernalization at low temperature.Exogenous zearalenone, cytokinin, and gibberellin can partially simulate the effects of a low temperature and shorten vernalization time (Fait, 2003; Fait,2007; Fedenko and Koksharoval, 2004; Beaabas and Csepely, 1978; Farina, 1976; Meng et al., 1986;Chai et al., 2000). As a demethylation reagent,5-azacytidine is used to treat the germinated seeds of Arabidopsis to reduce the level of the methylated cytosine. 5-azacytidine also induces blossoming in non-vernalization conditions. Vernalization and methylation are two separate regulated pathways of the methylation regulation, which in turn determines blossoming. This study hypothesized and confirmed that vernalization was regulated by DNA methylation(Burn et al., 1993; Finnegan et al., 1998; Ronemus et al., 1996; Lizal and Relichova, 2001; Genger et al.,2003).

A rate of four to six generations of the wheat per year has been obtained by inducing immature seeds to germinate 15 days to 20 days after anthesis by means of the treatment with hydrogen peroxide (H2O2)at low temperature (Depauw and Clarke, 1976; Mukade et al., 1973; Robertson and Curtis, 1967). When cereals are grown in plastic greenhouses with a waste heat system between January and June, the cereals exhibit complete vernalization and avoid winter kill. Breeding programs could be successfully accelerated by this growing type (Spunar and Sbornik,1988). F4and F5wheat seedlings were pretreated for 24 h at 4℃ and placed at room temperature until germination were fertilized using 0.25% solution containing 60% NH4HCO3and 40% KH2PO4, at the seedling stage of 2.5 leaves three times to four times at an interval of fi ve days. The resulting propagation coefficients of the wheat were 68.2 to 110.0 (Shu and Xiao, 2003). When winter wheat seedlings were grown at 18℃ to 20℃ with over 2 500 lux of the illumination in a cave, three generations per year could be grown under local conditions, with a growing period of 80 days to 90 days. The resulting wheat had a shorter plant height and spike length (Shun et al.,1989). Wheat was harvested in late September to early October and the seedlings were vernalized at 4℃ to 6℃ for 25 days, preheated to adapt to hot weather, and then planted on the north of side of buildings or under the shade of the trees to avoid the solar radiation (Gou et al., 2010).

Although the generation of the wheat has been accelerated by the above methods, some supporting facilities, such as greenhouse and vernalization room,were necessary, and a large number of the wheat materials could not be reproduced. In this study,shortening wheat cultivation to produce two generations a year was studied under field conditions with the use of vernalization room (for winter wheat and the semi-winter wheat)in Xundian County, Yunnan Province in China. The results would improve the progress of the wheat breeding.

Materials and Methods

Vernalization of strong winter wheat

Suyin 10, a winter wheat cultivar, was sown in germination boxes and placed in a vernalization room at 2℃. Suyin 10 seedlings were cultivated for 0, 10, 20,30, and 40 days, during which 0, 50, 100, 150, and 200 mg · L-1of gibberellin and 0, 15, 30, 45, and 60 mg · L-1of 5-azacytidine were sprayed on the seedlings once a day for 15 days. The completely randomized experiment was performed and the wheat seedlings were treated beginning on May 26. The growth periods and agronomic traits of the treated wheat were closely observed.

Sowing time of wheat in summer reproduction

Eleven spring wheat cultivars, namely, Yangmai 15,Yangmai 18, Yangmai 158, Yangmai 11, Ningmai 14,Ningmai 18, Zhenmai 8, Zhenmai 9, Yangfumai 4,Chuanmai 42, and Chuanmai 107, and one semiwinter wheat cultivar, namely, Luomai 21, were used in this experiment. The cultivars were sown in field with spacing of 3 cm for 10 times with an interval of fi ve days on May 26, May 31, June 5, June 10, June 15, June 20, June 25, June 30, July 5, and July 10. The growth periods and agronomic traits of the wheat were observed.

Determination of growth periods and agronomic traits

The effective tiller rate was expressed as the percentage of the ratio of the effective tiller to the total tiller. The propagation coef fi cient was the ratio of the harvested seeds to sown seeds. The amount of grain per spike, thousand kernel weight, and growth period was recorded in the fi eld.

