INTRODUCTION
Sri Lanka is an island in the Indian ocean and separated from Indian peninsula by Polk strati. It is located between latitude 5º 55’ N and 9º 53’N, and longitudes 79º 41’ E and 81º 53’E. Sri Lanka’s tropical location ensures perennially high temperature with monthly averages between 20 - 33°C in the lowlands. In the central highlands, higher altitude accounts for lower temperature with monthly average about 7°C and 21°C. The pattern of life in Sri Lanka depends highly on the availability of rainfall. The mountainous, south-western part of the country, known as the “wet zone”, receives a large amount of rainfall (an annual average of 2,500 mm). Most of the southeast, east, and northern parts of the country comprise the “dry zone”, which annual rainfall is between 1,200 and 1,900 mm. Much of the rain in these areas falls from October to January while the other seasons receives a low precipitation. The arid northwest and southeast coasts receive the least amount of precipitation (600 to 1,200 mm per year) and most of it occurs in the short period of the winter monsoon.
Agriculture is the most common livelihood of Sri Lankans and contributes 7 - 8% of its GDP. Vegetable crops account for 3% (105,062ha) of total agricultural lands and its production is 1,674,868 MT (Crop Production Programme 2017). About 80 different fruit and vegetable cultivars are grown in Sri Lanka (AgStat 2017). The cool and salubrious climates in hill country of Sri Lanka are ideal for temperate vegetable crops such as tomato (Solanum lycopersicum L.), carrot (Daucus carota L.), leeks (Allium ampeloprasum L.), cabbage (Brassica oleracea L. var. capitata), radish (Raphanus sativus L.) and beet root (Beta vulgaris L. var. vulgaris). The domesticated low country and dry wet areas are suitable for growing various tropical vegetables such as bitter gourd (Momordica charantia L.), okra (Abelmoschus esculentus L.), bringal (Solanum melongena L.), pumpkin (Cucurbita maxima Duch.), luffa (Luffa acutangula (L.) Roxb.) and snake gourd (Trichosanthes cucumerina L.) (Figure 1).
Considering both cultivated area and production, tomato, beans (Phaseolus vulgaris L.), capsicum (Capsicum annum L.), bitter gourd and brinjal can be leading vegetables in Sri Lanka. Table 1 and 2 show the cultivated area, production, productivity, net return and unit cost of five major vegetables.
MAJOR VEGETABLES AND THEIR LEADING CULTIVARS
1. Tomato:
As a result of tremendous efforts of tomato breeders, Department of Agriculture has released many inbred and hybrid tomato cultivars for farmer cultivation during past four or five decades (Table 3). Based on the basic seed pro-duction, ‘Thilina’ (Figure 2a) is one of the most popular cultivar among farmers and consumers though it was developed before 20 years. Semi determinate plant type, medium size fruits (average fruit size is around 85-95 g) with an average yield of 40 t/ha, relatively short growing period (first harvest in 75 days and around 12 picks thereafter), comparatively low number of seeds in a fruit and resistance to bacterial wilt are the main characters of the cultivar. It also has thick pericarp, which not only reduces post-harvest losses but is highly preferable for cooking and processing. ‘Maheshi’ (Figure 2b), is the first F1 hybrid cultivar developed by Department of Agriculture. ‘Maheshi’ has bigger fruits (average fruit size is around 125 g) and the yield is around 58t/ha. It also has resistance to bacterial wilt. Tomato cultivar ‘Bathiya’ (Figure 2c) has more consumer preference and higher market demand than other cultivars. It is a hybrid cultivar showing indeterminate growth with average yield of 61 t/ha. Medium size fruits (Per fruit weight 85 g) with thick pericarp, low cracking and resistance to bacterial wilt and curly top virus are the main characters of this cultivar.
2. Capsicum
Considerable number of cultivars have been developed for last two or three decades (Table 3). ‘Hungarian Yellow Wax’ (Figure 3a) was the most popular cultivar among farmers and consumers due to its fruit quality (long fruits with waxy appearance). However, the demand of this cultivar was recaptured by other newly released cultivars because of its low yield (average yield is about 10-15 mt/ ha), cultivated land limited to dry zone area and susceptible to bacterial wilt. The cultivar ‘Lanka yellow wax’ (Figure 3b) was developed by crossing ‘Hungarian Yellow Wax’ and ‘CA 8’ (Figure 3c) to overcome above constraints. ‘Lanka yellow wax’ is a high yielding inbred cultivar with resistance to bacterial wilt and suitable for island wide cultivation. The cultivar ‘Prarthana’ (Figure 3d) is the first and only F1 hybrid cultivar developed by Department of Agriculture by crossing ‘AC 7882’ with ‘HYW’. This hybrid is capturing a high demand from farmers and consumers since vigorous and erect growth habits, high yield (20-25t/ha), attractive waxy appearance and moderate resistance to bacterial wilt.
