Sorghum [Sorghum bicolor (L.) Moench] is one of the prime food and fodder crops of the world. The yield potential of this crop is affected by a number of diseases. Among them zonate leaf spot is one of the important destructive foliar disease caused by G. sorghi. Considering the destructive nature of this disease and availability of only little information on biological control, present investigations were carried out with objectives to study the (1) screening of biocontrol agents in vitro and glasshouse for growth promotion and control of disease, (2) effect of selected biocontrol agents on growth promotion, disease reduction, chlorophyll content and green fodder yield in field conditions, (3) expression pattern of defence genes in Pant Chari-4 and Pant Chari-5 cultivar of sorghum during priming and boosting through RT-PCR. Among all isolates tested in vitro for antagonism against the pathogen, TH-32 was most effective in reducing radial growth. In PC-4, maximum seed germination and vigour index was recorded in Th-31(88.67%) and Pf-31(950.7VI) respectively. In PC-5, maximum seed germination and vigour index was recorded in Th-32(89.33%) and Pf-31(1004.1VI) respectively. Bioagents screening in glasshouse on growth promotion of PC-4 cv. revealed that maximum root, shoot length and stem diameter was observed in Th-28(18.75cm), Th-32(71.71cm) and Pf-31(2.27cm) respectively. While in PC-5 cv. Th-32(18.99cm), Th-31(82.82cm) and Pf-31(2.31cm) treatments recorded maximum root, shoot length and stem diameter. Th-32 reported maximum reduction in disease severity in both PC-4(45.30%) and PC-5(43.04%) cultivars under glasshouse conditions. Further promising isolates were evaluated for growth promotion, disease reduction, chlorophyll content and green fodder yield in both cultivars in field condition. Th-32 was found best in increasing root length (26.89cm) and stem diameter (1.35cm) in PC-4 while it was 27.12cm (root length) and 1.41cm (stem diameter) in PC-5. However significantly increased shoot length of 172.12cm and 185.89cm was recorded with Pf-31 in PC-4 and PC-5 respectively at 45DAS. Among all isolates Th-32 reported maximum reduction in disease severity in both PC-4(28.74%) and PC-5(33.81%). Maximum chlorophyll content in PC-4 was observed in Th-32 treated plants (2.356 mg/g fr.wt.) while Th-31 recorded maximum (2.976 mg/g fr.wt.) in PC-5. Green fodder yield was observed maximum in Th-32 treated plots of both PC-4 (27.15kg/plot) and PC-5(38.19kg/plot) cultivars. Expression of defence genes was determined during priming with bioagents and boosting (post inoculation) with additional inoculation of G. sorghi. Samples were collected at different time intervals during priming and boosting for RNA extraction. Gene expression was measured for PAL, chitinase and CHS using real time polymerase chain reactions (RT-PCR). The response of sorghum cultivars to G. sorghi infection involves multiple defense genes. Real time PCR used to study the expression of sorghum defence in glasshouse grown plants showed that PAL was highly expressed during priming and boosting in moderately resistant cultivar PC-5 leaves. The expression of some other defense genes like chitinase and CHS was variable in both cultivars.