TABLE CONTENTS

Population Densities of Tylenchulus semipenetrans Related to Yield of
Clementine Mandarin in Spain
Verdejo-Lucas, S. (1), F.J. Sorribas (2), J. Pastor (3), C. Ornat (2) & J. Valero (2)
(1) IRTA. Crta. de Cabrils km2, E-08348 Cabrils, Barcelona. (2) Departament d’Enginyeria Agroalimentària i
Biotecnologia.Universitat Politècnica de Catalunya. Edifici ESAB, Av. Canal Olímpic 15. 08860 Barcelona, (3)
IRTA. Amposta, Ctra. Balada. E-43870, Tarragona, Spain.
Mandarin Clementine represents 75% of the hectarage in Catalonia where 77% of the
orchards are infested with T. semipenetrans. To determine the relationship between nematode
populations and yield of mandarin, trials were conducted in three drip irrigated orchards of
Clementine mandarin cv. Clemenules (El Pla and Mariclaire) or cv. Hernandina (Martorella)
for two consecutive years. The orchards were sampled in March and October (El Pla and
Martorella), or only in March (Mariclaire) to determine soil and root population densities.
Fruits were collected in a single picking. The economic threshold (nematode population at
which the value of the damage caused is equal to the cost of control) was calculated for each
mandarin cultivar and year considering the gain threshold (value of harvested mandarin that
equals the cost of control), and the relationship between population densities and yield. Yield
of cv. Clemenules was related to densities of females/g root in spring (R 2 = 0.469; P =
0.0001) but unrelated to juveniles in soil. Yield of cv. Hernandina, however, did not relate
either to females/g root or juveniles in soil probably due to the alternate behaviour of this
cultivar. The relationship between relative yield of cv. Clemenules and densities of females/g
root in spring was described by the Seinhorst damage function model (0.035 + 0.965 (0.9995)
(Pi – 287) , R 2 = 0.4782, P < 0.0001). The tolerance limit of cv. Clemenules on citranges Carrizo
and Troyer was 287 females/g root. The estimated economic threshold considering the price
of mandarins (0.25 and 0.17 €/kg year one and two, respectively) ranged from 330 to 710
females/g root if nematicides were used to control the nematode (lower and upper nematicide
treatment cost considered). These tolerance limit and economic threshold values can be taken
as a benchmark and will be helpful to provide guidance to the growers.
5 th International Congress of Nematology, 2008 263