The alternative strategies have included the search for new types of pesticides, which are often effective against a limited number of specific target species, are biodegradable into non-toxic products and suitable for use in integrated pest management programs (Al-Samarrai et al., 2012). Plant products effectively meet this criterion and have enormous potentials to influence modern agrochemical research. The use of botanicals or plant products is gaining popularity because they have been found to be non-toxic, more systemic with little mammalian toxicity (Bankole, 1996). Botanicals degrade more rapidly than most chemicals pesticides, and therefore are considered to be eco-friendly and less likely to kill beneficial pests than synthetic pesticides with longer environmental retention. Most botanicals degrade generally within a few days, and sometimes even within few hours (Siddiqui and Gulzar, 2003). Although botanicals have the potential of being safe agrochemicals but their effect on biochemical and physicochemical properties of vegetables have been poorly investigated. This work intends to study the effect of botanical extracts on some biochemical properties of treated tomato fruits. 

Source of materials used

The bacterial culture MMC-2112 (T) used in the experiment was procured from Microbial Culture Collection, National Centre for Cell Science.

Preparation of plant extracts (botanicals)

The aqueous plant extracts and their concentrations were prepared according to a method described by Obongoya et al. (2010), with minor modifications. Aqueous extracts of  easily  available  plants in Allahabad as listed below were prepared for the experiment at two concentrations (20% and 30%) each:T₁ -Ginger (Zingiber officinale) 20%, T₂ -Ginger (Zingiber officinale) 30%, T₃-Turmeric (Curcuma longa) 20%, T₄-Turmeric (Curcuma longa) 30%, T₅-Neem Seed (Azadirachta indica) 20%, T₆-Neem Seed (Azadirachta indica) 30%, T₇-Coriander (Coriandrum sativum L.) 20%, T₈-Coriander (Coriandrum sativum L.) 30%, T_0a-Sterile distilled water (Untreated Control), T_0b-Streptomycin sulphate (Treated control).

The plant materials were first oven dried (except neem seeds and turmeric which were dry) and grinded in to powder, using electric grinder (Mixer Grinder). Dried plant tissues (20 g/100 ml and 30 g/100 ml) were measured and soaked for 24 h in distilled water. Then suspension of each plant extract was filtered using 4 layer muslin cloth, 2 times. The plant extracts were then stored for later use in a refrigerator at 4°C. Discs of 12.7 mm were soaked in these extracts for 24 h and used as botanical treatment on the bacterial lawns under in vitro. While for streptomycin sulphate, only 1 g of powder was used in 100 ml sterile distilled water after which discs were soaked and used as above (positive control). In case of sterile distilled water (negative control), discs were just soaked and used as above.

Efficacy of four botanicals against bacterial soft rot of tomato fruits                                                   

Method described by Rahman et al. (2012a) was followed with little modifications. Efficacy of four botanical extracts was evaluated against bacterial soft rot of tomato fruits. The extracts were prepared as described above and each tomato fruit was drilled with 14 mm cork borer, then treated the cut section and it was covered with the plant extract for 30 min. Inoculum of the soft rot bacterium was prepared at concentration of 10⁷ cfu/ml and 12.7 mm paper discs were soaked in for 30 min. The plant extract treated tomatoes were inoculated with the paper disc soaked in the inoculum suspensions by introducing a disc into a fruits section and replacing the cap. Inoculated tomatoes were then incubated in loosely tight polyethene bags at room temperature along with controls. Visual observations were made at 2 and 8 days after inoculation where data on disease incidence among fruits, followed by some biochemical properties of the fruits such as reducing sugars, Vitamin C and pH due to treatments been valuated. Disease incidence was determined after 2 and 8 days of inoculation (Plate 1) using the formula below:

Estimation of ascorbic acid (Vitamin C): Volumetric Method described by Thimmaiah, (2009) was followed.

Estimation of reducing sugar by DNS Method: Standard method of DNS was followed.

Estimation of tomato fruit pH

pH is the measure of H⁺ ion activity (concentration); it measures active acidity. Standard method of pH determination using pH meter was followed and fruits were first crushed (macerated) using pistil and mortar and then juice produced was tested using standardized  pH meter which was standardized with 4 and 7 buffer solutions (Tilahun, 2013). After standardization 5 ml of the each tomato juice was diluted in 50 ml deionized water for the measurement.

