الملخص الإنجليزي
Two types of experiments were conducted to study the effect of resistant rootstocks on witches' broom disease of lime (WBDL) a) in vitro, This experiment was conducted at Sultan Qaboos University(SQU), Sultanate of Oman under laboratory conditions kept in a growth chamber at temperature range 16-28°c and relative humidity at 60-80%
Three different rootstocks; sweet lime (Citrus limettioides) sour orange (Citrus aurantium), and grapefruit (Citrus paradisi) were used in this trial, In vitro experiment lasted for 2 years involving , germinating of rootstocks seeds and healthy lime in culture tubes on MS medium including growth regulators (cytokinin and auxin) and with out growth regulators respectively; subculture rootstock and healthy lime seedling , micrografting healthy lime on the rootstocks as an interstock „micrografting infected lime on interstocks,.,b) In vivo experiment involved the rootstocks sour orange , sweet lime,and woodapple in the shade house was as follows : planting sour orange, sweet lime seeds at Najed Research Station and wood apple in Salalah Reasearch Station in Dhofar Governorate ,grafting of healthy lime on rootstocks in the same place, grafting of the infected lime on a disease -free interstock in SQU Agricultural Experimental Station. Seeds of rootstocks and healthy lime produced suitable seedlings for grafting in vitro .Healthy lime grafting on the three rootstocks was successful, however, the infected lime dried before showing any growth .This was attributed to the late stage of infection of these scions ; therefore ,scions are recommended to be in earlier stage of infection .In vivo seed germination of rootstocks and healthy lime was good.grafting of healthy and infected lime on the three rootstocks ,was successful .Witches' Broom symptoms appeared on the healthy lime grafted on the three rootstocks ,the healthy lime grafted on sweet lime and wood apple dried up then died shortly whereas healthy lime grafted on sour orange did not die yet ; PCR technique proved that the Phytoplasma was present .The appearance of symptoms on the grafted healthy lime could be related to the susceptibility of these stocks under the experiment conditions ,or the time period between grafting the healthy lime and the infected lime was not enough to develop resistance .It also indicate that the field grown rootstocks was infected because they are resistant to the vector in this respect larger number of rootstocks should be tested.
