Telluric and bacterial diseases
Bacterial leaf spot
Bacterial leaf spot due to Xanthomonas campestris pv. vitians first appears as oily-like spots on the leaves margins, which in a few days become necrotic and confluent. When conditions are favorable, the spread of the disease is very fast and devastating. The lack of licensed chemicals in Canada makes it difficult to control and copper-based bactericides are ineffective.
Current research, in collaboration with Saint-Jean-sur-Richelieu's CRD, aims to identify strains of Xanthomonas in lettuce production areas, determine their frequency, distribution and pathogenicity. Research projects conducted with VRIC aim to develop molecular markers of resistance to bacterial spot. The Foundation continues to focus on preselecting cultivars and non-advanced lettuce lines to identify sources of resistance, as well as crossbreeding and selection of offspring individuals.
First symptoms usually occur when head lettuce is approaching maturity. The fungus Rhizoctonia solani attacks the lower leaves in contact with the soil, causing ochre to brown lesions on the ribs. In humid weather, the infection can reach the entire limb, causing its destruction, or reach the taproot, causing crown rot. Hot and humid weather greatly favors the development of the disease. The fungus can easily survive in the soil for years. No resistant cultivars or fungicide are currently available.
The main agent causing this disease is the soil fungus Pythium sp. Characteristic symptoms include a lack of emergence, reduced plant growth (dwarfism), foliar yellowing, plant wilting, growth arrest and even death. Cold, damp and poorly drained soils are all aggravating factors. The fungus can survive for several years in the soil. Chemical control is inefficient and resistant varieties are still non-existent.
Telluric and bacterial diseases are particularly feared and their effects are very damaging. Our top priorities: research projects aimed at improving the knowledge of resistance and sensitivity factors of lettuce varieties and exploring the genetic diversity of lettuce to find sources of resistance to use in our plant selection program.