S01 - Session O9 - II - Phenotyping and genotyping of a lemon segregating population for mining genetic resistance to two-spotted spider mite

Authors: Chiara Catalano, Licciardello Giuliana, Sebastiano Seminara, Mario Di Guardo, Giovanna Tropea Garzia, Antonio Biondi, Stefano La Malfa, Alessandra Gentile, Gaetano Distefano *

Two-spotted spider mite ( Tetranychus urticae Koch) is a polyphagous mite, which represents a serious adversity for a huge number of open-field and protected crops, including citrus. Its control is extremely difficult since it easily develops resistance against acaricides, due to its short life cycle, abundant progeny and parthenogenic reproduction. Mites penetrate plant cells with their mouth parts, mainly on the underside of leaves, and feed on their content causing spot discoloration and photosynthesis impairment. Among citrus species, lemon ( Citrus limon Burm. f.) is one of the most affected by T. urticae and in severe cases russet symptoms are visible on attacked leaves and fruits, whose marketability is compromised. If phylloptosis occurs, this will negatively affect the production of the following year as well. Chemical control and the use of natural enemies are the main measures applied for the control of T. urticae , while recent research has also focused on host resistance and plant-pest interaction. A segregating population (130 individuals) of lemon obtained by crossing 'Interdonato' (♀) and 'Femminello Siracusano 2kr' (♂), was generated for a market-trait association analysis for understanding the genetic basis of resistance to another lemon disease called 'mal secco' ( Plenodomus tracheiphilus ), since the female parent is tolerant to this tracheomicosis, while the male is very susceptible but produce fruits of excellent quality. Since these plants were naturally attacked by two-spotted spider mite, showing a wide range of symptoms among the different genotypes, we decided to phenotype and genotype the lemon segregant population for the resistance to T. urticae attack, too. Therefore, bioassays were performed using detached leaves placed in a modified Huffaker cell and damage percentage was digitally assessed, confirming the wide range of damage between the different genotypes. According to these results, volatile substances involved in host resistance were studied in those genotypes showing contrasting responses to this phytophagous insect. A functional genomic study is in progress through the Single Primer Enrichment Technology (SPET), taking advantage of the recent de novo sequencing of the lemon genome. Afterwards, a QTL analysis with selected SNPs will lead to the identification of genomic regions significantly associated with resistance to two-spotted spider mite attack. Robust molecular markers linked to the trait of interest will be applicable in marker assisted selection (MAS) and in genetic transformation experiments.