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Use of chrysanthemum plantlets grown in vitro to test cultivar susceptibility to white rust, Puccini

Use of chrysanthemum plantlets grown in vitro to test cultivar susceptibility to white rust, Puccini

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Short Communication Use of chrysanthemum plantlets grown in vitro to test cultivar susceptibility to white rust, Puccinia horiana P. Hennings Y . T AKATSU 1 , K . O HISHI 2 , Y . T OMITA , M . H AYASHI 3 , M . N AKAJIMA 1 and K . A KUTSU 4 1 Plant Biotechnology Institute, Ibaraki Agricultural Centre, Iwama, Nishi-Ibaraki 319-0292, Japan; 2 Ornamental Research Institute, Aichi Agricultural Centre, Nagakute, Aichi 480-1193, Japan; 3 Horticultural Institute, Ibaraki Agricultural Centre, Iwama Nishi-Ibaraki 319-0292, Japan; 4 Ibaraki University, Ami Inashiki 300-0393, Japan. With 2 figures Received March 15, 2000/Accepted June 28, 2000 Communicated by G. