Study On Broad Bean Root Rot In The Cold And Humid Regions Of Gansu Province, China

1. Isolates of Fusarium solani,F. semitectum,F. dimerum, Glioeladium catenulatum , G.roseum, Alternaria alternata were obtained from field samples of broad bean (Vicia faba L.) with typical root rot symptoms. The major symptoms of the disease were described in detail: the infected plants grow more slowly, smaller on the size and leaves turn to yellow; the leaves on the lower part of plant pointed black and show dry black spots of variable size. In the case of severe incidence, the whole leaves turn to black and scorch; the tap-root and root cervical of underground parts turn to dark and shrink in size. Among species, Fusarium spp. was widely spread and it is accounted for the highest infection rate of 51.52 %, while Glioeladium sp. and Alternaria sp. are only accounted for 30.30 % and 18.18 %, respectively.2. The pathogenicity was tested using the artificially infested pot and culture plate method. All isolates were pathogenic to Lincan 7, a variety of broad bean. The isolates of F. solani1-18, F. semitectum1-4, F. dimerum1-2, A. alternata 1-7 showed high pathogenic; F. semitectum 5-8 and 10, F. dimerum 3-5 and 7; G .catenulatum1-5, G.roseum1-3, A. alternata8-10 showed medium pathogenic; F. semitectum 9, F. dimerum 6, G .catenulatum6-11, G.roseum4-9, A. alternata11-12 showed low pathogenic.3. Resistance of the broad bean varieties to the root-rot disease was evaluated. The results demonstrated that the eight broad bean varieties showed variable level of resistance to root rot disease. Qinghai12 was highly resistant, Qinghai11, Lincan8 and Lincan2 were medium resistant. Lincan5 was medium susceptible, and Lincan7 was high susceptible to the disease.4. Evaluated the efficiency of the fungicides on controlling the root-rot disease of the broad bean. The result indicated that 25% Azoxystrobin, 70% Topsin-M, 65% Mancozeb and 50% Carbendazim showed the better control effect. The (mean effective concentration)EC₅₀ of Carbendazim, Mancozeb, Topsin-M, Azoxystrobin for F. solani were 10.14022 mg/L, 13.64255 mg/L, 14.27054 mg/L, 22.66827 mg/L ,respectively. The correlation coefficient of four fungicides was over 0.9 (p value), and the positive correlation were found between the pharmaceutical concentration and the disease inhibition.