Guozhong WANG, Zhanqian LU, Enrui CHEN, Qianyi XIAO, Guofu ZHOU, Zhonglun DENG,Zuguo CHEN

1. Qiannan Autonomous Prefecture Academy of Agricultural Sciences, Guiding 551300, China;

2. Qiannan Autonomous Prefecture Commission of Rural Affairs, Duyun 558000, China

Chuanxiang No.2058 is a new combination of three-line late indica hybrid rice bred by Qiannan Institute of Agricultural Science[1]and officially approved by Yunnan Committee of Crop Variety Certification in April 2009 through variety testing,regional testing and production demonstration (No.2009020). The growth period of the crop averages 151 d,and the variety is suitable to be planted in indica regions with an elevation below 1 200 m.

In the regional test of hybrid indica rice in Yunnan during 2007-2008, the yield of Chuanxiang No.2058 averaged 9 750 kg/hm2, increasing by 8.70% compared with the control;the yield of production demonstration test averaged 9 001.5 kg/hm2, increasing by 8.94%. Recently, thanks for highly-yielding cultivation technol ogy, average yield of Chuanxiang No.2058 maintains 9 750 kg/hm2and even 11 730 kg/hm2in high-yield fields.In general,the variety performs well in comprehensive characters, covering large ear, high setting percentage,stable yield, and high tolerance to coldness. In order to accelerate the application, Cengong County conducted investigation on seed production techniques during 2009-2010 and average yield reached as high as 4 297.5 kg/hm2.

Characters of Chuanxiang No.2058 Parent

Female parent Chuanxiang 29A

Chuanxiang 29A was sown in early April in Cengong County,Guizhou Province and rice earing staged from late July. The florescence lasts longer, and seedlings bloom in a concentrated period.Earing of individual plant takes about 6 d; flowering of individual plant takes about 6 -7 d;flowering of individual ear takes about 3-4 d. The rice plant can grow to 120 cm, and the number of leaf of stem is about 15. It grows exuberantly with astrong tillering capacity,and plant type is just appropriate. The stalk diameter keeps larger, and it is resistant to lodging, with large flag-leaf. Besides,it is tolerant to rice blast and sensitive to Rhizoctonia solani and “920”.The flowering peak is during 10:00-12:00 am and flowering rate reaches over 70% before noon. The angle of glume opening is large; the stigma grows long and large, and the exposing rate is 82%; the outcrossing rate is higher;ear and seed (150 seeds per ear)grow larger; thousand-seed weight is 26.5 g; rice organs above ground smells fragrant and rice quality is semi-transparent[2].

Male parent Qiannanhui 2058

Qiannanhui No.2058, a male parent, is produced in Qionglai City,Sichuan Province. It is sown from late March to early April, and the sowing period lasts for 105-108 d,with growth period of 138-140 d. The plant type is appropriate, and plant height is in the range of 120-125 cm; the stem grows sturdy and thick and tillering capacity is strong.The number of total leaves of stems is 15.0 and leaves grow wide and large. It is of higher tolerance to cold temperature. The florescence is longer,and the flowering habit is good.The period from heading to full-heading lasts for 8-10 d;ear heading of individual plant takes 5-7 d; the flowering peak is from 10:00 am to 12:00 am;ears grow more and large,and the number of seed reach 180-210 seeds per ear; the setting percentage is over 85%. The pollen content is abundant and anther develops well; pollen dispersion rate is high; glume is yellow and glume tip is colorless; thousandseed weight is about 27 g[3].

High-yield Seed Production Technique of Chuanxiang No.2058

Selection of seed production base

The hills or mountainous regions with elevations of 300-500 g, characterized by convenient transportation,separation and low wind velocity are ideal choices for seed production bases, where mean temperature, diurnal temperature difference, and relative humidity all meet flowering of the parents. Ear temperature keeps in the range of 28-32 ℃; relative humidity is in 70%-85%; diurnal temperature difference is 8-9 ℃. Therefore, parents bloom well,which is conductive to outcrossing,so that seed production yield reaches higher. However, if ear temperature is below 27 ℃or higher than 35 ℃, fertilization rate and fruit setting rate would be affected.

