Antexenotic and allelochemicals study on snapmelon (Cucumis melo var. momordica) against melon fruit fly (Bactrocera cucurbitae) in arid region of Rajasthan, India

The 43 snapmelon genotypes were taken for preliminary screening against B. cucurbitae and significant differences were found in percentage fruit infestation and larval density per fruit. The larval density per fruit had a significant positive correlation with percentage fruit infestation (r = 0.988; p < 0.01). The genotypes IC-430190, DKS-AHS 2011/4, DKS-AHS 2011/3 and IC-430176 were found 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. The percentage fruit infestation increased with an increase in larval density per fruit and there was a significant positive correlation (r = 0.988; p < 0.01) between per cent fruit infestation and larval density per fruit. In pooled data, the per cent fruit infestation was highest in IC-430184 (69.67 %) and lowest in IC-430190 (11.21 %) followed by DKS-AHS-2011/4 (14.97 %). The larval density ranged from 8.63 to 17.57 and 8.30 to 17.20 larvae per fruit in the rainy, 2014 and summer, 2015, respectively. In pooled data, the larval density was maximum in IC-430169 (17.37 larvae per fruit) and minimum in IC-430190 (8.47 larvae per fruit) followed by DKS-AHS 2011/3 (8.8 larvae per fruit). The percentage fruit infestation and the larval density per fruit with free amino acid (0.97 & 0.96) and TSS (0.3 & 0.3) of fruit had a significant positive correlation whereas; flavonoid (-0.98 & -0.96), tannins (-0.97 & -0.95), phenols (-0.96 & -0.95) and total alkaloid (-0.97 & -0.94) had significant negative correlation. The length of ovary pubescence (-0.99 & -0.96), rind hardness at immature stage (-0.93 & -0.90), rind hardness at mature stage (-0.59 & -0.54) and pericarp thickness (-0.78 & -0.75) had significant negative correlations whereas; flesh thickness (0.62 & 0.61), fruit length (0.61 & 0.62) and fruit diameter (0.76 & 0.77) had significant positive correlations with the percentage fruit infestation and the larval density per fruit. Basis on Kaiser Normalization method, the extraction communalities for all the variables tested were ≥ 0.5 indicating that the variables were well represented by the extracted PCs which together explained a cumulative variation of 82.8 %. PC1 explained 53.41 % of the variation while PC2 explained 29.39 % of variation. PC1 had the loadings for flavonoid content (0.86), tannins content (0.88), total alkaloid (0.82), phenols content (0.88), free amino acid (-0.83), total soluble solid (-0.66), length of ovary pubescence (0.88), pericarp thickness (0.67) and rind hardness at immature stage (0.89). Rind hardness at mature stage (0.52), flesh thickness (-0.74), fruit length (-0.86) and fruit diameter (-0.68) were loaded in PC2. The flavonoid, total alkaloid, tannins, phenols content, length of ovary pubescence and rind hardness were the novel antibiosis and antixenotic characters found in snapmelon which were resistant to fruit fly. These above snapmelon genotypes could be used in future breeding programme as resistant sources