Results

Changes in average air temperature in Xundian County

In Xundian County, the monthly average air temperatures exhibited no significant changes from May to November from 2009 to 2011 (Fig. 1). The monthly average air temperature increased slightly from May to July, decreased gradually, and then decreased sharply after September. Until November, the average air temperature was 10℃, about 10℃ lower than in July.There was no signi fi cant difference in the average air temperature between Xundian County and Kunming City.

Fig. 1 Average air temperatures monthly in Xundian County and Kunming City of Yunnan Province, China (2009-2011)

Vernalization of strong winter wheat

Suyin 10, a winter wheat, was treated at low temperature with 5-azacytidine and gibberellin to induce vernalization (Table 1). Low temperature is the most important factor in vernalization of the strong winter wheat. The jointing, heading, and maturation stage,the propagation coefficient, and the thousand kernel weight were remarkably affected by 5-azacytidine.However, only the heading stage and the thousand kernel weight were affected by gibberellin.

All the wheat plants that had matured before October 25 were treated at 2℃ for at least 30 days.The strong winter wheat plants treated at 2℃ with 50 and 100 mg · L-1of gibberellin and 30 mg · L-1of 5-azacytidine for 30 days exhibited growth periods that were shorter by 11 days compared with the plants only cultivated at 2℃ for 30 days, and shorter by 52 days compared with the untreated wheat plants(Table 2). The propagation coefficient of the wheat plants treated for 30 days at low temperature with 50 mg · L-1of gibberellin was higher than that of others.However, the thousand kernel weights of all the wheat plants were highly similar. Most of the wheat plants treated for 10 days and 20 days did not mature until November 30 (the plants treated for 10 days and 20 days did not mature and were not analyzed).

The strong winter wheat treated at 2℃ for 30 days exhibited the shortest jointing, heading, and maturation stages, and the highest amount of grain per spike,propagation coefficient, and thousand kernel weight(Table 3).

As 5-azacytidine concentration increased, the growth period, including the jointing, heading, and maturation stages of the strong winter wheat initially increased and then decreased, with the plants treated with 30 mg · L-1of 5-azacytidine having the longest growth period. However, the total tiller number was not significantly different among the plants treated with different concentrations of 5-azacytidine (Table 4).

Table 1 Variance analysis of vernalization treatment factors (F value)

Table 2 Growth periods and agronomic traits of strong winter wheat treated at low temperature with 5-azacytidine and gibberellin for vernalization

Table 3 Significant difference (least-significant difference, LSD)of growth period and agronomic traits of strong winter wheat on days with low temperature

Table 4 Signif i cant difference (LSD)of growth period and agronomic traits of strong winter wheat treated with 5-azacytidine

No signif i cant difference was observed in the jointing and maturation stages of the strong winter wheat when the gibberellin concentration changed. Thousand kernel weight increased as gibberellin concentration increased (Table 5). The growth periods and agronomic traits exhibited a high correlation with the days with low temperature. The correlation of 5-azacytidine and gibberellin concentration was not significant (Table 6).

A highly linear relationship was found between the days with low temperature and the growth periods and agronomic traits of the strong winter wheat during vernalization. The propagation coefficient was partially affected by 5-azacytidine concentration,and the total tiller number and thousand kernel weight were partially affected by the gibberellin concentration(Table 7). The results showed that the days with low temperatures were the most important factors of the vernalization.

Table 5 Signif i cant difference (LSD)of growth period and agronomic traits of strong winter wheat treated with gibberellin

Table 6 Correlation coeff i cients of treatment and growth periods and agronomic traits

Table 7 Stepwise regression analysis of growth periods and agronomic traits and vernalization treatment factors

Sowing time treatments of spring wheat cultivars

Eleven spring wheat cultivars were sown at different periods with an interval of fi ve days (Table 8). Nearly all the growth periods and agronomic traits were significantly affected by variety of sowing time.Sowing time did not have a significant effect on thousand kernel weight.

