Key Words

Banana, plant extracts, fruit-rot, pathogenic fungi, antagonistic activity.

Introduction

Fruits have been an important part of our food from pre-historic times, as they are a chief source of vitamins, minerals, fats, fibres, trace elements etc. Of various fruit and vegetable crops, bananas are of paramount importance in the human diet. Banana (Musa paradisiaca L.) is one of the most popular and staple fruits of India. Banana is the largest fruit crop accounting for 31.7% of total fruit production from 12.6% arable area with a total production of banana, estimated as 16.9 million tonnes /annum from 4.9 lakh ha. Banana, a typical climacteric fruit, softens rapidly once ripening is initiated [1]. Ripe fruits are susceptible to attack, by a variety of microorganisms to which they are resistant during their attachment to the plant. Generally the rot-producing fungi result in spoilage and wastage of fruits even before reaching the consumers.

Though the use of synthetic fungicidal chemicals in plant disease control has been promising in protecting the plants against the pathogens, but many of them proved to be health hazardous [2]. In view of these, the antimicrobial properties of some plant constituents are being exploited [3, 4, 5]. Several workers including- Godara and Pathak [6], Abraham and Prakasan [7], Prasad and Naik [8], Swami and Mukadam [9] and Sumangala et al [10] have screened different plant extracts for their antimicrobial properties against fungal pathogens. Mukhopadhyay et al [11] and Sheela et al [12] regard biological control, using microbial antagonists as a good alternative for the management of diseases in many crop plants. Application of microorganisms or microbial products for the control of fruit pathogens has been widely reviewed [13, 14, 15, 16, 17, 18]. In fruit market, usually more than 10 % of the total banana crop is destroyed due to post-harvest diseases particularly fruit rots [19]. The present investigation was carried out to test the efficacy of some plant extracts and bioagents against the three fruit-rot fungi under in vivo condition.

Materials and Methods

In vivo evaluation of plant extracts

The present investigation was carried out in the Department of Microbiology, Kakatiya University, Warangal, (A.P.) during the year 2009. Evaluation of plant extracts and bioagents under in vivo conditions was assessed as suggested by [20]. Aqueous extracts of different plants viz Annona squamosa, Azadirachta indica, Psidium guajava, Ocimum sanctum, Vinca rosea, Eucalyptus globulus, Allium cepa and Allium sativum were prepared to test their antifungal activity. The plant extracts were obtained by grinding 10 gms of freshly collected leaves and bulbs with 100 ml of distilled water and filtering it through double layered muslin cloth. It was diluted with distilled water to 30 % and 50% concentrations.

Healthy fruits of banana were surface sterilized and inoculated separately with the pathogens by scalpel injury method [21]. Plant extracts (30% and 50%) were tested against the rot of banana as pre- and post-inoculation treatment. In the pre-inoculation treatment, the fruits were first dipped in plant extract for 30 minutes and then inoculated with the pathogen, while in the post-inoculation treatment the fruits were first inoculated with the pathogen and then treated with plant extract. Atleast five replicates were maintained. Untreated fruits served as control. The treated fruits were incubated at 25 ± 2°C in a humid chamber for 7 days. At the end of the incubation period the extent.

Table -1 : Effect of plant extracts on fruit-rot of banana by three pathogenic fungi

Table-1a: ANOVA- Effect of plant extracts on fruit-rot of banana by three pathogenic fungi

Table-2a: ANOVA -Effect of different antagonistic microorganisms on three fruit-rot fungi of banana

S-significant; NS-not significant

of the fruit-rot was assessed by scraping off the visibly infected part and the percentage of fruit-rot was calculated by the formula:

In vivo evaluation of bioagents

Efficacy of antagonistic microorganisms in checking the fruit-rot activity of the pathogens under study was assessed by preparing the spore suspensions of 7 days old cultures of two antagonistic fungi (Trichoderma viride and Penicillium citrinum) and two bacteria (Streptomyces spp. and Pseudomonas fluorescens) in sterile water. Rest of the details of inoculation, treatment and incubation are similar to the method of evaluation of plant extracts mentioned earlier.

