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Host Plant Resistance to Broad Mite, Polyphagotarsonemus Latus Banks in Chilli

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The broad mite, Polyphagotarsonemus latus Banksis a key pest of chilli (Capsicum annuum L.) and the economic yield loss due to the mite was estimated to be around 11 to 75% quantitatively and 60 to 80% qualitatively in the event of serious infestation. The nymphs and adults of chilli mite feed on terminal auxiliary tender shoots and typical symptoms noticed are downward curling, crinkling of leaves and elongation of leaf petiole followed by blister patches. If the plant is infested during flowering stage, the flowers are transformed into leafy shoots and may wither and dry. The damage of P. latus is more pronounced in hot and humid seasons.  The broad mite P. latus is spread worldwide. In the tropics and subtropics it reproduces the whole year round and has a wide host range. In temperate climates it is a serious pest on vegetables and ornamental plants in glasshouses. Due to its high reproductive potential, it can reach damaging densities within a very short time.

The generation time of P. latus is short. On chilli the developmental period from egg to adult at 25°C averages 4.1 days for both males and females. Adult female and male longevity is 11.4 and 15.3 days, respectively. Each female lays 25 eggs. The female/male sex ratio is 2.8 in the laboratory, and 2.3 on seedlings in the greenhouse. P. latus eggs are laid on the underside of leaves, tender stems, fruits, flower peduncles and flowers. Attack occurs during a short period of time. Discoloration of tissues is produced by mite feeding; fruits become deformed or fail to develop. Severely infected fruits fall. Leaves of attacked plants are stunted and yield is significantly reduced. Symptoms remain for a long period of time after control.

P. latus disperses by various means. Short-distance movement may be accomplished by walking. Mites may reach far-away uninfested plants by wind. Human transport of infested plants is another way of dispersal for this mite. There is also evidence that P. latus disperses through insects living on plants. Females of P. latus were observed to have a phoretic relationship with Bemisia tabaci on Phaseolus vulgaris in Colombia and on watermelons in Venezuela. Females of P. latus were found attached to the tarsi and tibiae of B. tabaci and B. argentifolii. The phoretic association between P. latus and insects is quite specific; whiteflies are most attractive to P. latus but other insects such as thrips and aphids are rarely used.

 Broad mites are difficult to control due to their polyphagous nature and high reproduction rate. In addition, their short generation time and cryptic habitat make the pest management very difficult, resulting in repeated application of pesticides. Foliar spray of dicofol; triazophos; thiodicarb; ethion; fenpropathrin; diafenthurion; pyriproxifen; profenofos;  abamectin and chlorfenapyr are recommended for the control of mite in chilli. Farmers take up nearly 18 to 26 rounds of pesticide sprays for the management of sucking pests in irrigated chilli, which in turn tremendously increases the cost of cultivation. Besides, the concern over indiscriminate use of chemical pesticides and the adverse effect on environment warrant eco-friendly approaches in pest management programs.

Host plant resistance plays a key role in formulating alternative pest management strategies. Over 700 chilli accessions have been evaluated for their reaction to P. latus in several field screening trials in India. The national gene bank at NBPGR holds over 4,480 chilli germplasms and a wider scope exists for the identification of untapped resistance sources against the mites in chilli. 

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Please note that this is the opinion of the author and is Not Certified by ICAR or any of its authorised agents.