Raj Verma

First Report of Zucchini yellow mosaic virus in Bottlegourd (Lagenaria siceraria) in India

In December 2002, bottlegourd (Lagenaria siceraria L.) plants grown as a commercial crop in Pune, India (western Maharashtra) showed severe mosaic, interveinal chlorosis, and leaf deformation that resulted in fern-leaf appearance and severe fruit distortion in approximately 70% of the plants. Crude sap of collected samples was used to mechanically inoculate uninfected glasshouse-grown bottlegourd plants that reproduced symptoms observed in the field. Sap extracts from these glasshouse infected bottlegourd plants were used to mechanically inoculate selected indicator hosts. Chlorotic local lesions were produced on Chenopodium amaranticolor, and systemic symptoms were produced on Benincasa hispida, Citrullus lanatus, Cucumis sativus, Cucurbita moschata, C. pepo, Luffa cylindrical, and Trichosanthes anguina. The virus was specifically identified with serological testing using direct antigen coating enzyme-linked immunosorbent assay. The virus reacted strongly to Zucchini yellow mosaic virus (ZYMV) antiserum and did not react to Papaya ring spot virus-P (PRSV-P), Cucumber mosaic virus (CMV), and Watermelon mosaic virus (WMV) antisera. Electron microscopic examination of leaf-dip preparation from infected plants showed flexuous filamentous particles (720 to 760 nm long) that are typical of potyviruses. Natural infection of bottlegourd by ZYMV has been reported in the Hawaiian Islands (1). To our knowledge, this is the first report of this potentially destructive virus in bottlegourd in India. Reference: (1) D. E. Ullman et al. Plant Dis. 75:367, 1991.

First Report of Zucchini yellow mosaic virus in Cucumber (Cucumis sativus) in India

In August of 2002, cucumber (Cucumis sativus L. cv. Himangi) plants grown in commercial fields in Pune, western Maharashtra, India, exhibited chlorotic spots, veinal chlorosis, mosaic, blister formation and shoestring symptoms on leaves, stunted growth, and distortion of fruits. Incidence of virus infection in the fields varied from 25 to 38%. Crude sap extracted from infected cucumber leaf samples was inoculated mechanically onto cucumber and indicator host plants. The inoculated glasshouse-grown cucumber plants showed virus symptoms similar to those observed in the field. The virus produced chlorotic local lesions on Chenopodium amaranticolor and chlorotic spots followed by veinal chlorosis, mosaic, vein banding, and leaf distortion on Citrullus lanatus, C. melo, C. sativus, Cucurbita maxima, Cucurbita pepo, Luffa acutangula, and Trichosanthes anguina. The virus did not infect Nicotiana benthamiana, N. glutinosa, and N. tabacum cv. White Burley (1,2). Cucumber and indicator plants were tested using direct antigen coating enzyme-linked immunosorbent assays. A positive reaction was obtained with monoclonal antiserum to Zucchini yellow mosaic virus (ZYMV) but not with antisera to Papaya ringspot virus-P, Cucumber mosaic virus, and Watermelon mosaic virus (Agdia, Inc., Elkhart, IN). The disease was observed again in the field during July to September 2003. Natural infection of zucchini (Cucurbita pepo) by ZYMV has been reported previously from India (3). To our knowledge, this is the first report of ZYMV in cucumber in India. References: (1) H. Pospieszny et al. Plant Dis. 87:1399, 2003. (2) R. Provvidenti et al. Plant Dis. 68:443, 1984. (3) S. J. Singh et al. Indian Phytopathol. 56:174, 2003.

