Nursery diseases of black pepper (Piper nigrum L.) in Kerala with special reference to the management of Phytophthora capsici Leonian, emend. Alizadeh and Tsao

Abstract

Nursery diseases are the major limiting factor in the production of quality planting materials of black pepper. Investigations were carried out to study the various diseases occurring in black pepper nurseries of northern districts of Kerala, the effect of nursery practices on the incidence of diseases and to evolve an integrated management strategy against Phytophthora rot in black pepper nursery. Four nursery diseases viz., Phytophthora rot, Colletotrichum rot, Rhizoctonia rot and Sclerotium rot were recorded from different nurseries surveyed. The pathogens causing the diseases were isolated and identified as Phytophthora capsici Leonian emend A. Alizadeh and P.H.Tsao, Colletotrichum gloeosporioides (Penz.) Penz. Sacc., Rhizoctonia solani Kuhn and Sclerotium rolfsii Sacc. Symptomatology of these diseases were studied. The pathogen P. capsid produced symptoms on all parts of the plant, while C. gloeosporioides infected mainly on leaves. R. solani and S. rolfsii infected both leaves and collar regions. The infected plants produced typical symptoms depending upon the pathogen and plant parts affected. Incidence of nursery diseases varied with locations and nursery seasons. Among the nursery diseases noticed during the survey, Phytophthora rot was the most predominant one. Incidence of other three diseases was comparatively less than that of Phytophthora rot. Various nursery practices followed for raising pepper nursenes viz., nursery structures, potting mixture, place of collection of planting materials, variety / cultivar planted, processing of runner vines, treatment of potting mixture, time of planting, frequency of irrigation and application of fungicides had an effect on the incidence of nursery diseases especially Phytophthora rot. However, cuttings raised under high density polyethylene sheet did not show any incidence of diseases. Screening for host resistance indicated tolerant and moderately susceptible reactions of Kalluvally-II and Panniyur-5 respectively against nursery diseases. The

biochemical parameters of these genotypes, which impart this type of reactions, were studied in comparison with susceptible Panniyur-l. Total phenols, OD phenol and total free amino acid contents and peroxidase, catalase and esterase activities were more in tolerant Kalluvally-II, while total carbohydrates, starch and acid phosphatase activity were maximum in susceptible Panniyur-l. Reducing sugar content was high in moderately susceptible Panniyur-5. Quantitative estimation of rhizosphere microflora from different pepper nurseries yielded bacteria, actinomycetes and fungi. Fungal antagonists exerted more antagonistic activity against P. capsid both under in vitro and in vivo conditions. Among these two isolates F 14 and F 48 were selected based on their better antagonistic efficiency against P. capsid and they were identified as Trichoderma harzianum Rifai and Trichoderma viride Pers. ex S.F. Gray aggr. The established antagonists T. harzianum and T. viride also exerted good antagonistic efficiency against P. capsid. The native and established antagonists were compatible with Akomin-40 and Ridomil MZ, while Bordeaux mixture and Fytolan were not compatible with any ofthe four fungal antagonists. Better growth and minimum disease incidence in pepper cuttings were recorded when nurseries were raised during February-March. Pepper cuttings raised in solarized potting mixture for 30 days showed more sprouting, better plant growth and less incidence of disease. Integrated management of Phytophthora rot in black pepper nursery was carried out using tolerant Kalluvally-II, moderately susceptible Panniyur-5 and susceptible Panniyur-l. In all the three black pepper genotypes, all the treatments had a significant effect in reducing the incidence of Phytophthora rot when compared with control. The minimum disease incidence in Panniyur-l and Panniyur-5 was recorded in cuttings in treatment T14 (Solarization of potting mixture for 30 days + T. viride +

Akomin-40), while in Kalluvally-II it was T20 (Solarization of potting mixture for 30 days + T. harzianum - F14 + Akomin-40). In general, solarization of potting mixture, application of Trichoderma spp. and fungicides like Akomin 40 and / or Ridomil MZ can be used for managing the incidence of Phytophthora rot in black pepper nursery