6.75
ASCOCHYTA BLIGHT OF CHICKPEA IN ALGERIA:GENETIC AND PATHOGENIC DIVERSITY OF ASCOCHYTA RABIEI AND SCREENING FOR RESISTANT CULTIVARS
ASCOCHYTA BLIGHT OF CHICKPEA IN ALGERIA: GENETIC AND PATHOGENIC DIVERSITY OF ASCOCHYTA RABIEI AND SCREENING FOR RESISTANT CULTIVARS Z. BOUZNADl, R. CORBIERE2, A. ELBIARI3 and M. LABDI4 l INA El Harrach, Algiers, Algeria, 2 INRA, Pathologie Vegetale, 49071 Beaucouze, France, 3 INRA, Pathologie Vegetale, 78026 Versailles, France, 4 ITGC Sidi-Bel-Abbbs, Algeria. introduction Chickpea is an important food legume which is grown extensively in Algeria. However, yields have dramatically decreased and present crop yields are among the lowest in the world (400 kg/ha). Genetic improvement of chickpea for resistance to Ascochyta blight caused by Ascochyta rabiei is required to control this disease which has become more serious in recent years. Breeding for resistance needs an extensive knowledge of the present populations of A. rabiei, and requires an evaluation of the resistance level of chickpea cultivars presently being grown in the region. Materials and Methods A collection of 24 isolates of A. rabiei was assembled from 1986 to 1994 during surveys of several Algerian chickpea-growing regions. They were compared to six ICARDA isolates which have been described as six different races [1]. Isolate diversity was studied by analysing isoenzymes using the isoelectric focusing method, and genomic markers using the random amplified polymorphic DNA method (RAPD). Their pathogenic variability was analysed in growth chamber inoculation studies using a differential set of chickpea cuitivars: ILC 1929, ILC 3279, ILC 215, ILC 249, ILC 482, ILC 5928 and ICC 3996. Chickpea resistance was evaluated on traditionnal cultivars grown in Algeria, on new cultivars that have been introduced recently or are presently being tested within the framework of the ICARDA program and finally on lines developed by the Algerian breeding program. Results and Conclusions Genetic diversity of A. rabiei was observed using isoenzymes (esterases and shikimate dehydrogenases) and RAPD markers, and isolates were grouped in several clusters according to their migration patterns. These polymorphisms suggest a genetic recombination among isolates by sexual reproduction in the field, as mentionned by Kaiser [2]. A great deal of pathogenic variability was also observed among isolates when inoculated on the differential set of cultivars. An analysi's of variance showed that isoiates were distributed according to a continuum from the Jeast to the most pathogenic ones, but they could not be clearly grouped into pathotypes. Moreover, precise identification of pathotypes was difficult, because cultivar behaviour could not always be translated as a typical response of susceptibility (S) or resistance (R); they also gave intermediate responses which were noticed as moderate susceptibility (M). However, several groups were distinguished according to their pathogenicity and some isolates exhibited a similar or a higher pathogenic level than R4 and R6 isolates, the most aggressive and virulent ICARDA races. Some isolates recently collected in Algeria were very aggressive, suggesting the appearance of new pathogenic groups. No correlation was observed between pathogenic structure, genetic variability and geographic origin of isolates. The behaviour of several hundred chickpea cultivars to Ascochyta blight was also studied. Local Algerian cultivars were very susceptible. Among introduced genotypes and local lines, only a few exhibited a stable degree of moderate susceptibility to the most aggressive isolates, and none of them were fully resistant. Our results point out that this selected material could allow farmers to maintain an acceptable production level which can be improved by application of foliar fungicides, when environmental conditions are favorable to Ascochyta blight. References 1. Reddy MV, Kabbabeh S, 1985. Phytopathologia Mediterranea 24, 265-266. 2. Kaiser WJ, 1997. Canadian Journal of Plant Pathology 19, 215-224.