Sprouting method of lettuce in high temperature season

Lettuce is an annual or biennial herb, 25-100 cm tall. The root extends vertically. Stem erect, solitary, distal panicle branched, all stem branches white. Basal leaves and lower stems large, undivided, oblanceolate, elliptic or elliptic-oblanceolate, 6-15 cm long and 1.5-6.5 cm wide, apex acute, shortly acuminate or rounded, sessile, base cordate or arrowhead-shaped semi-clasping, margin undulate or serrulate, acuminate upward, homomorphic or lanceolate to basal leaves and lower stems, leaves on lower branches of panicles and leaves on panicles very small. Ovate-cordate, sessile, base cordate or arrowhead-clasping, margin entire, all leaves glabrous on both surfaces. Inflorescences numerous or extremely numerous, arranged in panicles at the top of stem branches.

Involucral bracts of lettuce ovoid, 1.1 cm long and 6 mm wide; involucral bracts 5-layered, outermost broadly triangular, ca. 1 mm long, ca. 2 mm wide, outer triangular or lanceolate, 5-7 mm long and 2 mm wide, middle layer lanceolate to ovate-lanceolate, ca. 9 mm long, 2-3 mm wide, inner layer linear-elliptic, 1 cm long, ca. 2 mm wide, tip of all involucral bracts acute, outside glabrous. There are about 15 ligulate florets. Achenes oblanceolate, 4 mm long and 1.3 mm wide, compressed, light brown, with 6-7 veinlets on each side, apex acute into a fine beak, beak filiform, ca. 4 mm, as long as achenes. Crown hairs 2-layered, slender, scaberulous. The flowering and fruiting period is from February to September.

Lettuce is a straight root system, most of the lateral roots occur after transplantation, shallow and dense, mainly distributed in 20-30 cm soil layer. The stem is shortened. Leaves alternate, lanceolate or oval, etc., light green, green, dark green or purplish red, leaves spreading or wrinkled, entire or notched. The shortened stem gradually elongated and thickened with the plant growth. after the stem tip differentiated into flower buds, the stem grew thicker while the flower stem elongated, forming a rod-shaped fleshy tender stem. The flesh is light green, emerald green or yellowish green. Panicle with yellowish flowers, each inflorescence with about 20 flowers, self-pollination and sometimes cross-pollination. Achenes, black-brown or silver-white, with crown hairs.

Autumn lettuce is sown in high temperature season in summer and early autumn, and the temperature is high, so it is difficult for seeds to germinate, so special management should be carried out to cultivate strong seedlings. The optimum temperature for seed germination is 15 ℃ ~ 18 ℃, and the highest temperature is 28 ℃, and light is needed. Therefore, it is necessary to accelerate germination at low temperature before sowing lettuce in summer and autumn. The methods are:

1. Hanging well method: the seeds were soaked in newly proposed well water (about 15 ℃) or cold water for 5 hours, scrubbed 2 times, removed mucus impurities, removed and slightly dried, wrapped in wet cloth bags, suspended at 10 cm from the well surface, and the temperature was kept at about 15 ℃. Rinse with well water twice a day and sprout in 3 days.

2. Cold storage method: the seeds were soaked for 24 hours, scrubbed clean, wrapped with gauze, put in refrigerator or freezer, refrigerated at 3 ℃ ~ 5 ℃ for 24 hours, then placed in a cool and ventilated place, seeds germinated slowly. When the buds are white, spread them in a cool and ventilated place with scattered light, and pay attention to water spraying, moisturizing and anti-drying. 2-3 days later, when the germ appears light green, it can be sown. After sprouting and refining, the seedlings emerged neatly and had strong resistance to stress.

3. Sand mixing method: after soaking the seeds for 1 hour and 2 hours, mix with moist fine sand, put them on the edge of the air-raid shelter or water tank, keep cool and moist, and germinate in 3 to 4 days.

4. Irrigation covering method: after the seedbed has been roasted and whitened, the seedbed is leveled and fine, sowed with dried seeds, and covered with a thick layer of straw, then press the straw with a bamboo pole or brick. The seedbed was drenched with water every evening and the seeds germinated gradually in 2-3 days.

5. Growth regulator germination method: under the high temperature of 30 ℃ ~ 40 ℃, the seeds can also be soaked with 5 mg / L gibberellin for about 8 hours, and then rinsed with tap water, and the germination rate can be increased to about 80%. After sowing, it is necessary to build a shade shed (not covered on cloudy days) or a sunshade net, or sow seeds under melon racks or mixed with fast unearthed cabbage.