3. Beans
Bean has a vital position in Sri Lankan food pattern. It has showed a growing trend among farmers to cultivate high yielding foreign hybrids and inbreds of bean cultivars due to high consumer demand. Breeders working with bean in Sri Lanka made tremendous efforts to regain farmers’ demand for local cultivars (Table 3). Bean cultivars, ‘Kappitipola Nil’, ‘Lanka butter’ (Figure 4a), ‘Hordi green’, ‘Badarawela green’ (Figure 4b) and ‘Gannoruwa nil’ (figure 4c) are the results of that effort. All cultivars have average yields around 25-28t/ha.
4. Brinjal
Brinjal is the most widely-cultivated vegetable in Sri Lanka. Some cultivars have been developed by the Department of Agriculture during the last two or three decades (Table 3) and ‘Anjelee’ (Figure 5a), ‘Amanda’ (Figure 5b), and ‘HORDI Lana irii’ (Figure 5c), are the most popular cultivars among farmers and consumers. The pods of ‘Amanda’ is purplish pink with an average yield of 30-35t/ ha and it is moderate resistant to bacterial wilt. Resistance to bacterial wilt, high yield (35-40t/ha) and dark purple colour pods are the prominent characters of the cultivar ‘Anjelee’. ‘Hordi lana irii’ is the only brinjal hybrid cultivar. It is also moderately resistant to bacterial wilt with an average yield of around 40-48t/ha.
5. Bitter gourd
Bitter gourd is a popular vegetable in Sri Lanka due to its high medicinal value. Exotic and local bitter gourd cultivars (Table 3) are grown all over the country. ‘Thinnawelli white’ (Figure 6a), ‘Mathale green’ (Figure 6b) and ‘Niroga’ (hybrid cultivar, Figure 6c) are the popular local bitter gourd cultivars. ‘Thinnaveli white’ has yellowish white pericarps while other two cultivars, ‘Mathale green’, and ‘Niroga’ have dark green and light green pericarps, receptively. Average yield of these cultivars is around 20 t/ha.
BREEDING PERSPECTIVES OF MAJOR VEGETABLES IN SRI LANKA
Escalating population, declining agriculture resources such as water and arable land, increasing demand for quality vegetables, climate changes are the major challenges in vegetable production in Sri Lanka. Rising pest and disease incidence are also major problems in growing vegetables. Therefore, vegetable crop improvement programs in Sri Lanka should focus on developing high yielding and quality cultivars with abiotic stress tolerance and biotic stress resistance, as many breeding programs in the world have been focused on improving yield and quality as well as biotic and abiotic stress tolerances (Prohens et al.,2008a and 2008b). During past few decades, several biotic stress tolerant vegetable cultivars have been developed in tomato, brinjal, bitter gourd, okra, hot pepper and beans (Table 4). At present, vegetable breeders are trying to develop multiple disease resistant cultivars especially in tomato and brinjal. In tomato, multiple resistance for tomato leaf curl virus, bacterial wilt and early blight is at height of improvement. At the same time, many tomato and brinjal breeding programs have been focused on developing heat and water stress tolerant cultivars to expand the cultivated area in the dry zone.
High postharvest loss due to high perishability, lack of transport and storage facilities, mismanagement in marketing, is also one of the major constraints in vegetable industry in Sri Lanka. Breeding vegetable cultivars with postharvest traits that can increase shelf life by reducing the physiochemical changes should be a priority in Sri Lanka. In addition to postharvest traits, breeders in Sri Lanka are focusing on developing cultivars of different vegetables such as radish, cabbage, carrot and tomato which can be grown during off season for a year round supply of vegetables. Other traits including mechanization is also imperative due to increasing labor costs in rural area.
Farmers in Sri Lanka often suffer from the shortage of good seeds; the timely supply of seeds with improved yield and quality would be beneficial to farmers. Farmers are already shifting from open pollinated cultivars to F1 hybrid ones because of their superiority over open pollinated cultivars in some vegetables such as tomato, cabbage, hot peppers, cucumber, bitter gourd, luffa, brinjal, and radish. In the recent past, all vegetable farmers in Sri Lanka grew exotic hybrid cultivars but at present, there are growing demand for hybrid cultivars developed in Sri Lanka.
Breeding programs in Sri Lanka should put high priority on developing not only high yielding hybrid cultivars but related technologies as described in Dias et al. (2011). Hybrid seed production is costly if hand pollination techniques are used. However, the decrease in seed production cost can be achieved at commercial level by adopting several technologies such as male sterility, self-incompatibility and gynoecism. Sri Lanka has utilized these technologies in few vegetables such as hot pepper and onion.
Other important traits like bioactive properties have generally been considered as a second factor compared to yield, quality, and biotic and abiotic stress tolerance traits. There are different bioactive properties which are having health benefits (DeFelice, 2002). Natural pigments, anthocyanins, betaines, carotenoids and chlorophylls in plants are called as edible colors and these pigments play important metabolic functions in the plants. These bioactive properties are frequently exploited as the source of medicine to address a number of human ailments (Grotewold, 2006). One of breeding objectives in Sri Lanka is to develop new vegetable cultivars with increased bioactive properties as well as pigments.
Conventional breeding methods alone, which usually need significant time and resources, may not attain the nation’s demand. It is important and urgent to combine conventional breeding methods, mutation breeding techniques, genetic engineering, molecular biology, molecular genetic informatics and biochemistry (Aditika et al., 2017). At present, breeders have forethought to utilize molecular breeding or marker assisted breeding for the vegetable crop improvement program. Marker assisted breeding is based on genotyping traits rather than phenotyping (Foold et al., 2005) and it can improve the accuracy of selection and efficiency in generation advancement (Holland 2014). Development of multi-disease resistant cultivars by gene pyramiding using conventional breeding alone might be time consuming but it would be a lot faster by using molecular markers. Currently, marker assisted selections are utilized in tomato hybrid cultivar development with leaf curl virus resistance, mail sterile parental line development in hot pepper and onion hybrid cultivar production in Sri Lanka.
CONCLUDING REMARKS
Per capita vegetable consumption in Sri Lanka is only about 150g/day (AgStat 2017), which is far behind the daily vegetable requirements of 250g/day for a healthy life (Kathryn et al., 2014), although the country has favourable environment for year round production of vegetables. Low vegetable production due to unpredicted weather condition, high pest and disease incidence, unavailability of scientific cultivation plan, insufficient marketing and straggling transportation facilities are the main reasons for low vegetable pre capitate availability. While managing infrastructure facilities for vegetable industry, a great responsibility lies on the vegetable breeders. Although main breeding objective will help to continue yield increase to meet the requirement of increasing population, breeding for good quality, resistance and tolerance to abiotic and biotic stresses, respectively, are equally important. Incorporating of conventional breeding and molecular breeding technologies would enable vegetable breeders to approach their targets efficiently and accurately. With the combined technologies, it can be expected future vegetable cultivars with higher stress tolerance, good quality, better nutritional value, suitable for processing as well as with a wider adaptability to adverse weather and soil conditions, for a healthy nation.
적 요
스리랑카는 채소의 주년 생산에 적합한 기후를 갖고 있는 열대국가이다. 열대, 아열대 채소의 재배면적은 전체 농지 (105,062 ha)의 약 3%이다. 지난 50년 동안 스리랑카에서 채 소 육종에 관한 체계적인 연구가 이루어졌고 채소 부문은 지 속적으로 증가하였다. 하지만 채소 육종, 재배 및 가공과 관련 된 기술이 선진국에 비해 많이 뒤떨어져 있는 형편이다. 전통 육종법을 통해 개발된 다양한 농업적 형질을 가진 품종이 현 재까지 스리랑카의 채소 생산에 이용되고 있지만 생명공학적 방법을 접목한 채소 품종 육종법의 중요성이 점차로 부각되고 있다. 본 논문은 스리랑카에서 중요한 채소 작물인 토마토, 고 추류, 콩류, 가지 및 여주의 육종과 품종 현황을 소개하고 향 후 스리랑카 육종 전망에 대해 논의하였다.
