1.14.11
INTERACTION BETWEEN THE CEREAL CYST NEMATODE HETERODERA LATIPONS AND COMMON ROOT ROT, COCHLIOBOLUS SATIVUS, ON BARLEY

U SCHOLZ1, V VILICH 1, RP SCHUSTER 1, OF MAMLUK 2 and RA SIKORA 1

1lnstitut fur Pfianzenkrankheiten, Universitaet Bonn, Nussallee 9, 53115 Bonn, Germany; 2International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, PO Box 5466, Syria

Background and objectives
Numerous literature sources [1, 2] describe an interaction between plant parasitic nematodes and root rot-causing fungi. The nematode Heterodera latipons and the fungus Cochliobolus sativus are known as important pathogens. Under Mediterranean conditions, with low and irregular rainfall, the infected plants have additional difficulties in water uptake compared with healthy plants. The objective of this experiment was to study the possible interaction between H. latipons and C. sativus on barley.

Materials and methods
The experiment as a pot trial consisted of six treatments with seven replications each. The treatments were the following: control; H. latipons alone; C. sativus alone; H. latipons and C. sativus together; H. latipons first and C. sativus 9 weeks later; and C. sativus at first and H. latipons 9 weeks later. H. latipons inoculum was applied as an egg juvenile suspension of H. latipons (three eggs and juveniles per g soil dry weight). C. sativus inoculum was applied as a conidial suspension (300 conidia per g soil dry weight). The variety used was Arta, a susceptible barley variety for both pathogens. After harvesting, yield components such as grain and straw yield, discoloration of the subcrown internode (SCI), rating 1-5, as well as infection rate of different plant parts (crowns, subcrown internodes - SCI, seminal and nodal roots) by C. sativus and the final density of H. latipons were measured.

Results and conclusions
The highest grain yield decrease was found with the early application of the nematode, followed by the simultaneous application of nematode and fungus, and was significantly different from the other treatments. The treatment with simultaneous application of nematode and fungus reduced the straw yield to the greatest extent, followed by the treatment with the early application of nematodes, but no significant differences were detected. C. sativus alone did not reduce the yield, but it had an additional effect when the pathogen was applied simultaneously with H. latipons or 9 weeks after the nematode application. An explanation for the additional grain and straw yield decline by C. sativus under simultaneous presence of H. latipons is the increase of discoloration of the SCI, the more extended root lesions and the significantly higher infection of crown, SCI, seminal and nodal roots by C. sativus compared to the treatment C. sativus alone. A similar effect, but without significant differences, was observed, when the fungus was applied 9 weeks after the nematode application. On the other hand the presence of the fungus at the same time as H. latipons reduced the multiplication of H. latipons to a pf/pi value of 3.8 by additional pathogen pressure compared with the treatment with H. latipons alone, which resulted in a pf/pi value of 7.6.

References
1. Smiley RW, lngham RE, Uddin W, Cook GH, 1994. Plant Disease 78, 1142-1149.
2. DeBoer RF, Kolimorgen JF, Macauley BJ, Franz PR, 1991. Aust. J. Exp. Agric. 31, 367-372.