SELECTION AMONG SOME MELON STRAINS FOR TOLERANCE TO THE TWO-SPOTTED SPIDER MITE, Tetranych usurticae koch

Abstract

This study was conducted during the period from 2016 to 2018. Seven different strains of melon (Cucumis melo L.) were tested for their response to Tetranychus urticae. Data revealed that, all plant growth parameters were affected significantly with infestation of T. urticae; leaf area which considered the main source of mite feeding was the most affected one. However, (L5) had the lowest leaf area (24.98 cm2 ) while (L7) recorded the highest leaf area (41.26 cm). Also, accumulated moving stages in (L2) showed the lowest population density with an average of 1.70 individual /in2 during 4 weeks, of season 2016. During season 2017, the highest leaf area was in hybrids (L4×L1) and (L4×L2) with an average 62.93 and 61.86 cm2 . All hybrids explained three levels of infestation; high level was observed in hybrids (L6×L2), (L5×L2) and (L7×L1) and accumulated the population density of moving stages with an average of 80.70, 70.60 and 61.40 individual /in2 . While medium level was recorded in hybrids (L5×L1 and L7×L2) and the third, low level of infestation was recorded in hybrids (L6×L1, L4×L1, L3×L2, L3×L1 and L4×L2) and moving stages average were 2.70, 3.30, 3.70, 3.90 and 5.30 individual /in2 so these hybrids were resistant to infestation of T .urticae . Regarding horticultural characters obtained data on total yield ranged from 4015.0 to 2185.0 g/plant; (L4) gave the highest value of total yield. Estimates of broad sense heritability were high for all studied traits indicating minor role of the environment. The results showed significant and highly significant mean squares for both general combining ability and specific combining ability in all studied traits, indicating the important role of both additive and non-additive gene effects in the expression of these traits. Highly significant SCA effects in all studied traits were recorded for the crosses (L3×L2), (L5×L2), (L6×L2) and (L3×L1).