Rational arrangement of sowing gap stage

Seed production of hybrid rice requires suitable weather for flowering and pollination, as well as longer florescence for male and female parents meeting[4-5].It is notable that an appropriate sowing gap stage and a safe florescence stage are suitable for seed production of hybrid rice. In Cengong County, the sowing term and quantity of the seed production bases are as follows: Male and female parents are sown on March 26 and April 6 and the difference of 10 d is suitable;the sowing quantities of field are 60 and 15 kg/hm2, respectively. During flowering stage, it requires three successive sunny days, the temperatures during 11:00-14:00 of 23-35 ℃, relative humidity of 75%-90% and day-night temperature difference below 10 ℃.Therefore,it is necessary to determine sowing term according to climate information of seed production bases in order to guarantee flowering safety and improve outcrossing rate.

Seedling cultivation as per specific phases

Seedlings of male parent were cultivated as follows: The seedlings were cultivated in moist farmlands,but seedbed should be dry, available for both irrigation and drainage. Seeds are shown at 0.2 kg/m2uniformly and then covered with thin mulches. When two leaves grow,the mulch can be discovered for seedling hardening. In the 2ndphase, when 2.1-2.5 leaves grow,seedlings should be transplanted to paddy fields, at 13.3 cm×13.3 cm as per 2-3 seedlings per hole. The number of basic seedlings can be as high as 30 000 clumps/hm2, as per fined cultivation to guarantee male parent of 15 seedlings per clump averagely.

Female parents are sown in the compartments where irrigation and drainage are much convenient. Before sowing, the seeds are immersed in strong chlorine for 12 h, and then washed after draining off.The process can be repeated for multiple times.On the 7thand 14thd of sowing, mulches should be discovered for 2-4 h in a sunny day for soil hardening and the mulches should be totally collected in the period when two leaves and a heart leave grow in an evening with fine weather.If the weather is not fine,the practice should be postponed.

When seedlings grow for 15-20 d,fertilizer and water management and disease or insect prevention should be followed. When one leaf and a heart grow,urea is scattered at 30-38 kg/hm2; when two leaves and a heart grow, urea is applied uniformly at 45.0-55.5 kg/hm2; when three leaves grow,urea and K fertilizers are applied at 60.0 and 34.5 kg/hm2, respectively.The seedlings are irrigated as per different methods upon growth stages.For example, the rice was irrigated as per wetting irrigation and shallow irrigation.Seedling should be well irrigated before transplanting for the convenience.The transplanting of male parent has 3-4 tillers and the number of tiller is 1-2 lower for female parent. It is notable that 95% male/female parents should be transplanted together with tillers in order to improve the survival rate of seedling and the number of tillering.

Scientific arrangement of the ratio of the number of male/female parents per row

The male parents are transplanted when 7.5 leaves grow, and female parent transplanted within 30 d when 5.5 leaves grow. The leaf age should be strictly abided by at transplanting.Furthermore, the row direction should be from east to west or controlled vertically to valley wind to improve use rates of sunshine and pollen.The male parent-to-female parent ratio is kept at 2:14; the planting spacing of male and female parents are 33.3 cm×16.7 cm and 13.3 cm×13.3 cm; the male and female parents are transplanted to the farmlands at 45 000 and 435 000 clumps/hm2to guarantee the numbers of effective ear at 120 000 and 3 600 000 per hm2, respectively, and the ratio of effective ear of 1:3.

Management of fertilizer and water Fertilization management Abun-dant base fertilizer should be applied to control the quantity of N fertilizer.Then, 3-4 d before transplanting of male parent, decomposed manures are applied as base fertilizers at 15 000 kg/hm2, and specialized fertilizer for seed production is applied at 75 kg/hm2before transplanting of male parent. Subsequently, urea and specialized fertilizer are applied at 150 kg/hm2respectively 3 d after male parent transplanting, and urea and K fertilizer are applied at 75 kg/hm2during the 2nd-3rdstages of young male parent seedlings.