First Report of Papaya ringspot virus W in Sponge Gourd from India

During August 2004, symptoms resembling a virus disease were observed in commercial cultivation of sponge gourd (Luffa cylindrica (L.) M. Roem. [cv. Chikni]) in Pune, India. Affected plants exhibited mosaic mottling, vein banding, and downward marginal curling on leaves. The incidence of disease was 10 to 30% based on the symptoms and confirmed using enzyme-linked immunosorbent assay (ELISA). Six fields of sponge gourd were visited, and 30 samples were collected randomly. Samples from affected fields were analyzed for the presence of virus by mechanical inoculation. Symptoms typical of those observed in the original field plants appeared 10 days after inoculation on sponge gourd. The virus isolate produced local lesions on Chenopodium amaranticolor and systemic symptoms on Cucumis melo, Cucumis sativus, Cucurbita maxima, Cucurbita pepo, L. acutangula, and L. cylindrica, but did not produce symptoms on Carica papaya (cvs. CO2 and Red Lady), Nicotiana glutinosa, N. tabacum (cv. White Burley), or Vigna unguiculata. Field-infected sponge gourd and all indicator plants were tested using double-antibody sandwich (DAS)-ELISA. The virus was identified as Papaya ringspot virus-W (PRSV-W) using DAS-ELISA (Agdia, Elkhart, IN). A strong, positive reaction was obtained with antiserum to PRSV-W but not with antisera to PRSV-P, Cucumber mosaic virus, Squash mosaic virus, Zucchini yellow mosaic virus, and Groundnut bud necrosis virus. To ensure virus purity, the isolate was passed through three successive single-lesion transfers on C. amaranticolor. Flexuous filamentous particles 775 nm long were observed with electron microscopy of leaf-dip preparation from symptomatic sponge gourd leaves. The virus particles were then decorated with a second PRSV-W antiserum obtained from the Plant Virology Unit, IARI, New Delhi. PRSV-W on sponge gourd has previously been reported from Taiwan (1). To our knowledge, this is the first report of natural occurrence of PRSV-W on sponge gourd in India. Reference: (1.) C. H. Huang et al. J. Agri. Res. China 36:413, 1987.

Management of Viral Diseases Through Conventional Approaches in India

Viral diseases of crop plants cause enormous economic losses as most of the cultivated areas in India are in subtropical and tropical regions which provide congenial environment for multiplication of viruses and their vectors. Intensive agricultural practices for fulfilling the demand of food for the growing population has further contributed to the diseases and pests problems. Under favourable condition, the viral disease incidence can be as high as 100% resulting into serious losses to the farmers and consumers. The control of plant viral diseases has been challenging because of unavailability of effective direct method of control by chemical applications. Hence, indirect methods of managing viral diseases has been utilized such as use of modified cultural practices, use of virus-free planting materials, use of host resistance to viruses and their insect-vectors, cross protection, application of insecticides and oils for the control of virus viruses. Some success in viral disease management has been achieved by using a combination of these approaches in few crops. The range of conventional management approaches that have been studied and applied against plant viral diseases in India are summarized in this chapter.

Begomoviruses in India

Begomoviruses, a group of whitefly-transmitted single-stranded DNA viruses that are widely spread, cause significant economic losses in several important crops in tropical and subtropical regions of India. Begomoviruses have been known to be associated with and cause many diseases in cucurbitaceous, solanaceous, malvaceous vegetable and legume crops in most parts of the country. However, these viruses have emerged as a major threat to vegetable and legume production in India. Tomato, chillies, cucurbits, cotton, okra, legumes, papaya, and cassava are the most seriously affected crops. In recent decades, the most dramatic emergence of begomoviruses has been observed in tomato, chilli, and cucurbits throughout the country specially in tropical areas. The major factors responsible for the emergence of new viruses and their spread in the ecosystem are introduction of viruses, introduction of susceptible crops or genotypes, change in vector population, recombination in viruses, weather factors, and new intensive agricultural practices. This article presents the current understanding of begomovirus diseases in India and the driving forces for their emergence.

Viral Diseases of Banana and Their Management

Banana (Musa spp.) is one of the most important staple food crops which provide nutrition and income for the millions of farmers worldwide, especially in tropical regions. Asia being the major continent for banana production contributes more than half of the world banana production (101.9 million tonnes). Banana is vegetatively propagated using suckers or through tissue culture plants which grow, mature and fruit without seasonality throughout the year. Viral diseases are considered a major concern for banana production because of their effects on yield and quality as well as limitations to germplasm multiplication and the international germplasm exchange. There are many (about 20) different viruses reported to infect banana worldwide. However, the economically most important viruses are: Banana bunchy top virus (BBTV), Banana streak viruses (BSV), Banana bract mosaic virus (BBrMV) and Cucumber mosaic virus (CMV). Among these, BBTV and BSV are major threats for banana production. Of the two, BSV exist as episomal and endogenous forms and more widely spread worldwide than BBTV, though later is so far most economically damaging virus contributing to a yield reduction of up to 100 %. Due to lack of durable virus resistance in the Musa spp., measures such as phytosanitation, use of virus free planting material, strict regulation on movement of infected planting materials are effective means to control viral diseases in banana. Studies of several decades on the biology, epidemiology, survival, spread, sequence integration into the host genome of banana viruses and their integrated management strategies are summarized in this review.