| Root-invading fungi of lucerne (Medicago saliva) and winter wheat (Triticum aestivum)were studied under the forage legume-cereals rotation systems in the Loess Plateau of eastern Gansu province, China. Roots of wheat and lucerne were sampled at spring jointing (spring branching) , flowering, maturity and seedling or regrowth stage in 2002. Fungi were isolated from lucerne rootlet and wheat root system. Pathogenicity of these root-invading fungi to lucerne and wheat were determined in the laboratory. In addition, effects of fertilizer and fallow period on root-invading fungi of wheat were investigated.The results showed that 27 fungal species were isolated and identified from the field plots. Of which 26 fungi were isolated from wheat root and 23 fungi isolated from lucerne rootlet. Among the fungi isolated 22 species were shared by lucerne and wheat. They were Altemaria alternata, Cladosporium herbarum, Cylindrocarpon destructiuns, Fusarium acuminatum, F. avenaceum, F. decent, F. oxysporum, F. semitectum, F. solan j, Fusarium sp., Fusicoccum aesculi, Giiocladium sp., G. roseun, Mucor sp., Penicillium sp., Papulaspora sp., Phoma medicagmis, Rhizoctonia sp., Selinia sp., Staphylotrichum sp., Stemphylium botryosum and Verticillium sp.. Four fungi including Bipolaris sorokiniana, Melasmia sp., Periconia sp. and Phytophthora sp. were only found in wheat root, whereas only one fungal species isolated from lucerne rootlet and not isolated from wheat i.e. Mycotypha sp.However, the major root-invading fungi in lucerne and wheat were differed. The most common fungal species from lucerne, in order of decrease frequency of isolation, were F. oxvsporum (17.0%), Selinia sp. (15.4%), P. medicaginis (9.5%), F. solani (6.7%) and Cy. Destructuns (6.6%). The five most common fungi isolated form wheat were Periconia sp.(l5.0%), Populospora sp. (12.1%), C. herbarum (5.4%), Rhizoctonia sp. (4.0%) and F. oxysporum (3.9%). The total percentage of fungal isolation obtained from lucerne was higher than mat from wheat.As lucerne growing from Spring to Autumn, the percentage of fungal isolation from rootlet were increased. The percentage of fungal isolation at early growth stage in Spring was 49.1%, which was significantly lower than that at maturity (p<0.05) . However, rootlet inviading fungi incidence of lucerne at flowering, maturity and at regrowth stage after 3rd cut was 70.3%, 8J.9% and 76.3%, respectively. There were no significantly differences among these percentages (p>0.05) .Incidence of fungal isolation from wheat at jointing, flowering and maturity was 43.1%, 71.0% and 94.8%, respectively, And was 30.9% at seedling stage in Autumn after sowing. All of these were differed significantly between one and another (p<0.05).The pathogenicity test results showed that all the fungi tested under the laboratory conditions had pathogenic effects to lucerne and wheat in some extent. In general, all the fungi tested have more severe pathogenicity to seed and seedling of lucerne than to that of wheat.Accorging to integrated accessment of measurement including relative germination, decayed seed percentage, relative shoot length, relative root length and disease index, fungi isolated from lucerne rootlet including Selinia sp., F. oxysporum, F. solani, F. decem, S. botrysum, C. herbarum, F. avenaceum and P. medicaginis were pathogenic to lucerne seed and seedling. Compared to the no inoculated control, decayed seed percentages in inoculated treatments were 21.0%~32.0%,relative germination was decreased by 23.0%~57.0%, disease index was 63.8?9.5. Whereasonly F. oxysporum and Stemphylium botrysum showed pathogenicity to wheat seedling, disease index was 89.5 and 63.8, respectively. The relative germination was decreased by 31.0% by F. oxysporum.Fungi isolated from wheat including F. acuminatum, F. oxysporum, F. avenaceum, F. solani, Fusarium sp., Periconia sp. and Papulospora sp. showed pathogenicity to seed and seedling of lucerne. Compared to the no inoculated control, the inoculation treatements had 20.0%~4...
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