Management of a major fungal disease in black pepper (Piper nigrum L.)

Abstract

Black pepper (Piper nigrum L.) is one of the major spice crops and plantation crops that grow as the sole crop or intercrop in Kerala. In nurseries of black pepper major biotic stress are caused by bacteria, fungus, virus and nematode, out of this fungal infection are the leading one. The seedling blight, anthracnose and collar rot were found to be more severe in the nursery. With this background, the present study was conducted to identify the major fungal pathogen associated with black pepper nursery and formulate disease management strategies against that pathogen. A survey was carried out in black pepper growing nurseries to record the different diseases. Seedling blight, anthracnose and collar rot were observed. The fungal isolates associated with seedling blight in nurseries at Padannakkad and Kanakappalli were designated as Pc1 and Pc2 respectively. Anthracnose affected seedlings were collected from Padannkkad, Balal, Panniyur and Periya black pepper nurseries and the fungal isolates associated were designated as Cg1, Cg2, Cg3 and Cg4 respectively. The collar rot samples were collected from Padannakkad, Periya and Panniyur and isolates were designated as Sr1, Sr2 and Sr3. In the case of seedling blight infection, highest disease incidence (DI) (74%) was recorded in Pc1. The highest percent disease index (PDI) in case seedling blight (32%) was recorded in Pc1 as compared to Pc2 isolate. In the case of anthracnose, higher DI (30%) and PDI (25%) were recorded in Cg1 in comparison with Cg2, Cg3 and Cg4. In case of collar rot, higher DI (20%) was recorded in case of Sr1 isolate. All the isolates were tested for its pathogenicity; in case of seedling blight, the isolate Pc1 recorded higher radial growth (7.90 cm) and recorded lesser time (2days) for the symptom development as compared to Pc2 isolate. In case of anthracnose, isolate Cg1 recorded higher radial growth (8.0 cm) and took lesser time (5days) for the symptom development in comparison with Cg2, Cg3 and Cg4. In case of collar rot isolate Sr1 recorded higher radial growth (8.96 cm) and recorded lesser time (2days) for the symptom development as compared to Sr2 and Sr3. A trial was laid out to identify the most susceptible variety of black pepper as well as the most virulent strain of the pathogen among different isolates on pepper varieties viz., Panniyur (P) 1-6, P8, P9, Vijay and Karimunda. Panniyur 2 was identified as most susceptible variety and Pc1 was the virulent isolate. Based on cultural and morphological characters and molecular characterization, Pc1 was identified as Phytophthora capsici. In vitro evaluation of biocontrol agents, chemical fungicides and organic preparations were carried out to study the efficacy against P. capsici. Under in vitro conditions biocontrol agent T. harzianum (2%) exhibited maximum inhibition (55.56%) followed by P. fluorescens (53.33%). Among the chemical fungicides copper oxychloride (0.3%) and metalaxyl (8%) + mancozeb (64%) at 0.3 percent recorded 100 per cent inhibition. Among the organic preparations, ready to use neem oil garlic soap (3%) and garlic extract at 0.3 percent recorded maximum inhibition 31.11% percent and 28.88% percent respectively in the mycelial growth of the pathogen. The best-performing treatments from the in vitro evaluation were selected for pot culture experiment on variety Panniyur 2. After 7 days of inoculation, the least PDI (0.00 %) as well as the least lesion development (0.00%) was recorded in case of metalaxyl (8%) + mancozeb (64%) at 0.6 per cent. The higher PDI (86.66%), as well as maximum lesion development (46.66%), was recorded in ready to use neem oil garlic soap (3%). The study reveals that, the seedling blight caused by Phytophthora capsici can be effectively managed with the foliar application of metalaxyl (8%) + mancozeb (64%) at 0.6 per cent.