BREEDING FOR QUALITY IMPROVEMENT IN PLANTATION CROPS

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1 This article may be cited as, Vinod K K and M Suryakumar (2004) Breeding for quality improvement in plantation crops. In: Proceedings of the training programme on Plant Breeding Approaches for Quality Improvement of Crops", Tamil Nadu Agricultural University, Coimbatore, India. Downloaded from pp K.K.Vinod and M.Suryakumar Rubber Research Institute of India, Kottayam Introduction BREEDING FOR QUALITY IMPROVEMENT IN PLANTATION CROPS Plantation crops are perennial crops, occupying larger growing areas. They are commercially important for they produce a wide range of produces from spices, condiments, beverages, oil, industrial raw materials, medicines, fruits and other allied materials. The use of the term plantation crops is restricted to a few crops viz., coffee, tea, rubber, coconut, cocoa, cardamom, oil palm etc. Since many of these produces are export oriented, maintaining the quality is important to cater the needs of international markets. In many plantation crops, conventional breeding still has much to offer. Breeding progress has been particularly slow in some vegetatively propagated crops. Identifying and cloning good individuals from existing commercial seedling fields offers the illusory prospect of much faster progress than a long term breeding programme. The sterility of this approach is illustrated by experience with tea, though: the best clones in most tea growing countries were released in the fifties and sixties, and have not been improved on since. Tea (Camellia sinensis L.) Tea belongs to the family Theaceae, is originated in Asia, centred around Himalayan mountains. The cultivated species, Camellia sinensis (L) O. Kuntze, is a diploid (2n = 30) has two major types, commonly known as Chinese tea (Camellia sinensis) and Assam tea (C. assamica). A less known third type Cambod tea (C. assamica ssp. lasiocalyx) also exists. The Chinese and Assam types are also known as C. sinensis var. sinensis, C. sinensis var. assamica (Sharma and Venkataramani, 1974). Quality in tea is controlled by several factors. Tea bushes: Some clones and some seed sources ( jats ) make better tea than others. China type plants make poor black tea because the leaves have a lower Presented in Centre for Advanced Studies in Genetics and Plant Breeding Training programme on Plant Breeding Approaches for Quality Improvement of Crops held at Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore , between Jan 28 February 17,

2 content of flavanols than Assam type tea. The climate: Tea grown in a warm, tropical, lowland area grows very quickly but the leaves are of poor quality. In contrast, leaves from tea grown in tropical highlands are usually of high quality. Where the climate is such that there is a season of dormancy, leaves of very high quality are formed as a first regrowth after the first plucking when the dormancy breaks. The second flush of Assam tea is renowned for its quality. The age of the leaves: The content of flavanols is highest in the bud, is lower in the first leaf and continues decreasing as the leaves age. The stalk has an even lower content. Therefore tea made from the buds only will have a very high quality; this was done in the past and the product known as tips. The yield was very small and the practice has long since been discontinued. Nevertheless, the word tips indicates high quality and it is still used today, applied to good quality brands (Willson, 1999). Plucking two leaves and a bud (fine plucking) should produce a better tea than three leaves and a bud (coarse plucking). Plucking inevitably includes some stalk but this is mostly eliminated in the manufacturing process. Other factors may have small but significant effects on quality. The effects of fertilizer nutrients have been reported on a number of occasions (Willson and Choudhury, 1969; Dev Choudhury, 1993). Crop improvement Quality is equally important like yield in selecting potential clones. Since the vegetative characteristics of tea plants vary over various growing conditions the quality of the tea produced vary widely. The first step in improving overall yield and quality was to select individual plants which gave high yields of high quality tea and to propagate these vegetatively as clones. Clones have been selected from fields of tea in production, from seedling nurseries and from special plantings of selected seeds. The potential of individuals may be indicated by the vigour of their growth, which can be assessed by the number of flushing stems in a given surface area multiplied by the area of the top of the bush. Specific traits, like leaf colour, leaf angle, pubescence, size (weight) of two leaves and a bud and leaf area index may be selected where other superior plants have been found to have similar characteristics. There is evidence (Fig 1) that pubescence is related to quality 536

