WATERMELON BREEDING IN BRAZIL

Watermelons (Citrullus lanatus) are cultivated on 70,000 hectares in Brazil, scattered in different regions of the country. The kinds grown are American cultivars having large fruits of good quality, but they are very susceptible to the watermelon biotic stresses Sphaerotheca fuliginea, Didymella bryoniae, papaya ringspot virus-watermelon strain, and watermelon mosaic virus. Considering the genetic variation of watermelon in the traditional agriculture of northeastern Brazil, a Watermelon Germplasm Bank housing 600 accessions was organized at Petrolina-PE, Brazil. Some accessions were evaluated in field and greenhouse experiments for resistance to Sphaerotheca fuliginea and Didymella bryoniae. Contrasting parents were crossed in a diallel scheme and a combining ability analysis was performed using the parents and reciprocal F₁s. Sources of resistance to powdery mildew were crossed with ‘Crimson Sweet’ and resistant lines were selected. Sources of resistance to Didymella were also found. Gene action for earliness, fruit weight, fruits per plant and total soluble solids was predominantly additive. Seedlings of powdery mildew-resistant lines were treated with colchicine to double their ploidy. Tetraploid plants were identified and crossed with diploid lines from commercial cultivars to obtain triploid hybrids, which were then evaluated in field experiments. Some of the triploid hybrids showed good yield per plant and high sugar content. They will be evaluated in different watermelon growing regions of the country.