Lasiodiplodia theobromae causes a damaging dieback of cocoa in India

Abstract

Central Plantation Crops Research Institute, Regional Station, Vittal, 574 243, Karnataka, IndiaCocoa (Theobroma cacao) is mainly grown as a mixed crop in coco-nut ⁄arecanut gardens in India. In September 2000 a rapid dieback ofcocoa was first observed in Hunsur Taluq of Mysore district, Karnataka,India. Affected trees show sudden yellowing and browning of leaves fol-lowed by rapid dieback of branches from the tips. Infected twigs havebrownish,shortverticalstreaksinthevasculartissues.Affectedtreescon-tinue to decline for several days and they soon die, although new flushesstilldevelopatthecollarregionsduringthemonsoon.Podsdonotdevelopin diseased trees but if formed earlier become mummified. Trees areaffected at all growth stages and throughout the year. Mortality is mostseverefromMarchtoMay.Investigations of the disease began in 2003 but it was not until 2007that the cause was consistently associated with a fungus isolated fromaffected twigs. Colonies were initially milky white on potato dextroseagarplates,laterturningtogrey-whitewithblackpycnidiaonthesurface.Young conidia were hyaline, unicellular, ovoid in shape and on maturityone-septate and ellipsoidal and confirmed as Lasiodiplodia theobromaeby CABI, UK (IMI 394314). Sterile cotton swabs containing L. theobro-mae mycelium were rubbed on pre-wounded stems of eight-month-oldseedlings. Typical vascular streaking and dieback symptoms appearedwithin20 days,exhibitingasimilaraggressiveresponsetoL.theobromaeon cocoa in Cameroon (Mbenoun et al., 2008). Lasiodiplodia theobro-mae was reisolated from the inoculated seedlings. Control swabs withsterilewaterdidnotproducesymptoms.Lasiodiplodia theobromae is a non-prominent pathogen of sixty planthosts inIndia (Varma& Bilgrami, 1977) and is the causeof charcoal podrotofcocoa(Nambiar&Nair,1972).Thisis,however,thefirstreportofa damaging dieback and death of cocoa plants, as witnessed in Mysoredistrict. Currently confined to an area of 260 ha, the incidence of the dis-easeincocoagardensvariesfrom10to56%.Withtherapidexpansionofcocoa in India underway, this disease is a potential threat to future pro-duction.References