Screening of germplasm and damage potential of Tetranychus urticae Koch (Acari: Tetranychidae) in marigold
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Date
2019
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CCSHAU
Abstract
The three germplasms each of African marigold, tall golden, tall orange, lemon red and French marigold,
black Jafari, Hisar Jafari-2, Hisar beauty supported T. urticae population but showed significant variation in mite
numbers during screening in accordance with susceptibility index. The germplasm tall orange African sheltering
lowest mite populations (9.82 mites/leaf) was marked as the least susceptible; black Jafari French (19.43 mites per
leaf) as slightly susceptible; tall golden African (26.17 mites/leaf), lemon red African (24.13 mites/leaf) and Hisar
beauty French (27.18 mites/leaf) were marked moderately susceptible; Hisar Jafari-2 French with 32.21 mites/leaf
was categorized as highly susceptible. In general, French germplasm was comparatively more susceptible (57%) to
T. urticae infestation as compared to African germplasm (43%). Irrespective of germplasm, significantly higher
number of mites was recorded on grown up leaves followed by tender and older leaves of marigold.The mite number
was found to significantly increase with each observation period till the attainment of peak in population in the
month of January (35.51 mites/ leaf) while least number of mites were recorded in the month of October (6.65
mites/leaf). During severe infestation, leaves were completely damaged and turned white, the mites spread to buds,
flowers. The plants were seen completely covered with profuse webbing by T. urticae and dried up.Under screen
house conditions, the studies on population dynamics of T. urticae showed the first peak in the third (144.95
mites/leaf) and fifth (96.24 mites/leaf) week of April in French and African marigold. The second peak was
recorded on fourth week of November (130.59, 87.00 mites/leaf) in both the germplasms. Under field conditions,
the first and second peak in T. urticae population on African marigold was recorded during third week of May, 2018
(67.09 mites/leaf) and first week of March, 2019 (37.13 mites/leaf). Statistically, ventral surface (lower side) of leaf
harboured higher number of mites (72 and 74%) as compared to the dorsal (upper surface) (28 and 26 %) in both
French and African marigold, respectively under screen house conditions. Season wise, statistically higher
population was recorded in summer season followed by winter and rainy season, respectively. Among abiotic
factors, a significant positive correlation of mite population was recorded with maximum temperature(r=0.469),
sunshine hours(r=0.490) and evaporation (r=0.567). A highly negative significant correlation was recorded for
morning relative humidity (r= -0.824), evening relative humidity(r= -0.798) and minimum temperature(r= -0.674).
Under field conditions, highly significant positive correlation with minimum temperature (r=0.90) and average wind
speed (r=0.76) was found. Sunshine hours showed non significant correlation with mite population. Significantly
lower amount of total chlorophyll, chlorophyll ‘a’, chlorophyll ‘b’, carotenoids, total sugar, non reducing sugar,
nitrogen, phosphorus and potassium in infested leaves was observed as compared to the uninfested leaves of
marigold; depicting significant negative correlation with T. urticae population. A significant increase in reducing
sugars, total phenol and proline was reported as compared to the uninfested leaves.The decrease/ increase in the
phytochemicals was more pronounced in summer as compared to winter season in T. urticae infested marigold
leaves. Highly significant negative correlation was found between number of mites and fruit parameters like no. of
flower (r= -0.953), flower diameter (r=-0.933), flower weight (r=-0.81), and yield per plant (r= -0.923). Statistically,
higher yield was observed in uninfested plants (224.05 g/plant) as compared to infested plants (124.98 g/plant).
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