Introduction to the Bo II You 15 Rice Variety
[Basic Situation] The Bo (Bo II) You series hybrid rice combinations are the mainstay combinations for late rice in Guangdong, Guangxi and Hainan provinces (regions). However, after years of cultivation, combinations such as Bo You 903 and Bo You 3550 have shown problems such as declining yield potential and weakened disease resistance, causing a marked decrease in planting area. In the early season of 1996, the male-sterile line Bo II A, bred by the Agricultural Science Institute of Bobai County, Guangxi, was crossed with our newly selected high-quality restorer line HR15 (Aihuangzhan x Qingliuai No. 1) to form the combination, producing Bo II You 15, which performed outstandingly in regional trials and production trials in Guangdong Province and the southern rice region. It has characteristics such as high and stable yield, strong resistance to rice blast, good adaptability and relatively good grain quality. It has been well received by farmers in production demonstrations, and its planting area has expanded rapidly. It is expected to become a major promoted combination for the new generation of late rice in South China.
[Characteristics] Bo II You 15 is a weakly photoperiod-sensitive combination. When planted in the late season in South China, its whole growth period is about 118 d, basically the same as Bo You 903. Tillering ability is medium, plant type is moderately compact, stems are thick and strong, it is tolerant of fertilizer and resistant to lodging, and the panicle type is relatively large. The upper functional leaves are thick and erect, and color turns well in the later stage. Plant height is 101-110 cm, effective panicles are 2.4 million-2.7 million/hm2, total grains per panicle are 140-160, seed-setting rate is about 85%, and 1000-grain weight is 22.5-23.0 g.
According to testing by the Rice and Rice Products Quality Supervision and Testing Center of the Ministry of Agriculture, the brown rice rate is 81.2%, the milled rice rate is 73.1%, the head rice rate is 62.0%, and the alkali spreading value is grade 6.4. These 4 indicators reach the ministry-issued first-grade standard for high-quality rice. Grain length is 6.0 mm, length-to-width ratio is 2.6, transparency is grade 2, and gel consistency is 42.0 mm. These 4 indicators reach the ministry-issued second-grade standard for high-quality rice. Chalkiness degree is 6.6%, and amylose content is 25.8%. According to evaluation by the Guangdong Provincial Grain and Oil Testing Center, the appearance quality of Bo II You 15 is grade 2, the same as Bo You 903.
According to identification by the Guangdong Provincial Crop Pest and Disease Forecasting Station, Bo II You 15 is resistant to rice blast (whole-population resistance ratio 85.0%, among which the resistance ratio to the dominant blast pathogen group C reaches 84.61%), and its overall rating for bacterial blight resistance is grade 7. According to identification in regional trials in the southern rice region, the average leaf blast rating is grade 3, the panicle blast rating is grade 1, and the bacterial blight rating is grade 7. When planted in multiple rice blast areas in Guangdong Province, Bo II You 15 showed resistance to rice blast.
In 1999, it participated in the Guangdong Provincial late-season weakly photoperiod-sensitive group regional trial, with an average yield of 6.68 t/hm2, ranking 2nd among the tested combinations, increasing yield by 7.49% compared with Bo You 903 (CK1) and by 3.18% compared with Bo You 3550 (CK2). In the late season of 2000, it participated in the second-round regional trial and production trial in Guangdong Province. The average yield in the regional trial was 6.48 t/hm2, 1.19% lower than the control Bo You 122, and the average yield in the production trial across 16 sites was 7.17 t/hm2. In 2000, it participated in the southern rice region South China late indica group regional trial, with an average yield of 7.70 t/hm2, increasing yield by 9.96% and 8.82% compared with Bo You 903 (CK1) and Jingxian 89 (CK2), respectively, both reaching extremely significant levels, and ranking first among the 9 tested combinations. In the late season of the same year, Bo II You 15 was demonstrated on 20 hm2 in Sanhe Village, Shengjiang Town, Luoding City, with an average yield of 8.36 t/hm2, among which farmer Zhu Shaoyuan planted 870 m2 with an average yield of 10.00 t/hm2.
[Breeder] College of Agriculture, Zhanjiang Ocean University
[Region and Technology] a) Sow at the right time and raise strong seedlings. For late-season planting in South China, Bo II You 15 should be sown in early July and transplanted from late July to early August. Do not sow too late, which would delay heading and shorten the vegetative growth period, thereby affecting yield. Sow sparsely to raise strong seedlings. Generally, the seeding rate in the seedling bed is 130-150 kg/hm2, and the seed rate for the field is 15.0-22.5 kg/hm2. The seedling bed should be given sufficient base fertilizer, a well-applied weaning fertilizer, a timely transplanting fertilizer according to seedling condition, and a good transplanting-protection pesticide spray.
b) Rational close planting and sufficient basic seedlings. The general transplanting density is 300,000 hills/hm2, with a spacing of 13 cm x 25 cm or 16 cm x 20 cm, and 900,000-1,000,000 basic seedlings/hm2.
c) Fertilizer and water management in the field. On the premise of applying sufficient base and surface fertilizer, apply tillering fertilizer early so as to promote early growth and rapid development in the early stage; in the middle stage, apply heavy panicle-strengthening and flower-protecting fertilizer according to seedling condition, and pay attention to combined application of nitrogen, phosphorus and potassium, while avoiding excessive late-season greenness. In terms of water layer management, it is advisable to transplant with shallow water or throw seedlings with muddy water, keep 1 cun of water for reviving, use shallow water to promote tillering, expose and sun the field in time once enough seedlings are reached, use moist irrigation in the middle stage to strengthen the panicle, use shallow water for heading and flowering, and keep alternating wet and dry conditions in the later stage. Do not cut off water too early, so as to avoid affecting the seed-setting rate and 1000-grain weight.
d) Pest and disease control. In high-incidence areas and severe outbreak years of rice blast, attention should still be paid to rice blast control, and importance should be given to controlling sheath blight and pests such as the striped stem borer, rice planthopper and rice leaf roller.
The male parent HR15 has relatively strong tillering ability, a relatively tall plant, large panicles with many grains, sufficient pollen amount, is sensitive to temperature, fertilizer and "920", and shows large differences in growth period between warm and cold years. The female parent Bo II A has medium tillering ability, strong lodging resistance, relatively good fertilizer tolerance, relatively large panicles, good flowering habits, a high stigma exsertion rate, a high outcrossing rate, and is sensitive to "920". For seed production of Bo II You 15 in early spring on the Leizhou Peninsula, the leaf age difference between the parents is about 5.5 leaves, while for winter seed production in Sanya, Hainan, the sowing interval between the parents is about 14 +/- 3 d, and the leaf age difference is about 3.8 leaves. Other cultivation and management techniques are the same as for seed production of general hybrid rice combinations.