4. CULTIVARS AND GENETIC IMPROVEMENT

Overview

Lychee has been cultivated and undergone intensive selection for thousands of years in Asia. The main cultivars in China include “Fay Zee Siu”, “Bah Lup”, “Lanzhu”, “Baitang-ying”, “Haak Yip”, “Kwai May” (Red), “No Mai Chee” and “Wai Chee”. Some industries are mainly based on cultivars that are of Chinese origin. “Tai So” and “Wai Chee” form the basis of production in northern Thailand, while “Tai So”, “Kwai May Pink” and “Wai Chee” dominate plantings in Australia. In contrast, local seedling selections of Chinese cultivars are used in Viet Nam, India, Nepal, Bangladesh and southern Thailand. Cultivars developed in the last 50 years that are becoming increasingly important include “Donguan Seedless”, “Hexiachuan” and “Maguili” (Guangdong), “Sah Keng” (Taiwan Province of China), “Kom” and “Chacapat” (Thailand), “UPLB Red” (The Philippines) and “Salathiel” (Australia). Cultivars differ greatly in growth, yield and fruit quality. Opportunities exist for improving productivity in the Region by breeding new selections, with the emphasis on traditional breeding rather than on biotechnology.

4.1 Introduction

The first official mention of lychee in China appeared in the second century BC, while unofficial records date back 1,600 years earlier. A “Lychee Register” indicated that there were 16 cultivars in Guangdong in 1034 and 30 in Fujian in 1059. These figures had climbed to 100 by 1076 in Guangdong and a similar number, somewhat later (1597) in Fujian. Limited descriptions of cultivars were provided in the eleventh century, and full descriptions in the seventeenth century. Growers could distinguish the best ecotypes for the plains or hills. Marcotting was used in the fourth century and grafting in the fourteenth century. Propagation by seed was eventually eliminated in the sixteenth century.

The Chinese claim that lychee has more cultivars than any of their other fruit. A monograph on this species written by Ts'ai Hsiang in 1059 is considered to be the first publication in the world devoted to fruit culture. However, only about 15 of the 100s of cultivars available, are exploited commercially. In many other countries, production is based on one or two cultivars.

4.2 Standardization of names and classification of cultivars

A large number of cultivars are grown around the world, although the same cultivar may be known under several different names in different places, or even within a given country. This leads to confusion amongst researchers, advisors, growers and nurserymen. The standardization of cultivar names has been reviewed in Australia (Table 5), although some workers prefer the Pinyin spelling.

Chinese researchers report that the shape of the skin segments and protuberances can be used to identify cultivars. These characteristics are more reliable than fruit size, shape or taste. The key to the major cultivars is as follows.

A. The protuberances are protruding and hard.

1. The protuberances are relatively fine, dense and sharp-pointed. The skin segments are small and irregularly arranged. Group 1. “Tai So” type.

2. The protuberances are large, sharp and short-pointed. The skin segments are small and regularly arranged. Group 2. “Kwai May” type.

3. The protuberances are relatively blunt and short. The skin segments are relatively large, and irregular in size and arrangement. They are often small segments among the normal skin segments. Group 3. “Jin Feng” type.

B. The protuberances are hair-like or sparse, fine and sharp-pointed.

1. The skin segments are irregularly in size and arrangement. The fruit shoulder is extremely wide and pronounced. The stalk is thick and strong. Group 4. “Sum Yee Hong” type.

2. The skin segments are regular in size and arrangement. The fruit shoulder is flat. Group 5. “Haak Yip” type.

C. The protuberances are smooth or not evident.

1. The skin segments are obviously protruding, usually long and narrow-shaped, and arranged in longitudinal rows. Group 6. “No Mai Chee” type.

2. The skin segments are smooth or slightly protruding, usually near round in shape and irregular in arrangement. Group 7. “Wai Chee” type.

4.3 Productivity

The average yield of orchards in China is only 1.6 to 2.9 tonnes per ha. Not all trees are of bearing age, and many of the orchards are neglected. A well-managed orchard can produce 15 tonnes per ha in an 'on year'. Mature trees may produce 150 to 250 kg of fruit.

