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Summary: Leaf mould, caused by Fulvia fulva, is a devastating disease of tomato plants. In many commercial tomato cultivars, resistance to this disease is governed by the Cf‐9 locus, which encodes five paralogous receptor‐like proteins. Two of these proteins confer resistance: Cf‐9C recognises the previously identified F. fulva effector Avr9 and provides resistance during all plant growth stages, while Cf‐9B recognises the yet‐unidentified F. fulva effector Avr9B and provides mature plant resistance only. In recent years, F. fulva strains have emerged that can overcome the Cf‐9 locus, with Cf‐9C circumvented through Avr9 deletion. To understand how Cf‐9B is circumvented, we set out to identify Avr9B.Comparative genomics, transient expression assays and gene complementation experiments were used to identify Avr9B, while gene sequencing was used to assess Avr9B allelic variation across a world‐wide strain collection.A strict correlation between Avr9 deletion and resistance‐breaking mutations in Avr9B was observed in strains recently collected from Cf‐9 cultivars, whereas Avr9 deletion but no mutations in Avr9B were observed in older strains.This research showcases how F. fulva has evolved to sequentially break down the Cf‐9 locus and stresses the urgent need for commercial tomato cultivars that carry novel, stacked resistance genes active against this pathogen. [ABSTRACT FROM AUTHOR]

Leaf mold of tomato is caused by the biotrophic fungus Cladosporium fulvum which complies with the gene-for-gene system. The disease was first reported in Japan in the 1920s and has since been frequently observed. Initially only race 0 isolates were reported, but since the consecutive introduction of resistance genes Cf-2, Cf-4, Cf-5 and Cf-9 new races have evolved. Here we first determined the virulence spectrum of 133 C. fulvum isolates collected from 22 prefectures in Japan, and subsequently sequenced the avirulence (Avr) genes Avr2, Avr4, Avr4E, Avr5 and Avr9 to determine the molecular basis of overcoming Cf genes. Twelve races of C. fulvum with a different virulence spectrum were identified, of which races 9, 2.9, 4.9, 4.5.9 and 4.9.11 occur only in Japan. The Avr genes in many of these races contain unique mutations not observed in races identified elsewhere in the world including (i) frameshift mutations and (ii) transposon insertions in Avr2, (iii) point mutations in Avr4 and Avr4E, and (iv) deletions of Avr4E, Avr5 and Avr9. New races have developed by selection pressure imposed by consecutive introductions of Cf-2, Cf-4, Cf-5 and Cf-9 genes in commercially grown tomato cultivars. Our study shows that molecular variations to adapt to different Cf genes in an isolated C. fulvum population in Japan are novel but overall follow similar patterns as those observed in populations from other parts of the world. Implications for breeding of more durable C. fulvum resistant varieties are discussed.

The entomopathogenic fungus Akanthomyces muscarius strain IMI 268317, previously known as Lecanicilliummuscariumand Verticillium lecanii, is currently used as a microbial insecticide to protect tomatoes from serious leaf-inhabiting pests in greenhouses. However, its persistence on tomato leaves has been unidentified. Understanding the events and processes of phyllosphere colonisation by this strain should help in developing its practical applications. This study assessed the epiphytic abilities of this strain on tomato leaves in humid conditions, simulating closed greenhouse environments. Conidia applied on tomato leaflets strongly adhered 12 h after inoculation. The mucilage-like materials were found around the germinated conidia after 3 days after inoculation (dpi), which possibly strengthened the adhesion. A total of 15% of conidia germinated at 3 dpi, of which 2% formed typical conidium or an enlarged structure on germ-tube tips. Many conidia were produced on phialide tips that branched from elongated hyphae at 7 dpi; however, invasion into leaf tissue was not observed. On the leaflets, inoculated conidia suspensions of 1 × 105 and 1 × 106 conidia/mL, colony forming units increased 52.6 and 8.8 folds from 0 to 14 dpi, respectively. These results suggested that A. muscarius strain IMI 268317 has high epiphytic abilities on tomato leaflets in a humid condition. [ABSTRACT FROM AUTHOR]

Beauveria bassiana, known for its entomopathogenic characteristics, is the most widely used biocontrol agent against many insect pests and may also be active against soil-borne pathogens. It inhabits the surfaces or inner tissues of various plant species without causing any visible signs or symptoms. Here we show that B. bassiana strain GHA, the active ingredient of a commercial microbial insecticide, colonises tomato plants. GHA grew on intact leaf surfaces of tomato in high humidity, but never entered stomata. Viable hyphae and conidia were detected, and the population on inoculated leaves significantly increased until 14 days after inoculation. On tomato leaves, GHA conidiated normally via conidiophores and phialides, and also via microcycle conidiation (conidiophores and phialides form directly from germ tubes and produce conidia). Hyphae were also detected inside the rachis, even more frequently after plant surfaces were scarified. These results suggested that B. bassiana strain GHA can grow epiphytically and endophytically on tomato plants. [ABSTRACT FROM AUTHOR]