The commercial and potential rootstock seedlings to be screened for tolerance to burrowing nematode were moved from the laboratory to the rebuilt greenhouse in early April and inoculated with Radopholus similis in late May. A new screenhouse was constructed and the Swingle citrumelo and Carrizo rootstock Valencia trees were moved from the laboratory, pruned to initiate new root and shoot growth. They will be inoculated with citrus nematode and graft-inoculated with CLas in the first week of June. A trial comparing the effects of burrowing nematode and CLas on rootstocks susceptible and resistant to burrowing nematode was terminated. Neither pathogen significantly affected the shoot weight of either rootstock; however burrowing nematode increased the root weights (P=0.001) and the effects differed for the two rootstocks. On the susceptible Carrizo citrange the nematode increased root weight by 12% (17.2g vs 19.2g) and on the resistant Kuharske Carrizo by 24% (54.1g vs 66.8g). Unlike the adverse effect of CLas on citrus nematode populations (July 2021 report), nearly twice as many burrowing nematodes per gram of root occurred on Carrizo seedlings infected by CLas than on seedlings only infected with burrowing nematode (65.9 vs 34.3), but the effect was not significant. There were no burrowing nematodes recovered from the resistant rootstock Kuharske. The repeat experiment is ongoing. The project ended on 30 April. Covid-related delays related in the NCE request and the unannounced 3-month closure of our greenhouse have delayed the completion of several experiments that include a repeat of the trials evaluating interactions between CLas and burrowing nematode described above and citrus nematode in which the nematodes increased the virulence of Las in citrus plants, whereas Las-infected plants were less suited to nematode population growth than non-infected plants. These and the trial screening rootstock resistance to the burrowing nematode are ongoing and will be completed and reported in a supplemental report in 2022.