There is a paucity of published yield records of cultivars from replicated trials. Jawanda and Singh indicated that average yields of ten cultivars in India ranged from 12 to 130 kg per tree. The highest yields were obtained from “Calcutta” followed by “Seedless Late”, although the former cultivar is biennial bearing. Menzel et al. grew four cultivars in a replicated trial in Nambour in sub-tropical Australia. Yields after eight years varied from 0.1 to 28.5 kg per tree, equivalent to a maximum of 6.6 tonnes per ha at a density of 230 trees per ha. “Wai Chee” was superior to “Bengal” and “Tai So”.

Productivity is a problem in many orchards in the Region, with the reason for low average yields varying with country and district. Poor floral induction, fruit set or retention can affect individual orchards, districts or regions. Depending on climatic conditions within a given area, early- or late-season cultivars may be more regular. This often depends on when the trees flower and set fruit. Biennial bearing can also be a problem where orchards are neglected. Some cultivars are more susceptible than others.

Table 5. Standard names for cultivars in Australia.

(“Kwai May Pink” grown in Australia is not known as a separate cultivar in China. “Tai So” is similar to “Mauritius” in many countries).

4.4 Characteristics used to identify cultivars

4.4.1 Harvest season

The harvest normally lasts five to ten weeks for a range of cultivars in any one location. Cultivars can be broadly classified as early-, mid- or late-maturing, although the order varies from year to year, depending on seasonal conditions. There is also some variation in the Region, presumably due to differences in environment or culture.

4.4.2 Tree

You can learn to identify cultivars using tree characteristics, however, they change with weather, soil and culture. Differences in tree size and shape, and length and spread of branches are commonly used. For example, “Brewster” is vigorous and erect, with very wide strong crotch angles; “Tai So” is vigorous, with a spreading habit and sharp weak crotch angles; while “Wai Chee” is slow, compact and dome-shaped.

4.4.3 Leaves

Useful characteristics include leaf size, shape and colour. For example, “Tai So” has large, glossy, dark green leaflets that have an upward curl from the midrib to be almost canoe-shaped. “Bengal” has large leaflets, mid-green in colour with a distinctive twist along their length. “Haak Yip” has dark, glossy green leaflets that are long, narrow- pointed and slightly curled at the tip. “Wai Chee” leaflets are small, oval-shaped and curve upwards from the midrib and down along their length. The new flush of growth is red in “Wai Chee” and “Kwai May Pink” and green-bronze in “Tai So”.

4.4.4 Fruit

The shape of some cultivars is very distinctive (Figure 11). The round fruit of “Kwai May Pink” distinguishes it from the egg shape of “Tai So” or the heart shape of “Haak Yip”. The shoulders of the fruit can be smooth or flat as in “Wai Chee” and “Kwai May Pink”, or uneven as in “Souey Tung” and “Bengal”. The apex or tip of the fruit can be round as in “Kwai May Pink” and “Wai Chee”, obtuse or blunt as in “Souey Tung” and “Brewster”, or pointed as in “Bengal”.

Typical colours are bright red (“Bengal”), dull red (“Wai Chee”), purple-red (“Haak Yip”) or pink-red (“Brewster”). The skin can be thick as in “Wai Chee”, “Bengal” and “Kwai May Pink”, or thin as in “Haak Yip” and “Souey Tung”. Skin segments at full maturity can be smooth (“Haak Yip”), swelling (“Wai Chee”) or sharp-pointed (“Kwai May Red”). Similarly, the protuberances on each segment can be smooth as in “Haak Yip”, sharp-pointed as in “Kwai May Red” and “Bengal”, or hair-like and sharp as in “Tai So”. The presence or absence of an obvious suture line can distinguish some cultivars such as “Haak Yip” and “Souey Tung”.

The texture, juiciness, taste and aroma of the flesh can aid description, although experience is needed to make clear distinctions. For example, “Wai Chee” is watery, “Kwai May Red” is firm, “Kwai May Pink” is spicy and “Bengal” is very sweet.

The proportion of small or shrivelled seeds is important, but varies with season and orchard. Cultivars with a high proportion of chicken tongue seeds are favoured. In Australia, “Salathiel” nearly always produces fruit with small seeds, while “Bengal”, “Souey Tung”, “Haak Yip” and “Wai Chee” produce hardly any. Other cultivars such as “Tai So” and “Kwai May Pink” vary.

4.5 Major cultivars in the Region

Major cultivars in the Region are listed in Table 6.

The most important cultivars in Guangdong are “Bah Lup” (27,000 ha), “Baitang-ying” (27,000 ha), “Haak Yip” (34,000 ha), “Fay Zee Siu” (27,000 ha), “Kwai May” (60,000 ha), “No Mai Chee” (60,000 ha) and “Wai Chee” (40,000 ha). “Wai Chee” accounts for over 80 percent of plantings in Guangxi, and bears consistently because it flowers late and avoids cool weather in spring. In Fujian, “Lanzhu” dominates plantings. Some new cultivars have been developed recently including “Donguan Seedless” and “Hexiachuan” that produce seedless or small-seeded fruit, and “Maguili” that crops late in the season.

“No Mai Chee” and “Kwai May” have excellent eating quality and a high proportion of chicken tongue or aborted seeds. “Fay Zee Siu” is also popular because of its excellent eating and size (24-32 g). Some cultivars are best eaten fresh, while others are more suitable for canning or drying. Cultivars exported include “Sum Yee Hong”, “Fay Zee Siu”, “Haak Yip”, “Kwai May”, “Wai Chee” and “No Mai Chee”.

“Haak Yip” is the most popular cultivar in Taiwan Province of China and accounts for over 50 percent of plantings. Other important cultivars are “Sum Yee Hong”, “Chong Yun Hong”, “No Mai Chee” and more recently “Sah Keng”.

Figure 11. Fruit characteristics used to describe different cultivars.

Eight cultivars are grown commercially in Viet Nam; however, production is dominated by a single cultivar, “Vaithieu” that accounts for 80 percent of plantings. Because the industry is based on a single cultivar, the harvest is unduly short, lasting only four to six weeks.

The main cultivars in northern Thailand are “Tai So” (“Hong Huay”, 65 percent of production) and to a lesser degree “Wai Chee”, “O-Hia” (“Baidum”) and “Chacapat” (“Chakrapad”). A different set of ecotypes has been developed for the areas around Bangkok, including “Kom” (11 percent of plantings), “Luk Lai”, “Sampao Kaow”, “Kaloke Bai Yaow”, and “Red China”. The quality of these selections is not as good as those in the north.

Table 6. Major cultivars in Asia and the Pacific.

Most of the cultivars in India have been selected from seedlings sent from China, although a few appear to be renamed Chinese cultivars, as in Thailand and Australia. Selections have been developed which can crop in the hot and dry conditions. Of the 30 or so cultivars grown, only six are commercially important: “Shahi” (“Muzaffarpur”), “China”, “Calcuttia”, “Bedana”, “Late Bedana” and “Longia”. These generally have large fruit and excellent quality. In West Bengal, “Bombai”, “Shahi” and “Rose Scented” can produce 40 kg per tree compared with 15 to 25 kg per tree in many of the other cultivars.

In the hilly areas of Nepal, commercial production is based on various seedlings, whereas there are established cultivars in the plains (“Majafpuri”, “Raja Saheb”, “Deharaduni”, “China” and “Calcuttia”). Most of these probably came from India. The most important cultivars in Bangladesh are “Bombai”, “Muzaffarpuri”, “Bedana” and “China Number Three”. “Bombai” is the oldest cultivar. “Bedana” has the best quality, but is low yielding.

“Mauritius” and a local selection from China, “Sinco” dominate production in the hilly areas of the Philippines, while an introduction from Thailand, “UPLB Red” is planted in the lowlands. The Department of Agriculture is also evaluating two new selections for the warmer areas. Lychee is a minor crop in Indonesia, with a few Government nurseries selling clonal material.

Lychee plants (seedlings?) were growing in the Sydney and Brisbane Botanical Gardens in Australia in the 1850s. Air-layers of “Tai So” and “Wai Chee” were not introduced until the 1930s. Plant material was subsequently distributed further along the eastern coastline, and production now extends from Cairns and The Atherton Tableland in northern Queensland to Coffs Harbour in northern New South Wales. “Kwai May Pink”, accounts for more than 50 percent of plantings, with “Tai So”, “Souey Tung”, “Fay Zee Siu”, “Salathiel” and “Wai Chee”, the other main cultivars.

