Overview
Trees can be propagated by marcotting (air-layering), grafting and cutting. Many old orchards in Asia were based on seedlings, but these have generally been replaced by clonal material. Seedlings of course, are the source of new cultivars. Lychee nurseries generally supply marcots for new plantings, although grafting is also used in China and Viet Nam. Marcotting gives a strike rate of at least 80 percent, whereas grafting is more variable. The use of rootstocks for manipulating tree size, production and fruit quality is not well developed.
Propagation by seed is not usually recommended, since most seedlings take ten years or more to bear, and have poor to average fruit quality. Nevertheless, new cultivars can only be developed from the selection of seedlings with improved characteristics. New cultivars might bear more regularly, earlier or later than existing cultivars. They might also have larger fruit, brighter skin or smaller seeds. Some may store better than others.
Seed will keep for four weeks in the fruit after harvest, but begin to lose viability within a day if removed, and none germinate after four days at low humidity. More seeds germinate when stored in water for a day than when stored in vermiculite or air. Seed removed from fruit keep for eight weeks if stored in moist peat moss or similar media at 8°C.
Eighty percent of fresh seed germinate after three weeks, provided soil water and aeration are adequate. Large seeds germinate better than small seeds, and also have stronger growth initially. In contrast, chicken-tongue seeds are not viable. Growth is usually best with organic mixes, acid pH and inoculation with mycorrhiza. The seedlings should also be watered regularly and protected from strong winds. Temperatures from 25° to 30°C with high humidity are ideal. Seedlings that are to be evaluated as potential new cultivars can be planted out after a year. They are usually spaced one metre apart, much closer than in commercial orchards.
Few commercial plantings are based on stem cuttings. Success depends on choosing the correct type of wood, misting or fogging, and good temperature control in the propagation house. The rooting media also needs to be free draining. Some cultivars can provide an 80 percent success rate, however, cuttings take four months to root and another eighteen months in the nursery before they can be planted out. Young plants about 50 to 60 cm high are recommended. Smaller specimens often die.
Sixty to eighty percent of semi-hardwood and hardwood cuttings rooted in Australia with shoots are collected from older wood behind the soft tips in May prior to flowering. Soft terminal cuttings were unsuccessful. Authors in India and elsewhere report better results if the shoots were girdled a few months before taking the cuttings. Carbohydrates presumably accumulated above the girdle. Auxins also improve rooting, with the best response obtained with 100 to 200 mg per litre after soaking for a day, or with 5,000 to 10,000 mg per litre in a dip. Higher doses are toxic.
Some reports in India and Florida indicate that rooting is better when the cuttings are grown under partial shade. Provided the leaves do not dry out, full sun generally gives a quicker turnaround. Intermittent misting, or better still, fogging keep the leaves wet and cool without waterlogging the soil. Air temperatures of 20° to 25°C and roots at 30° to 32°C are recommended. The cuttings can be grown in sand with a little peat or vermiculite, but the pot must be well drained. Some workers also favour the application of fungicides. If the plants are growing quickly and not over-watered, diseases are less of an issue.
Marcotting or air-layering has been practiced in China for thousands of years, and is the most popular method of propagation. A branch on the parent tree is girdled down to the central hardwood to encourage adventitious rooting at the distal cut surface. Care must be taken to remove all the cambial tissue surrounding the white central wood. Otherwise, more vascular tissue is produced rather than new roots.
The marcot is detached from the tree after a few months and planted out in the field after a year or so. The success rate for commercial nurseries is normally more than 80 percent. Marcots come into bearing earlier than slower-growing cuttings or grafted trees, but have a shallow root system, with some cultivars susceptible to wind damage.
Upright branches about 2 cm in diameter and 80 cm long from well-developed trees, free from pests and disease are recommended. Rooting is best on sun-lit branches with mature growth. Marcots taken from thin, shaded branches often die or take longer to establish. Most authors recommend marcotting during the warm humid part of the year, when the roots are less likely to dry out.
The traditional method used soil, organic matter, sawdust and woodchips wrapped in cloth to enclose the marcot. However, moist peat moss and polyethylene bags are now exploited in many areas (Plate 5). The use of the plastic alleviates the problem of daily hand watering. A medium consisting of 100 percent peat moss and limed to a pH of 6 is ideal. Auxins sometimes improve rooting, but are not essential. Similarly, there is no need to girdle the branches beforehand.
