Colonization by arbuscular mycorrhizal in mandarin 'Montenegrina': interaction between rootstocks and sazonality

The objective was to evaluate the influence of seasonality on mycorrhizal colonization in roots of six rootstocks in an orchard of 'Montenegrina' mandarin (Citrus deliciosa Tenore). Rootstocks evaluated were: 'Flying Dragon' [Poncirus trifoliata var. monstrosa (T. Ito) Swing.]; 'Troyer' citrange [C. sinensis (L.) Osb. × P. trifoliata (L.) Raf.]; 'Swingle' citrumelo [C. paradisi Macf. × P. trifoliata]; 'Rangpur' lemon (C. limonia Osb.); 'Volkamer' lemon (C. volkameriana Ten. & Pasq.); 'Caipira' orange (C. sinensis). Roots were collected in the four seasons. The density of structures, root colonization (number of infected segments/total analyzed) and spore density were determined. The rootstocks showed high percentages of colonization in the spring (above 96.60%). In winter, only 'Swingle' and 'Rangpur' showed high colonization rates (96.60 and 95.00 %, respectively). On the other hand, 'Flying Dragon', 'Troyer' and 'Volkamer' showed low colonization in winter (11.60 to 33.30 %). 'Flying Dragon' showed an increase in mycorrhizal colonization from the winter season (33.30 %) to spring (100.00 %) and a subsequent decrease from summer (95.00 %) to autumn (63.30 %). Mycorrhizal colonization occurs naturally and at a high rate on rootstocks, varying between rootstocks and seasons. There is a negative correlation between foliar nutritional content and the presence of AMFs.