Rational management of water After transplanting, rice should be well irrigated to activate roots, and then, watering should be controlled.If seedlings of female parent reach 4 200 000-4 500 000 per hm2, water should be drained and farmlands dried. When seedling differentiation reaches the 5thstage, the seedlings should be irrigated to some extent to advance seedling development. In flowering stage, seedlings should be well irrigated to increase farmland humidity and reduce ear temperature in order to improve pollen quantity of male parent and stigma activity of female parent, and enhance fertilization rate and setting rate. Finally, 5 d before harvesting, water of farmlands should be drained and farmlands dried. It is notable that water drainage can be postponed to improve thousand-seed weight in shallow fields.

Adjustment of florescence with hormones

Fields, seedlings, florescence,and weather should be observed before using hormones in order to choose optimal irrigation method. In sunny days at higher temperature,spray irrigation is available before 11:00 or after 17:00 and spray irrigation should be conducted for a whole day in cloudy days. In rainy days, irrigation should be conducted once rains stop. Furthermore, seedlings should be irrigated if it rains 4 h after pesticide application. In seed producing farmlands where the planted female parents start heading stage 3 d earlier or the same as local one, Tiaohuabao, a plant growth regulator,and “902”can be applied at 60 and 30 g/hm2on female parents when 8% -10% ears grow. When 15% -20% ears grow,“920” should be applied on male and female parents at 120 and 150 g/hm2,respectively. If plant heights of male and female differ insignificantly, “920”should be applied just on male parent at 30 g/hm2in order to guarantee male parent plant height 20 cm higher. In contrast, in seed producing farmlands where heaadign stage of male parents starts 3 d earlier, “920” should be successively applied on female parents and male parents at 150 and 60 g/hm2, respectively, when 10%-15%ears of female parent grow.

Work on hand pollination

Hand pollination accelerates anther cracking and dispersion, improving pollen use rate and outcrossing rate. It is notable that the environment with temperature of 25-30 ℃and humidity of 80%-90%is optimal for hand pollination. Considering 10:20 am is flowering peak of male parent, and 10:30 of female parent, therefore,10:30 am is ideal for artificial pollination. Specifically, pollinating should be conducted 3-4 times during peak period, and the pollinating distance is about 30 m per time.In initial flowering stage and final flowering stage,pollination frequency can be reduced until a halt of male parent flowering. Specifically, the bamboo poles should be appropriate in size and the length should be controlled at 2 m. Besides, artificial pollination should proceed under the principle of “slightly pushing, heavily shaking and slowly returning”.

Comprehensive treatments on disease and pest damages

From transplanting to ripening stages, prevention priority should be given to rice blast, banded sclerotial blight, rice leaf folder and striped rice borer, and to neck blast, Rice kernel smut and rice planthopper in earing stage. The prevention work should be carried out under the principle of prevention first, supplemented by comprehensive controlling. Besides, seed disinfection, moth-killing lamp, and pesticides are all available.

Timely removing of abnormal and poorly-qualified plants to guarantee seed quality

Abnormal and poorly-qualified plants should be removed in multiple times during the whole seed producing process. In seedling stage, the plants with different colors or special plant types should be removed; in tillering stage,abnormal plants and maintainer line should be removed. The initial stage of earing is a key phase for removing abnormal and poorly-qualified plants.Abnormal plants and mutational varieties of male or female parents should be removed strictly. From transplanting to ripening stages, abnormal plants and mutational varieties are removed timely after artificial pollination. After full heading, late-season hybrid rice should be completely removed, followed by twice field examination.The first examination should be conducted when early-season hybrid rice represents 0.05% and the 2ndexamination carried out in milk-ripe stage, when late-season hybrid rice should be kept at 0.005%.

If 80% seeds ripe, the rice should be harvested in sunny days.However,male parents should be harvested firstly, followed by removing abnormal rice. Subsequently, female parents can be then harvested. The harvested male and female parents should be sunned separately in case of mixing.In addition, the collected seeds can be stored when moisture contents maintain below 13%.

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