Evaluation of the Resistance of 10 New Citrus Rootstocks to Root Rot Caused by Phytophthora Parasitica

In Morocco, the sour orange (Citrus aurantium L.) is the most anciently used rootstock, it remains dominant. Due to its better affinity with most commercial varieties, its adaptation to a wide range of soils and mainly due to its resistance to root rot caused by Phytophthora spp. However, it gives susceptible associations to tristeza. In vivo, several methods were used for the screening of citrus rootstocks in relation to Phytophthora spp. The objective of our experimentation is the development of an in vitro screening test of rootstocks caused by Phytophthora parasitica. Plants of Citrumelo (57. 98. 502), Poncirus Trifoliata, Citron troyer, Citron Troyer c 35 B 6 A11, Cleopatra mandarin tree x CC 30 575, Cleopatra mandarin tree xP.T 30 584, Cleopatra mandarin tree x cc B2 30 576, Mandarin tree changsa B2, Mandariniecleop X CC 30,577 and a South African Hybrid aged 2 months were watered daily and fertilized every 15 days using a nutrient solution. Inoculation was done by soaking the root systems in a spore suspension of P. parasitica for 24 h. Inoculation with P. parasitica caused root rot (Rot-tips) with a reduction in feeder fiber production and colonization of root systems that varied between rootstocks. Indeed, the Mandarin hybrids Cleopatra x cc 30 575 and the Mandariner Cleopatra x cc B2 30 576, were the most susceptible rootstocks to P. parasitica while the hybrids Citrange Troyes, Citrange Troyer C 35 B 6 A11 and the hybrid of South Africa are the most resistant rootstocks. Variability of rootstocks colonization by P. parasitica is thought to be variability in the production ability of 6, 7-dimethoxycoumarin (DMC) in root tissues of rootstocks.