Plant Pathologv {\^)92) 41, 274 281 Influence of the amount of blackgram mottle virus in different tissues on transmission through the seeds of Vigna mungo A. VARMA, M. KRISHNAREDDY* and V. G. MALATHI Advanced Centre for Plant Virology, Division of Mycology & Plant Pathology, Indian Agricultural Research Institute, New Delhi - IWO 12, India Blackgram mottle virus (BMoV) was transmitted via up to 16% of seeds of different cultivars of blackgram, as determined by seedling symptom tests. The percentage of seed infection by BMoV as determined by ELISA was even higher. Seed transmission was highest in cv. PLU-277( 15-9%), followed by CVS T-9 (I l-8"n), PLU-2I3 (7-0%) and UH-Sl-7 (1-3%). Seed transmission was correlated with the amount of virus present in the embryonic axis and later in primary leaves. The presence of virus in the testa alone did not result in its transmission through seeds. Virus concentration in different tissues varied; the mean amount of virus in the three cultivars was found to be 48-1234 ng per embryonic axis, 15-24 ng per cotyledon, and 12-20 ng per testa. The infection of primary leaves through the seed also resulted in systemic infection if the amount of virus in primary leaves exceeded 100 ng/100 mg of tissue. Close agreement was found between the percentage of seedlings with systemic infection and the percentage of seeds and embryonic axes containing more than 100 ng virus. The cultivars that resisted seed transmission contained relatively small amounts ofthe virus in embryonic axes. INTRODUCTION Virus diseases are a major constraint in improv- ing the produetion of blaekgram {Vigna mungo) in India (Chenulu &. Varma, 1988). Several of these viruses are transmitted through blackgram seed, and ihe most common was found to be blackgram mottle virus (BMoV) (Phatak, 1974; Scott & Hoy, 1981; Reddy & Varma, 1988; Krishnareddy, 1989). However, the Indonesian isolate ofthe virus is reported to be transmitted through the seeds of mungbean {Vigna radiata) but not biaekgram (Saleh et ai, 1986; Tantera, 1986). Saleh et al. {1986) detected the virus in 10- 99%. of the seeds of mungbean collected from diseased plants of different cultivars, but actual seed transmission was limited to 1-5%. The present investigations were undertaken to exa- mine the effect of plant genotype, and of the amount of virus in different parts of seeds, on the transmission of BMoV through blackgram seed. MATERIALS AND METHODS Source of seed Seeds of differeni blackgram eultivars were col- * Present address: Plant Virus Section, Indian Insti- tute of Horticultural Research, 255 Upper Palace Orchards, Bangalore - 560006, India. lected from (i) field-grown plants infeeted with BMoV alone, as tested by seroiogy and electron microscopy and (ii) artificially inoculated plants grown in an insect-proof glasshouse. Seedling symptom test For the seedling symptom test, 50-300 seeds were planted (20 seeds per pot) in 15-cm clay pots in an insect-proof glasshouse, and tested at different growth stages for the presence of virus. The primary leaves do not develop any distinct symp- toms, but trifoliate leaves show typieal mottling and mild distortion. However, symptoms alone are not of diagnostic value. Detection of virus in different seed parts and leaves Seeds of blaekgram, collected from diseased and healthy plants 8 months earlier, were soaked in water overnight and different seed parts carefully dissected. The dissected parts were washed with three changes of distilled water to avoid surface contamination. For the detection of BMoV, either individual parts from single seeds, groups of parts, whole seeds or 100 mg of tissue of primary or trifoliate leaves were separately homo- genized in extraction buffer (I : 10 w/v; see below).