3 (Wight and Gilchrist, 1959). The selected material has then to be bulked to produce sufficient plants to give enough leaf for processing for quality assessment. Fig 1. Leaf pubescence is positively correlated to quality in tea. Potential selections are raised vegetatively and then pruned and allowed to regrow. Where regrowth has reached a reasonable height, the growth can be measured by pruning again and weighing the prunings. Alternatively, the top of the bush can be levelled ready for plucking and the tippings (the foli age removed above the level surface) weighed. Leaves can then be harvested from each bush. By comparison of the weights from individual bushes, those giving the higher yields can be selected and a preliminary estimate of fermentability can be made by the chloroform test (Sanderson, 1963). The phloem index (Wight and Gilchrist, 1959) (the frequency of calcium oxalate crystals in parenchymatous cells of the leaf petiole) is also a useful parameter indicating quality. Chemical analysis to determine the proportion of thea flavins present in the leaf can also be used to assess quality potential (Hilton and Ellis, 1972). The general breeding procedure takes up to 10 years, to the isolation of a few clones of superior characteristics in terms of yield and quality. It has been estimated that about one in 40,000 seedlings will have superior yield potential. Testing of these selected clones will continue, with comparative trials on larger areas and in other ecological zones. A few clones have become widely accepted; many new plantings in recent years have been clonal 537

4 occasionally in monoclonal blocks but more commonly in mixed stands of several clones. Either way a substantial improvement in yield and quality is guaranteed compared with seedling plantings. The even growth of clonal plantings makes it easier to schedule plucking and other operations such as pruning at the optimum time. Processing of tea from monoclonal fields separ ately from the normal run of manufacture has been carried out. The potential for yield and quality improvement by selection within specific plantings may be limited by the limited genetic base, as many seedling plantings will have been on seeds from one seed orchard which is known in the industry by the Assamese word bari. Seed from a specific bari is known as a jat. Attempts to produce improved seed by making a bari from plants selected within a seedling population, using criteria similar to those employed in selecting clones did not produce any significant advances in yield or quality. Controlled pollination among selected parents has led to some greatly improved plants. The approach starts with hand pollination of selected plants. The progeny have then to be compared in a long term trial and the best of these are then planted in an isolated bari. The progeny from natural pollination is then evaluated either as mixed seedlings or as selected clones. From start to release of seed takes about 25 years. The most successful improvement programme has been to plant selected clones in an isolated orchard and to select clones from the resultant progeny. The selected clones will include improved genotypes; some plants of their progeny should therefore incorporate higher proportions of these genotypes and have superior characteristics. The progeny may come either from con trolled cross pollination of two selected clones or by random fertilization within the orchard. Some biclonal seed has already been released for distribution (Singh, 1992). The use of wild species of Camellia which do not produce tea have usually been left out of programmes of controlled hybridization. Such hybrids produce inferior tea and were not acceptable. The relatively limited genetic base of much of the world s tea suggests that widening the genetic base could be beneficial in the long run. There may be scope for introducing non conventional approaches to tea improvement. Polyploids occur to a limited extent and there are indications 538

5 that some would have valuable characteristics. Radioactive mutation could produce improved plants. Tissue culture could speed up differentiation and selection. The potential of such methods is limited by lack of knowledge of some aspects of tea genetics. Coffee (Coffea sp.) Cultivated coffee belongs to the family Rubiaceae and is derived mainly from two species, Coffea arabica (2n=44, arabica coffee) and C. canephora (2n=22, robusta coffee). Another species C. liberica is produced and traded in limited scale belong to west coast of W. Africa (Willson, 1999). The quality of coffee is a combination of flavour and aroma. These come from the chemical constituents of the coffee beans. Chemical reactions take place during processing. particularly in the fermentation stage of wet processing, which produce the desired chemicals. The quality of the cherries influences the quality of the product; underripe, overripe, diseased and damaged cherries reduce quality, as do cherries that have been delayed between harvesting and processing. The final assessment of quality is made subjectively by skilled tasters, who consider appearance, flavour and aroma. The quality so assessed has a marked influence on the price at which the coffee can be sold. In general dry process coffee is regarded as of lower quality than wet process coffee. There are exceptions, such as the valued mocha type coffees from Brazil. Robusta coffee is of lower quality than arabica. Crop improvement Coffea arabica The major proportion of research into the improvement of coffee plants has been carried out on C. arabica, whose product is of higher quality than that of C. canephora and therefore commands a higher price. The earliest improvement work was directed towards improving yield and the stability of yield from one year to the next. All the early plantings used trees which came from a narrow genetic base. Nevertheless, selection within the existing populations identified cultivars with superior characteristics of yield and quality. Several expeditions have collected coffee trees from the districts of origin of C. arabica in Ethiopia in order to widen the 539

