Etiology

The evidence for the viral nature of the disease was first established in 1945 with the successful transmission of virus through the banana aphid P. nigronervosa Coq. (Uppal et al., 1945). Studies in Guatemala and India have shown the association of flexuous rod-shaped virus particles measuring 650 nm in length and 10—12 nm in diameter in dip and purified preparations (Naidu etal., 1985; Gonsalves etal., 1986; Usha and Thomas, personal communication). Purified preparations of six strains also revealed homogenous flexuous particles (Fig. 6.3). Presence of inclusion bodies was also reported from leaf tissues of car-MV infected plants. Based on morphology of virus particles and presence of characteristic pinwheel-shaped inclusion bodies, it was suggested to include car-MV in 'poty virus' group (Naidu etal., 1985). In Guatemala, mosaic-affected cardamom leaves revealed pinwheel type inclusion bodies, which is a common feature in other poty viruses. Leaf dip extracts showed particles of 660 nm length and those of purified preparation showed 700—720 nm long particles.

Serological affinity of car-MV of Guatemala with some poty viruses was demonstrated through indirect ELISA. Four viruses viz., Zucchini yellow mosaic, papaya ringspot types w and p, cow pea aphid borne mosaic virus and a severe strain of bean common mosaic virus consistently gave positive reaction in indirect ELISA. Presence of inclusion bodies, particle morphology and serological affinity of car-MV have confirmed the inclusion of it in the poty virus group (Dimitman et al., 1984; Gonsalves et al., 1986). Sequence analysis of the coding regions for coat protein and the 3'-untranslated region of the Yeslur isolate (from Saklespur, Karnataka) placed katte virus as a new member of the genus Madura virus of Potyviridae (Jacob and Usha, 2001). Considerable genetic diversity was noted among various isolates (Jacob et al., in press).

Some consider katte as a complex disease caused by more than one component, or viruses (Rao, 1977a). So far the studies conducted in India and Guatemala does not support the complex nature of katte disease.

2.6.1 Strains of car-MV

Presence of three natural strains was first reported on the basis of symptomatology on the main host and cross-protection studies (Rao, 1977a). Further, occurrence of different natural strains was reported from the studies using 68 representative isolates of all cardamom growing zones of India. Three important biological criteria namely symptoms on the main host, transmission through P. nigronervosa f. caladii and reaction on the set of zingiberaceous differentials consisting of Elettaria cardamomum Maton var. Malabar, Alpinia mutica, Amomum microstephanum and A. cannaecarpum were used to identify the strains (Naidu et al, 1985).

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