Ph.D

“Breeding for resistance to fruit fly (Zeugodacus spp.) in oriental pickling melon (Cucumis melo (L.) var. conomon Mak.)

ABSTRACT

Melon fruit fly (Zeugodacus spp.) is one of the major pests in cucurbits and it causes a loss of 32-100 per cent depending upon seasons and prevailing climatic conditions. The developing resistant varieties either by selection from germplasm lines or through backcross breeding is an economical way to reduce fruit loss in oriental pickling melon. Keeping this in view, the present investigations entitled “Breeding for resistance to fruit fly (Zeugodacus spp.) in oriental pickling melon (Cucumis melo (L.) var. conomon. Mak.)” was undertaken to identify sources of resistance to fruit fly infestation form germplasm; to incorporate fruit fly resistance into high yielding genotypes and to study the genetics of inheritance. Two separate experiments were designed for the study.
Fifty three oriental pickling melon accessions were catalogued as per Minimal Descriptor of Vegetable Crops- Cucumis melo (L.)- NBPGR (2000). High variability was observed for all the morphological traits except flower colour. Oblate followed by globular and elongate were the predominant fruit shapes. White, creamy white, white with orange shade were observed for flesh colour. Fruit taste was sour, sweet; none of the accessions had bitterness. The traits viz., node of first female flower, vine length, number of seeds per fruit, number of fruits per plant, days to last harvest and percentage of fruit fly infestation exhibited high GCV, PCV, heritability and GA which indicated that these traits were highly heritable and could be improved through selection.
Yield per plant was positively, significantly correlated with number of branches per plant, fruit diameter, fruit girth, fruit length, fruit weight, seed cavity length, seed cavity breadth and number of fruits per plant. High heritability was exhibited by all these traits. Therefore, simultaneous selection for these traits would improve yield. Significant negative correlations to fruit fly infestation were observed for traits viz., fruit diameter, fruit rind thickness, flesh thickness, marketable yield per plant, days to fruit fly infestation after anthesis. These traits exhibited high heritability hence, direct selection of higher mean values would improve yield and fruit fly resistance.
Mahalanobis D2 analysis grouped the 53 accessions into 8 clusters. Cluster I had maximum number of accessions (12) followed by cluster II (9). The maximum inter cluster D2 value was between cluster VI and cluster V. Cluster mean for yield contributing traits were high in cluster V which consisted the promising accessions viz., CM022, CM045, CM047 and CM051. Cluster mean for fruit fly resistance contributing traits were high in cluster IV and cluster VI, where the promising accessions with respect to fruit fly resistance viz., CM012, CM033, CM034 and CM056were distributed. Two species of fruit fly were identified viz., Zeugodacus cucurbitae and Zeugodacus tau during the crop seasons.
Hybridization was undertaken to incorporate fruit fly resistance into high yielding accessions from wild as well as resistant genotypes. Accessions viz., CM022, CM033, CM045, CM047, CM051, CM060, CM061 and CM062 selected as female parents; fruit fly resistant genotypes (Cucumis melo var. agrestis (W-10), Cucumis melo var. agrestis (W-51), Cucumis melo ssp. callosus and CM033) were selected as male parents. Thirty one F1’s were evaluated for morphological characters and resistance to fruit fly. High variability was observed for all the morphological traits except flower colour. Oblate followed by elliptical and elongate were the predominant fruit shapes. White, creamy white, white with orange shade were observed for flesh colour. Fruit taste was sour, sweet and bitter. Based on yield, quality, absence of bitterness and resistance to fruit fly, four F1’s were selected viz., CM045 x CM033(3.04kg) (Cross I), CM061 x CM033 (3.26kg) (Cross II), CM051 x Cucumis melo ssp. callosus (2.34kg) (Cross III), CM033 x Cucumis melo ssp. callosus (1.96kg)(Cross IV) for generation mean analysis.
Generation mean analysis revealed that earliness traits were predominantly determined by dominance (h) gene effects coupled with duplicate epistasis. Hence improvement of earliness in flowering, fruiting and harvesting may be achieved by heterosis breeding. Yield contributing traits were governed by additive x additive (i), additive x dominance (j) and dominance x dominance (l) coupled with duplicate epistasis which indicated that hybridization followed by selection is appropriate. Fruit fly resistance traits were largely determined by additive x additive (i), additive x dominance (j) and dominance x dominance (l) effects coupled with duplicate epistasis. Selection and or hybridization followed by selection can be used. Number of fruits per plant, fruit rind thickness (Cross I), fruit girth (Cross II), fruit diameter (Cross II & III), day to last harvest (Cross III) exhibited complementary epistasis with significant additive (d), additive x dominance (j) and dominance x dominance (l) gene effects revealed that selection from segregating population could improve these traits.
Correlations of biochemical traits of six generations to fruit fly infestation revealed that lower content of total soluble solids, total soluble sugars, total sugars; higher content of crude protein, total phenols, silica and tannins favoured resistance to fruit fly infestation.
Evaluation of sensory qualities of fresh, cooked fruits of six generations in four crosses revealed that highest overall acceptability for fresh, cooked fruits was in CM045 (P1) Cross I and CM061 (P1) CrossII.
The present investigations revealed that high variability was observed for all the morphological traits and resistance to fruit fly in oriental pickling melon accessions. Two species of fruit fly viz., Zeugodacus cucurbitae and Zeugodacus tau were identified during the crop seasons which infested different accessions. High heritability was observed for yield and fruit fly resistance. Fruit diameter, fruit rind thickness and flesh thickness exhibited high heritability, significant positive correlations with yield and significant negative correlations with fruit fly infestation. Simultaneous selection based on these traits would improve yield as well as fruit fly resistance. High magnitude of fruit rind thickness, flesh thickness and days to fruit fly infestation after anthesis along with hairiness on stem and fruit contributed to fruit fly resistance. High crude protein, total phenols, tannins and silica content of fruits contributed resistance to fruit fly whereas, high sugars, total sugars, total soluble solids favored fruit fly infestation. Generation mean analysis revealed that selection from segregating generations, heterosis breeding would be appropriate to improve yield along with fruit fly resistance.