Establishing inoculum threshold levels for Bean common mosaic virus strain blackeye cowpea mosaic infection in cowpea seed

Bean common mosaic virus strain blackeye cowpea mosaic (BCMV-BlCM) is an important seed-borne virus infecting cowpea and is transmitted both by seeds and aphids. Infected cowpea seeds can act as primary source of inoculum for disease epidemics. Four field experiments were conducted during 2003 - 2006 to assess the role of different amounts of seed-borne inoculum in the dissemination of BCMVBlCM virus in cowpea under field conditions. The identity of BCMV-BlCM was confirmed by ELISA and IC-RT-PCR. Plants infected at an early growth stage appeared to serve as the primary source for subsequent virus spread by aphids. The mean disease incidence during four field experiments reached88-93% in plots sown with 10% infected seed. The disease incidence in plots sown with 5% infected seed recorded 46-63% while for plants raised from 3 and 2% BCMV-BlCM seed infection, disease incidence reached 32-49% and 17-23%, respectively. Mean yield losses in terms of seed yield per plant from four field experiments were 74 and 54% for initial seed infection of 10 and 5%, respectively. Seed infection of 2% BCMV-BlCM incidence resulted in an average of 24% mean seed yield loss/plant-1. The infection appeared to decrease the seed yield in terms of number and size. The BCMV incidence in harvested seed ranged from 0.3 - 19% for the different levels of initial seed infection. The field experiments demonstrated that sowing > 1% BCMV-BlCM infected seed can lead to significant losses in grain yield, while the spread of BCMV-BlCM infection resulting from sowing 1% infected seed did not significantly decrease seed yield. The role of establishing damage or inoculum thresholds from BCMVBlCM seed-borne infections is discussed in the present study.Keywords: Cowpea, potyvirus, seed-borne virus, thresholds, yield los

Biochemical characterization of Fusarium oxysporum f. sp. cubense isolates from India

The Fusarium wilt caused by Fusarium oxyspoum f. sp. cubense (Foc) is a major biotic constraint for banana production. The characteristics of F. oxyspoum f. sp. cubense isolates were investigated using electrophoretic studies of isozyme and whole-cell protein. The morphological characteristics of the isolates were very similar to each other. All the Foc isolates were pathogenic to banana cultivar 'Nanjangud Rasabale' but they did not induce any disease symptoms on cultivar 'Cavendish'. F. oxyspoum (Isolate 6) did not induce wilt symptoms on either 'Nanjangud' or 'Cavendish' cultivar. Isozyme banding patterns showed 46 scoreable markers and cluster analysis with UPGMA using genetic distance showed that the isolates belonged to three main groups. Group 1 contained isolates 1, 2, 4, 5, 7 and isolate 3 and 6 were placed in group 2 and 3. Results indicated that the estimated intra-specific variation may be more pronounced with isozyme analysis than with protein markers. The level of isozyme variability detected within F. oxysporum f.sp. cubense suggested that it is reliable, efficient and effective in determining genetic relationships among Foc isolates

Management of bean common mosaic virus strain blackeye cowpea mosaic (BCMV-BlCM) in cowpea using plant extracts

Efficacy of certain plant extracts in reducing Bean common mosaic potyvirus strain blackeye cowpea mosaic (BCMV-BlCM) disease in cowpea was evaluated. All the six botanicals Azadirachta indica, Boerhaavia diffusa, Bougainvillea spectabilis, Clerodendrum inerme, Psidium guajava, and Thuja occidentalis improved the germination and vigour index of cowpea. The disease incidence was reduced to 7% when 0.75% (w/v) of B. diffusa leaf extract was used as seed treatment under screen house conditions when compared to 80% in control. Under field conditions B. diffusa reduced the disease incidence up to 40% at 0.75% (w/v) concentration of extract. In spray treatment, B. diffusa and B. spectabilis reduced the disease incidence up to 13 and 12% under screenhouse conditions, whereas B. diffusa and C. inerme reduced the disease incidence up to 31 and 32% under field conditions. When plant extracts were mixed with BCMV-BlCM inoculum and young seedlings inoculated, B. spectabilis, C. inerme and M. jalapa extracts reduced the disease incidence up to 42, 40 and 48% respectively under screenhouse conditions when compared with the control

Detection and identification of the blackeye cowpea mosaic strain of Bean common mosaic virus in seeds of cowpea from southern India

In different legume-growing regions of India, a total of 136 seed samples of cowpea (Vigna unguiculata (L.) Walp.) were collected and tested for the presence of the blackeye cowpea mosaic strain of Bean common mosaic virus, Cowpea aphid-borne mosaic virus, Cowpea mosaic virus, Cucumber mosaic virus and Bean yellow mosaic virus using growing-on test, enzyme linked immunosorbent assay, differential host test, electron microscopy and immuno-capture reverse transcription polymerase chain reaction. Among the 136 seedlots tested, 43 cowpea seedlots were found to be infected with BCMV-BlCM. The identity of three of these isolates as BCMV-BlCM was further supported by nucleotide sequencing in the 3' region of the genome. The incidence of seeds carrying transmissible virus ranged from 0.67% to 13.49%. In most cases, only symptomatic seedlings in a growing-on test were found infected with the virus

Management of bean common mosaic virus strain blackeye cowpea mosaic (BCMV-BlCM) in cowpea using plant extracts

Efficacy of certain plant extracts in reducing Bean common mosaic potyvirus strain blackeye cowpea mosaic (BCMV-BlCM) disease in cowpea was evaluated. All the six botanicals Azadirachta indica, Boerhaavia diffusa, Bougainvillea spectabilis, Clerodendrum inerme, Psidium guajava, and Thuja occidentalis improved the germination and vigour index of cowpea. The disease incidence was reduced to 7% when 0.75% (w/v) of B. diffusa leaf extract was used as seed treatment under screen house conditions when compared to 80% in control. Under field conditions B. diffusa reduced the disease incidence up to 40% at 0.75% (w/v) concentration of extract. In spray treatment, B. diffusa and B. spectabilis reduced the disease incidence up to 13 and 12% under screenhouse conditions, whereas B. diffusa and C. inerme reduced the disease incidence up to 31 and 32% under field conditions. When plant extracts were mixed with BCMV-BlCM inoculum and young seedlings inoculated, B. spectabilis, C. inerme and M. jalapa extracts reduced the disease incidence up to 42, 40 and 48% respectively under screenhouse conditions when compared with the control

Effect of plant extracts and ascetone precipitated proteins from six medicinal plants against tobamovirus infection

The present study was taken up to evaluate the effect of leaf extracts and acetone-precipitated protein of medicinal plants on seed-borne Tobacco Mosaic Virus (TMV) and Tomato Mosaic Virus (ToMV) infection. The antiviral activity was tested on indicator plant Nicotiana glutinosa. Acetone precipitated proteins and solvent extracts of six medicinal plants were tested for their effect on tobamovirus infection. The aqueous leaf extracts of Guava, Phyllanthus and Thuja were effective in reducing the infection by ToMV. The acetone-precipitated fractions of Tridax, Thuja, Guava and Tulsi were effective in reducing the infection by TMV. The solvent extract of Guava was effective in reducing the ToMV infection. Guava extract was subjected to TLC and the fractions were tested for their antiviral activity. Fraction with RF value of 0.014 proved to be effective in reducing the ToMV infection. The solvent extract of Thuja was effective in reducing TMV infection. TLC fraction of Thuja extract with the RF value of 0.12 reduced the TMV infection. Along with this, effect of aqueous leaf extracts on seed quality parameters of tomato and bell pepper was studied