Abstract
Cotton leaf curl disease (CLCuD) is the major biotic constraint to cotton production in Pakistan and northwestern India. The disease is caused by monopartite begomoviruses in association with a specific DNA satellite, Cotton leaf curl Multan betasatellite. The virus-betasatellite complex is also frequently associated with another DNA satellite-like molecule; an alphasatellite. A quantitative real-time PCR (qPCR) assay to detect all three components of the monopartite begomovirus/betasatellite/alphasatellite complex which causes CLCuD was established. This was used to investigate the relationship between symptoms and virus/satellite titre. Not surprisingly the analysis showed that, overall, there was a reasonable correlation between symptom severity and virus/satellite titre more severe symptoms usually being associated with more virus/satellite. However, cotton plants were identified with no or very mild symptoms with relatively high virus/satellite titres and plants with severe symptoms but relatively low virus/satellite titres. This may be attributed to the resistance/susceptibility of the cotton variety tolerant plants being able to sustain a relatively high virus/satellite titre whilst exhibiting mild symptoms. The usefulness of this qPCR procedure in the screening for resistance in cotton against CLCuD is discussed.