GROWTH COMPARISON OF CITRUS ROOTSTOCKS AFTER ARTIFICIAL INFECTION WITH PHYTOPHTHORA

摘要

Phytophthora is one of the most economically important soil-borne pathogens affecting Florida's citrus industry. The most effective control in the field is based on the use of tolerant rootstocks in connection with sound management strategies. This study describes the rapid greenhouse evaluation of seven rootstocks for tolerance to Phytophthora root diseases. Seedlings of the rootstocks Sun Chu Sha, Cleopatra mandarin, US-897, Sour orange, 'Pineapple' sweet orange, Carrizo cit-range, and Swingle citrumelo were inoculated with citrus roots derived from a field site known to be heavily infested with Phytophthora and maintained in tubs containing a commercially available potting mix. The experiment was terminated after four weeks and shoot length, shoot mass, and root mass were determined. Infection with Phytophthora was quantified using enzyme-linked immunosorbent assays (ELISA), and species were identified by restriction fragment length polymorphism analysis in combination with polymerase chain reaction (PGR). Shoot length, root mass and shoot mass were significantly reduced in Carrizo, 'Pineapple', and Swingle, exhibiting overall reductions of 44%, 48%, and 50%, respectively, whereas total reductions observed for Sun Chu Sha and Cleopatra were less than 25%. Values for Sour Orange and US-897 ranged in between the two groups. Results obtained in this study are in accordance with results obtained from field trials and provide valuable information to aid in the development of new citrus rootstocks that are tolerant to Phytophthora.