MSc

Disease free planting stock significantly ensures a better field survival while at the
same time reducing the burden of economic loss. Teak, mahogany and Indian
laburnum which are extensively used for afforestation programmes in India are
attacked by several fungal pathogens at nursery stage. Hence an investigation was
undertaken to identify the fungal diseases associated with above mentioned seedlings
in Kerala and also to assess the efficacy of selected fungicides and bio-control agents
against these pathogens through in vitro studies. Purposive sampling survey was
conducted in eighteen Government tree nurseries of Thrissur (10 nos.) and Palakkad
(8 nos.) districts during the summer (February-May), monsoon (June- September) and
post monsoon (October-January) seasons for monitoring the occurrence of fungal
diseases and collection of diseased samples. Out of the fifteen fungal diseases
observed, nine was from teak, two was from mahogany and four was from Indian
laburnum seedlings. Fungal diseases observed from teak seedlings included teak leaf
blight (TLB), teak leaf spot-1 (TLS-1), teak leaf spot-2 (TLS-2), teak leaf spot-3
(TLS-3), teak leaf spot-4 (TLS-4), teak collar rot, teak root rot-1 and teak root rot-2.
In the case of mahogany, mahogany leaf blight-1 (MLB-1) and mahogany leaf blight-
2 (MLB-2) were noticed. Four foliar diseases were observed from Indian laburnum
viz., Indian laburnum leaf blight-1 (ILB-1), Indian laburnum leaf blight-2 (ILB-2),
Indian laburnum leaf spot-1 (ILS-1) and Indian laburnum leaf spot-2 (ILS-2). TLB
was found to be most severe foliar disease in teak and maximum Percent Disease
Index (PDI) and Percent Disease Severity (PDS) of 63.50 and 18.72 per cent
respectively were recorded from Vellanikkara in Thrissur district. Collar rot (PDI
18%) was observed only from Chettikkulam in Thrissur district. Chittur (Teak root
rot-1) recorded maximum PDI of 34.5 per cent. In mahogany, MLB-1 observed from
Aatoor recorded maximum PDI (57.50 %) while maximum PDS (10.4%) was
recorded from Vellanikkara. In Indian laburnum, ILS-2 observed from Vellanikkara
recorded maximum PDI (38.50%) as well as PDS (5.76%). TLB showed positive
correlation with temperature while it showed a negative correlation with relative
humidity. TLB symptoms originated as small irregular grey to blackish spots
surrounded by yellow halo scattered over the lamina. Symptoms of teak leaf spot
(TLS-1, TLS-2, TLS-3 and TLS-4) started as small necrotic spots and were generally
observed in old, mature leaves. Leaf blights in mahogany (MLB-1 and MLB-2) was
characterized by necrotic regions with definite black margin. Leaf blight diseases of
Indian laburnum (ILB-1 and ILB-2) were observed as necrotic regions in the tip as
well as base of the leaf. Leaf spots (ILS-1, ILS-2) occurred as medium sized spots on
the upper surface of the leaf. Pathogenicity of the thirteen isolates was proved by
Mycelial Bit Inoculation Method (MBIM) as well as Micro Droplet Inoculation
Technique (MDIT). Spore suspension method was adopted for collar and root
disease. Cultural as well as morphological characters of pathogens were studied and
morphological identification done with the expert advice of National Centre for
Fungal Taxonomy (NCFT), New Delhi. Molecular identification of selected pathogen
was done at Rajiv Gandhi Centre for Biotechnology (RGCB), Thiruvananthapuram.
The causative pathogen in TLB was identified as Curvularia eragrostidis, in TLS-1
as Alternaria alternata, in TLS-2 as Macrophomina phaseolina, in TLS-3 as
Botryodiplodia theobromae, in TLS-4 as Colletotrichum gloeosporioides, collar rot
pathogen as Alternaria alternata, root rot-1 pathogen as Fusarium solani and root
rot-2 pathogen as Fusarium oxysporum. Olevea tectonae was confirmed as the
pathogen of teak rust fungus. MLB-1 and MLB-2 were caused by Curvularia
geniculata and Alternaria alternata respectively. In Indian laburnum, Alternaria
alternata (ILB-1), Colletotrichum gloeosporioides (ILS-1) and Phoma cassiocarpa
(ILS-2) were the disease causing pathogens. The identity of obligate parasite causing
ILB-2 was also confirmed as Cercospora sp. in vitro evaluation studies revealed that
carbendazim 12% + mancozeb 63%, difenoconazole 25EC, carbendazim 50WP to
beefficient against teak foliar diseases. Similarly carbendazim 12% + mancozeb 63%,
carbendazim 50WP, hexaconazole 5EC showed promising results against collar and
root diseases of teak. Carbendazim 12% + mancozeb 63%, hexaconazole 5EC,
cymoxanil 8% + mancozeb 64%, propineb 70WP, carbendazim 50WP were observed
to be efficient against foliar diseases of mahogany. In Indian laburnum, hexaconazole
5EC, difenoconazole 25EC, carbendazim 50WP, carbendazim 12% + mancozeb 63%
were found to be efficient. The fungal antagonist Trichoderma asperellum showed
promising results compared to the bacterial antagonist Pseudomonas fluorescens.