Closterovirus in India: Distribution, genomics and genetic diversity of citrus tristeza virus

Abstract

Only one closterovirus species (Family: Closteroviridae), Citrus tristeza virus (CTV) is known to occur in India. CTV is one of the most important plant viruses in India and extensive studies have been conducted over the last 60 years. The failure of Malta sweet orange on sour orange root stocks provided the evidence of tristeza disease in India. CTV infects nearly all the citrus species and citrus relatives and hybrids showing variables biological symptoms. Most citrus species and cultivars are susceptible to infection but some are tolerant inducing no obvious symptoms. Citrus orchards in Northeast India are severely affected by citrus decline, and several orchards in this region have been wiped out and many Sweet orange orchards in South and Central India are facing problem of decline. Toxoptera citricida is an efficient vector for the local natural spread of CTV in India. Stem pitting symptoms caused by CTV are not common in India. The Indian CTV isolates are genetically diverse and seven to ten genetic variants have been recognized in India. The complete genome (19,253 nt) of a mandarin decline inducing CTV strain, Kpg3 from the Darjeeling hills was sequenced. This chapter presents the work conducted on CTV in India.