January 9-13, 2010
Town & Country Convention Center
San Diego, CA
Mohammad A Rahman1 , Umesh K Reddy1 , Yan R Tomason1, 2 , Sathish K Ponniah1 , Gopinath Vajja1 , Chintha R Reddy3 , Padmavathi Nimmakayala1
Seedless triploid watermelon is produced by crossing the diploid with a tetraploid line, which is a unique ploidy reconstruction that has to be laboriously carried every growing season. This makes triploid breeding very challenging and the seed very expensive. In the current study, a segregating F2 tetraploid population was generated by selfing a F1 seedling of the cross (Citrullus lanatus var. citroides, PI 482252 × Citrullus lanatus var. lanatus, PI 248178), which was treated with 0.2% colchicine and subsequently screened for ploidy levels. The confirmation of tetraploids was carried by determining the ploidy levels in 500 progeny of the above cross by both flow cytometry and counting chloroplasts per guard cell pair. Ninety two progeny were confirmed as tetraploids. The absolute DNA content ranged from 1.69 to 1.84 pg among the tetraploids in comparison with the standard diploid DNA content of 0.88 pg. Tetraploid and diploid populations were evaluated under field conditions to compare phenotypic performance especially fruit traits. The map consisted of 11 linkage groups spanning a total length of 423.2 cM. A QTL analysis was performed to locate the QTLs linked to different fruit related traits. 19 QTLs for fruit traits with varied effects were identified. There is no systematic QTL study that throws some light on inheritance of QTLs in tetraploid progenitors of the triploid hybrids. This is the first mapping and QTL study ever done in synthetic tetraploid population of any plant genome including watermelon.