1 Introduction

Snapmelon (Cucumis melo L. var. momordica (Roxb.) belongs to family Cucurbitaceae, that is a native of India (Duthie, 1905), and is used as vegetable in a variety of ways. Immature fruits are cooked or pickled; the low sugar mature fruits are eaten raw. India being a centre of snapmelon diversity is endowed with great variability in terms of morphological characters, especially fruit size and shape, fruit cracking and peeling patterns, flesh colour, skin texture, and primary and secondary colour of fruit skin (Pandey et al., 2011). The resistance (HPR) to insects is an effective, economical, and environment friendly method of pest control. The most attractive feature of HPR is that farmers virtually do not need any skill in application techniques, and there is no cash investment by the resource poor farmers. Plants are generally exposed to a variety of biotic and abiotic factors that may alter their genotypic and phenotypic properties resulting in expression of different mechanisms of resistance to pest attack (Gogi et al., 2010; Haldhar et al., 2015b). Tephritid fruit flies (Diptera: Tephritidae) are the most devastating insect pests having a foremost influence on global agricultural products affecting yield losses, and dropping the value and marketability of horticultural crops. In addition, tephritid fruit flies are among the mainly persistent pest species of fruits and vegetables in the world causing direct and indirect economic fatalities due to their injury (Sarwar, 2006). The extent of losses by fruit fly varies between 30 and 100%, depending on the cucurbit species and the season. As the maggots damage the fruits internally, it is difficult to control this pest with insecticides (Nath and Bhushan, 2006). Development of snapmelon genotypes resistant to fruit fly has been limited in India owing to inadequate information on the sources of plant traits associated with resistance to pest infestations. The present study was designed to screening of snapmelon genotypes associated with resistance against melon fruit fly in terms of fruit infestation and larval density under field conditions.

 

2 Materials and Methods

We Forty three genotypes of snapmelon viz., IC-430154, IC-430155, IC-430156, IC-430157, IC-430158, IC-430159, IC-430160, IC-430161, IC-430162, IC-430163, IC-430164, IC-430165, IC-430166, IC-430167, IC-430168, IC-430169, IC-430170, IC-430171, IC-430172, IC-430173, IC-430174, IC-430175, IC-430176, IC-430177, IC-430178, IC-430179, IC-430180, IC-430181, IC-430182, IC-430183, IC-430184, IC-430185, IC-430186, IC-430187, IC-430188, IC-430189, IC-430190, IC-369788, DKS-AHS 2011/1, DKS-AHS 2011/2, DKS-AHS 2011/3, DKS-AHS 2011/4 and DKS-AHS 2011/5 were sown at experimental farm of ICAR-Central Institute for Arid Horticulture, Bikaner (28°06’N, 73°21’E). The crop was sown in summer season, 2014 and summer season, 2015 with three replication for each genotype with a randomized block design. The area of each bed was 5 m×2 m and the plant to plant distance was maintained at 50 cm with drip irrigation system. All the recommended vegetable practices (e.g. weeding, fertilization, hoeing, etc.) were performed equally in each experimental bed. Two pickings were done during the entire growing season of snapmelon. Ten fruits were randomly selected from each picking from each experimental bed (replication) of each genotype and were brought to the laboratory for microscopic examination for fruit fly infestation. The infested fruits were sorted and percent fruit infestation was calculated. Ten fruits from all infested fruits from each picking of each genotype were randomly selected for further examination, and the numbers of larvae were counted in each infested fruit. The genotypes were categorized by following the rating system given by Nath (1966) for fruit infestation as: immune (no damage), highly resistant (1-10%), resistant (11-20%), moderately resistant (21-50%), susceptible (51-75%) and highly susceptible (76-100%).

 

2.1 Calculation of host plant susceptibility indices (HPSI)

The objective of the present study was to determine the role of genotypes towards susceptibility in percentage within the test materials. The HPSI was calculated by the following formula (Aziz and Hasan, 2010).

 

Percent HPSI=100–(B-A)/B×100

 

Where, A is larval population per fruit or percent fruit infestation in individual genotype of snapmelon and B is larval population per fruit or percent fruit infestation on all genotypes of snapmelon on average basis.

 

2.2 Statistical analysis

Angular transformed value was used to achieve normality in the data before analysis but untransformed means were also presented in all the tables. The data on percentage fruit infestation and larval density per fruit were analyzed through one-way ANOVA using SPSS 16 software (O’Connor, 2000). The means of significant parameters among tested genotypes were compared using Tukey’s honestly significant difference (HSD) tests for paired comparisons at probability level of 5%.

 

3 Results

The forty three snapmelon genotypes were taken for screening against melon fruit fly. The significant differences were found in percentage fruit infestation and larval density per fruit among the tested genotypes during screening. The larval density per fruit had a significant positive correlation with percentage fruit infestation (r = 0.988; p < 0.01). Pooled data showed that the genotypes IC-430190, DKS-AHS 2011/4, DKS-AHS 2011/3 and IC-430176 were found resistant; IC-430160, IC-430162, IC-430163, IC-430165, IC-430166, IC-430167, IC-430173, IC-430174, IC-430175, IC-430179, IC-430180, IC-430181, IC-430185, IC-430188, IC-430189, IC-369788, DKS-AHS 2011/2 and DKS-AHS 2011/5 were moderately resistant whereas IC-430154, IC-430155, IC-430156, IC-430157, IC-430158, IC-430159, IC-430161, IC-430164, IC-430168, IC-430169, IC-430170, IC-430171, IC-430172, IC-430177, IC-430178, IC-430182, IC-430183, IC-430184, IC-430186, IC-430187 and DKS-AHS 2011/1 were the susceptible genotypes against melon fruit fly (Table 1). The larval densities ranged from 8.32 to 18.93 larvae per fruit and were found significantly lower in resistant genotypes than in the susceptible genotypes. The larval density was the highest in genotype IC-430187 (18.93 larvae/ fruit) followed by IC-430182 (18.72 larvae/ fruit). The minimum larval density was found in IC-430190 (8.32 larvae/ fruit) followed by DKS-AHS 2011/3 (8.67 larvae/ fruit). The per cent fruit infestation was the highest in IC-430187 (72.91 %) and the lowest in IC-430190 (10.79 %) followed by DKS-AHS 2011/4 (14.46 %). The fruit infestation ranged from 10.79 to 72.91% which was significantly lower in resistant genotypes and higher in susceptible genotypes (Table 1).

