Etude de Ascochyta rabiei (Pass.) Labr., agent del’anthracnose du pois chiche (Cicer arietinum L): variabilité pathogénique, antagonisme et sources de résistance des espaces spontanées de Cicer

Abstract

The aims of this work is to study the pathogenicity, pathogenic variability, chemical control and antagonism on Ascochyta rabiei isolates, the agent of ascochyta blight in chickpea, and sources of resistance of chickpea germplasm and its wild Cicer species against this disease. The study of pathogenic variability based on the determination of pathotypes and physiological races of the pathogen and pathogenicity by the effect of inoculum concentration on the severity of symptoms. We found only one isolate (6.25%) from pathotype I (the least aggressive), 12 isolates (75%) from pathotype II (moderate aggressive) and three isolates (18.75%) from pathotype III (highly aggressive). Four races of A. rabiei were determinated in this region (races 1, 4, 5 and 6). Races 1 and 2 were established in pathotype I, race 4 was represented by the pathotype II, and pathotype III included the two races 5 and 6, which were virulent isolates. The results obtained showed that the disease severity increased with increasing of inoculum concentration from 105 conidia/ml for the resistant line, while the susceptible one was affected with all the tested fungal conidial concentrations. Screening of chickpea germplasm and its wild relatives Cicer species accessions for resistance to A. rabiei, was carried out by using 3 isolates representing the 3 pathotypes of A. rabiei. 28 chickpea lines and 25 lines of 5 wild species (Cicer Judaicum, C. bijugum, C. cuneatum, C. echinospermum and C. reticulatum) were inoculated with three isolates of A. rabiei which represent the three pathotypes of the pathogen. 16 chickpea germplasm exhibited highly resistant response (ILC8068, ILC5902, ILC5921, ILC6043, ILC6090, ILC249, ILC182, ILC187, ILC200, ILC202, ILC3856, Flip4107, Flip93-93C, INRA199, ICC3996 and Flip 10-5/11), 2 lines were susceptible (ILC263 and ILC1929), and 10 chickpea germplasm (ILC4421, ILC2506, ILC7795, ILC482, ILC483, ILC484, ILC3279, ICC4309, ILC 8068 and Flip 1025), displayed tolerant reaction. Sources of resistance in wild Cicer species are in all lines of Cicer judaicum, in 2 lines of the species C. echinospermum (ILWC0 and ILWC246), and 3 lines for the species C. reticulatum (ILWC81, ILWC104 and ILWC247), C. cuneatum (ILWC37, ILWC40 and ILWC232) and C. bijugum (ILWC195, ILWC285 and ILWC286). Antagonism of A. rabiei isolates with Trichoderma harzianum showed existence of inhibitory effect between 20 and 68%, is highly significant for both tests (direct confrontation with the antagonist and the pathogen confrontation with volatiles substances emitted by the antagonist). Values of mycelial growth of isolates confronted with T. harzianum obtained are always lower (1.23 to 4.16 mm / day) than the control (3 to 7.5 mm / day). This inhibition is followed by a complete cessation of growth on the seventh day. In the chemical control test, we studied the in vitro effect of three synthetic fungicides, maneb "Manebe80 ®" chlorothalonil "Bravo ®" and azoxystrobin "Ortiva ®" on the mycelial growth of five isolates of Ascochyta rabiei. The results, statistically reliable (C.V. <20%) indicate that the in vitro test of chemical control using these three isolates on fungicides, has a highly significant effect (P <0.01) on the mycelial growth of the pathogen. Three fungicides cause a significant inhibition rate (TI%) of mycelial growth which varies generally between 30 and 66.35% depending on the region and isolates. Induced a significant share chlorothalonil (54 to 65.30%), followed closely by azoxystrobin (46-63%) and maneb (30 to 65.35) is observed. The in vivo test of chemical control by detached leaflets showed a remarkable percentage of reduction in the severity of Ascochyta blight varies between 20 and 80%. We noticed that the systemic fungicide like (azoxystrobin) gave an encouraging reduction in disease reduction ranging between 71 and 80%, for against other two contact fungicides (chlorothalonil and maneb), citing reduced an unable to 50% (from 20 to 47%).