COFFEE PATHOSYSTEM MODELLING : 2 - ASSESSMENT OF HOST AND PATHOGEN BIODIVERSITIES
COFFEE PATHOSYSTEM MODELLING : 2 - ASSESSMENT OF HOST AND PATHOGEN BIODIVERSITIESD NANDRIS1, F KOHLER1, D FERNANDEZ2, P LASHERMES2, J RODRIGUES3 and F PELLEGRIN1
1ORSTOM, BP A5, 98848 Nouméa, NEW CALEDONIA; 2ORSTOM, BP 5045, Montpellier, FRANCE; 3CIFC, 2790 Oeiras, PORTUGAL.
Background and objectives
Modelling investigations were performed in New Caledonia on the Coffea arabicaHemileia vastatrix, Colletotrichum gloeosporioides) and to the diversity of the host. Consequently, in addition to the epidemiological survey, four complementary biological studies were carried out.
Results and conclusions
1. Analysis of host genetic diversity.
The existence of rust resistant coffee hybrids (C. canephora x arabica) growing in some coffee plots in New Caledonia may be a source of genetic heterogeneity that must be assessed in terms of susceptibility of the trees. For each of the 15 plots in the epidemiological survey, biomolecular analyses (RAPD) of the genome of the surveyed coffee trees were performed in Montpellier using the methodology developed by Lashermes et al. . On the one hand, among the studied trees, no canephora character was found, thus excluding any effect on their behaviour vs. diseases. On the other hand, a molecular polymorphism indicates the existence of two cultivated coffee types typica and bourbon as well as intraspecific hybrids, with respective ratios varying within the plots. The resetting of the initial data files by "plot" into subfiles by "coffee cultivated types" shows differences in the respective susceptibility of these categories of trees.
2. Analyses of Hemileia vastatrix population.
a - races identification: after the sampling of spores from every tree in every survey plot, a rust race identification was done in Oeiras using the CIFC method . Three different races (I, II, III) were identified, with race II definitely appearing as the most common one. In some plots, the coexistence of the II & I or II & III races was observed.
b - molecular polymorphism: complementary studies were developed to detect possible genetic diversity between the 25 collected rust samples (20 from New Caledonia, 3 from Papua New Guinea, 2 from Vanuatu). Among the ITS, REP, ERIC and RAPD methodologies tried, only RAPD (with severe constraints for spore collection & DNA extraction) performed with OPA9 and OPC8 primers reveals a pattern polymorphism between the rust sources. Trials to link these results with the characteristics of the identified races and with the dynamics of the diseases are under way.
3. Analysis of Colletotrichum gloeosporioides population.
Using biomolecular tools (RAPDs), 125 isolates collected in 6 surveyed plots (4 in New Caledonia, 1 in Vanuatu, 1 in Papua New Guinea) were analysed . A high level of genetic diversity was found in all populations and each isolate exhibited a unique RAPD haplotype. Genetic differentiation was found between three out of the six populations (Wright's index, Fst= 0.27), but no relationships could be evidenced between the genetic variability of the populations and other traits such as environmental or epidemiological characteristics of each plot. A high recombination rate could be hypothesised to explain this situation.
Once included in the statistical model, the results of these biological investigations constitute important complementary information, for devising a decision-making tool for integrated management of coffee diseases.
References1. Nandris D, Kohler F, Monimeau L, Pellegrin F, 1997. Proceedings 17th International Conference on Coffee Science, ASIC, Nairobi, Kenya, in press.
2. Lashermes P, Trouslot O, Anthony F, Combes MC, Charrier A, 1996. Euphytica 87, 59-64.
3. Rodrigues Jr CJ, Bettencourt AJ, Rijo L, 1975. Annual Review of Phytopathology 13, 49-70.
4. Faugeron S, 1996. Mémoire de DEA, USTL-ENSA, Montpellier. 21 pp.