Efficacy of Trichoderma harzianum on Inhibition of the Causal Agent of Pummelo Tan Spot Disease (Phyllosticta citriasiana)

Abstract

The efficacy of Trichoderma harzianumon for inhibition of Phyllosticta citriasiana, a causal agent of pummelo tan spot disease, was examined under laboratory condition at Chiangrai Horticulture research center during 2014-2015. Forty four isolates of T. harzianum were obtained from soil samples collected from pummelo orchards at Wiangkaen district, Chiangrai province and Chiangdao district, Chiangmai province using soil
dilution spread plate method. Three pure culture of P. citriasiana; CR-L01, CR-F09, and CM-F05 were isolated from tan spot symptom on leaf and fruit of pomelo using tissue transplanting method. The mycelia growth of P. citriasiana isolate CR-F09 was cultured on eight types of agar media based on CRD criterion with five replications for each treatment. OMA, PoDA, and PSA were effective media to cultivate P. citriasiana as they provided the highly percentage of mycelium growth with 98.2, 96.4 and 88.9%, respectively after 14-day
of incubation. The inhibition efficacy of 17 isolates of T. harzianum on P. citriasiana was determined by dual culture method in vitro. After 3-day incubation, T. harzianum isolates T4, T9, T10, T14, T21, T29, and T35 presented the mycelium growth inhibition at 43.3, 50.0, 50.0, 46.7, 43.3, 43.3, and 50.0 %, respectively. Strain of T35 and T10 showed highly percentage mycelium growth inhibition after 5-day of incubation with 52.1 and 51.0 %. The efficacy of T. harzianum isolates T35, commercial product of Trichoderma and azoxystrobin 25% W/V SC to control pummelo tan spot disease were also determined under field condition based on RCBD criterion with four replications for each treatment. The results showed that application of azoxystrobin at 10 ml/20 L of water was the most effective method to control pummelo tan spot disease compared to T. harzianum isolates T35 and commercial product of Trichoderma.