In vitro evaluation of different phytoextracts and biocontrol agents against Alternaria alternata (Fr.) Keissler causing Alternaria leaf blight of isabgol

Abstract

Isabgol (Plantago ovata Forsk.) is known to affect by many fungal diseases. Among them, Alternaria leaf blight caused by Alternaria alternata (Fr.) Keissler has become a serious problem of isabgol in recent years in Saurashtra region of Gujarat state. Looking to the importance of disease, attempts were made to evaluate the efficacy of different ten phytoextracts, six fungal and six bacterial biocontrol agents against A. alternata in vitro. The results revealed that among ten phytoextracts maximum mycelial growth inhibition was observed in rhizome extract of Zingiber officinale Rosc. (65.42%), but it was remained statistically at par with leaf extract of Calotropis gigantea L. (64.68%), bulb extract of Allium cepa L. (63.94%) and clove extract of Allium sativum L. (62.83%) each at 10 per cent concentration. While, minimum mycelial growth inhibition of 9.02 per cent was observed in bulb extract of Allium cepa L. followed by leaf extract of Aegle marmelos L. (12.57%) each at 5 per cent concentration. Trichoderma harzianum JAU isolate (2×106 cfu/g min.) among fungal biocontrol agent gave maximum mycelial growth inhibition of 47.02 per cent in vitro. While, Trichoderma viride JAU isolate (2×106 cfu/g min.) remained least effective treatment with 14.06 per cent mycelial growth inhibition. Bacillus amyloliquefaciens NAU isolate (1×108 cfu/ml min.) on the other hand exhibited maximum mycelial growth inhibition of 44.82 per cent among bacterial biocontrol agents. But, it was remained statistically at par with Pseudomonas fluorescens JAU isolate 1 (1×108 cfu/ml min.) with 44.10 per cent mycelial growth inhibition. Whereas, Bacillus subtilis JAU isolate 1 (1×108 cfu/ml min.) showed least effective treatment with 27.40 per cent mycelial growth inhibition of A. alternata under laboratory condition.