Researchers of the IFAPA Center in Malaga have worked together with the University of Pretoria, South Africa to research the tolerance of avocado rootstocks to the main agents that cause root rot in Andalusian productions, analyzing the response of seed plants of various origins against infection with the fungus Rosellinia necatrix. This fungus, together with Phytophthora cinnamomi, are the most common pathogens causing these diseases in avocado crops in Andalusia.
The work, in which the University of Malaga and the Institute of Sustainable Agriculture of the Higher Center for Scientific Research (CSIC) have also collaborated, includes among its conclusions the characterization of the mechanisms responsible for tolerance to R. necatrix, which are very different from those that induce resistance to P. cinnamomi. The people responsible for the work have concluded that "resistance to R. necatrix seems to be related to the production of protease inhibitors (enzymes that break other proteins) and of the proteins that play a role in the plant's defense against saline and osmotic stress."
These results, say the scientists, "constitute a very useful tool to accelerate the selection process of genetic material within the framework of the avocado rootstock improvement program. It also has great international relevance, given the growing importance that the fungus R. necatrix is gaining in various producing countries." In recent years, the pathogens have been detected in California, Israel, Mexico, Korea and South Africa.
The people responsible for the project say that what makes controlling this disease difficult "is that, despite the development of early detection techniques, the first symptoms appear when the pathogen is already well established in the soil and roots." Therefore, they have stated that "to achieve effective control of the disease it is necessary to use preventive measures, rather than curative ones."
According to the conclusions of the study, fungicides do not seem to be totally effective in field conditions, and solarization, which is the best alternative, only eradicates the pathogen from the soil temporarily, so it is necessary to continue applying it every two years. Therefore, according to the researchers, "the fight against the white rot of avocado must be addressed through integrated control that includes physical methods, chemical methods and the use of disease-tolerant plant material."
For their part, California and South Africa have been developing programs for the selection of P. cinnamomi-tolerant material for more than two decades, so a number of rootstocks with varying degrees of pathogen tolerance are already on the market, as well as some effective chemicals and soil solarization treatments that are successful in their control.