Introduction

The study on the incidence pattern of mango fruit borer (Autocharis albizonalis Hampson) was carried out along with the different aspects of infestation and their varietal preference. The fruit borer infestation occurred from pea to marble sized stage of the fruit and continued till maturity stage. The first pest brood was seen in the first fortnight of March and continued till June. Study of the incidence pattern and the varietal preference of mango fruit borer during 2008 to 2009 and 2009 to 2010 showed that in the year 2009 to 2010 the infestation of the pest started from the first week of April when fruits were in the pea to marble size , infestation reached maximum during 2^nd fortnight of April ( i.e. 2.29 %) when temperature , relative humidity and rainfall regime were in the range 29.04 and 42.48 °C. The relative humidity range 14 & 100% and rainfall regime 0 mm respectively. Later the population was found to decline. Lowest infestation was found at the end of May when temperature , relative humidity and rainfall were in the range of 25.3-36.2 °C , the humidity ranged between 63 & 97% and rainfall being 5.7 mm respectively.

In the next year early appearance of the pest was noticed at the pea stage of the fruit. Peak damage (i.e. 3.81%) was observed during last week of March in the year 2010 when temperature, relative humidity and rainfall regime were in the range of 36.6 and 16.9 °C, 31 and 98% and 0 mm respectively. The infestation of the mango fruit borer was lowest during second week of May when the temperature, relative humidity and rainfall varied from 38.4 and 22.8 °C, 51.6 and 93% and 27.1 mm respectively. The fruit borer bored into the fruits both at the young marble stage to more mature ones producing tiny pin head size small circular hole at the point of entry encircled by a dark brown ring. Larvae feeding on the fruit pulp formed network of tunnels to reach the seed, the later instar larvae fed on the seed, filling up the inner content of the fruits with excreta.

Materials and Methods

Biochemical analysis of the fruit in regard to the phenol content of different stages and parts of mango samples were conducted in Plant Physiology laboratory of Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal to evaluate the effect of phenol through correlation studies of these chemicals with percentage damage of the fruits by borers. For the experiment in laboratory, mango fruits of different stages were collected from the orchard of Regional Research Station, Gayeshpur, Nadia, West Bengal. The fruits were cut into pieces to separate the pulp and the seed i.e. cotyledon part which were dried in a drier for 4 to 7 days and the full dried mango pulp and seed were then ground in the grinder machine thoroughly to get parts of the fruits in dust form and then the analyses were conducted.

Phenols are best described as the aromatic compounds with hydroxyl groups which are widely distributed in the plant kingdom occurring in all parts of the plants. Disease and pest resistance in plants are attributed due to phenol content. Total estimation were carried out with the Folin-Ciocalteau reagent where under alkaline condition phenol reacted with an oxidizing agent phosphomolybdate resulting in the formation of a blue coloured complex, the molybdenum blue which was measured at 650 nm calorimetrically (Bray and Thorpe, 1954)

The Folin-Ciocalteau reagents comprise of the following: 80% Ethanol, 20% Na₂C0₃ standard, 100 mg catechol in 100 ml of water diluted 10 times for a working standard. 10 ml of 80% ethanol was added to the 0.5 g of sample taken in a test tube. The mixture was centrifuged at 4800 rpm for 20 minutes and later the mixture were kept over a hot air oven to evaporate the ethanol and the dried supernatant were collected. The residue was dissolved in 5 ml distilled water, 0.2 ml pipette out into a test tube and the volume was made up with 3 ml of water. Furthermore to it 0.5 ml of Folin-Ciocalteau reagent was added. 3 minutes later , 20 ml Na₂C0₃ solution was added to it mixed thoroughly. The prepared solution was then placed in boiling water for a minute when the materials turn deep blue. The phenol content of the sample was evaluated by the absorbance value of the coloured solution at the 650 nm wavelength in the spectrophotometer and the absorbance value was compared with the standard phenol curve thus prepared by various catechol concentration.

Results and Discussion

Results of the biochemical analysis of phenol against mango fruit borer showed the level of its phenol content of pulp and seed at different stages of fruit development of the mango cultivar. It could be noticed that pulp phenol level of the fruits of the mango cultivars ranged from 5.707 mg kg^-1 to 23.57 mg kg^-1 at marble stage, 2.537 mg kg^-1 to 13.493 mg kg^-1 at egg stage and from 1.023 mg kg^-1 to 11.023 mg kg^-1 at maturity stage of the fruit. The variations in the pulp content level of mango cultivars under study were significant at all three stages indicating inherent differences in this respect among the cultivars. The pulp phenol content level of all the cultivars was recorded to be highest at marble stage, gradually decline with the development and found to be lowest at the maturity stage. Whereas the seed phenol level of the cultivars at egg stage ranged from 17.520 mg kg^-1 to 25.090 mg kg^-1. The variation in seed phenol level of the cultivars was highly significant indicating significant difference among the cultivars in this respect. At maturity stage, the seed phenol level of the cultivars ranged from 23.543 mg kg^-1 to 4.983 mg kg^-1. The variation in seed phenol level at the fruit maturity of the cultivars was also significant indicating inherent difference among the cultivars in this respect.

From Table 1 it is clear that Himasagar at marble stage had phenol content 21.060 mg kg^-1 in the pulp. Infestation of the fruit borer was seen in the Himsagar. Gradually the phenol content declined to 11.023 mg kg^-1 in the pulp at maturity when infestation of the pest on the variety grew to reach its

Table 1: Total Phenol content of pulp and seed at different stages of fruit development of the mango cultivars

highest. From Table 2 Himsagar showed mean percentage damaged fruits by the borer of 2.59% and 2.415% in 2009 and 2010 respectively. Prabha shankar showed first attack along with Himsagar when phenol content in the pulp at marble stage was 13.473 mg kg^-1 , thereafter the infestation grew up at maturity when the pulp phenol content declined to 1.033 mg kg^-1. Arka Anmol showed uniformly high level of phenol content from marble to maturity stage and thus showed tolerance to the pest.

Table 2: Varietal preference of mango fruit borer in terms of percent damaged fruits in 2009 & 2010

Table 3: Correlation values of fruit borer infestation with phenol content at different stages of fruit development

Conclusion

The result of the present experiment was at variance with such previous information. The most interesting part of the findings of the present experiment was that the preference of the borer that reside within the seeds and feed on its cotyledon had no bearing with seed phenol level. Whereas its infestation appeared to have strong and positive association with the pulp phenol level of the fruit at egg and maturity stage.

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