03-08-2013, 04:18 PM
Apple Scab: The Interesting Interplay of Venturia and Malus
ABSTRACT
Apple scab is one of the most serious diseases of apple. The disease is caused by the fungal pathogen Venturiainaequaliswhich is a heterothallic, haploid ascomycete, reproducing sexually and asexually. The fungus overwinters in fallen leaves, as a saprophyte. It reproduces sexually and produces ascospores, which constitute the primary source of infection. The fungus can infect leaf, fruit, stem and green twigs, however, the main targets are leaves and fruits. The leaves become curled and distorted resulting in defoliation. Similarly, the fruits become deformed. When the disease advances, skin ruptures and the exposed tissue gives brown or black velvet like appearance. These become active as soon as spring starts. The pathogen increases its biomass considerably within 7 to 10 days and further infection takes place by asexual spores called conidia. For the control of apple scab several sprays of fungicides are made, which lead to health and environmental concerns.
V. inaequalis has emerged as a useful model to study host pathogen interaction due to several reasons which include its ability to grow in culture, presence of uninucleate conidia, chances of in vitro mating, existence of distinct races and extensive population diversity, stability of the genotype and phenotype of the progeny even after several rounds of sub-culturing and above all, availability of an efficient protocol for genetic manipulation. Apple scab can be visualized as an interesting interplay between the host and the pathogen.