Performance of 10 Hevea brasiliensis clones in Ecuador, under South American Leaf Blight escape conditions

Abstract Rubber ( Hevea brasiliensis ) growing in Latin America is severely limited by South American Leaf Blight, a disease caused by the Ascomycete fungus Microcyclus ulei , recently renamed Pseudocercospora ulei . Sustainable ways of controlling it may be genetic, using resistant cultivars, or may consist in seeking so-called “escape zones”, where disease incidence is low thanks to climatic conditions unsuitable for the fungus. After identifying one such zone on the Pacific coast of Ecuador, between 2006 and 2014 we used an 8.2 ha trial to compare the agronomic performance of ten rubber clones originating from Asia and Africa. The study focused on tree growth, susceptibility to the disease and clone phenology. For most of the assessed clones, the results obtained over 8 months showed good adaptability and a good agronomic performance during the immature period, so that tapping could begin on the earliest trees at 6½ years. An examination of the monthly values for climatic factors such as rainfall, relative humidity, minimum temperature and dew point temperature, showed that conditions during the dry season, which lasted 5 months, were detrimental to P. ulei fungus development, even though the mean relative humidity of the driest months did not fall below 75%. In addition, between September and December, the minimum temperature remained above the dew point temperature, preventing dew formation on the leaf surface. These conditions enabled the trees to complete their natural refoliation without any risk of parasite pressure, and to conserve a foliar density over 90% up to natural defoliation the following year. The results obtained during the early growing phase, i.e. the immature phase, confirmed the suitability of this zone for rubber growing, especially for materials with a high yield potential, despite their known susceptibility to the disease. These escape zones consequently offer an undeniable alternative for developing rubber, due to a low phytosanitary risk arising from P. ulei .