Annals of the Sri Lanka Department of Agriculture. 2008.10:273-282.
DISTRIBUTION, EXPLORATION AND CONSERVATION OF MANGO GENETIC DIVERSITY IN SRI LANKA I.K. WARSHAMANA1, I. MEDAGODA2, W.A. WIJITHAWARNA3, S. EKANAYAKA4 and C.K.RANAWANA4 1 National Plant Quarantine Service, Katunayaka 2 Horticultural Crops Research and Development Centre, Gannoruwa 3 Regional Agriculture Research and Development Centre, Aralaganwila. 4 Fruit Research Unit, Gannoruwa
ABSTRACT A rich genetic diversity is found in mango grown in Sri Lanka due to the use of seedlings of cross pollinated seeds as a method of propagation in the past. This diversity is being eroded due to many social, economic and technological pressures. Therefore, it is vital to study this diversity systematically in order to collect and conserve valuable mango genetic resources. To achieve this it is necessary to map the probability distribution of genetic resources. An eco-geographic survey was conducted with the help of agricultural extension officers and village leaders to locate diversity. This study was conducted using geo-referenced data of 121 mango accessions collected from several areas of Sri Lanka. Mapping the diversity and probability distribution was done using DIVA and Flora map software. The information generated from this study and the maps are valuable to study the climatic adaptation of collected materials, identify geographical areas for future collection and conservation of sites, and selecting elite mango lines. KEYWORDS: Collection, Conservation, Diversity, Genetic, Mango.
INTRODUCTION Mango is one of the popular fruit crops in Sri Lanka that belongs to the Genus Mangifera, Family Anacardiaceae comprising 69 species (Kostermans and Bompard, 1993), among which two were recorded in Sri Lanka (Dassanayake and Fosberg, 1983). The species, Mangifera zeylanica is endemic to SriLanka, and the whole plant has a medicinal value, but it is not a cultivated species. The other species Mangifera indica, the common edible cultivated species with an enormous number of cultivars is an introduction to Sri Lanka .During the year 1992 a number of exotic varieties were introduced, but none of them developed flowers satisfactorily under the local conditions. A rich genetic diversity is found in Mangifera indica species grown in Sri Lanka probably due to the use of seedlings of cross pollinated seeds as the only method of propagation in the past. It also has a long history of domestication and cultivation. (Weerarathna et al., 2005). The existence of a range of agro ecological zones in close proximity within the island also contributes to the high diversity in this crop. The important agronomic characteristics of the diverse materials found in mango are numerous. This
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provides an opportunity to select materials for direct and indirect uses in crop cultivar development. Due to numerous economic and social pressure associated with the increasing population over the past decades, there has been a progressive erosion of the genetic diversity of crop plants in Sri Lanka, a trend equally well observed elsewhere globally. IUCN Red List of Threatened Plants (Jarvis et al., 2002) suggests that 34.000 plant species are threatened globally (equivalent to some 12.5 % of the estimated world flora). Some estimates suggest that 25%- 35% of the genetic diversity could be lost in the next 20 years. Therefore, it is vital to study the diversity of this crop plant systematically in order to collect and conserve valuable genetic resources for future use. Conservationists, therefore, need methods for identification of action priorities both in geographical space and biological importance. To achieve this it is necessary to map the distribution of genetic resources. This paper describes preliminary work of a geographical approach used to identify genetic diversity hotspots and priority regions for exploration, conservation, evaluation, documentation and selection of elite mango genotypes. MATERIALS AND METHODS This study was initiated during 2001 at the Regional Agricultural Research and Development Centre (RARDC), Aralaganwila, in collaboration with the Horticultural Crops Research and Development Institute, Gannoruwa. A questionnaire was sent to all provincial and interprovincial agricultural officers, requesting information on the superior mango trees, and to identify and locate superior seedlings trees of mango. Information were also gathered by visiting the relevant growing areas mainly in Anuradhapura, Pollonanaruwa, Kandy, Matale, Kurunegala and Gampaha districts with the help of village leaders and farmers. Fruit samples collected during the visit were dissected for detailed information and sensory evaluation. During the study a total of 121 accessions were noted together with geo-reference data (Latitude and Longitude) using a Global Position System (Garmin Etrex Summit) unit. Collected accessions were characterized according to IPBGRI descriptors. During the collection mission, 44 accessions were selected based on fruit quality and other characteristics and were grafted and planted in the field gene bank at RARDC, Aralaganwila. The size of the fruit was categorized as large (>300g), medium (150g â&#x20AC;&#x201C; 300g) and small (<150g) (Sing, 1990). The shape, skin colour and flesh colour were recorded according to the IPBGRI descriptor. The quality and remarks were recorded by the testing panel. In this study, DIVA-GIS (Hijmans et al., 2000) geographic information system software was used for the management and analysis of
