Department of Plant Pathology, CPPS,
Tamil Nadu Agricultural University
Papaya (Carica papaya) is one of the most important fruit crops in the world and is mostly
cultivated in tropical and subtropical regions. Mostly, it has been cultivated due to its sweet nature
with medicinal properties (papain) and nutritional values viz., proteins, edible fibers, vitamins (B2,
niacin and C) and minerals. Across the world, India is represented as the top producer of papaya
followed by Brazil, Nigeria, Indonesia and Mexico. In India, papaya is cultivated around an area
of 1.39 m. ha with a production of 5831.0 MT. Of this production, Andhra Pradesh occupies the
highest production with 1288.5 MT. Popular varieties like, Red lady, Sinta and Co 8 were mostly
cultivated in a total area of 1.76,000 ha with moderate production of 403.1 MT from Tamil Nadu.
A vast survey was conducted for papaya growing in the western Ghats districts of Tamil Nadu.
During this period a new disease incidence was recorded, especially in the Coimbatore district.
Based on symptomatic and molecular analysis it was confirmed to be bacterial crown rot (BCR)
caused by Erwinia papayae. In the field, the whole plant was infected at an age of 5 months being
completely drooped, and recorded an incidence of up to 60%. The cultivar Red Lady was highly
infected as compared to other local elite varieties like Co7 and Co8. The infected trees, whole
shoot, branches, leaves, fruits and young crown also had typical symptoms of water-soaked lesions
in fruits, crowns with pale white lesions, emitting a foul odor. When split the infected stem region
showed pale brownish discoloration with bacterial outburst. It was caused by a gram negative, rod
shaped, peritrichous, single colonizing phytopathogenic bacteria called as Erwinia papaya (2-3
mm diameter) that survived on infected fruits and seeds, mostly predominant in and spread by
infected seeds as nature.
Analysis of the eleven collected strains (CCRP1 – CCRP11) through biochemical methods proved
as gram-negative phytopathogenic and sequencing through 16S rRNA gene (MT322147 to
MT322823)-it showed a similarity of >95% with E. papayae from a strain of Malaysia.
Analysis of ORFs in all strains, 3 to 10 ORFs were contributed in gene sequences and the
maximum ORFs (10) being present in strains viz., MT322147 (Leaf), MT322787 (Stem) and
MT322792 (Branch). Out of these eleven strains, the least number of ORFs (3) were in strain
MT322823 (Leaf). Hence, it proved to be of an adaptive nature and showed diversification in
phylloplane hosting pathogenic bacteria. In bases analysis of all strains, adenine (A) and thiamine
(T) were majorly playing a vital role in ratio at (3:2). This was confirmed by pathogenic bacteria
thriving and surviving through nitrogenous synthesis and accumulation nature in eco-system. That
has helped in survival and pathogenic expression.
The outbreak of bacterial crown rot disease seems to be new and is conditioned as an emerging
threat to farmer in Tamil Nadu. It has been more severe in local elite cultivars like, Co 7, Co 8 and
Red Lady. As a result, prior to cultivation, it is important for plant protection officers to follow
practices that are essential for management of this bacterial disease. I hope this article helps you
gain clarity to the disease outbreak of bacterial crown rot (BCR) in papaya (Carica papaya L.) and
in gathering knowledge to the students, researchers in future.