Resistance of the citrus rootstock forner-alcaide 5 to Tylenchulus semipenetrans in replant situations

Abstract

The resistance of the citrus rootstock Forner-Alcaide 5 to Tylenchulus semipenetrans was assessed in comparison to the susceptible Carrizo citrange (S) in two replant situations. Changes in soil and root population densities were monitored after planting the new trees to detect tree infection and nematode population growth over time. The efficacy of pre-plant control methods such as fumigation with 1,3 Dichloropropene (1,3D) or 2-year fallowing was also assessed. Fumigation and fallowing reduced juveniles + males/250 cm3 soil to undetectable levels for 3 and 2 years, respectively, and postponed root parasitism on Forner-Alcaide 5 for 3 and 2.5 years, respectively. Forner-Alcaide 5 supported lower densities of juveniles + males/250 cm3 soil and females/g root than Carrizo citrange in both replant situations The efficacy of the resistant rootstock was enhanced when combined with 1,3D fumigation or 2-year fallowing because the pre-planting control reduced densities of juveniles + males in soil before establishing the orchard, and the resistant rootstock, the female densities in the roots. Selection for virulence within the field population did not occurr after 9-years of exposure of Forner-Alcaide 5 to the nematode. The durability of the resistance can be enhanced by combining rootstock resistance with pre-planting control methods in order to delay root parasitism, and therefore, diminish the selection pressure exerted on the resistant rootstock. Forner-Alcaide 5 exibited higher scion diameter and yield than Carrizo citrange.