Etiology and management of shisham die-back disease in Pakistan forests

Abstract

The etiology of shisham (Dalbergia sissoo) die-back has been a subject of considerable scientific debate for hundred years. No single pathogen species is responsible for die-back outbreaks, making shisham die-back challenging to study. Symptoms of the disease include yellowing, the water-soaked appearance of leaves, thinning of leaves and crown, branch die-back (single or whole), bark splitting, gummosis, and lesion development. Symptomatic shisham were sampled from 117 sites across Pakistan. One hundred and ninety-two fungal isolations were made from 1170 shisham samples and were identified as Ceratocystis sp. and Fusarium sp. based on cultural morphology. Koch's postulates were completed using 23 isolates of Ceratocystis sp. and four isolates of Fusarium sp. on three shisham age groups a) 6-12-month-old nursery seedlings growing under greenhouse conditions, b) 1-3-year-old plants growing under natural field conditions, and c) 10-15-year-old tree growing under natural field conditions. Inoculation with Ceratocystis isolates resulted in typical shisham die-back symptoms. Inoculation with Fusarium sp. did not produce any symptoms alone or in combination with Ceratocystis sp. Four fungicides were evaluated for efficacy against Ceratocystis sp. using in vitro tests and field trials. In in vitro test, propiconazole resulted in the highest level of inhibition (88.88%) at day seven, followed by difenoconazole (84.75%), hexaconazole (81.11%), while benzimidazole (77.73%) was least effective against the tested fungus. The efficacy of these fungicides has declined throughout greenhouse trials conducted in this study. Additionally, these fungicides could not prevent tree loss in trees inoculated with Ceratocystis sp. in the field trials. Thus, shisham die-back continues to be of concern in shisham-growing areas in Indo- Pakistan. However, chemical management and continuing research on the epidemiology of this disease may provide a solution