4.6 Description of major cultivars

“Sum Yee Hong” is the earliest cultivar in Guangdong, and finds a ready market in spite of its average quality compared with later cultivars. It is grown along watercourses particularly in the suburbs of Guangzhou and Zhong Shan District and can be a heavy cropper. “Sum Yee Hong” has also been imported into Australia, but is found only in northern areas. The tree is medium in size with an open, spreading habit and long, thin, fragile branches. The leaves are long, narrow, shiny dark green and much thicker than other cultivars. The fruit are exceptionally large (26-42 g) with bright red, thick skin that peels easily. The flesh is very juicy, and sweet-acid. The seeds are generally large.

“Souey Tung” is a popular early cultivar in Fujian. It has been distributed to Australia, but is not as widely grown. “Souey Tung” tolerates a high water table and is planted along watercourses in China. It is reported that rain near harvest causes the fruit skin to discolour, due to black mildew. The tree is relatively low with thin, long, open, spreading branches that point downwards. Leaflets are large, flat, dark glossy green and pointed. The new flush of growth is bronze changing to red and green with maturity. Fruit are medium (20-22 g), and heart-shaped with distinctive uneven shoulders. The skin is thin, dull dark red to purple, and smooth. The fruit tip is obtuse or blunt. The flesh is soft, juicy, sweet and of excellent quality. Seeds are variable in size, but mostly medium giving a good flesh recovery of 65 to 75 percent. There are only 5 to 10 percent abortive seeds.

“Bah Lup” is a productive Chinese cultivar and has better quality than others available at the same time such as “Sum Yee Hong” and “Souey Tung”. It is grown in Dian Bai and Gao Zhan Counties in Guangdong and is an important early variety for export. The tree is medium in vigour and dome-shaped. Leaflets are long, narrow, dark glossy green with a short point. Fruit are near heart-shaped, medium to large (20-29 g) with thin, soft, brilliant red to slightly purple skin. Protuberances are obtuse. The flesh is juicy and delicately sweet. Fruit usually have large oval seeds. Flesh recovery is up to 77 percent.

“Tai So” is a common cultivar in China, Thailand and Australia, although yields tend to be irregular. Trees often flower poorly or have insufficient numbers of female flowers to provide good fruit set. Trees are vigorous and spreading with an open crown, and have branches with weak crotch angles that can split. Even large trees may suffer damage. Leaflets are large, glossy dark green and have an upward curl from the midrib to be almost canoe-shaped. The new flush of growth is bronze changing to dull mid-green to pale green with advancing maturity.

Fruit are large (22-26 g) and somewhat egg-shaped, with flat shoulders and a round tip. The thin skin is bright red changing to dull red at maturity (Plate 1). Protuberances are hair-like/sharp-pointed when the fruit are ready to harvest. Fruit are not of good quality until fully mature. Flavour is sweet-acid when immature, sweet when fully ripe, and bland when overripe. Flesh is slightly chewy becoming moderately crisp when fully mature. Seeds are medium, giving a fair flesh recovery of 60 to 70 percent. Up to 50 percent of fruit have chicken tongue seeds, depending on the season. Fruit often split or brown in hot dry weather.

“Fay Zee Siu” is ranked as one of the best export lychees in China, and has been recently imported into Australia. The fruit is described as having the colour of amber, the size and shape of a goose egg, and the sweetness of honey. It is mainly grown in and around Guangzhou, with fruit maturing early in the season, before “Tai So”. The tree is vigorous with long, sparse, fragile branches that can break. Leaflets are large, narrow and deep glossy green. Fruit are large (24-32 g), round to oval-shaped with thin, light red, splotchy skin. The flesh is firm, sweet, delicious and very fragrant. Seeds are variable, giving a flesh recovery of 77 to 82 percent.

“Haak Yip” is a very popular cultivar in China, Taiwan Province of China and northern Thailand (“O-Hia”), but has undergone limited distribution elsewhere. It is commonly canned in Taiwan Province of China. Fruit mature about a week after “Tai So”. Trees are medium, with dense foliage and long, thin, fragile branches. The leaflets are very dark, glossy green, long, narrow-pointed and slightly curled at the tip.

