Identification of disease tolerance loci to Phytophthora palmivora in Carica papaya using molecular marker approach.

Papaya diseases such as root rot and aerial blight caused by Phytophthora palmivora, powdery mildew caused by Oidium caricae, and fruit anthracnose caused by Collectotrichum gloeosporioides, and leaf black spot caused by Asperisporium caricae, reduce yields and increase production costs due to the lack of genetically resistant cultivars. Among these diseases, Phytophthora is particularly devastating because it becomes established in wet, rainy weather when the fungicides are ineffective. The goal of this study is to identify and develop molecular markers linked with P. palmivora tolerance in Carica papaya. We used an F2 population derived from an F1 of the most tolerant Hawaiian cultivar Kamiya, crossed with a highly susceptible cultivar SunUp, to evaluate genetic reaction to Phytophthora infection using a laboratory leaf inoculation, followed by a fruit inoculation. These same progeny were scored for DNA markers associated with resistance using methods of amplified fragment length polymorphism (AFLP) and several polymorphic bands linked with tolerance traits in F2 population has been identified. These markers are further characterized to form sequence characterized amplified region markers. Breeders could utilize these markers to select papaya varieties that carry a P. palmivora-tolerant phenotype. These markers may also assist in the identification and cloning of genes involved in plant defense mechanisms, which would further elucidate the defense mechanisms towards oomycete pathogens.