Statistical Analysis

All the experiments were repeated for five times. The statistical analysis (ANOVA) on the data was performed with the SPSS program version 12.0.

Results and Discussion

Effect of plant extracts

Table 1 and 1a, Figure 1, 2 reveals that the plant extracts tried could check the fruit-rot caused by the three pathogenic fungi to a significant level. However, the degree of protection varied with the pathogen and plant extract. In general percentage of fruit-rot decreased with the increase in the concentration of plant extract. Pre-inoculation dip was less effective than the post-inoculation dip. Plant extracts of Azadirachta indica and Eucalyptus globulus were effective against N.oryzae. F.oxysporum and M.phaseolina were comparatively insensitive. The aqueous extracts (50%) of bulbs (Allium cepa and Allium sativum) also effectively inhibited the growth of all the three fungal pathogens under study. Though extracts of Psidium guajava and Vinca rosea were not effective at lower concentration in pre-inoculation dip, but inhibited the fruit-rot by the fungi under investigation to a considerable extent at higher concentration. In contrast to this, postinoculation dip was very effective. The extracts of Ocimum sanctum were selective in action as they were effective only against N.oryzae when compared with other two pathogens. The extracts of V.rosea could effectively check the growth of M.phaseolina at higher concentration. Extracts of Annona squamosa were intermediate in its efficacy, as they could check pathogens activity to a limited extent. Thangavelu et al [22] and Babu Lal et al [19] have also reported the efficacy of plant extracts employed by them against Colletotrichum musae and C. gloeosporioides causing anthracnose of banana.

The present investigations revealed that the postharvest diseases of fruits can be checked by the use of phytoextracts. The plant extracts are useful in the plant protection by inhibiting the activity of endoenzymes or as they produce toxic metabolites which inactivates the pathogens.

Effect of bioagents

From Table 2 and 2a, Figure 3, 4 it is clear that the bioagents tried could control the growth of fruit-rot pathogens by their antagonistic activity which however, varied with the antagonist. Penicillium citrinum and Streptomyces spp. could control the fruit-rot caused by all the three fruit-rot fungi (Macrophomina phaseolina R-4242, Fusarium oxysporum sp. QJC-1403 and Nigrospora oryzae NRRL 54030) under investigation to a considerable extent. Trichoderma viride and Pseudomonas fluorescens were next in their degree of inhibition of growth of N.oryzae. On the other hand, fruit-rot caused by F.oxysporum was checked effectively by T.viride followed by P.citrinum, while Streptomyces spp. and P. fluorescens were responsible for protection of banana fruits to a moderate level. Similarly T.viride and Streptomyces spp. followed by P.citrinum and P. fluorescens could check the pathogenic activity of M. phaseolina in a descending order.

Babu Lal et al [19] could control fruit-rot of banana caused by Colletotrichum gloeosporioides using Trichoderma species. Dutta and Das [14] could control the collar-rot of tomato by using the species of Trichoderma. Sastry [20] also reported that P.citrinum and Streptomyces spp. were effective in checking the tuber rot of carrot caused by M.phaseolina.

Conclusion

Control of plant diseases by plant extracts is on ascendancy due to failure of fungicide efficacy and intoxicating nature of these chemicals. Fungicides can easily contaminate agriculture product, drinking water and soil and can directly enter food chain of human and animals intoxicating considerably. The management of diseases of fruits including the extensive use of plant extracts particularly of those plants, which have medicinal importance provide a scope for further use of these botanicals or their active compounds to control pathogenic fungi due to their fungistatic or fungicidal activity.

The eco-friendly measures of plant disease control when integrated with potent bioagents can also increase the bioefficacy and ensure complete disease management.

Acknowledgement

The authors thank Head, Department of Microbiology, Kakatiya University, Warangal, Andhra Pradesh for providing necessary facilities.