The heart-shaped fruit are medium (20-22 g) and formed in large compact clusters (15-30 fruit). The purplish red skin is thin and soft and prone to insect attack, and has a distinctive suture line. Shoulders are wide and even. The skin is smooth, with no raised protuberances. The flesh, which separates easily from the seed, is sweet, crisp, slightly aromatic and of excellent quality. Seeds are medium and fully developed, giving a flesh recovery of 68 to 76 percent. Fruit are exported from China. “Haak Yip” can be distinguished from the related “Souey Tung” by its slightly later maturity, even shoulders, obvious suture line, firmer flesh and more uniform and slightly larger seeds. Both are good marketing types when grown well.

“Brewster” was obtained from Fujian by the Reverend W. M. Brewster and propagated in Florida in 1903. It was also sent to Australia, but is not popular. In 1948, W. Groff suggested that “Brewster” was, in fact, the recognized Chinese variety “Chen Zi” (“Chen Family Purple”) and recent information indicates that they are the same cultivar. Production in Australia has been disappointing, whereas in Fujian, trees grown along the rivers yield consistently, with a high proportion of small seeds. Fruit with chicken tongues shed more readily under drought or heat than those with full seeds.

Trees are small and upright, with wide, strong crotch angles and dense foliage. “Brewster” is one of the few cultivars with distinct lenticels or corky outgrowths on the branches. Leaflets are large, dark green and pointed at the tips. The new flush of growth is reddish-brown. The medium to large fruit (20-26 g) are heart-shaped and have a bright pink-red, thick, rough skin, and are borne in small loose clusters. The shoulders are uneven, with one raised ridge along the suture line of the shoulder. The fruit tip is round in full seeded fruit to pointed in chicken tongue fruit, and have small nipple-form protuberances. The flesh is slightly fragrant, juicy and sweet when fully ripe, but acid when immature. Seeds are small to medium, with up to 80 percent undeveloped after cool weather. Plump seeds are oblong with a blunt tip. Flesh recovery is 65 to 75 percent.

“Kwai May Red” is highly regarded in China, but is not grown widely elsewhere. Fruit are of good quality, although the tree is a shy bearer. Panicles normally carry only a few fruit due to poor set. In Australia, trees resemble those of “Kwai May Pink”, but are more spreading. They have long, thin branches that curve upwards towards their tips. Leaflets are small, oval-shaped and shiny green. Leaflets are slightly larger than “Kwai May Pink” and flatter. The new flush of growth is red. Fruit are almost identical to those of “Kwai May Pink”, except that “Kwai May Red” has red rather than pink-orange skin, firmer flesh, a higher proportion of chicken tongues (50-60 percent), higher flesh recovery (70-80 percent), and a slightly better flavour. The fruit are distinctly aromatic and are exported from China.

“No Mai Chee” is one of the most highly-prized cultivars in China and widely grown in the suburbs of Guangzhou, Dong Guan, Zong Cheng, Pan Yu and other districts. It appears on the market late in the season and commands a high price; usually three to four times that of other cultivars. The fruit are large (21-28 g) and nearly all with chicken tongues, giving a flesh recovery of 75 to 85 percent. The flesh is very smooth, firm and clean, with a distinctive sweet fragrant flavour. It is suitable for fresh fruit and drying. The tree is large and tall with a dense canopy and slim branches that hang down. The leaves are small, soft and thin, with a wavy edge. “No Mai Chee” has been in Australia for a long time, but is not widely grown. It does not appear to crop as heavily as in China.

“Wai Chee” is one of the most common cultivars in China and is also popular in Thailand (“Kim Cheng”) and Australia. It is fairly regular across most districts in China, but variable in Australia. Trees often flower lightly in the warm northern areas, and may be biennial in southern districts. Mature fruit can hang on the tree for several days. This adds some flexibility to harvesting and extends the production season. Trees initially lack vigour and establish slowly after planting. They are low, dome-shaped with thick branches, compact foliage and many growing points. They are susceptible to wind damage, unless thinned out and the lower branches removed. The small leaves are oval-shaped and curve upwards from the midrib and down along their length. New flushes of growth are deep red.

The small (16-18 g) rounded fruit are formed in small loose clusters. The skin is deep red (Plate 2). Shoulders are flat, although often ridged on one side along the suture line. The skin is of medium texture (less rough than “Haak Yip”). The flesh is soft, very juicy and sweet. Most seeds are fully developed giving a flesh recovery of 63 to 73 percent. Although fruit have full flavour, their large seeds and soft flesh reduce eating quality and price in Asia compared with “Haak Yip”, “Kwai May Red” and “No Mai Chee”.

“Kom” was developed in Thailand from material imported from China. It crops under tropical conditions, but fruit are not as good as those from cultivars grown in the north. It is the most popular of the tropical cultivars. “Kom” has been imported into Australia, but has not been distributed elsewhere. Fruit mature about a week before “Tai So”, and are variable in size, shape and flesh recovery, depending on the season. They tend to be small in southern Queensland when cool weather extends into early summer. Average fruit size is a little better in Thailand. Although “Kom” is high yielding, its poor quality in southern Queensland limits its potential. It is not considered a good marketing type because of its small fruit and poor flavour. Trees are vigorous and erect, and have long, strong branches and dense foliage. Leaflets are narrow, pointed, medium and dark green. They are generally flat, but curve downwards slightly towards the tip. The new flush of growth is red changing to green with maturity.

Fruit are variable in size (8-20 g), and long-heart to nearly round, depending on the season. They tend to be small and long heart-shaped after cool weather. The very thick skin is blotchy yellow to purplish red at maturity. Shoulders are flat or even, and the fruit apex obtuse. The skin segments are smooth at maturity and variable in size, shape and arrangement. The protuberances are sharp-pointed. Fruit are borne in small loose clusters. The flesh is tough to fibrous, and mild becoming bland once mature. Seed and fruit size are in proportion, with small fruit having chicken tongues. Flesh recovery ranges from 60 to 80 percent.

“O-Hia” (“Baidum”) is the third most important cultivar after “Tai So” and “Wai Chee” in northern Thailand. It resembles “Haak Yip”, but does not match it in all characteristics. Fruit of “O-Hia” are slightly smaller, less uniform in size, have blotchy markings on the skin, which is yellow-red rather than purple-red at maturity. Fruit are not as sweet as “Haak Yip” and have more chicken tongues. Fruit are available mid-season. Trees are medium, with dense foliage on long, thin branches (not as long as Haak Yip). Leaflets are large, narrow, dark green and slightly curled upwards from the mid-rib. The new flush of growth is reddish-brown. Fruit are medium (20-22 g) and heart-shaped. The skin changes from blotchy yellow to deep red with maturity. Skin segments are irregular in size, shape and arrangement, swelling, with smooth to obtuse protuberances. Flesh is juicy and sweet. Seeds are mostly plump (10-15 percent chicken tongue), giving a flesh recovery of 65 to 75 percent.

“Chacapat” is grown in Thailand and has also been imported into Australia. It is the last cultivar in both areas, and very popular in Thailand. Fruit are sweet and acceptable in Thailand, but often acid in Australia. Cropping ability in Australia is also average. Trees may set small fruit with small seeds. Under these conditions, it is not considered a good marketing type. Trees of “Chacapat” are moderately vigorous, erect, and have long branches and dense foliage. Leaflets are small, long, narrow, pointed and dark green. They curl upwards from the midribs and downwards along their length towards the tip. The new growth is green.

Fruit are normally large (28-32 g) and round to slightly heart-shaped. The skin is thin and soft, deep red with yellow markings (not as prominent as Salathiel). Shoulders are flat and the fruit tip round. Skin segments are swelling with obtuse protuberances. Flesh is moderately juicy, remaining acid when fully ripe. Seeds are nearly all large, giving a flesh recovery of 60 to 70 percent.

“Shahi” (“Muzaffarpur”, “Rose Scented”) is the most popular cultivar in Bihar, and can also be found in other parts of India, as well as in Bangladesh. Fruit are medium (20-25 g), oval-shaped with crimson-red skin. Flesh is juicy, sweet and fragrant. Seed size is variable. Yields are heavy and regular, with large trees carrying 100 to 150 kg of fruit early in the season. However, they often crack.

“China” (“Purbi”, “Calcuttia”, “Bengalia”, “Bombaiya”) is an important cultivar in India that ripens when most of the other cultivars have been harvested. Its origin has not been determined, although there is a similar cultivar in Bangladesh - “China Number Three”. Trees are relatively short and high-yielding, but alternate bearing. Fruit are large (25 g) and orange-red. The flesh is soft, juicy and very sweet, but not as good as “Shahi”. Seeds are normally small.

