Garlic Virus-Free Propagation Technology: Using Aerial Bulbils as Seed
Garlic is usually propagated asexually through cloves (underground bulbs). Cloves are modified lateral buds and are part of the mother plant. Long-term asexual reproduction inevitably leads to the accumulation of viruses within the plant as well as the buildup of other undesirable traits, causing degeneration of garlic seed stock. However, the aerial bulbils produced by sexual reproduction of garlic undergo a natural virus-elimination process during the alternation of generations between sporophyte and gametophyte. According to many years of production practice, using garlic aerial bulbils (garlic beads) as seed can accelerate the propagation of elite varieties and has the effect of reducing virus accumulation and improving seed vigor. That is, in the 1st year, aerial bulbils are used as seed and most grow into single-clove garlic; in the 2nd year, the single-clove garlic is used as seed and grows into normal garlic heads; in the 3rd year, these garlic heads are used as seed for field production, and the yield can be increased by 30%-50%, with better seed stock quality. The key to this technology is to do a good job in the 1st year of production; the 2nd year is the same as conventional autumn-sown garlic production.
1 Seed reservation
When reserving seed from aerial bulbils, the garlic scapes should not be harvested. Wait until the garlic heads are fully mature and the plants have dried up, then harvest the aerial bulbils at about 70% maturity, and select those with a diameter of about 0.5 cm for storage through the summer. According to many years of field production experience, after the garlic bolts in the late growth stage, do not harvest the scapes, and delay the garlic head harvest period (when the plant leaves begin to yellow and wither, with 2-3 green leaves at the top and the pseudostem becoming soft) by 13-18 days. When the scapes turn yellow and the garlic plants are about to dry up, the aerial bulbils generally reach about 70% maturity.
2 Site selection and land preparation
Garlic has fibrous string-like roots with relatively weak water and fertilizer absorption capacity, and the bulbs grow and expand in the soil, so garlic should be cultivated on plots with loose soil, good drainage and rich organic matter. Garlic should not be continuously cropped; the previous crop is best as corn, legumes, cucurbits, tomato, potato and other crops.
Before planting, deep plow the land more than 25 cm. Along with plowing, apply heavy basal fertilizer. For every 667 sq m, apply 6000 kg of fully decomposed organic fertilizer or 4000 kg of chicken manure, and evenly mix in 50 kg of diammonium phosphate, 35-40 kg of potassium sulfate, and 1.0-1.5 kg of zinc sulfate (or the equivalent amount of compound fertilizer). Break up the soil finely and rake it level, then open beds and make furrows. During land preparation, depending on the specific situation, 2-3 kg/667 sq m of 5% phoxim granules may be mixed in to control underground pests.
3 Sowing
The optimal period for sowing aerial bulbils is to allow the plants to grow to 5-6 leaves before overwintering. At this time, the plants have the strongest cold resistance, will not be frozen to death in severe winter, and lay a good foundation for the plants to successfully pass vernalization. In the Yangtze River Basin and areas to its south, sowing is generally done in mid-to-late September. If sown too early, the seedlings grow too vigorously before overwintering and consume nutrients, which reduces overwintering ability and may also undergo vernalization again, causing secondary growth and the formation of multi-clove garlic in the 2nd year, reducing seed garlic quality. If sown too late, the seedlings are small, the tissues are tender, the root system is weak, less nutrients are accumulated, cold resistance is lower, and many die during overwintering. Therefore, the sowing period for aerial bulbils must be strictly controlled. In the 1st year, broadcast them in flat beds with about 1.5 cm of covering soil, keeping 120,000-150,000 plants per 667 sq m; in the 2nd year, cultivation is the same as field production, keeping about 40,000 plants per 667 sq m.
4 Field management
4.1 Seedling stage management
For garlic grown from aerial bulbils, the seed cloves provide very little nutrition during the seedling growth stage. In order to promote seedling growth and increase the plant's nutrient area, topdressing must be applied at the right time. Also, because garlic roots have a weak ability to absorb water and fertilizer, the topdressing should use quick-acting fertilizers to avoid nutrient deficiency that causes yellowing leaf tips.
① Seedling-promoting fertilizer: After the aerial bulbils have all emerged and before Frost's Descent, apply light decomposed human and livestock manure urine about once every 7 days to promote seedlings. During this period, do not apply ammonium bicarbonate to prevent burning the seedlings.
② Vigorous-growth fertilizer: 60-80 days after emergence, apply a heavy dressing of decomposed human and livestock manure plus chemical fertilizer, with 20-30 dan per 667 sq m (50 kg/dan, the same below) of decomposed human and livestock manure, 10 kg of ammonium sulfate, and 5 kg of potassium sulfate or potassium chloride. This promotes vigorous seedling growth and thick, strong stems and leaves, so that when garlic undergoes "mother clove decay" there is little or no yellowing of leaf tips.
4.2 Mid-stage management
The characteristics of mid-stage growth and development are that flower buds and bulbils differentiate successively and the plants enter the scape elongation stage. During this period, leaves 1-4 of the plants show yellow tips (the external manifestation of "mother clove decay"), old roots senesce, a large number of new roots emerge, and at the same time the stems, leaves and garlic scapes also elongate rapidly. Leaf area reaches its maximum, and the garlic heads also begin to expand slowly, so nutrient demand is high. Management mainly aims to reduce the degree of yellowing leaf tips. The measures are: first, clear ditches and drain waterlogging; second, apply heavy quick-acting potassium and nitrogen fertilizer (compound fertilizer is better). Generally in late March to early April, fertilize according to seedling condition. If seedling vigor is good, apply less to avoid causing the already formed young garlic clove buds to turn green and grow leaves again, consuming nutrients from the cloves. If seedling growth is poor, irrigate with 20-30 dan/667 sq m of dilute decomposed human and livestock manure and 6-8 kg/667 sq m of urea; third, remove scapes in time to reduce nutrient consumption. At the same time, weed frequently.
4.3 Late-stage management
After removing the scapes, garlic leaves and roots can be maintained for about another 20 days, then gradually yellow, wither and wilt. At this time, management should protect the leaves and roots, prolong their functional period as much as possible, and promote garlic head enlargement. When removing scapes, try not to damage the leaves.
5 Timely harvest
The signs for harvesting seed garlic at the right time are: the leaves are completely dry, that is, the upper leaves are dry and drooping, the pseudostem has begun to harden, and the garlic heads are fully grown. If harvested too early, the garlic heads are tender with high moisture, the tissues are not compact and not plump, they tend to shrivel after storage, and vigor the following year is also lower. When harvesting and storing seed garlic, use a hoe to dig on hard ground, or pull them out directly by hand on soft ground. To ensure that seed garlic has good vigor the following year, pay special attention to 2 points during harvest and drying of seed garlic: first, do not let it get rained on, to prevent the seed garlic from becoming moldy and rotting; second, avoid direct sunlight on the garlic heads, to prevent sunscald of the seed garlic.