6 available genetic base. The early work on improvement of C. arabica by selection within existing populations identified a number of cultivars with COLLECTION C. canephora C. arabica Parents chosen, selfed for 2 cycles Crossed Doubling of chromosomes Crossing Crosses with compatible types Arabusta hybrids Cross assessed Selection of hybrids Second cycle Families select Families discard Hybrids discard Clones, select, trialled, reselect Clones discard Clones used per se Clones as parents of seedlings Cultivation Fig 2. Scheme of coffee breeding superior yield characteristics, several of which have been planted on a large scale. Improvement of C. arabica can be divided into several stages, of which the first is selection and testing of possibly superior trees. Testing can identify the superior examples, which can be propagated by seed. Two cycles of selfing before testing will stabilize the characters of each line, then the superior varieties can be crossed one with another, in double or multiple crossings, and further improved trees can be selected within the progeny. Back crossing may produce more improved varieties. Trees so produced will not reproduce exactly from their seed, so propagation must be vegetative, to produce both examples for testing and trees for field planting if the clone is released for large scale planting. 540

7 Two cycles of selfing of the clones will fix the major genetic characters. Crossing of pairs of these by hand pollination will produce F1 hybrids, which can be propagated using the hybrid seed. Further cycles of selfing will produce varieties that are sufficiently stable to propagate from seed. In vitro propagation by nodal cultures (Dublin, 1980) speeds up the cycles, which need plants that have been propagated vegetatively. The plants pro duced in this way have a long tap root, which is better than the several shorter roots produced by a cutting. Coffea canephora C. canephora is self incompatible. Each seedling is therefore a hybrid and it is not possible to find uniformity among plants from the same source. The wide geographical range of natural populations of C. canephora gives scope for widening the genetic base by crossing between separated populations. This could lead to greater variability between progeny and a wider scope for selection. The variability of open pollinated seedlings means that superior individuals can be selected, but only vegetative propagation will produce uniform plants. When planting clonal orchards, it is important to ensure that the clones are cross compatible so that pollination is adequate. Crossing of selected clones can produce some seedlings with improved characteristics. Van der Vossen (1985) includes a further brief discussion of the improvement of C. canephora. Interspecific hybridization Direct hybrids between C. arabica and C. canephora are triploid and sterile, although Hibrido de Timor, discovered recently on the island of Timor, which is fertile and grown commercially, is believed to be a natural hybrid. In the hope of producing a hybrid that would grow in lowland Equatorial regions but produce coffee of quality approaching that of arabica hybridization has been achieved after doubling the chromosome number of C. canephora by treatment of germinating seed or shoot tips with colchicine (Capot, 1972). The resultant hybrids are known as Arabusta. They have characters intermediate between the two parents but rather closer to robusta. Superior individuals can be selected from these hybrids. They give better quality coffee with a lower content of caffeine than C. canephora and can grow well in tropical lowlands. Back crossing can produce some individuals with even better characteristics. 541

8 Interspecific hybridization for the production of arabusta in 1970, was started in 1962 by treating the robusta clones with colchicine and subsequent hybridisation (Capot, 1972). Arabusta has been described as an amiable compromise between robusta and arabica, with less caffeine than robusta (Jobin, 1982). Arabusta, which has a larger bean and better flavour than robusta, combines fertility with resistance to disease, particularly to CLR. The caffeine content of arabusta is about 2 per cent, compared with arabica 1.5 per cent and robusta 2.5 per cent. The chemical constituents of arabusta are closer to arabica than robusta. The ratio of bean to cherry in arabusta seems to be much lower than either robusta or arabica, which is a big disadvantage when pulping. It can be grown at the lower altitudes where arabica does not grow well and can yield as well as robusta. At present only cuttings can be used to maintain and multiply arabusta (Wrigley, 1988). Doubling the chromosome number of triploid hybrids with colchicine pro duces hexaploids which are fertile and similar in many ways to C. arabica. Little work has been done with these as there are simpler ways to achieve the desired properties. Low caffeine genetically engineered coffee The demand for decaffeinated coffee is increasing because the stimulatory effects of caffeine can adversely affect sensitive individuals by triggering palpitations, increased blood pressure and insomnia. Japanese researchers from the Nara Institute of Science and Technology have genetically engineered C. canephora (robusta) which contains substantially less caffeine than conventional coffee. Transgenic coffee plants were produced, through a model transformation procedure via Agrobacterium method. A gene encoding a protein possessing 7 methylxanthine methyltransferase (theobromine synthase) activity was isolated, and it was designated as Coffea arabica 7 methylxanthine methyltransferase; CaMXMT (Ogita et al., 2002). In the new strain, the structure of the caffeine from precursor proteins is suppressed. Three N methyltransferase enzymes are involved in caffeine biosynthesis in coffee plants CaXMT1, CaMXMT1 (theobromine synthase) and CaDXMT1 (caffeine synthase), which successively add methyl groups to xanthosine in converting it into caffeine. Transgenic coffee plants were constructed in which expression of the gene encoding theobromine synthase (CaMXMT1) is repressed by RNA interference (RNAi). The caffeine content of these plants is reduced by up to 70%, indicating that it should be feasible to produce coffee 542

