Introduction to the Jishu No. 15 Sweet Potato Variety and Its Cultivation Key Points

"Jishu No. 15" is a new high-yield, disease-resistant, high-quality special-purpose sweet potato variety bred by the Crop Research Institute of the Shandong Academy of Agricultural Sciences through a hybrid combination using the institute's innovatively developed excellent intermediate materials (female parent Jishu 85003, male parent Jishu 78268), and was approved and named by the National Crop Variety Approval Committee in August 2001.

I. Main Characteristics:

1. Yield performance: In 56 trials of Jishu No. 15 conducted over 9 consecutive years, the average fresh tuber yield per mu was 2,261.82 kg, a 13.62% increase over the control variety Xushu 18; the average dried tuber yield per mu was 782.77 kg, a 23.22% increase over Xushu 18.

In the 1989 seedling selection trial, this variety's fresh tuber yield was 25.8% higher than Xushu 18, and its dried tuber yield was 40.8% higher.

In nine identification trials conducted over three consecutive years from 1990 to 1992, the average fresh tuber and dried tuber yields per mu were 2,806.8 kg and 1,035.6 kg respectively, increases of 18.6% and 31.8% over Xushu 18; in 11 trials at different soil fertility levels from 1993 to 1997, the average fresh tuber yield per mu was 2,662.2 kg and the average dried tuber yield per mu was 985.01 kg, increases of 16.6% and 27.5% over Xushu 18 respectively.

In the Shandong Provincial Regional Trials from 1998 to 1999, based on yield results from 14 trial sites over 2 years, the average fresh tuber yield per mu was 2,460.0 kg, a 14.4% increase over Xushu 18, and the average dried tuber yield per mu was 895.0 kg, a 22.6% increase over Xushu 18. In the 2000 production trial at 7 sites, the average fresh tuber yield per mu was 2,064.6 kg and the average dried tuber yield per mu was 640.6 kg, increases of 12.3% and 18.9% over Xushu 18 respectively.

In the National Sweet Potato Northern Regional Trials from 1998 to 1999, based on yield results from 18 trial sites over 2 years, the average fresh tuber yield per mu was 1,957.2 kg and the average dried tuber yield per mu was 648.1 kg, increases of 6.8% and 17.2% over Xushu 18 respectively. In the 2000 production trial at 6 sites, the average fresh tuber and dried tuber yields per mu were 1,620.1 kg and 492.3 kg, increases of 13.04% and 21.3% over Xushu 18 respectively. The average dry matter rate was 30.2%, 2.1 percentage points higher than Xushu 18. In both major regional trials, its dried tuber yield ranked first.

2. Quality traits: This variety's drying rate and starch content were 2-3 and 1.82 percentage points higher than Xushu 18 respectively, ranking first among the varieties tested in the two major regional trials. Test results from the Food Quality Supervision and Inspection Testing Center of the Ministry of Agriculture (Jinan): Jishu No. 15 summer sweet potato drying rate 30.24%, 1.21% higher than Xushu 18; crude starch content 60.00%, 5.95% higher than Xushu 18. The sun-dried and oven-dried tuber slices are flat and smooth with bright color, with an overall quality rating of Grade 1. When steamed or roasted, the taste is sweet and fragrant, the flesh is fine and mealy, and the eating quality is rated above average.

3. Disease resistance: From 1990-1995 and 1998-1999, Jishu No. 15 participated in disease resistance identification trials conducted by the institute itself as well as the provincial and national northern regional trials. Identification results: the average disease index for root rot was 24.1, compared with 30.9 for Xushu 18; the average disease index for stem nematode disease was 30.6, compared with 49.3 for Xushu 18; in black spot disease-infested fields, seedling beds during the seedling-raising period, storage-period cellar-removal surveys, and disease resistance trial identifications, Jishu No. 15's resistance to black spot disease was of the resistant type. Results from years of resistance identification and trials show that Jishu No. 15 is highly resistant to root rot and resistant to stem nematode disease and black spot disease.

4. Storage tolerance and sprouting ability: Jishu No. 15 is tolerant to storage, and both spring and summer sweet potatoes can be kept for seed; cellar-removal surveys showed no dry tail, dry rot, soft rot, black spot, or skin shrinkage. It has good sprouting ability, emerging 2-3 days earlier than Xushu 18, with more than 50% more sprouts.

5. Morphological characteristics: Jishu No. 15 has light green terminal leaves, dark green leaves, green veins with purple vein bases, heart-shaped leaves that are slightly small; green vines that are short with many branches, and a semi-upright plant type. The tuber shape is spindle-shaped, the skin is purplish-red, the flesh is light yellow, and the tubers are uniform.

II. Cultivation Technical Key Points:

1. Cultivating strong seedlings: This variety has good sprouting ability and produces many sprouts. When raising seedlings, plant the seed potatoes sparsely, with a suitable planting density of about 25 kg per square meter. After sprouting, use constant-temperature seedling growth and low-temperature hardening to cultivate strong seedlings.

2. Appropriate close planting: This variety has short vines and is suitable for close planting. Density trials show that 4,500-5,000 plants per mu in hilly land and 4,000 plants per mu in dry flatland give high yields and a high proportion of large tubers.

3. Adaptability: Jishu No. 15 is drought-tolerant, relatively tolerant of poor soil, and highly disease-resistant. It is suitable for