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A study on "Etiology and management of die back disease of mango grafts in
nursery" was carried out in the Department of Plant Pathology, College of
Horticulture, Vellanikkara during 2007 - 20008 to study various aspects,
particularly the etiology, symptomatology, varietal reaction and management of
die back disease.
Surveys were conducted at ten different nurseries on the occurrence of die
back disease of mango grafts and during the survey different leaf blight diseases
were also noticed along with die back incidence. Pathogens associated with these
diseases were isolated and proved pathogenicity by artificial inoculation under in
vitro and in planta conditions. Isolation of pathogen on PDA medium yielded
Colletotrichum sp. and Botryodiplodia sp. from die back symptom and
Colletotrichum sp., Pestalotiopsis sp., Cylindrocladium sp., Drechslera sp. and
Alternaria sp. from leaf blight symptom.
Studies on symptomatology showed that die back and leaf blight
symptoms produced by the respective pathogens at different locations were same,
but different pathogens produced different type of symptom on mango grafts. The
die back caused by Colletotrichum sp. was observed as small necrotic spots on the
tip of shoot and at the base of leaf petiole which later coalesced and developed
,
large brownish black necrotic area. The leaves on the infected shoot dried up and
fell down. Black discolouration and darkening of the bark of young green twigs
were observed in mango grafts infected by Botryodiplodia sp. This infection
spread downwards and resulted in typical die back symptom. In severe infection
leaf shedding was also observed. The leaf blight caused by Colletotrichum sp. was
also noticed on young leaves and appeared as dark brown circular spot with
yellow halo which coalesced to form large blighted area. The pathogen produced
the fruiting body, acervulus, on infected area and also showed shot hole symptom.
Pestalotiopsis sp. infected matured leaves and produced light brown necrotic area

from the leaf tip or margin which later spread towards the midrib with silvery grey
coloured area on upper surface of leaf. The other three pathogens viz.,
Cylindrocladium sp., Drechslera sp. and Alternaria sp. initially produced dark
brown spots on leaves. In all these infections, the spots were coalesced and
produced large brown coloured blighted area on leaves.
Cultural and morphological characters of the six pathogens were studied
on PDA medium. Based on the etiological studies and cultural and morphological
characters of organisms the pathogens causing die back disease were identified as
Colletotrichum gloeosporioides (Penz.) Sacc and Botryodiplodia theobromae Pat
and the leaf blight inciting pathogens were identified as Colletotrichum
gloeosporioides (Penz.) Sacc, Pestalotiopsis mangiferae (Henn.) Steyaert,
Cylindrocladium mangiferae sp. nov, Drechslera australiensis (Bugnicourt)
Sub ram & Jain ex M.B.Ellis and Alternaria alternata (Fries) Keissler. There was
no earlier report of C. mangiferae on mango and hence it is the first report of this
fungus as a leaf blight pathogen on mango. The result of the genetic dissimilarity
index computed by the seven different isolates of C. gloeosporioides showed a
slight variability among the isolates.
An in vitro experiment was conducted to evaluate the effectiveness of
fungicides and antagonists against die back and leaf blight pathogens. Among the
fungicides, Bordeaux mixture at all the three concentrations recorded cent per cent
,
inhibition on the growth of all the six pathogens. Carbendazim showed cent per
cent inhibition on the growth of C. gloeosporioides, P. mangiferae and C.
mangiferae at all the three concentrations but it was not very effective against D.
australiensis. Hexaconazole was found effective to control the growth of D.
australiensis and recorded more than 85 per cent inhibition over control. The two
fungal antagonists viz., T. viride (KAU) and T. harzianum (nSR) showed
complete inhibition on the growth of all the six pathogens whereas the bacterial
antagonist, P. jluorescens showed more than 50 per cent inhibition on the growth
of C. gloeosporioides, B.theobromae, P. mangiferae and D. australiensis.


After the in vitro evaluation of fungicides and antagonists, an in planta
experiment was conducted two times to know the effect of various treatments on
the management of die back and leaf blight diseases. Observations on per cent
disease severity of die back and leaf blight disease revealed that all the treatments
were superior to control. The data recorded on ten days after the last application
of treatments during the first experiment revealed that the highest reduction in
disease severity (90.47 per cent) was observed in plants treated with one per cent
Bordeaux mixture, 0.3 per cent copper oxychloride, 0.1 per cent carbendazim,
0.15 per cent copper hydroxide. The treatments T9 (P. fluorescens), T10 (T.
viride) and T11 (quinalphos) were also on par with the above treatments. The
highest reduction in disease severity of leaf blight (79.63 per cent) over control
was recorded in plants sprayed with one per cent Bordeaux mixture and was on
par with all other treatments except mancozeb and zineb.

The results of the second experiment revealed that the highest per cent
reduction in disease severity of die back (80.02 per cent) over control was
exhibited by one per cent Bordeaux mixture and was on par with all other
treatments. Similarly Bordeaux mixture recorded the highest reduction in disease
severity of leaf blight (85.64 per cent) over control, and was on par with all other
treatments. Hence it is concluded that all the five fungicides viz., one per cent
Bordeaux mixture, 0.15 per cent copper hydroxide, 0.3 per cent captan, 0.1 per
cent hexaconazole and 0.1 per cent carbendazim and the bioagents viz., T. viride
(20 g/ lit) and P. fluorescens (2.0 per cent) were equally effective in the
management of die back and leaf blight disease of mango grafts.

The data on the screening of mango grafts of different varieties revealed
that the two varieties, viz., Alphonso and Mulgoa were highly resistant to die back
and leaf blight diseases. The highest total phenol content of 393.69J.lg/g was
recorded in Alphonso and was followed by Mulgoa which recorded 283.59 J.lg/
of total phenol per gram of plant sample. . ..;