Marcots are detached from the parent tree once they have formed sufficient roots to survive on their own. The appearance of old roots which turn brown is a good indication. Branches should be trimmed to form a good framework and 50 percent of the leaves removed to reduce transpiration. The marcot should be carefully removed from the plastic since the roots are very delicate at this stage, and planted in a well drained potting mix in a warm protected spot. A little shade at this stage often helps. Intermittent misting is also a good idea. You can retain more of the leaves and improve the turn-around of plants. Marcots seldom recover once they have lost their leaves.
Fertilizers can be applied once the young plants begin to produce new growth. The marcots should be gradually hardened off after completing two leaf flushes under full sun, before being transplanted in the field. Bare defoliated marcots sometimes sent overseas without soil can be difficult to establish.
Grafting and budding are used in some nurseries in China and Viet Nam. However, marcotting is more popular in other countries. The Chinese grafted and budded new cultivars several centuries ago, but they relied mainly on marcots for commercial propagation. It is only recently that this material has been evaluated in high-density orchards. Little thought has been given to using rootstocks to control tree growth, productivity and fruit quality as in apple and stonefruit. Related species and ecotypes have been suggested as potential rootstocks, but no commercial orchards have been developed on these systems.
Budding and grafting often fail because of incompatibility between the scion and stock. Poor grafting technique, grafting at the wrong physiological stage and poor care in the nursery can also cause problems. Incompatibility has been reported in some countries in the Region. For instance, “Wai Chee” is a better rootstock for “Salathiel” than “Tai So” in southern Queensland. “Wai Chee” is often used in China. Grafting techniques are well developed in fruit crops, and readily apply to lychee. Attention to the type of wood, protection from heat and sun, and the use of girdling all need to be considered.
Both marcotting and budding are popular in China. For the marcots, paddy soil with straw, sawdust or coconut husk are used for the potting media. Marcotting can be undertaken all year in Guangdong, but is generally carried out from April to July. Seedlings of “Wai Chee” are often used as rootstocks for “No Mai Chee”, “Kwai May”, “Bah Lup” and “Baitangying”, while “Haak Yip” and “Tai So” are used for “Fay Zee Siu”. The rootstocks are grown in field nurseries, 20 cm x 13 cm apart. The scions are taken from one year old twigs in late spring and early autumn to avoid hot, chilly or rainy weather, and the grafted plants planted out in the field after six months.
Marcotting has been traditionally used in Viet Nam; however, grafting has become popular since the 1990s. Sour lychee seedling rootstocks are used, with the scions taken from well-selected mother trees. Government nurseries covering some 8 ha produce one million plants a year.
Marcotting is the most common form of propagation in Thailand, India and Bangladesh. The best time to place the marcots on the trees is from late spring to early summer, with the new material ready for planting after eight months. In India, there are many Government and private nurseries supplying material, with about 300,000 plants produced every year. The Government nurseries are very popular selling good quality material at a low price. Prices are also lower in the Government nurseries in Thailand. In Bangladesh, there are 70 Government nurseries selling about 90,000 marcots annually. Seedlings were mainly used in Nepal, however the focus has now shifted to clonal material (marcots). There are many Government establishments, a few private nurseries, and some imports from India. The best time to strike the marcots is from March to May, with a reported 90 percent success rate.
There are a few private and Government nurseries selling marcots for about US$2.50 in the Philippines. The number of nurseries selling material reflects the limited cultivation of lychee in this country. Production of nursery material is also very limited in Bali, with only a few mother trees in Government plantings. Material for new plantings in Australia is normally only available as marcots. Cutting and grafting are very rare. Private nurseries account for most of the sales (US$6 per marcot).
Bibliography
Menzel, C. M. 1985. Propagation of lychee: a review. Scientia Horticulturae 25, 31-48.
Menzel, C. M. 1991. Litchi. In Plant Resources of South-East Asia Vol. 2. Edible Fruit and Nuts (E. W. M. Verheij and R. E. Coronel, Editors). Pudoc, Wageningen, The Netherlands pp. 191-5.
Zhang, Z. W., Yuan, P. Y., Wang, B. Q. and Qui, Y. P. 1997. Litchi Pictorial Narration of Cultivation. Pomology Research Institute, Guangdong Academy of Agricultural Science (no page numbers).