Highly signif i cant differences were observed among the 11 spring wheat cultivars in terms of growth period and agronomic traits (Table 9). The highest values for the heading and maturation stages were 90.3 days and 130.8 days, respectively, with Yangmai 15 having the longest heading and maturation stages. The agronomic traits, such as effective tiller number, effective tiller rate, grain number per spike, propagation coeff i cient,and thousand kernel weight, of the treated plants were significantly lower than those of the plants sown in season.

Table 8 Variance analysis of sowing time (F value)

With the passage of the sowing time, the growth periods of the wheat in summer reproduction were delayed accordingly (Table 10). On the whole, the growth periods gradually increased with the passage of the sowing time, whereas the agronomic traits gradually decreased. The correlations among the growth periods and agronomic traits are shown in Table 11. Effective tiller number, effective tiller rate, and the amount of the grain per spike were negatively related with sowing time, heading stage, and maturation stage, respectively.The amount of the grain per spike was positively correlated with the effective tiller number and effective tiller rate. The propagation coefficient was negatively related with the heading stage, but positively correlated with the effective tiller number, effective tiller rate, and the amount of the grain per spike.

Table 9 Signif i cant difference (LSD)of growth period and agronomic traits of 11 spring wheat cultivars

Table 10 Significant difference (LSD)of growth period and agronomic traits of 11 spring wheat cultivars with different sowing times

Table 11 Correlation coeff i cients of growth periods and agronomic traits in summer reproduction

Discussion

Optimal location and sowing time are very important for the summer reproduction of the wheat. To improve the sowing of the wheat in different seasons in China,the seeds for use in summer reproduction should not mature after October 25. Kunming City was selected as the location for the summer reproduction of the wheat 30 years ago, and most of wheat breeding units of China cultivate their wheat materials and new cultivars here every year in summer. However,given the demands of different types of the wheat for vernalization at low temperature, not all the wheat materials and cultivars could be routinely reproduced in Kunming City, because winter wheat, particularly strong winter wheat, should be treated at low temperature for some time.

The monthly mean temperature of Xundian County is similar to that of Kunming City, with no signif i cant changes from May to November observed over three recent years. The air temperatures during the earlier growth period of the wheat are relatively low, and are thus particularly well suited for the growth and booting of the wheat. Furthermore, the air temperature in Xundian County during the later growth period of the wheat is relatively high, which is particularly well suited for the fl owering and fi lling of the wheat. Thus,Xundian County should be considered as another suitable location for summer wheat reproduction.

Low temperature is the most important factor in the vernalization of the wheat, and a period of low temperature should be the most necessary and basic condition for the vernalization of the wheat. At least 30 days of the low temperatures is necessary for Suyin 10. Although the concentration of the gibberellin and 5-azacytidine had no signif i cant effect on the growth period and agronomic traits of strong winter wheat,the growth period of the strong winter wheat plants used in this study was shorted by 11 days when treated with specif i c concentrations of the gibberellin (such as 50 mg · L-1)and 5-azacytidine (such as 30 mg · L-1)under low temperature, compared with the growth periods of the plants merely cultivated at low temperature. These results indicated that gibberellin and 5-azacytidine might be partially involved in the process of the vernalization.

With the passage of the sowing time, the growth period of the spring wheat in summer reproduction became delayed, and the agronomic traits gradually decreased. Thus, the sowing time of the spring wheat should not be too late. The spring wheat varietied sown before June 25 matured before October 31,which did not significantly affect the sowing of the wheat in seasons. With the passage of sowing time,the propagation coefficient of spring wheat varieties gradually decreased. In consideration of the ripening stage, propagation coefficient, and seed plumpness,spring wheat varieties should be sown at the earliest to improve summer reproduction.

The semi-winter wheat variety had not ripened before October 25, when sown after June 5. However,wheat is not yet mature in most of China at that time,which means that the semi-winter wheat cultivars should not be reproduced in summer without any vernalization treatments. In this experiment, the semiwinter wheat cultivars exhibited head sprouting and ripening when treated at 2℃ for 10 days.

We wish to thank Academician Cheng Shunhe,Lixiahe Region Agricultural Research Institute of Jiangsu Province for guidance of the experiment design.

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