Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/14/2002
Publication Date: 10/1/2005
Citation: Levi, A., Thomas, C.E. 2005. Polymorphisms among chloroplast and mitochondrial genomes of citrullus species and subspecies.. Genetic Resources and Crop Evolution. 52:609-617. Interpretive Summary: Production of watermelon in the U.S. has increased from 1.2 M tons in 1980 to 2.2 M tons in 1999, with a farm product value of $289 million. Watermelon was cultivated in Africa over five thousands years ago. The African wild species Citrullus lanatus is the progenitor of cultivated watermelon. Due to many years of cultivation watermelon has a narrow genetic base, in which most of the watermelon varieties developed in the U.S. in the last 200 years have common parents and similar genes. As a result, watermelon varieties are not sufficiently resistant to pathogens and pests. Indeed many pathogens and pests invade watermelon plants and cause them significant damage. Thus, there is an immediate need to find genes that make watermelon resistant to diseases and pests. Wild species like Citrullus colocynthis or the subspecies Citrullus lanatus var. citroides are related to watermelon. This study examines the possibility of fusing these wild species as essential sources of genes that can be used fo the improvement of watermelon. As such it provides basic information necessary to the development of resistant varieties.
Technical Abstract: Twelve and six DNA clones that represent various parts of chloroplast and mitochondrial genomes, respectively, were used for restriction fragment length polymorphism (RFLP) analysis of DNA samples from five watermelon cultivars and 23 Citrullus accessions collected from diverse geographical locations. Cluster analysis based on 24 and 16 RFLP markers produced by these clones, respectively classified the accessions into four major phylogenetic groups: Watermelon cultivars (Group I), Citrullus lanatus var. lanatus (Group II), C. lanatus var. citroides (Group III), and C. colocynthis (Group IV). The chloroplast and mitochondrial genomes of cultivars were closely related to these of C. lanatus var. lanatus, while these of C. lanatus var.citroides and C. coloynthis accessions were distinct, indicating that C. lanatus var. citroides is the progenitor of both C. lanatus var. lanatus and C. coloynthis. DNA analysis of BC1 and BC4 4plants showed that chloroplast and mitochondria are maternally inherited i crosses between C. lanatus and C. coloynthis. This study examines the possibility of enhancing watermelon germplasm by replacing the chloroplast and mitochondrial genomes of cultivated watermelon (C. lanatus var. lanatus) with those from the wild species, C. coloynthis.