EXPLORATION AND CONSERVATION OF MANGO 19
genetic resources data to elucidate genetic ecological and geographic pattern in the distribution of crops and wild species, to map diversity and identify the diversity hotspots. Flora map, (Jones and Gladcov, 1999) which is a specialized computer programme was used to develop possible climatic model areas to predict the distribution of mango within the study area. Plants established in the field gene bank bore after 3-4 years and fruit quality of these were analysed in the Food Research Unit, Gannoruwa. RESULTS AND DISCUSSIOIN During the survey, information of existing superior mango trees were collected from North Central, Central, Uva, Western and Wayamba provinces and are shown in Table 1. Table 1. Number of accessions collected from different provinces. Province North Central Western Uva Central Wayambe Sabaragamuwa Total
Number of accessions 54 31 16 14 03 03 121
According to the results, the highest number of accessions was recorded in the North Central Province. The collection point coordinates for mango accessions noted from 06 provinces of Sri Lanka were mapped with DIVA-GIS and are shown in Figure 1. According to the results, the red areas indicate higher diversity spots where Polonnaruwa, Anuradhapura, Kandy, and Matale districts are located (Fig. 1). The green areas indicate poor distribution of mango germplasm. With the help of this diversity map it is possible to identify the areas from where no collections were made in the past and these areas can be marked as areas where the mango collection should be undertaken in Sri Lanka in the future. These germplasm geo-reference data were analysed with climate surfaces using Flora map to identify areas where the cultivars of
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mango might occur, but had not been actually exposed. Such probability distribution maps of mango are shown in Figure 2.
EXPLORATION AND CONSERVATION OF MANGO 21
These results indicate that higher diversity of mango cultivars might occur in DL1, DL2, IL1, and WL3 and 4 (Fig. 2). These areas can be considered as potential areas for promoting mango cultivation and the sites for ex situ conservation and future collection. Jones et al. (1997) have shown that genebank databases linked with climatic databases can be used for predicting the chance of finding a species in areas that have not been explored. These results indicate that Diva- GIS and Flora map linked to agro climatic and other databases can effectively be used to create maps showing the most likely distribution of similar genotypes of mango in nature. Such maps are extremely valuable tools for tasks such as planning, collection, expeditions and deciding where to locate programmes for conservation. Furthermore, the information is useful to identify areas in other parts of the world where similar crop varieties are found. This is important in exchanging germplasm in order to identify adaptable crop varieties for a given region. Moreover, using GIS tools, the costs in exploration, conservation and evaluation of introduced plant varieties can be minimized. During the collection mission, some accessions noted for different purposes such as fresh fruit market, juice production and pickle production are shown in Table 02. According to these results, the size of the fruit varied from small, medium to large. The shape varied from round, oblong to ellipsoid. The skin colour varied from green, yellow, green with crimson blush to pink and flesh colour varied from yellow, orange, whitish yellow to yellow-orange. The flavour was tested as sweet, starchy, sour, and some were juicy and fibrous. These different types of fruits could be used for different purposes as fresh fruits, juice production and for pickle production along with other value addition processes. This diversity of fruits indicate that there is a high scope for future improvement of this crop. Within 3-4 years 85% of the grafted plants established at field gene bank at RARDC, Aralaganwila produced fruits. Physicochemical characters of some accessions from the established gene bank are shown in Table 3.
