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Since 2007, serious damage to tomato from leaf mould caused by Passalora fulva has frequently been observed in commercial greenhouses in Gifu Prefecture, Japan. One of the factors relating to this damage was suspected to be a decrease in azoxystrobin sensitivity of the pathogen. Biological and molecular studies were conducted to characterize fungicide resistance. In in vitro sensitivity tests using mycelial homogenate placed on fungicide-amended medium, the minimum inhibitory concentrations (MIC) of azoxystrobin for mycelial growth of the isolates divided into two ranges, 0.031-0.5 mg L À1 and 8-32 mg L À1 . Isolates with MICs within the two ranges were considered as sensitive and resistant, respectively, to azoxystrobin because, in in vivo tests, the percentage protection conferred by this fungicide (100 mg a.i. L À1 ) against these isolates was 89.7-100% and 4.5-31.1%, respectively. Resistant isolates had a replacement of phenylalanine with leucine at codon 129 (F129L) in cytochrome b. Forty-five percent of the 271 isolates collected from 63 tomato greenhouses from 2007 to 2008 were resistant to azoxystrobin. In many greenhouses where the isolation frequency of resistant isolates was 80% or more, azoxystrobin had been used twice per crop for approximately 6 years. In 2012, 27% of the 405 isolates collected were resistant to azoxystrobin, and there was a marked difference in the frequency of occurrence of resistant isolates in the field populations between the three locations sampled. The occurrence of azoxystrobin-resistant P. fulva isolates (F129L mutants) inflicted considerable damage on greenhouse tomatoes.

Four isolates of hypovirulent binucleate Rhizoctonia (HBNR), G1, L2, W1, and W7 were used for control of Fusarium wilt of tomato (FWT) caused by Fusarium oxysporum f. sp. lycopersici (FOL). HBNR isolates could significantly reduce disease severity (foliar symptoms and discoloration inside the stem) among five experiments under single and double applications. Reduction of disease severity by HBNR isolates, however, differed depending on HBNR isolates and treatments. Of four isolates, isolate HBNR W7 could significantly and consistently reduce (P ϭ 0.05) disease severity. Application of HBNR isolates significantly reduced (P ϭ 0.01) the number of colonyforming units of FOL in stems and roots of tomato. Among the HBNR isolates, G1, W1, and W7 could significantly increase (P ϭ 0.05) fresh weight of the plants (stems and leaves). These results indicate that isolates of HBNR have a greater potential as biocontrol agents against FWT. This is the first report of biocontrol of FWT by HBNR under greenhouse conditions.

Muslim, A., Horinouchi, H., and Hyakumachi, M. 2003. Control of Fusarium crown and root rot of tomato with hypovirulent binucleate Rhizoctonia in soil and rock wool systems. Plant Dis. 87:739-747.Hypovirulent binucleate Rhizoctonia (HBNR) isolates L2, W1, W7, and Rhv7 were studied as potential antagonists of Fusarium crown and root rot of tomato (FCRR) caused by Fusarium oxysporum f. sp. radicis-lycopersici, in either soil or hydroponic rock wool systems. Reduction of FCRR on tomato by HBNR isolates was different depending on the isolate, days after inoculation of pathogen, and experiments. In the greenhouse soil system, HBNR isolates significantly (P = 0.01) reduced vascular discoloration and discoloration of total roots systems by 90 to 100% and by 73 to 89%, respectively, in three experiments. Under field soil conditions, HBNR W1 provided significant (P = 0.05) reduction of vascular discoloration by 71%. In the rock wool system, all HBNR isolates except L2 in experiment 1 significantly reduced (P = 0.05) vascular discoloration by 18 to 100% in four experiments. Plants treated with all HBNR isolates had foliar symptoms reduced by 41 to 100% in four experiments under the rock wool system. Application of HBNR also resulted in increases of marketable and total yields of tomatoes as much as 70 and 73%, respectively, over the untreated plants. The number of colony forming units of F. oxysporum f. sp. radicis-lycopersici per gram fresh weight of roots and stems was significantly reduced (P = 0.05) in plants treated with HBNR in both soil and rock wool systems. HBNR was re-isolated at a high frequency from roots grown inside paper pots containing soil infested with HBNR, but rarely isolated from the roots grown in soil infested with only F. oxysporum f. sp. radicis-lycopersici outside the paper pots. HBNR was not re-isolated from the tomato stems. Stem extracts from HBNR-treated and pathogen-challenged plants in the rock wool system inhibited germination and production of budding cells of F. oxysporum f. sp. radicis-lycopersici. Additional keyword: Lycopersicon esculentumCorresponding author: M. Hyakumachi