Evaluation on selected chemical fungicides for controlling bacterial heart rot disease (Dickeya zeae syn Erwinia chrysanthemi) in MD2 pineapple variety / Norsahira Mohd Sidik

Bacterial heart rot (BHR) disease in pineapple variety MD2 is caused by Dickeya zeae
syn. Erwinia chrysanthemi. The present study aimed to screen the effectiveness of
systemic chemical fungicides in different dosages for controlling the BHR pathogen in
vitro and to evaluate the effectiveness of delivery techniques of the selected chemical
fungicides to control BHR disease under rain shelter (in vivo) conditions. The disease
pathogen was isolated from symptomatic pineapple leaves with the appearance of
water-soaked and heart rot disease symptoms such as rotten basal tissues. Pathogenicity
tests were carried out to fulfil the Koch’s postulates. Evaluation on the effectiveness of
fungicides in controlling the causal pathogen was conducted via in vitro study. From
the result obtained, mancozeb and difenoconazole demonstrated the ability to control
the pathogen at the lowest concentration of 250 mg a.i/L from the recommended rate.
Subsequently, these results were tested on in vivo stages to find the effective method of
fungicides application. The experiment was planned in a completely randomised design
(CRD). Ten replications were assigned for each treatment. The treatments of present
study were (i) Control (pathogen only), (ii) Difenoconazole + Pathogen, (iii) Mancozeb
+ Pathogen, and (iv) Benomyl + Pathogen. The two methods of application were
dipping only and combination method with dipping and spraying. For the dipping
method, the data were collected based on mean disease incidence (DI) (%) for 6-week
assessment. While for combination (dipping and spraying) method, the data was
collected based on mean disease severity (DS) (%) for 6-week assessment. For calculate
the mean of DI (%) per week, total number of leaves could be pulled out from the plants
was noted. While for DS (%), the total area of leaf demonstrating rotting symptoms of
BHR disease was calculated for data of mean per week. The DI (%) and DS (%)
analysed have significant differences among the means (P< 0.05) for each of the
treatments from week 1 until week 6. According to the results obtained, as expected,
the highest heart rot infestation was found to be at the control treatment DI with 96.97%.
While the best fungicides that reduce the infestation was difenoconazole with 7.65%
(DS) by using combination method (dipping and spraying) application. However, these
results need to be re-evaluated in the fields to re-confirm the best application method
for these selected fungicides by using the combination method (dipping and spraying).