BP Singh

222 Ra'anpracticed in Australia and other countries to control the nematodes.Sets are treated for 25 min. at 55°C.With hot water treatment, problem is to kill the quiescent preadultjuveniles or wool on ,the outsides or between dry scales.Efficient HWT of planting material is obtained only if the materialbeing treate~ is dormant and free of soil.(d)Treatment for the s,eedsWhite tip a seed borne disease of rice caused by A. besseyi iseasily controlled by HWT of seed for 15 min, at 52-54"C For thesame nematode on Setaria and other minor millets, time andtemperature requirements are slightly different ..Heat tolerance and heat hardeningThe chances of successful hot water treatment increase as thedifference between thermal sensitivity of host and nematodesincreases, with the latter being more sensitive. The smaller thisdifference, more accurately the temperature and time of thetreatment must be controlled, and the more important it becomesto treat only the most heat resistant plant propagules available.As a precautionary measure material should be plunged into coolwater to terminate the treatment.ft should be realised that both the host and the nematode aremore tolerant to heat in a dehydrated and dormant stage than ina stage of active metabolism. In many cases the plant can be grownor pretreated so as to produce tolerant stock. Rhizomes of bananagrown in relatively dry soil were more tolerant to hot watertreatment to control R. similis than were mOTe succulent ones ofthe same size grown in relatively moist peaty soil in Surinam.In Britain and The Netherlands, early lifting and subsequentstorage at 25-35°C made it possible to treat narcissus bulbs forcontrol of D. dipsaci at temperatures up to 47.7"C instead of 43.3"Cfor three hours, without damage to the bulbs. However, thisadvantage has to be balanced against the fact that warm storageincreases the resistance of the nematodes as well. Good results ofhot water treatment of strawberry runners to control leaf and stemnematodes were obtained in Ireland, when runners were taken inSeptember, preheated in warm water and immersed in cold waterafter hot water treatment at 45 L1 C for 15 minutes. Thermal injmywas reduced and uniformity of growth increased after hot water