“Early Bedana” (“Early Seedless”) is a popular early cultivar from Bihar, Uttar Predesh, the Punjab and Bangladesh. Trees are medium in height and yield, with regular fruit production. Fruit are medium (15-18 g), oval or heart-shaped, with rough deep red skin at maturity. The flesh is white, soft, juicy and sweet. Overall fruit quality is rated as “good.”

“Late Bedana” (“Late Seedless”) is a late cultivar from northern India. Trees are vigorous, with average yields of 60 to 80 kg for ten year old specimens. Fruit are medium, with good flesh recovery. The flesh is creamy white, soft, juicy and sweet. Seeds are usually small.

“Bombai” is an important early cultivar from West Bengal in India, and Bangladesh. Trees are vigorous and yield 80 to 90 kg of fruit. Ripe fruit are an attractive deep red, with grey white, soft, juicy and sweet flesh. It is similar to “China” grown in other areas.

“Dehra Dun” (“Dehra Rose”) is an important cultivar from Uttar Pradesh and the Punjab. Trees are medium, and produce medium to high yields. Fruit are bright pink-red at harvest, and very attractive. Fruit have small seeds, but are susceptible to cracking.

“Bengal” is a seedling of the Indian cultivar “Purbi” sent to Florida in 1929. It was selected in Florida in 1940 and does not resemble any Chinese cultivar. It was the second most important cultivar after Tai So in Australia, but has now lost favour. Fruit are attractive and pleasant tasting, but have large seeds and poor flesh recovery. They also ripen unevenly. Average cropping is disappointing, although trees can have very high yields in an 'on year'. Trees are vigorous and spreading with thin branches, but are reasonably resistant to wind damage. Leaflets are large, mid-green and have a distinctive twist or curl along their length. The new flush of growth is reddish-brown.

The fruit (23-27 g) are formed in large clusters of up to 50 or more. The thick skin is very rough and attractive bright red. The fruit are egg-round to lopsided heart-shaped, with uneven shoulders. The fruit tip is distinctively pointed. Protuberances are sharp-pointed to wedge-shaped. The flesh is soft, sweet and moderately juicy. Fruit do not keep their flavour if left to hang. There are very few abortive seeds. Under drought conditions, the aril is often undeveloped and may not cover the seed at the pointed end. This gives a flesh recovery of 50 percent or lower. For these reasons, “Bengal” is not considered a good marketing type.

“Kwai May Pink” is thought to have originated in China possibly as a variant or seedling of “Kwai May Red”. It is popular in Australia, with large numbers of trees planted, but relatively unknown elsewhere. Bearing ability is good in most districts. It has a long harvest, possibly due to the development of acceptable sweetness and flavour well before fruit mature. Fruit are available mid-season. Trees are large and very erect, and have long, slim branches that point upwards. They are reasonably strong in storms. Leaflets are narrow, long, oval-shaped and shiny light green. They curl upwards slightly from the midrib and downwards along the length. The new flush of growth is an attractive red.

Fruit are medium (18-22 g), and round, with very rough thick skin. The skin changes from yellow to yellow-pink to orange-pink with maturity, with some green on the shoulders (Plate 3). Fruit are over-mature when fully coloured. Shoulders are usually flat, but one is sometimes raised along the suture line. Flesh is firm, crisp, sweet, juicy and aromatic. Fruit are sweet well before full maturity. Seeds are variable, with up to 70 percent chicken tongues. Flesh recovery is 67 to 77 percent. Fruit are exported.

“Salathiel” was found growing near Cairns in northern Australia, but its parentage is unknown. It is similar to “No Mai Chee” from China, but is not identical in all characteristics. Yields are variable in sub-tropical districts and light in tropical areas. Fruit are harvested late, just before “Wai Chee”. Trees are small and compact, and sometimes produce long branches with undeveloped leaves. Leaflets are small, broad and curve down slightly at the tip. The tip of the leaflet is round with a short distinctive point. The new flush is red changing to green with maturity.