Biochemical properties of tomato after in vitro evaluation

Reducing sugars

The    highest    reducing    sugar   content    percent  was recorded in neem 30% (T₆=3.45) then, turmeric 20% (T₃=3.43) followed by fresh tomato (T_0a=3.41), while treated control (T_0c=2.89) has the least mean followed by ginger 20% (T₁=2.98) as presented in Table 2. The result in general indicated the potential advantage of using these botanicals against the concerned pathogen as they do not hamper the fruits biochemical constituents.

The total reducing sugars content per cent of tomato fruits ranges between 1.7 to 4.7% (Yilmaz, 2001) and similar results were reported by Tadesse et al. (2012) with ranges between 2.728 – 3.561% at eight days of storage, while Hossain et al. (2010) with ranges between 2.36%-2.74% for various genotypes grown at Rangpur, Bangladesh. From the above information, it’s possible that most of the botanicals did not decrease the reducing sugars content of the fruits but rather a slight increase was recorded when compared to the three controls, which could imply an advantage in using them. But this view needs to be further studied as is first attempt its kind.

Ascorbic acid content of tomatoes

Vitamin C (mg) content of the tomatoes were also found to differ among the treatments only slightly but significant, the maximum mean value been recorded in untreated control (T_0b=20.47) followed by turmeric 20% (T₃=20.40), then neem 30% (T₆=20.27) while least mean value was found in treated control (T_0c=18.99) followed by coriander 20% (T₇=19.59) which is second to lowest (Table 3).

All the mean values were found to be within standard range as reported by Hossain et al. (2010), that vitamin C content of tomato varies from 17.32 mg/100 g to 26.59 mg/100 g. Similar result was also reported by Kallo (1985). Treatment means, botanicals and concentration were significant, but as this is an attempt to trace the effect of botanicals on some biochemical properties of tomato, it is suggested that further investigation should be done.

pH of tomatoes after eight days of inoculation

pH means values were found to differ significantly among the treatments. The highest pH mean value was in neem 20% (T₅=4.68), followed by treated control (T_0c=4.67) then turmeric 20% (T₃=4.66) while least pH mean value was in untreated control (T_0b=3.89), then untreated un-inoculated control (T_0a=3.92) followed by coriander 30% (T₈=4.18) (Table 4). The high pH in neem 20% (T₅=4.68) and treated control (T_0c=4.67) may be explained by the way it’s active ingredients work, possibly is by rising pH to inhibit microbial growth as suggested by Czajkowski et al.  (2011).

While low pH in untreated control can be due to the respiration of the tomato fruits, since it does not appear to be extremely low. The result presented (Table 4)  here  is also in agreement with several earlier reports which shows positive but irregular correlation between reducing sugars, pH, (Georgelis et al., 2004), pH, reducing sugars and vitamin C, and /or total soluble solids but negative with total acidity as reported by Tilahun (2013) that pH and reducing sugar content of harvested tomato fruits are affected by its maturity state and time taken respiring by fruit off plant. In general, the high pH, reducing sugars, and vitamin C mean values recorded in this experiment might be attributed to fact that the tomato was produced under organic system of farming or due to a slight increase due to treatments.

Significant results were obtained when the four botanicals were screened in vitro. In the present study turmeric 30% (T₄) proved to have highest potential to be used for the management of bacterial soft rot of tomato caused by Pectobacterium carotovora susp. carotovora compared to the rest botanicals, whereas neem 30% (T₆) appeared to maintain the highest fruit reducing sugars, compared to the other treatments. Turmeric 20% (T₃) appeared to maintain highest fruits’ vitamin C value while fruit pH highest mean value was by neem 20% (T₅). Turmeric 30% can be best recommended fort the management of bacterial soft rot of tomato fruits while turmeric 20% and neem 30% can be used if biochemical properties of tomato genotype are so low and might be jeopardized. The results of the experiment are based on single trial conducted under Allahabad, UP, India.

The authors have not declared any conflict of interest.