The varieties, which hold the promise of sustainable NR agronomics in the future, were developed at Michelin’s Itubera estate in Brazil, and are now in quarantine at CIRAD in Montpellier, France.
The fact is that NR is currently technically unavoidable for some purposes, despite stiff competition from synthetic rubber (SR). Hevea brasiliensis, which originated in the Amazon basin, however, flourished only in Asia and Africa, mainly because of the South American leaf disease caused by the fungus.
It is in this context that the disease-resistant varieties being developed by CIRAD and Michelin assume significance.
Genesis of New Breeds
It was in late December 2005 that plants of 13 high-yielding NR varieties resistant to microcyclus were shipped to CIRAD from Michelin’s Itubera estate. In quarantine, they will remain for two years and undergo a range of tests to ensure that they do not carry any spores of the parasite.
These varieties represent the first major step forward in more than 20 years of research at CIRAD and later with Michelin, in Montpellier, French Guiana and Brazil. They are controlled crosses produced by hand pollination, and have been assessed for 12 years at Itubera.
Asia now produces 93% of the world’s NR. It is Thailand that leads the market, with three million tonnes or 35% of global output. Africa accounts for 4% and South America 3%.
The plants that have been in the CIRAD glasshouses for the past many weeks are the first varieties produced under the CIRAD-Michelin joint research programme to reach the pre-development stage.
Latest Phase of Tests to Begin
The latest phase of tests ¬– at Michelin’s estate in Bahia – are to see whether the new breeds are both resistant and high yielding, will remain so under other environmental conditions, particularly in Asia, and even in other parts of South America.
CIRAD’s microcyclus ulei fungus collection in Kourou, French Guiana, which includes several strains from different countries, could help to answer that question. The tests will also address issues like the risks of plants being susceptible to other parasites.
The planting material was transferred to France in the form of budded stumps of the 13 genotypes involved after administering pesticide and fungicide treatments against microcyclus and other parasites, as laid down in French law. They are now growing, and testing will begin in a few months, once they’ve leaves.
The parasite may not immediately be visible, which is why non-resistant control plants have been placed next to the test plants. If the plants pass this first test, a second round of budding should rule out any risk of ‘dormant’ spores. If this stage is successful, the plants will be sent to partner-research organisations in Africa and Asia, where they will again be quarantined and put to further tests. Trees of varieties created subsequently in Brazil will be tested in the same way each year.
Improving the Breeding Technique
Simultaneously, researchers are working to improve the breeding technique and have plans to use genetic markers. But things are not that simple.
Natural resistance to microcyclus in rubber uses mechanisms involving a number of genes. But the fungus has proved capable of overcoming resistance.
What are the mechanisms involved? The answers that researchers manage to come up with in the coming years should shed light on how resistance develops and make it easier to breed-resistant individuals.
Source: CIRAD
