Pomegranate (Punica grantum L.) is a high value commercial horticultural
crop grown extensively throughout northern Karnataka. Among the different diseases
on pomegranate Alternaria leaf spot and fruit rot caused by Alternaria alternata (Fr.)
Keissler, is becoming a serious and emerging problem to growers in northern
Karnataka.
In the present investigation, the survey in Bijapur, Bagalkot and Koppal
districts revealed the disease incidence between 15 to 80 per cent with Atharga
(Bijapur) and Kanakgiri (Koppal) standing out as hot spots (80% incidence each). The
disease appeared as small, oval to irregular dark brown spots on leaves and fruits. A.
alternata produced hyaline to golden brown conidiophores measuring 52.81-180.54 x
9.94-20.32 µm while conidia were typically muriform having 6-8 transverse and 0-3
longitudinal septa.
The fungus reached maximum growth on the 12th day whereas Potato dextrose
agar and Sabouraud’s agar among the solid media and Richard’s medium in liquid
media supported maximum growth. The fungus was favoured by temperature 300C
and pH 6.5-7.0 for mycelial growth and spore germination with lactose and
ammonium oxalate as the best carbon and nitrogen sources respectively.
In vitro bioassay revealed non-systemic fungicide; copper oxychloride @ 3000
ppm and propiconazole (@ 1000, 2000 and 3000 ppm as well as hexaconazole @
1000 and 1500 ppm among the systemic fungicides were the best for the inhibition of
the pathogen, whereas chilli fruit extract @ 15% and Trichoderma virens were highly
inhibitory to A. alternata.
In vivo evaluation of systemic and non-systemic fungicides against A.
alternata on pomegranate revealed that, propiconazole (PDI-10.6%) and thiophanate
methyl (PDI-14.7%) as well as copper oxychloride (PDI-23.4%) were highly
efficient. Screening of 17 pomegranate genotypes for disease resistance revealed that
only Cv. Yercaud was promising moderately susceptible reaction.