Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a major vegetable crop in the world, accounting for 6.8% of the world area devoted to vegetable crops. Wa- termelon is a useful vegetable crop for genetic research because of its small genome size, and the many available gene mutants. The watermelon genes were originally organized and summarized in 1944, and have been expanded and updated periodically. However, the action of some watermelon genes has not been described clearly in some cases. Also, the interaction of multiple gene loci that control similar traits needs to be described more clearly. Finally, it is necessary to identify the inbred lines having each published gene mutant, for use as type lines in studies of gene action, allelism, and linkage. The objective of this work was to update the gene list, identify the cultivar or line having each gene mutant, and collect seeds of the lines for use by interested researchers. In addition, the gene descriptions were expanded and clarifi ed, information on gene interactions was added, and errors in naming or citing previously described genes were corrected. New genes that have not previously been described (cr, Ctr, dw-3, ms-2, Ti, ts and zym-FL) were added to the list, for a total of 163 watermelon gene mutants. Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a major cucurbit crop that accounts for 6.8% of the world area devoted to vegetable crops (FAO, 2002). Watermelon is grown for its fl eshy, juicy, and sweet fruit. Mostly eaten fresh, they provide a delicious and refreshing dessert especially in hot weather. The watermelon has high lycopene content in the red-fl eshed cultivars: 60% more than tomato. Lycopene has been classifi ed as use- ful in the human diet for prevention of heart attacks and certain types of cancer. Watermelon is native to central Africa where it was domesticated as a source of water, a staple food crop, and an animal feed. It was cultivated in Africa and the Middle East for >4000 years, then introduced to China around 900 AD, and fi nally brought to the New World in the 1500s. There are 1.3 million ha of watermelon grown in the world, with China and the Middle Eastern countries the major consumers. China is the largest watermelon producer, with 68.9% of the total production. The other major watermelon producing countries are Turkey, Iran, Egypt, United States, Mexico, and Korea (FAO, 2002). In the United States, watermelon is used fresh as a dessert, or in salads. U.S. production is concentrated in Florida, California, Texas, and Georgia (USDA, 2002), increasing from 1.2 Mt in 1980 to 3.9 Mt in 2002, with a farm value of $329 million (USDA, 2002). Watermelon is a useful crop species for genetic research because of its small genome size, and the many available gene mutants. Genome size of watermelon is 424 million base pairs. DNA sequence analysis revealed high conservation useful for comparative genomic analysis with other plant species, as well as within the Cucurbitaceae. Like some of the other cultivated cucurbits, watermelon

/pdf/the-genes-of-watermelon-2v8x61ofpi.pdf

The Genes of Watermelon

This is the latest version of the gene list for watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai). The watermelon genes were originally organized and summarized by Poole (1944). ). The list has been expanded by Robinson et al. (1976), the Cucurbit Gene List Committee (1979, 1982, and 1987), Henderson (1991 and 1992), Rhodes and Zhang (1995), and Rhodes and Dane (1999). The current list provides an update of the known genes of watermelon. This year, the list has 162 total mutants, grouped into seed and seedling mutants, vine mutants, flower mutants, fruit mutants, resistance mutants, protein (isozyme) mutants, DNA (RFLP and RAPD) markers, and cloned genes.

Gene List for Watermelon

A study of the variation of 29 characteristics of 585 varieties or seedlings of okra revealed that 17 West African varieties could be distinguished from all others on the basis of 5 discriminating characteristics. In addition, seedlings of the 3rd outcrossing generation of a population differed from a varietal collection in several characteristics, the most important of which were more seeds per pod and more pods per plant. This is believed to be the result of mass-selection. Country groups differed significantly in characteristics but these differences are believed to be due to small sample size. No such distinguishing characteristics were evident among country groups represented by large numbers of varieties.

Variation in Okra

Vegetables for the tropical region.

The cultivation of resistant varieties has been recognized as the most effective, ideal and economical method of reducing crop losses (Stakman and Harrar 1957). The breeding for resistance is generally no way different than breeding for other traits. However, in resistance breeding the two biological entities, host plant and parasite, are involved, whereas in breeding for other traits the breeder deals with the variability in test material only. The first step in resistance breeding programmes is the collection of natural variability followed by finding out the sources of resistance. The information on these aspects has been described in detail in Chap. 5. The next step is to incorporate the resistance gene(s) from the donor parent(s) using various methods including induced mutations, where the susceptible alleles are altered by the use of mutagens. These methods are discussed in this chapter. In view of the dynamic nature of parasites, the resistant gene(s) fall susceptible after a few years or are no longer effective. Therefore, the resistance breeding programme is a continuous one. An attempt is also made in this chapter to describe how best the race-specific or non-specific genes may be managed so that the life span of resistant gene(s) is prolonged and also the disease losses are avoided or reduced.

Breeding for Resistance to Diseases and Insects

Inheritance of resistance to the fruit fly Dacus cucurbitae Coq., was studied in intervarietal crosses of watermelon Citrullus lanatus (Thunb.) Mansf. Two sources of resistance J 18-1 and J 56-1 were used. The resistance of watermelon to the fruit fly was controlled by a single dominant gene. The symbol Fwr has been proposed to denote the resistant gene.

Inheritance of resistance to fruit fly in watermelon

Inheritance of fruit hairiness, fruit skin colour and leaf lobing was studied in intervarietal crosses of okra, Abelmoschus esculentus (L.) Moench. Fruit hairiness was found to be monogenically controlled, the alleles for prickly hairs and smooth hairs showing interaction. Fruit skin colour was controlled digenically. Light cream colour and pink shading were both dominant over green. The inheritance of leaf lobing was monogenic with incomplete dominance.

Inheritance of fruit hairiness, fruit skin colour and leaf lobing in okra, Abelmoschus esculentus.

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Inheritance of resistance to fruit fly in watermelon

Inheritance of fruit hairiness, fruit skin colour and leaf lobing in okra, Abelmoschus esculentus.