Evaluation of the resistance of american hybrids of citrus rootstocks to root infection by Phytophthora citrophthora (inoculation test on laboratory seedlings)

Abstract

Seedlings of several hybrids of citrus rootstocks of various crosses between Cleopatra mandarin x trifoliata Swingle; Cleopatra mandarin x Citrange carrizo; Swingle x C.E.S. rough lemon; and Sunki mandarin x trifoliata Swingle, introduced from the Dates and Citrus Station-Indio-California-U.S.A., were tested in laboratory for resistance to Phytophthora citrophthora. They were planted individually in small cylinders, with sand washed and sterilized at 127°C for two hours. One hundred and twenty days after planting, their intact roots systems were exposed to a suspension of zoospores. After 24 days incubation, the roots of each seedling were treated with 2, 3, 5 triphenyl tetrazolium chloride to identify the proportion of injured roots. The statistical plan was undesigned. There were no significant statistical differences among the treatments (hybrids). However, hybrids of Cleopatra mandarin x trifoliata Swingle 63-206; Cleopatra mandarin x trifoliata English 63-242; Cleopatra mandarin x Citrange carrizo 63-224, 63-227; and hybrids of Sunki mandarin x trifoliata Swingle 63-308, showed the smallest average of lateral roots infected by this pathogen. Seedlings of rangpur lime, used in the same test, showed high susceptibility to the pathogen, with infection of 80% to 100% in the lateral roots.