Screening of germplasm and damage potential of Tetranychus urticae Koch (Acari: Tetranychidae) in rose
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Date
2019
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CCSHAU
Abstract
The three germplasms each of hybrid tea rose, pink, yellow, white and Floribunda rose, dark pink, orange, pinkish white supported T. urticae population but showed significant variation in mite numbers during screening in accordance with susceptibility index. The germplasm pinkish white and orange rose sheltering lowest mite populations (5.06, 5.41 mites/leaf) was marked as the least susceptible; dark pink (8.94 mites/leaf), yellow rose (7.75 mites/leaf) and white rose (5.77 mites/leaf) were marked moderately susceptible; pink rose with 14.86 mites/leaf was categorized as highly susceptible. Hybrid Tea roses were more susceptible to T. urticae as compared to Floribunda roses. Between screen house and field crop, statistically higher number of mites were recorded under screen house (9.29 mites/leaf) than in field (6.64 mites/leaf) crop. Under screen house conditions, the studies on population dynamics of T. urticae in desi rose showed that first peak appeared in second week of August and second peak was recorded in the fourth week of March. Grown up leaves harboured significantly greater population of mites (9.59 mites/leaf; 45-52%) as compared to older (6.71 mites/leaf; 27-32%) and tender (4.78 mites//leaf; 21-23%). Under field conditions, T.urticae population showed a first peak in the first week of September, 2018. A significant positive correlation of mite population was recorded with maximum temperature (r =0.669), minimum temperature (r =0.872), evening relative humidity (r= 0.354), wind velocity (r=0.666) and rainfall (r =0.462) under screen house conditions. Under field conditions highly significant positive correlation with maximum (r=0.703) and minimum temperature (r=0.855) and wind velocity (r=0.645) was found. T. urticae population showed a significant negative correlation with total chlorophyll (r= -0.77) chlorophyll ‘a’ (r= -0.74), chlorophyll ‘b’(r= -0.85) and carotenoid (r= - 0.89) content in rose leaves. The percent decrease of photosynthetic pigments, chlorophyll ‘a’, chlorophyll ‘b’, total chlorophyll and carotenoids in the month of June (44.59, 40.98, 38.04 and 37.50 %) was more as compared to month of September (13.66, 1.49, 12.50 and 13.89%) respectively.Total sugar and non reducing sugar content depicted a significant decline in T. urticae infested leaves (26.95 and 9.32 mg/g dry weight) than in uninfested leaves (31.78 and 16.61 mg/g dry weight), respectively. An increase in reducing sugars, total phenol and proline (18.64 mg/g dry weight, 0.54 mg/g, 54.75 μg/100g) was reported as compared to the uninfested leaves (15.60 mg/g dry weight, 0.45 mg/g and 44.54 μg/100g).Significantly lower nitrogen, phosphorous and potassium content was recorded in infested (1.68, 0.78, 0.20 % dry weight) leaves as compared to uninfested leaves (2.03, 0.93, 0.31% dry weight) respectively. A highly significant negative correlation of mite population with total sugar (r=-0.91), non reducing sugars (r =- 0.96), nitrogen (r =- 0.97), phosphorous (r =- 0.94) and potassium(r= - 0.88) was recorded. A positive correlation between T. urticaepopulation and content of reducing sugars (r= 0.99), total phenol (r =0.83) and proline(r =0.92) was recorded during the present study. Significant decrease in number of flowers (30%), flower diameter (5.97%), flower weight (9.77%) was reduced due to T. urticae infestation as compared to uninfested desi rose plant. A significant decrease in flower yield (38.45 yield/plant; 30.35%) was observed at high infestation (15.50mites/leaf) level as compared to uninfested (55.21yield/plant) plant.
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