Post harvest eco-friendly management of fruit rot of tomato caused by Alternaria solani

Introduction

Tomato (Lycopersicon esculentum Mill.), a member of the Solanaceae family and native to tropical America, is one of the world's largest vegetable crops. Introduced to India by the Portuguese in the 18th century, tomatoes are now widely grown year-round, with India cultivating them on about 8.15 lakh hectares. They are rich in nutrients, including vitamins A and C, minerals, lycopene, and antioxidants, and are consumed both fresh and processed. Tomato crops face numerous diseases, including Early blight (Alternaria solani), which is highly damaging. Early blight causes symptoms like dark brown lesions with concentric rings, resulting in significant economic losses by affecting storage and transportation. It thrives in humid climates and severely impacts tomato yield by causing fruit rot, leaf spots, stem lesions, and damping-off in seedlings.

Materials and Methods

The harvested fruits were transferred to the laboratory and selected based on size uniformity, maturity (semi-ripe), and absence of physical injuries. Healthy fruits were surface sterilized with 1% Sodium hypochlorite and rinsed with sterilized water. The sterilized fruits were then dipped in various concentrations of the tested GRAS chemicals, botanicals, and essential oils and then pin-pricked followed by inoculation of test pathogen in post inoculation method while the fruit is inoculated first by test pathogen and then by GRAS chemicals in pre-inoculation method. After treatment, the fruits were air-dried on filter paper at room temperature. Three sets of ten fruits were maintained for each treatment, along with a control set. Both treated and untreated fruits were stored in plastic baskets at room temperature for further observation. The likely effect of chemical treatment on the final quality of fruits was evaluated on 8 th day using the effectiveness of GRAS chemicals, botanicals, and essential oils for controlling fruit rot of tomato caused by Alternaria solani using both pre-and post-infection treatment methods. Also, the physiological weight loss and spoilage were calculated.

Standard disease score chart for accessing PDI of fruit rot of tomato (0-5 scale)

Rating scale

Per cent disease on fruit surface 1.

Per cent Disease Intensity (PDI) was calculated by using following formula proposed by Wheeler, (1969).

For per cent weight loss the fruits under each treatment were weighed before treatment. It was recorded as initial weight (g) and final weight was recorded at the time of termination of the experiment. Per cent loss in each treatment was calculated by using the formula, Washing and immersion in Salicylic acid 1% for 5 min 3.

Washing and immersion in Calcium chloride 1% for5 min.

4.

Washing and immersion in Ginger rhizome extract @ 20% for 5 min 5. Washing and immersion in Garlic clove extract @ 10% for 5 min 6. Washing and immersion in Eucalyptus oil @ 500 ppm for 5 min 7.

Washing and immersion in Mint oil @ 500 ppm for 5 min 8.

Results and Discussion

The effectiveness of GRAS chemicals, botanicals, and essential oils was evaluated for controlling fruit rot of tomato caused by Alternaria solani using both pre-and post-infection treatment methods. The results showed that all tested treatments significantly reduced fruit rot severity compared to the control.

In the pre-inoculation method, Calcium chloride (1%) was the most effective, reducing fruit rot severity to 45.55% by the 8 th day. Other effective treatments included Mint oil (51.58%), Garlic (54.34%), Salicylic acid (58.99%), Nilgiri oil (66.11%), and Ginger (67.03%). Similarly, in the post-inoculation method, Calcium chloride (1%) again proved most effective, reducing fruit rot severity to 17.85% by the 8 th day. Other treatments like Mint oil (18.51%), Garlic (19.62%), Salicylic acid (21.10%), Nilgiri oil (22.68%), and Ginger (25.92%) also showed significant effectiveness. These findings align with previous studies, such as those by Chavan and Tawade (2012) [4] on Garlic bulb extracts, Senevirathna and Daundasekera (2010) [8] on various CaCl 2 concentrations, and Perveen and Bokhari (2020) [7] on the effectiveness of Mentha oil against Alternaria alternata. Effect of fruit dip treatments with chemical, botanicals and essential oils on the quality of fruits was evaluated on 8 th day of treatment using indices viz., spoilage and physiological loss weight. (Table 3, Fig. 1)

Impact on Spoilage

Fruit was considered spoiled when it showed dehydration, rotting or other abnormal symptoms on more than 10% of its surface. The study assessed the effectiveness of dipping healthy, fresh tomato fruits in various concentrations of chemicals, botanicals, and essential oils to minimize spoilage compared to the control (73.55% spoilage). The most effective treatment was washing and immersing the fruits in Calcium chloride (1%) for 5 minutes, which reduced spoilage to 26.32%. The next best treatment was Mint oil (500 ppm), resulting in 30.75% spoilage.

Other treatments also showed effectiveness: Garlic clove extract (10%) resulted in 32.96% spoilage, Salicylic acid (1%) in 40.96%, Nilgiri Oil (500 ppm) in 43.96%, and Ginger rhizome extract (20%) in 47.00% spoilage. Bleaching and rinsing with air drying (2%) and simple rinsing and air drying recorded higher spoilage rates of 65.76% and 73.38%, respectively. (Table 4, Plate 1 and Fig. 2)

Impact on Physiological Weight

The study examined the effects of various treatments on the physiological weight loss of tomato fruits after 8 days. The control group experienced a weight loss of 71.73%. The most effective treatment was washing and immersing the fruits in 1% Calcium chloride for 5 minutes, which resulted in the least weight loss at 23.82%. Mint oil (500 ppm) was the next best, with a 28.19% weight loss. Other treatments showed the following weight losses: Garlic clove extract (10%) at 36.43%, Salicylic acid (1%) at 37.50%, Nilgiri Oil (500 ppm) at 42.31%, and Ginger rhizome extract (20%) at 55.26%. Bleaching, rinsing, and air drying (2%) and simple rinsing and air drying had the highest weight losses of 66.38% and 69.84%, respectively. These findings align with previous research. Vir et al. (1967) [9] reported that aureofungin as a post-harvest dip extended tomato fruit life by 11-12 days compared to 2-3 days for untreated fruits. Bengerth et al. (1972) [2] found that postharvest Calcium treatment extended the storage life of many fruits by maintaining firmness and reducing respiration and rotting. Nasrin et al. (2008) [6] noted that treating tomatoes with Chlorine, packing in perforated polyethylene bags, and storing at room temperature reduced decay and weight loss, extending shelf life up to 17 days. Senevirathna et al. (2010) [8] observed that vacuum infiltration with 6% CaCl2 at 20 kPa was most effective in extending the shelf life and maintaining post-harvest quality of tomatoes. (Table 4, Plate 1and Fig. 2)

References

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