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Brinjal belonging to the family Solanaceae is of great importance in human
nutrition and is considered as the King of Vegetables. Despite being a versatile crop
adapted to various agroclimatic regions and seasons, brinjal is affected by many
diseases like Phomopsis blight and fruit rot, little leaf, damping off and bacterial wilt.
In addition to these, recently a fruit rot caused by Phytophthora nicotianae is also
reported from various parts of India (Jain et al., 1982 and Chowdappa et al., 2015). A
preliminary study of the same has been conducted by Jose and Beena (2016).
Considering the importance of Phytophthora spp. in the agricultural scenario of Kerala,
the present investigation was carried out with the objectives to study the
symptomatology and etiology of fruit rot of brinjal, screening popular brinjal varieties
for resistance and to develop management strategy for the disease.
Purposive sampling survey was conducted in different locations of Thrissur and
Palakkad districts during June to October 2019, infected brinjal fruits were collected
and symptoms were recorded. The incidence and severity of the disease in different
locations ranged from 10 to 84 and 10 to 66 per cent respectively. Presence of a white
mycelial growth was consistently observed on the infected fruits which on examination
under microscope showed hyaline, coenocytic hyphae and pear shaped sporangia with
papillae. The microorganism was isolated on carrot agar and pathogenicity was tested.
Symptoms produced on artificial inoculation were also recorded. A total of four isolates
of the pathogen were collected, purified and maintained for further studies. The isolates
were named after the place of collection as VKA Ⅰ, VKA Ⅱ, KPD and NMA.
Cultural and morphological characters of the isolates were studied on three
different media viz., carrot agar, potato dextrose agar and coconut water agar. Colony
characters like growth rate, colour, shape, texture of colony and sporulation varied
among the isolates and media. All the four isolates produced coenocytic, hyaline,
branched mycelium and thick walled, hyaline, globose chlamydospores. Non caducous,
papillate, ovoid and obturbinate sporangia were borne terminal or intercalary on the
sporangiophore in a simple sympodial fashion. Variation in dimensions of sporangia
was observed among the isolates grown on different media.
Based on morphology, all the isolates were identified as Phytophthora sp. Oospore
production was not noticed on pairing of isolates suggesting that these belong to single
mating type and express the typical heterothallic behaviour of the genus.
Molecular characterisation of the four isolates revealed maximum similarity to
P. nicotianae and phylogenetic analysis showed that isolates VKA Ⅰ, VKA Ⅱ and NMA
are more closely related than KPD. Host range studies proved that the pathogen can
infect other crops like tomato, chilli, bhindi, bitter gourd, arecanut, coconut, nutmeg,
cocoa, papaya, rubber and black pepper on artificial inoculation. The most popular
varieties of brinjal, released from Kerala Agricultural Universiy viz., Surya and Haritha
were found to be susceptible to the pathogen.
The results of in vitro evaluation showed that cymoxanil 8%+ mancozeb 64%,
metalaxyl+ mancozeb, mancozeb, copper hydroxide, fosetyl- Al at 0.05 per cent
concentration and Bordeaux mixture (0.5%) recorded cent per cent inhibition of the
pathogen. However, azoxystrobin (0.05%) recorded 37 per cent inhibition only.
Similarly Trichoderma sp. and Pseudomonas fluorescens recorded cent per cent and
69.40 per cent inhibition respectively. The leaf extracts of Capsicum frutescens and
Boerhavia diffusa also gave significant inhibition of pathogen. In bioassay on detached
fruits the highest disease reduction was recorded by mancozeb (72.38%) followed by
cymoxanil 8%+ mancozeb 64% (66.26%). However biocontrol agent Trichoderma sp.
also recorded 51.67 per cent reduction over control which was on par with fosetyl- Al,
copper hydroxide and azoxystrobin. Leaf extract of Capsicum frutescens also reduced
the disease by 39.18 per cent.
Phytophthora fruit rot is an emerging disease and if left uncontrolled it will be
a serious threat to brinjal cultivation. The study has confirmed the etiology and
symptomatology of the disease and the wide host range of the pathogen. It was also
proved that the four isolates of P. nicotianae collected in the study are confined to same
mating type. The investigation has also revealed the efficacy of lower doses of
commonly used fungicides, against P. nicotianae. Results of the study also suggested
the potential of biocontrol agents and botanicals against the pathogen.