Fruit are small (15-18 g), egg-shaped to ball-shaped in cooler areas, and borne in small loose clusters. The skin is thick, moderately rough with prominent markings. The skin changes from blotchy-yellow to deep red at maturity (Plate 4). The fruit tip is obtuse changing to round in cooler areas. Flesh is thick, crisp, juicy and very sweet. Fruit are sweet long before they are fully coloured. Most fruit have chicken tongue seeds, giving a flesh recovery of 76 to 80 percent. Occasionally, fruit can be almost seedless, although these fruit are very small and unmarketable. Fruit attract a high price in domestic markets and are also exported to Asia.

“Sah Keng” was developed in Taiwan Province of China in the 1970s and appears to be a seedling of “Haak Yip”. It was introduced into Australia, but is not grown commercially outside Taiwan Province of China. “Sah Keng” produces large and small seeded fruit, with significant variation amongst trees in a single orchard. Fruit are available mid-season. Yields are heavy, but irregular. Trees are medium, dome-shaped with short, fragile branches. Leaflets are 6 to 8 cm long and mid-green. The new flush of growth is green. Fruit are large (30-35 g), heart-shaped, with purple-red skin. The skin segments are swollen and protuberances blunt. The flesh is soft and sweet. Seeds are variable, often small, giving a flesh recovery of 75 percent.

“Kaimana” was developed in Hawaii about 20 years ago from a population of “Haak Yip” seedlings. It has been distributed to Australia for further commercial evaluation. Small trees can bear heavily in Kona and in some parts of Australia. Fruit are available mid-season. Trees are medium, spreading with long, strong branches. Leaves are large, elongated and mid-green. The new flush of growth is green. Fruit are large (25 g), heart-shaped with purple-red skin. The skin segments are swollen and the protuberances smooth when the fruit are mature. The flesh is crisp, sweet and excellent quality. Seeds are medium.

4.7 Plant improvement

The chromosome number of lychee has been reported as 2n = 28, 30, 32 or 34. There is little information available on the inheritance of morphological or physiological characters. Yang and Chen, however, indicated that shrivelled seed was inherited in the related longan. Different cultivars have been separated through the use of genetic markers. Various cultivars have been shown to have similar parentage.

New cultivars have mainly been developed from the selection of open-pollinated seedlings from existing cultivars. Most of the modern cultivars have been developed in China, with new cultivars still being released in Guangdong. Some of the industries elsewhere in Asia are based on seedlings of cultivars imported from China. Breeding programmes have generally been limited to a few thousand seedlings.

Breeding objectives include regular high yields, good tree structure, large fruit, bright red skin, small seed or seed abortion, better flavour and texture, and early or late fruit maturity. Resistance to pests and diseases and extremes of environment, acceptable fruit ripening pattern and acceptable shelf life have received less attention. Seedlings from a cultivar generally resemble the parent tree, but few bear regularly. Cultivars developed in the last 60 years include “Salathiel” in Australia, “Sah Keng” from “Haak Yip” in Taiwan Province of China, “Bengal” from “Purbi” in India and several new types from Guangdong.

The development of better cultivars is very slow, because it takes several years for most seedlings to begin bearing fruit. When they do fruit, less than 1 percent of the seedlings are worthy of selection. Storey et al. selected “Groff” out of a population of 500 “Tai So”, “Brewster” and “Haak Yip” seedlings, but these are not premium cultivars. In any case, “Groff” has never been grown commercially. Future efforts in plant breeding need to concentrate on the cross pollination of selected cultivars with desirable traits. Yen et al. had a population of 2,500 seedlings from open- and controlled-pollination; however, he did not indicate whether all the male flowers on the mother tree were removed to exclude the possibility of self-pollination. Seedlings can be planted close together at a density of 2,000 to 2,500 trees per ha. Standard densities are normally 70 to 280 trees per ha.

Various methods of biotechnology have been explored for their role in developing new cultivars, especially in China. These include tissue culture of young embryos, anther or pollen culture to obtain haploid plants, and protoplast culture. No new cultivars have been developed at this stage.

Wild plants have been sought as sources of disease resistance or dwarfing in other sub-tropical trees such as citrus, avocado and mango. This approach may have potential in lychee. The Sapindaceae family contains many species and genera in the tropics and warm sub-tropics. Longan has been suggested as a source of cold or drought tolerance or resistance to erinose mite. Lychee x longan hybrids have been produced in China and Australia, but no commercial cultivars have been released to industry.

Bibliography

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