Deleterious effects of water in plant virus inoculations.

Abstract When bean leaves were inoculated by rubbing them with a brush dipped in virus-water suspension, the number of lesions of tobacco mosaic virus (TMV) first increased as the brush gradually dried out and then decreased. The number of lesions per brush stroke increased with number of brush strokes up to 4 brush strokes with dry inoculum but decreased progressively with more than 1 brush stroke with wet inoculum. When leaves were sprayed with inoculum which was then allowed to dry on the leaves, the subsequent infection was greater when the leaves were rubbed with a dry brush than when rubbed with a wet brush. The interrubbing of healthy and mosaic tobacco plants resulted in more infections when the plants were dry than when the plants were wet. When detached bean leaves were wilted to 95 to 90% of their fresh weight and then inoculated, more lesions formed on wilted leaves than on unwilted control leaves. When leaves were wilted to 95 to 65% of their fresh weight after inoculation in the turgid condition, more and larger lesions developed than on unwilted leaves. Bean leaves which were rubbed with dry Carborundum and then dipped in a virus-water or virus-phosphate-water suspension developed more lesions than leaves which were rubbed with wet Carborundum and then dipped in the same virus suspension. If the dry-rubbed leaves were floated with the rubbed surface on a virus-phosphate-water suspension at 42°, more infection resulted than if similarly rubbed leaves were immersed in the virus-phosphate-water suspension. Bean leaves which were inoculated by rubbing them with a virus-water suspension and then quickly dried produced more virus lesions than leaves which were similarly inoculated but were slowly dried. The increase in infection from quick drying was greater with dilute inoculum than with concentrated inoculum. When bean leaves were inoculated with a virus-water suspension and then washed with water for about 10 seconds, the amount of infection was greater than for unwashed leaves, but if the wash period was greater than about 20 seconds, infection was less than on unwashed leaves. For leaves which were inoculated with a virus-phosphate-water suspension, washing of leaves always decreased infection. The time from inoculation till the time when infection could no longer be reduced by a 1-hour water treatment of the inoculated leaves was about 3 hours at 31° and about 9 hours at 20°. When leaves were dry-rubbed with Carborundum but without virus for 1 to 3 strokes before regular wet inoculation, infection was increased over untreated leaves, but if leaves were wet-rubbed for 1 to 3 strokes before inoculation, infection was decreased. Wet or dry rubbing without virus after wet inoculation always decreased infection. The addition of K2HPO4 to the inoculum or to the wash water usually prevented the otherwise inhibitory effect of water on the infection process. The deleterious action of water on the infection process was demonstrated with the viruses of tobacco mosaic, tobacco necrosis, tomato spotted wilt, apple mosaic, alfalfa mosaic, and a virus from peach yellow bud mosaic. To explain the deleterious action of water in virus infections, the hypothesis is advanced that certain ions, diluted or removed by water treatments, are necessary for the attachment of the virus to a suitable site for multiplication.