ARTICLE Plant Genetic Resources Newsletter, 2000, No. 121: 15·19 Implications of the introgression between Citrullus colocynthis and C. lanatus characters in the taxonomy, evolutionary dynamics and breeding of watermelon José Geraldo de Aquino Assis118, Manoel Abílio de Queiroz2, Samira Miguel 4 4 Campos de Araújo3, Gerhard Bandel and Paulo Sodero Martins 1 Instituto de Biologia, Universidade Federal da Bahia Rua Barão de Geremoabo, s/n, Ondina, Salvador, Bahia, Brazil CEP 40.170-110. Email: [email protected] . 2 Centro de Pesquisa Agropecuária do Trópico Semi-Arido, Empresa Brasileira Pesquisa Agropecuária (EMBRAPA) 3 Departamento de Biologia Geral, Faculdade de Ciências Agrárias e Veterinárias de Jaboticabal, Universidade Estadual Paulista 4 Escola de Agricultura "Luiz de Queiroz" (ESALQ), Universidade de São Paulo Summary Résumé Resumen Implications of the Conséquences de Implicaciones de Ia introgresión introgression between Citru/lus I'introgression entre des entre caracteres de Citrullus colocynthis and C. lanatus caraetêres de Citru/lus colocynthis y C. lanatus en Ia characters in the taxonomy, colocynthis et C. lanatus sur Ia taxonomía, Ia dinámica evolutionary dynamics and taxonomie, Ia dynamique de evolutiva y Ia genética de Ia breeding of watermelon I'évolution et I'amélioration de sandía Citrul/us colocynthis is a wild species Ia pastéque Citrullus colocunihis es una especie silves- counted among the ancestors of the cul- Citrullus coiocunthis est une espece sau- tre considerada ancestro de Ia sandía cul- tivated watermelon, C. lanatus. Cross- vage figurant parmi les ancêtres de Ia tivada, C. lanatus. La compatibilidad compatibility between these species pasteque cultivée, C. lanaius. La compat- recíproca entre estas especies por hibri- through both natural and artificial hy- ibiJité entre ces espêces par hybridation dación tanto natural como artificial se ha bridization has been widely reported. naturelle ou artificielle a été largement seii.alado frecuentemente. Estudios real- Watermelon landraces were collected décrite. On a récolté des variétés locales izados con variedades nativas de sandía from the northeast of Brazil and studies de pasteque dans le nord-est du Brésil et recolectadas en el nordeste dei Brasil showed evidence of introgression from démontré l'introgression de C. colocun- revelaron Ia introgresión de C. COlOC1jll- C. colocynthis to C. lanatus, although this dans C. lanaius, bien que C. COlOC1jn- this a C. lanatus, a pesar de que C. COlOC1jll- C.colocynthis is not distributed in Brazil. this ne soit pas présent au Brésil. La this no se ha extendido en Brasil. Este This paper discusses the implications of présente étude examine les conséquenc- trabajo analiza Ias implicaciones de esta this introgression in the taxonomy, evo- es de cette introgression sur Ia taxon- introgresión en Ia taxonomía, Ia dinárni- lution dynamics and the improvement omie, Ia dynarnique de l'évolution et ca evolutiva y Ia mejora genética de Ia of watermelon. l'amélioration de Ia pasteque. .sandía. Key words: Brazil, Citrullus colocynthis, Citrullus lanatus, evolution, introgres- sion, watermelon Introduction The Citrullus genus includes three species, of which water- and southwest areas of Africa and Asia, which ean be di- melon (Citrullus lanatus) is the cultivated species. Romão vided into two different races, one found on the Mediterra- (1995) reports on its broad morphological intraspecific vari- nean coast and in Israel, the other found in the deserts of ability; it also has low isozymic variability. Both morpho- Negev and Sinai, and C. ecirrosus, which is endemic to the logic and isozymic variability have been found in C. lanatus Namibian desert (Jeffrey 1975; Zamir et a1.1984). in several parts of the world where it has undergone intro- Citrullus lanatus (Thunb.) Matsumura and Nakai is a gressive hybridization with the wild species C. colocynthis. cultivated speeies, originating in south or maybe central The resulting species has been classified as C. lanaius varo Africa; Whitaker and Davis (1962) also deseribe the exist- citroides. This paper reports on the occurrence of this variety enee of a seeondary diversification eentre in India. The spe- in Brazil and discusses its implications for the evolution and eies is charaeterized by large green leaves with three to five the genetic improvement (breeding) of the species. deep lobes on the edges, or more rarely none, mediurn-sized monoie flowers with short pedieels, medium to large fruit Taxonomy of the Citrullus genus with smooth skin and flesh with a high water content, and The genus Citrullus (Cueurbitaeeae) consists of three dip- oval to oblong seeds of a white or brown colour. loid species (2n=22): (i) C. lanatus (Thunberg) Matsumura Aecording to Fursa (1981), the eultivated speeies C.lanatus and Nakai, including the cultivated watermelon widely includes three subspecies: (i) lanatus, (ii) vulgaris which grown in severa! parts of the world, (ii) C. Ianaius var. has two varieties, var, vu/garis and var. cordophanus, and citroides, a wild form found in South Afriea and also culti- (iii) mucocospermus. An eeogeographie classifieation of vated in other parts of the world mainly for feeding ani- cultivated watermelons has no taxonomic purpose, how- mais, and (iii) C. colocynthis (L) Schrad, found in the north ever, with the aid of colleetions the influenee of eeologi- 16 Plant Genetic ResourcesNewsletter, 2000, No. 121 cal conditions, as well as of controlled crossing, on the These characters have been the two most important ones development of different types of varieties could be in the domestication process as there is strong pressure for shown. Based on the regions cultivating the variety, the red flesh and a non-bitter taste. According to Navot et aI. leaf morphology and anatomic structure, physiological (1990), selection for the rare mutants, which have eliminated indexes (water retention capacity) of leaves and the the bitterness and added red colour, has been responsible sexual type of the plants, varieties have been grouped for the isozymic monomorphism found in cultivated water- into three types: Russian, Asian and Occidental. melon accessions. Maheshwari (1978) recognizes severa 1watermelon vari- eties cultivated in different parts of the world, e.g. India, Hybridization occurrence between Pakistan, Malaysia, Polynesia, [apan, China, Iraq, Europe, C. lanatus and C. colocynthis Africa, and South and Central America. Among other char- Natural hybrids between C. lanatus and C. colocynthis have acters, such varieties differ in size, shape and colour of fruit already been found. Singh (1978) found one of these hybrids skin, colour of flesh (red, pink, white and yellow), and the in India, where both species are well represented in the colour and size of seeds. The author is aware of 13 varieties semi-arid regions of Rajasthan. Citrullus lanatus, called 10- of C. lanatus: var. lanatus a wild watermelon native to south- cally 'Matiro', C. colocynthis called 'Tumba' and other inter- em Africa; var. viridis a 'giant' watermelon from Iraq and mediate forms called 'Khar' or 'Tatumba' have been found cultivar 'Black Tom Watson': var. albidus in the nigro- growing dose to each other. Morphological and cytological seminius and albidus forms bred in the central areas of Iran; observations reinforce the dose relationship between both var. variegatus; var. rotundus; var. pulcherrimus; var. shami; species. Maheshwari (1978) also described a variety called var. oblongus whose common name is 'Fairfax'; var. virgatus; 'Neri' as an almost intermediary form between C. colocynthis var. pumilus which is called 'New Hampshire': var. caffe a and C. lanaius. In Arizona, Fulks et aI. (1979) found natural sweet cultivated watermelon and var. citroides, whose com- hybrids growing between C. colocynthis and C. lanatus cv. mon names are, respectively, 'citron melon' and 'preserving Citron, which had white flesh, bigger fruit and no character- melon'. istic bitter taste. Furthermore, Shimotsuma (1963) obtained According to Anghel (1969), C. colocynthis (L.) Schrad artificial hybrids. Natural hybrids have ais o been reported originates from North Africa and south Asia. Mohr (1988) in Australia (Herrington et aI. 1986) and in Texas, USA has described it as a perennial species differing from C. Ianatus, where they invade plants growing on sandy soils such as mainly in the size of the plant organs. Its leaves are small, cotton and sorghum. On some infested cotton fields they with grey narrow hairy lobes, the flowers are small and reduce production from 20 to 35% and interfere in mechani- monoecious and the seeds small and brown. The fruits are cal harvesting. Similar problems occur with peanut cultiva- small, 15-20 em wide in diameter, and spongy with a thin tion (Smith and Cooley 1973). rindo When ripe they are a green to light-green or light- Hybridization between the species has produced a spe- yellow colour, with white or compact flesh with a bitter cific dassification for plants with intermediary characters, tas te. This species also possesses medicinal properties the nomendature C. lanatus var. citroides being used. Based (Koshoo 1955). Smith and Cooley (1973) described the wild on isozyme data, Navot and Zamir (1986) consider this watermelon as having fruit of 15-20 cm in diameter, which South African variety to be the wild progenitor of the culti- produce from 600 to 1000 seeds per fruit. The pericarp is vated watermelon. Based on immunochemical analyses, white with a low sugar content