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Anuradhapura
Polonnaruwa
Matale Gampaha
Kandy
Figure 1. Mapping diversity of mango in Sri Lanka. Probability 0–1 • 1 – 2.457
EXPLORATION AND CONSERVATION OF MANGO 23 Table 2. Fruit quality characteristics of some accessions of mango.
Acc: No.
Size
Shape
Skin colour
Flesh colour
Flavour
Quality
Remarks
01
Medium
Ellipsoid
Green
Yellow orange
Excellent
05
Medium
Oblong
Yellowish green
Deep orange
Excellent
Fruit is same as Karthacolomban Fruit end with small beak
07
Medium
Ellipsoid
Greenish yellow
Yellow
Excellent
Fresh fruit market
28
Small medium
Round
Green with crimson blush
Whitish yellow
Delightul very sweet Delightful very sweet Sweet and starchy Sweet
Excellent
Edible before ripening
51
Small
Oblong
Green
Orange
Good
Juice product
74
Medium
Oblong
Orange
Good
Fresh fruit market
78
Round
Fair
Attractive fruits
89
Medium to large Large
Yellowish green with crimson blush Pink
High sweet juicy fiber Delicious with slight aroma Not so sweet
Ellipsoid
Green
Yellow
Fair
Pickle production
90
Small
Ellipsoid
Yellow
Good
Fresh fruit market
98
Medium
Oblong
Yellowish green with crimson blush Green
Stachy juicy sour Sweet
Yellow
Sweet starchy
Fair
Fresh fruit market
100
Medium
Ellipsoid
Green
Yellow
Sweet starchy
Good
Fresh fruit market
109
Small
Round
Yellowish green
Yellowish orange
Sweet starchy
Good
Juice production
111
Medium
Ellipsoid
Green
Yellowish orange
Sweet starchy
Very Good
Fresh fruit market
Yellow
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Probability
Figure 2. Probability of occurrence of mango in Sri Lanka.
EXPLORATION AND CONSERVATION OF MANGO 25 Table 3. Physicochemical characteristics of 5 accessions of mango at field gene bank RARDC, Aralaganwila. o
Brix
pH
28
23
3.46
0.832
70.87
40
16.5
3.54
0.81
78.91
16
20
3.29
0.85
74. 02
36
15
3.54
0.80
76.86
7
17
4.31
0.65
83.34
Accessio n
% of acidity as anhydrous citric acid
% Moisture
Organoleptic quality
Sweet, Starchy, Less fibrous, taste - good Moderately sweet, Acidic , starchy, taste- good Sweet, moderately acidic Slightly starchy, taste - good Moderately sweet, acidic, Starchy, taste - good Sugar :acid â&#x20AC;&#x201C; good, less juicy sweet, slightly acidic
According to these results, total soluble solids (oBrix) of these accessions were higher than the popular mango variety Karthacolomban where the oBrix was 11. The moisture percentage was around 70 which indicates higher dry matter content. Accession number 28, 40, 16 and 36 were good in taste. These results indicated the possibility of selecting elite mango germplsm from the collected accessions. However, further observation on yield need to be taken for several years to obtain any conclusive results. CONCLUSIONS The distribution map of genetic diversity of mango germplasm in Sri Lanka has been developed, and such maps are extremely valuable for planning collection, expeditions and selection of conservation sites. Furthermore, this information is useful to identify areas in the Asian region where similar crop varieties are found. Out of 121 accessions, 44 accessions were conserved at the field gene bank at RARDC Aralaganwila. Sri Lanka has a rich genetic diversity of mango which indicates that there is a high scope for improvement of the crop and possibility of selecting elite lines of mango. ACKNOWLEDGEMENTS Technical and financial assistance provided for this work under the ADB IPBGR I project on Conservation and Use of Native Tropical Fruit Species Biodiversity in Asia is greatly appreciated. Special thanks go to Dr.P.N. Mathur, Associate Coordinator for south Asia, NASC complex, Pusa campus, New Dellhi 110012, India. Authors also wish to acknowledge Dr. (Mrs) E.D.S.P Edirimana and Mrs. K. Weerakoon for reading the manuscript and type setting.
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