A Single Species of Betasatellite is Prevalent in Chilli across North Central Pakistan and Shows Phylogeographic Segregation

Chilli leaf curl disease is an important constraint to production of chilli peppers ( Capsicum annum L.) across the Indian subcontinent and is caused by begomoviruses in association with betasatellites. Betasatellites are symptom modulating single-stranded DNA satellites associated with the majority of monopartite begomoviruses and are responsible for diseases of many crops including chilli peppers. Here, we have studied the diversity of a betasatellite of chillies in the Punjab and North Western Frontier Province of Pakistan. Sequence analysis of thirteen full-length clones showed that a single species of satellite, Chilli leaf curl betasatellite (ChLCB), is prevalent in chilli throughout the surveyed region. ChLCB has only been identified in Pakistan and infecting chilli. It thus probably represents a chilli adapted satellite. The ChLCBs fall into two groups, the first occurs in the less intensively cultivated north and shows a high level of sequence diversity (relative to the second group), while the second occurs in the southern cotton-growing areas and shows little sequence diversity. Between these two areas there is a region of overlap where both ChLCB types occur. The phylogeographic segregation of ChLCB we attribute to geographic isolation (in the north), leading to divergence and intensive cultivation (in the south), leading to homogenization. However, the lack of diversity (only a single species) bodes well for the prospects of achieving resistance to the disease by either conventional or pathogen-derived strategies.