9 beans that are intrinsically deficient in caffeine (Ogita et al., 2003). Cocoa (Theobroma cacao L.) Theobroma cacao is a diploid (2N=20) belongs to the family Sterculiaceae belongs to the rain forests of the western hemisphere from 18 N to 15 S, that is from Mexico to the southern edge of the Amazon forests. Theobroma cacao is the only species which is cultivated widely, the other better known species in the genus being T. bicolor and T. grandifiorum (Toxopeus, 1985). Fig 3. Breeding scheme for cocoa. BF clones between families, CW clones within families, ICG,T International Cocoa Gene Bank, Trinidad In cocoa, there are several aspects to quality and the word may be used in various senses. In a narrow sense quality covers flavour and keeping quality, but here the word is used in a wider sense to include certain other aspects which affect the value and acceptability of a parcel of beans. The quality of 543

10 cocoa determines the demand for the product. Based on flavour, there are two types of cocoa: bulk cocoa which constitutes about 95% of world production, and fine or flavour cocoas, about 5% of world production. The fine types have special flavours which are required for dark (plain) chocolates and high quality coatings. Traditionally, fine coco as come from Criollo or Trinitario trees and bulk cocoa from Forastero trees, but there are exceptions to this rule. The standard for bulk cocoa is based on the Ghanaian product (Willson, 1999). Crop improvement No much detailed breeding procedures other than selection had been described in cocoa improvement. The improvement approaches followed at International Cocoa Gene Bank at Trinidad describes about selection of superior parents from the collection available and inter crossing of the chosen parents and evaluation of progeny families. The improved selections are propagated by cloning. The major efforts on cocoa breeding were oriented towards yield improvement and resistance to pests and diseases. Improvement of flavour was also given importance (Fig. 3). Rubber (Hevea brasiliensis Muell. Arg.) Para rubber, Hevea brasiliensis (2n = 36) is a monoecious perennial tree belonging to Euphorbiaceae. The genus Hevea consists of ten species, of which H. brasileinsis is the only commercially exploited source of natural rubber. The crop has its origin from Amazon basin in Brazil (Webster and Paardekooper, 1989). Crop improvement The major thrust of quality improvement in Hevea does not orient to the quality of rubber, but on the quality of secondary products like Hevea wood. Rubber trees produce enormous quantity of semi hardwood at every replanting cycle. The shrinking availability of natural timber from the forests has made this so valuable. The wood on appropriate chemical treatment could be used as a best substitute for timber for furniture making and for similar uses. The treated wood is now being used to produce very high quality furniture, panel boards, house hold articles and for flooring purpose. Owing to the growing importance of rubber wood, the improvement in the direction of developing timber latex clones is in progress. The clones 544

