MOLECULAR CHARACTERIZATION AND MANAGEMENT OF BUD NECROSIS VIRUS INFECTING TOMATO (LYCOPERSICON ESCULENTUM MILL.) IN ANDHRA PRADESH

The complete nucleotide sequence was determined for coat protein (cp) gene of Groundnut budnecrosis virus infecting tomato in Andhra Pradesh. The sequenced region in GBNV-To isolate contained a single open reading frame of 831 bases that could potentially code for a coat protein of 276 amino acids. The coat protein (cp) gene sequence of GBNV -To has 93 to 99 per cent sequence homology with that of the gene sequences of other GBNV isolates prevalent on different hosts in India. In the present studies it is determined that the GBNV-To isolate of tomato prevalent in A.P is regarded as the same strain of GBNV already existing in India. Host range studies indicated that the virus could induce different types of symptoms on cultivated plant species viz., Arachis hypogaea, Vigna unguiculata, Cajanus cajan, Vigna radiata, Dolichos lablab, Phaseolus vulgaris, Glycine max, Nicotiana tabacum, Physalis minima and Capsicum annuum and weed species such as Datura stramonium, Amaranthus viridis, Commilina bengalensis. While none of the symptoms were observed on Parthenium hysterophorus, Pisum sativum, Helianthus annuus, Laginaria sicenaria etc. Insect transmission tests revealed that Thrips palmi is considered as the vector of the virus causing bud necrosis disease in tomato and cowpea. The larvae of Thrips palmi could acquire the virus with a minimum access period of 15 min. and the adults only transmit the virus with 1h inoculation access period (IAP). However, optimum virus transmission obtained with 48h of AAP in the larval stage and 48h of IAP in the adult stage, but beyond 48h of AAP and IAP resulted in decreased virus transmission. A single adult Thrips palmi could able to transmit the virus with a transmission rate of 32 per cent and maximum transmission rate (100%) was achieved with 10 adults per seedling. In the screening trail 98 genotypes and cultivars tested under field conditions, among the 50 NBPGR lines, 20 AICRIP genotypes, 5 IIHR genotypes and 23 cultivars and hybrids, EC514117 and EC514190 NBPGR lines were found resistant to GBNVTo. Among the various combinations of treatments included in the integrated disease management, the treatments imposed with the cultural practices such as the crop surrounded by a strip of sorghum all around planted on July 1 (normal planting time) at a spacing of 60x45cm and fertilizer application at 150kg/ha with seed treatment of Imidacloprid at 5g/kg seed followed by two sprays of Imidacloprid (0.4 ml/L) resulted in lowest GBNV incidence. Virus –vector population revealed that the factors dates of sowing, spacing levels and nitrogen levels had significant influence on the occurrence of thrips population. Lowest thrips population recorded in early planted (June 1 ) crop, with closer spacing (60x30cm) and lower nitrogen application (100kg/ha). Thrips populations were low at early stage of the crop and increased progressively up to 50 DAP, and then the population decreased significantly. Correlation studies with weather parameters on thrips population revealed that positive correlation of thrips was recorded with maximum temperature, minimum temperature and relative humidity and negative correlation with disease incidence, evening relative humidity and rainfall during kharif season. The coefficient of multiple determinations R values was equal to 0.953 and contribute 95.3 of variation in the development of the disease was explained by weather parameters.