Coffee is the largest exported agricultural product of Tanzania and contributes about US$115 million to their foreign exchange earnings and supports the livelihoods of about 400,000 small farmer families and many more in the processing and trading sectors26. Thus the importance of coffee for Tanzanian economy cannot be overemphasized. A similar situation can be expected in the context of the many coffee producing countries of Africa.
Coffea arabica the lone tetraploid (2n=4x=44) species of the genus Coffea was considered to have been derived from two diploid species of the same genus by spontaneous hybridization and doubling of chromosomes in the interspecific hybrid. Many researchers agree and sought evidence to prove this hypothesis. Presently, it is accepted by scientists that C. eugenioides could be the possible evolutionary female progenitor of C. arabica, having contributed one set of 22 chromosomes (2n=2x=22) and its cytoplasm. The other set of chromosomes appear to have been contributed by C. canephora (Robusta) or C. congensis or even by C. liberica, the species that were proposed to be the possible evolutionary male progenitor of C. arabica1-12. There is evidence that C. arabica could be a species that has inherited genes from other diploid species like C. racemosa13 or even C. stenophylla and C. excelsa (unpublished data). However, all schools agree that C. eugenioides is the putative female progenitor. This implies that most of the Arabicas carry the cytoplasm of C. eugenioides, but possibly the genes of several species, a situation akin to the nature of ‘compilospecies’14,19. This also calls for the understanding that simple breeding techniques would not lead to dependable results in resolving the complex problems of susceptibility to diseases like leaf rust, CBD, stem borer and leaf miner, the major biotic adversaries of coffee claiming over 50-60% of production cost. Observed resistance to most of these adversaries in the diploid species of Coffea and the compilospecies nature of C. arabica21,22 indicate that breeding involving interspecific hybridization is the only way to achieve resistance in C. arabica. In this context, some unique germplasm generated in the Indian coffee breeding programme, such as Devamachy (Natural hybrid of Robusta and Arabica), Robarbica (Artificial hybrid of Robusta and Arabica), Racemusta (Artificial hybrid of C. racemosa x C. canephora) and Ligenioides (Amphiploid from the artificial hybrid of C. liberica x C. eugenioides) hybrids have proven to be of value24,25. These germplasm were created as part of a long term exercise in coffee breeding in India and the initial efforts took place in the 1930s. Present proposal is with the idea of creating such germplasm in Tanzania and possibly other African countries where some of the 100 known species of Coffea are native.
Tanzania is home for 16 diploid species of Coffea. Some of the species are C. racemosa, C. sessiliflora, C. kimbozensis, C. eugenioides, C. zanguebariae, C. fadenii, C. charrieriana and C. anthonyi. These species constitute the secondary gene pool carrying important traits for the improvement of C. arabica. As C. arabica is tetraploid, and these species are diploid, it becomes necessary that these species be hybridized and diploidized to render the hybrids tetraploid and be able to cross with C. arabica and transfer the genes of interest to that species.
In the genus Coffea, the reproductive isolation barriers are incomplete and allow the intercrossing of diploid species. In fact, interspecific hybrids appear spontaneously when two or more species are growing together in any location. During the current project, it is proposed to collect as many Tanzanian diploid species of Coffea as possible through seeds and establish a germplasm bank at the University of Dodoma and possibly Tanzania Coffee Research Institute to eventually generate hybrids from all possible combinations of these species. As Coffea species are perennial plants, their initial establishment is expected to take, at least, 3-4 years and the generation of hybrids can be done in the subsequent period of another 4-5 years. Thus, the proposed project takes about 10 years to realize the proposed products. However, genetic, cytological, biochemical and molecular characterization of these species can be carried out in the course of establishing the germplasm bank itself and the study of hybrids commences after their being generated.
A situation of considerable relevance is that of Maize. During 1960s, cytoplasmic male sterile (CMS) lines were extensively used in USA to produce hybrid seed that helped in doubling the corn production. However, during early 1970s, all these hybrids fell susceptible to southern corn blight (caused by Helminthosporium maydis). It was found that a particular CMS line from Texas was involved in the derivation of all the hybrids rendering the cytoplasm of all the hybrids uniform. Later, this cytoplasm was named as T-cytoplasm. This exerted the selection pressure on the pathogen and resulted in the evolution of a single race (race-T) that could cause devastation of the entire lot of hybrids20. We have an analogous situation, in that most of the Arabica coffees carry the cytoplasm of C. eugenioides. According to the available information, the earliest appearance of CBD was also on C. eugenioides17. Later, it has spread to most Arabicas. This is further supported by the fact that CBD resistance is found only in the interspecific hybrids like Hibrido de Timor (HDT). Rume Sudan Arabica that possesses resistance was also shown to be distinct from pure Arabicas and closer to some lines of HDT by DNA fingerprinting studies13. Maize hybrid seed production in USA could be continued using diverse CMS lines other than Texas and a similar exercise of Arabica coffee breeding involving the cytoplasm of other species is most likely to lead to positive results. In the proposed project, tetraploid genotypes carrying diverse cytoplasmic endowments of the diploid different species will be combines with a tetraploid nucleus that can transfer genes to C. arabica will be created and will prove to be of great value in breeding this important crop plant.
On account of the value of C. arabica to the economy of all African coffee producing countries and the value of these species to the breeding of this important cash crop, the project is justified. C. arabica is susceptible to diseases like coffee berry disease (CBD), coffee leaf rust (CLR) and pests like coffee berry borer (CBB) and stem borer and innate genetic resistance to these adversaries is resident in the diploid species proposed to be collected. At present, over 50% of production cost is towards the control of these adversaries and resistant plants are expected to reduce the cost of production considerably.
Apart from the utilization of this germplasm in African countries, it can also be shared with other coffee producing countries, on mutually agreed terms to derive IPR benefits for the Institutions and to the countries of origin23.
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- Narasimhaswamy, R.L., Vishveshwara, S. 1961. Report on hybrids between some diploid species of Coffea L. Indian Coffee 25:104-109.
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- Ram, A.S., Sreenivasan, M.S. 1981. A chemotaxonomic study of Coffea arabica L. In: Genetics, Plant Breeding and Horticulture (Proc. PLACROSYM IV, Ed. S. Vishvehshwara) pp. 368-374. Indian Society for Plantation Crops, Kasaragod, India.
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- Srinivasan, C.S., Ramachandran, M. 1997. Selection 5B – S.2931 (S.333 / Devamachy hybrid) – An old arabica hybrid rediscovered with promising features. Indian Coffee (11):4-6.
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- Mogk, M. 1975. Investigations on the origin of leaf rust and coffee berry disease in the provinces of western Kenya. Mimeo Report. Coffee Research Foundation, Ruiru, Kenya.
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