 

Table 1 Larval density and percent fruit infestation of fruit fly on different genotypes of snapmelon in arid region

 

The results presented in Table 2 are regarding HPSI in different genotypes of snapmelon based on the larval population per fruit and percent fruit infestation of fruit fly during 2014, 2015 and pooled of 2014-15. It was observed that the genotype IC-430187 showed maximum HPSI based on larval population i.e., 139.42% followed by IC-430182 showing 137.83 % HPSI. The minimum HPSI based on larval population recorded was 61.24% for IC-430190 that was the most resistant genotype followed by DKS-AHS 2011/3 (63.82% HPSI). On the basis of percent fruit infestation, the highest HPSI was recorded on IC-430182 (155.10%) that genotype was found highly susceptible to fruit fly and lowest HPSI was found in IC-430190 (22.79%) that is resistance to fruit fly.

 

Table 2 Host plant susceptibility indices (HPSI %) for fruit fly on different genotypes of snapmelon in arid region

 

4 Discussions

In The results show the overall host plant resistance study in snapmelon against fruit fly, B. cucurbitae. In the present study, the genotypes IC-430190, DKS-AHS 2011/4, IC-430176 and DKS-AHS 2011/3 were found to be resistant to fruit fly infestation in different genotypes of snapmelon. The percentage fruit infestation and larval density were found to be significantly lower in resistant and higher in susceptible genotypes of snapmelon. Direct defenses are mediated by plant characteristics such as mechanical protection on the surface of the plants (e.g., hairs, trichomes, thorns, spines, and thicker). But the productions of toxic chemicals (such as terpenoids, alkaloids, anthocyanins, phenols, and quinones) are supposed to be “indirect defences”, as they are only active through the insect feeding being part of the secondary metabolism of plants. And the plant defense mechanism can affect the herbivores through antibiosis and antixenosis, and not just through biology, killing or retarding their development (Hanley et al., 2007). Host plant selection by insects is either expressed by the occurrence of a population of insects on the plant in nature or by feeding, oviposition or use of the plant for complete offspring development (Rafiq et al., 2008). Numerous studies have shown that genotypes of the same insect species could significantly differ in their resistance to insect pests (Dhillon et al., 2005; Sarfraz et al., 2006; Gogi et al., 2010, Haldhar et al., 2013a, Haldhar et al., 2013b, Cartea et al., 2014; Haldhar et al., 2015a) and it is caused by biochemical traits of plants. Similar our findings also incorporated with Gogi et al. (2010) and Haldhar et al. (2015b) that study the lower fruit infestation and larval densities were observed on resistant varieties/ genotypes of bitter gourd and ridge gourd than on their susceptible varieties/ genotypes.

Lower values of host plant susceptibility indices based on fruit infestation (HPSI) were recorded on genotypes IC-430176, DKS-AHS 2011/4, IC-430190 and DKS-AHS 2011/3 (39.35%, 30.54%, 22.79 and 38.42%, respectively) and its used as a source of resistance for developing snapmelon genotypes resistant line to fruit fly. According to Shahid et al. (2014), the genotype Cool Sun-70 showed 27% HPSI followed by Cauliflower Desi 26%. The minimum HPSI was calculated 9% for Pari F1 H and Shumila F1 H. The genotypes Cashmere and White Island were categorized as intermediate with 14% and 15% HPSI, respectively. The genotype Cool Sun-70 showed a maximum population of P. brassicae and was found to be comparatively susceptible with 30.02 populations per plant whereas the genotype Pari F1 H appeared comparatively resistant with the lowest population of P. brassicae i.e., 3.44 per plant. Haldhar et al. (2013b) reported that the lower values of host plant susceptibility indices based on fruit infestation (HPSI) were recorded on resistant varieties/ genotypes, AHRG-29, AHRG-57 and PusaNasdar (36.12%, 32.69% and 37.29%, respectively) and used as a source of resistance for developing ridge gourd varieties/ genotypes  resistant to fruit fly. The present study explores new horizons of providing detailed characteristics of various snapmelon genotypes regarding susceptibility and resistance to fruit fly. The cultivation of IC-430190, DKS-AHS 2011/4, DKS-AHS 2011/3 and IC-430176 in such condition can be suggested on the bases of present findings but further investigations are required to elucidate the response of these genotypes against other pests. Thus, from the foregoing account, it could be argued that reduction in fruit fly infestations on resistant genotypes could be due to phenotypics (biophysical) and antibiosis (allelochemicals). Snapmelon genotypes IC-430190, DKS-AHS 2011/4, IC-430176 and DKS-AHS 2011/3 were classified as resistant to B. cucurbitae and these could be used in future breeding program as resistant sources.

Acknowledgements

The authors are thankful to Director, ICAR-Central Institute for Arid Horticulture, Bikaner, India, for providing facilities and advice required for experimentation, and to R. Swaminathan, Professor, Department of Entomology, MPUAT, Udaipur, India and Majeet Singh, Professor, SKRAU, Bikaner for critical discussion and suggestions.

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