11 combining better yield, high vigorous growth, short life span, high quality strong wood, free from diseases and with good branching habits are preferred. Rubber tree is a prolific producer of honey. Honey is produced on extrafloral nectaries located on the Hevea leaves. High honey production can give additional income to plantation sector, and population that yield more honey are preferred. Though rubber products are being used for so many decades, recently, the problem of latex protein allergy has emerged mainly in America. The allergy is reported to be caused by the proteins present in the latex, which are found in traces in the finished products. However, the allergy reported is mainly of type IV allergy of cutaneous origin. There are several processing methods available for the deproteinisation of the rubber products. However, it would be better to look out for genotypes, which do not accumulate harmful proteins in the latex. Biotechnology in plantation crop improvement There is no doubt that biotechnology has something to offer the plantation sector, but the most promising targets are associated with product quality; relatively simple changes might be needed to produce caffeine free coffee or tea, for example. Such a product could command sufficient premium in the market to make the investment in transformation worthwhile. The lesson is that a single, apparently simple, change in a synthetic pathway may have unexpected side effects. Successful transformation programmes have been those where the transformation work is integrated into a conventional breeding programme, allowing individuals with the required phenotype to be developed from a range of transformants. Molecular markers The one area of biotechnology with clear applications in plantation crops is that of molecular markers. Marker assisted selection offers prospects of accelerating the process of long term breeding objectives offered by the conventional approaches. An important first step towards developing linked markers is the construction of a linkage map. Maps have been published for oil palm (Mayes et al, 1997), 545

12 cocoa (Lanaud et al, 1995), and coffee (Paillard et al, 1996), and some work has been done on rubber (Seguin et al, 1996) and tea (Unilever, unpublished). A map allows the selection of markers which are evenly distributed over the genome, thus enhancing the probability of finding markers linked to quantitative trait loci (QTL). In cocoa, markers associated with growth and flowering characteristics have been identified (Crouzillat et al, 1996). Molecular markers that are linked to these QTL will co segregate with the genes involved in desirable traits and could be used efficiently to follow introgressions and accumulation of favourable traits during recombination cycles. REFERENCES Capot, J. (1972) L amélioration du caféier, en Côte d Ivoire. Les hybrides arabusta. Café, Cacao, Thé, 16 : Crouzillat, D., Lerceteau, E., Petiard, V., Morera, J., Rodriguez, H., Walker, D., Phillips, W., Ronning, C., Schnell, R., Osei, J., and Fritz, P., Theobroma cacao L.: a genetic linkage map and quantitative trait loci analysis. Theoretical Applied Genetics, 93: Dev Choudhury, M.N. (1993). Effect of phosphorus on the quality of made tea. Two and a bud, 40: Dublin, P. (1980). Inductions de bourgeons néoformes et embryogenèse somatique. Deux voies de multiplication végétative in vitro des caféiers. Café, Cacao, Thé, 24 : Hilton, P.J. and Ellis,R.T. (1972). Estimation of Central Africa tea by theaflavin analysis. Journal of the Science of Food and Agriculture, 23: Jobin, P. (1982) Les Cafés produits dans le monde. Le Havre, 463 p. Sanderson,G.W. (1963). The chloroform test a study of its suitability as a means of rapidly evaluating fermenting properties of cones. Tea Quarterly, 134: Sharma, V.S. and Venkataramani, K.S. (1974) The tea complex. 1. Taxonomy of tea clones. Proccedings of the Indian Academy osf Sciences., 80 B: Singh, I.D. (1992). Release of biclonal seed stock TS 520. Two and a bud, 39: 46. Toxopeus, H. (1985) Botny, types and populations. In: Cocoa (G.A.R. Wood and R.A.Lass, ed.), Longman, New York. pp van der Vossen, H.A.M. (1985) Coffee selection and breeding In: Coffee, Biochemistry and Production (M.N.Clifford and K.C.Willson, eds.). Croom Helm, London. pp Webster,C.C and Paardekooper Botany of the rubber tree In: Rubber (C.C. Webster and W.J. Baulkwill, eds). Longman Scientific and Technical, U.K. Wight,W. and Gilchrist,R.C.H.H. (1959). Concerning the quality and morphology of tea. In: Annual Report of Tocklai Experiment Station. Tea Research Association, Calcutta. pp Willson, K.C. (1999) Coffee, Cocoa and Tea. CABI Publishing, Oxon, UK. 300p. Willson, K.C. and Choudhury, R. (1969). Fertilisers and tea quality. Tea, 9: Wrigley, G. (1988). Coffee. Longman Scientific and Technical, New York. pp Lanaud, C., Risterucci, A. M., Ngoran, A. K. J., Clement, D., Flament, M. H., Laurent, V., and Falque, M., A genetic linkage map of Theobroma cacao L. Theoretical Applied Genetics, 91: Mayes, S., Jack, P. L., Marshall, D., and Corley, R. H. V., Construction of a RFLP genetic linkage map for oil palm (Elaeis guineensis Jacq.). Genome, 40:

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