Disease survey in nurseries and plantations of forest tree species grown in Kerala.

TLDR: During the disease survey in Tectona grandis, Bombax ceiba, Ailanthus triphysa, Gmelina arborea, Dalbergia latifolia, Ochroma pyramidale and Eucalyptus spp.

Abstract: During the disease survey in Tectona grandis, Bombax ceiba, Ailanthus triphysa, Gmelina arborea. Dalbergia latifolia, Ochroma pyramidale and Eucalyptus spp. a total of 65 pathogenic and 13 other diseases (unknown etiology, non-infectious and phanerogamic parasite) were recorded. With these diseases altogether 88 pathogens were associated, of which 64 are new host record, including seven new species viz. Pseudoepicoccum tectonae and Phoinopsis variosporum on T, grandis, Meliola ailan thii on A . triphysa, Griphospharria gmelinae on G. arborca, Physalospora dalbergiae on D. latifolia and Cytospora eucalypti and Valsa eucalypticola on Eucalyptus spp., while 29 are first record from India, T. grandis had fifteen diseases, two in nursery and fourteen in plantations; one being common to both. Ten organisms were associated with these diseases; mostly causing foliar damage; six pathogens are new host record and four first record from India. None of the two diseases in nurseries were serious whereas in plantations die -back caused by insect-fungus complex and a phanerogamic parasite, Dendrophthoe falcata were serious diseases capable of causing large-scale destruction. Three diseases viz. pink disease (Corticium salmonicolor), Phomopsis leaf spot and a disease of unknown etiology appeared to have potential to become serious. In B. ceiba there were eight diseases, four in nursery and six in plantations; two were common to both. Four pathogens are new host record. Collar rot and seedling blight were the severe diseases causing appreciable loss to stocking. None of the plantation diseases were found to be serious, except Myrothecium leaf spot which in certain humid areas could pose some problem due to extensive premature defoliation. A . triphysa had a total of nine diseases of which eight were in nursery and four in plantations; three were common to both. All the eight pathogens are new host record while two were first record from India. Among relatively large number of seedling diseases, two viz. collar rot and seedling blight were very widespread and damaging as they resulted in large-scale mortality. In plantations though none of the diseases were very serious, three viz. Botryodiplodia stem canker, pink disease and shot-hole were potentially serious, especially the former two, which killed the affected trees in certain localities. There were ten diseases in G. arborea, three in nursery and eight in plantations; one was common to both. All the ten pathogens associated with these diseases are new 2 host record while three are recorded for the first time from India. In nurseries onlv seedling blight was of serious consequences though stem infection (Phoma nebulosa) also appeared to be potentially serious in certain localities. In plantations a die-back disease caused by Griphosphaeria gmelinue was the major disease as it resulted in heavy mortality. In D . latifolia none of the four diseases of foliage recorded were of serious nature. Leaf spots caused by Physalospora and Colletotrichum are new diseases while for leaf rust and Phyllachora leaf spot D. latifolia is a new host. Only two diseases were recorded in plantations of 0. pyrumidale and none in the nursery. One of the diseases, die-back, resulting in large-scale mortality, was caused by two pathogens, Calonectria rigidiuscula and Fusarium moniliforme, the former being the first record from India. Eucalyptus spp, recorded the highest number of 30 diseases, 13 in nursery and 21 in plantations; four were common to both. Of the 46 pathogens associated with these diseases, 30 are new host record and 18 first record for India. In nurseries, damping-off, seedling blight and leaf and shoot blights were serious seedling diseases affecting the nursery stock considerably, especially in high rainfall areas. In plantations, pink disease and leaf and shoot blights (Cylindrocladium spp.) were the major limiting factors during the first one to three years of establishment. A number of provenances of various species of Eucalyptus screened against pink disease following toxin bio-assay revealed variation in susceptibility between species and within provenances of a species. Other potentially serious diseases were web blight (Rhizoctonia solani) in nursery and stem cankers caused by Cryphonectria cubensis and Cytospora eucalypticola (both recorded for the first time from India), which can result in heavy mortality. Control measures for 18 seedling diseases of various tree species were worked out and field tested for the efficacy of the fungicide and its dosage.