Challenges of Traditional Breeding in Watermelon

Watermelon (Citrullus lanatus) is an economically important crop belonging to cucurbitaceae family grown throughout the world and considered healthyl as it is almost free from fat, sodium and cholesterol. It is known as a 'mood food' because of its levels of Vitamin B6 and its rind contains an important natural compound called citrulline, an amino acid that the human body makes from food. Watermelon has evolved from wild watermelons having small fruits containing hard, pale-coloured, bitter-or bland-tasting flesh to present-day watermelon with a greater number of fruits containing crisp, sweet and red flesh with a thin peel, due to domestication and contemporary breeding. The loss of bitterness traits associated with the convergent domestication of wild watermelon may be due to a syntenic gene cluster of transcription factors that regulates the tissue-specific production of cucurbitacins. The fruits show great diversity in fruit size, shape, rind thickness, colour, flesh, texture, sugar content, carotenoids, flavonoids and nutritional value. Many cultivars have been developed through traditional breeding efforts all over the world but many of them have a common genetic background. The limited genetic base of dessert watermelon cultivars makes improving disease resistance a constant problem for researchers and breeders. Primitive landraces and related materials could be a good source of genes for improving genetic diversity and hybrid vigour in seedless watermelon cultivars, especially in diploid and triploid types. Recent developments in molecular biology have been used in examining genetic diversity, population structure and identifying gene loci that contribute to heterosis as well as those that confer resistance to biotic and abiotic stresses.