| Ten pathogenic strains were isolated from galls collected from several areas of Shandong province in late 2000. One of them belonged to biovar I of A.tumefaciens (A.tumefaciens in new classification), and all the others belonged to biovar II of A.tumefaciens (A.rhizogenes in new classification) according to the results of biochemical and physiological test. In natural conditions, these strains could infect all dicotyls except for chest nut, pomegranate, and evergreen euonymus; they could infect gingkgo biloba L.of gymnosperm as well as welsh onion of monocot. This experiment confirmed the previous ideas that the effect of wound on crown gall occurrence was induction, and confirmed that nematodes could make wounds severe enough to induce A.tumefacien.The resistance of stone fruit rootstocks and Duli pear to crown gall was tested by artificial inoculation with four strains of above pathogenic isolates, together with studies on effects of several factors on occurrence of crown gall and effects of crown gall on biological functions of infected rootstocks in 2001. The results were written as follows.1. Res i stance to tumor format i on Chinese cherry, Maotao peach, Mountain cherry expressed symptoms quickly. Together with Mazzard, these rootstocks had greater disease incidence than other rootstocks such as Duli pear, Daqingye cherry and Mountain apricot. The three latter expressed high resistance to occurrence of crown gall-2. Resistance to tumor development According to the volume of stem galls, the classification of resistance to tumor development was finished as follows: Mountain peach, Round leaf Daqingye cherry, Colt, Mountain cherry were high susceptive; Laiyang dwarf cherry, Maotao peach, Chinese cherry, Mazzard were middle susceptive; Daqingye cherry was middle resistant; Mountain apricot, Duli pear were high resistant. We found that Daqingye cherry was a promising cherry rootstock for crown gall resistance in practice.3. Effects of several factors on occurrence of crown gall The occurrence of crown gall on shoots was more quickly than that on stems. The following sequence of tumor size could be concluded: Gall formed on crown in soil > that on stem > that on shoots, which confirmed that soil environment was suit to forming tumors. According to the size of resultant tumors, the following relationship could be obtained: Galls induced by 3-1 > that by Zl-1 > that by L3-1 > that by A4-0, which confirmed that the aggressiveness of 3-1 was strongest, and A4-0 was to the contrary.3. Effects of soil types on occurrence of crown gall The occurrence of crown gall on rootstocks planted in sandy soil was more quickly than those planted in other soil types. However, the disease incidence and the velocity of tumor development in clay soil were highest when occurrence of crown gall was in stable phase.484. Effects of crown gal I on vital ity of rootstocks The growth of shoot length and stem diameter of infected rootstocks was reduced in late phase of crown gall occurrence. In turn, the growth of shoots also played roles in occurrence of galls. The more quickly the shoots grew, the more quickly the tumors occurred. This disease also affected content of leafy chlorophyll and Pn of plants. As for a rootstock, the stronger resistance to crown gall it had, the less content of leafy chlorophyll and Pn decrease it would be forced in. Crown gall could promote root activity, which not resulted in growth increase of host, but in development increase of tumors.5. Effects of crown gal I on the contents and distributions of whole nitrogen and phosphorus in late growth and dormant period of rootstocks Consistently higher concentrations of N and P occurred in shoot tumors on pot cherry rootstocks compared to nontumorous shoot tissue. Tumor was one of the strongest growth center, which occurred on shoots could rob root system of P at first, together with other sites above soil, then take part in competition of P among sites above soil. Crown gall interfered with nitrogen back...
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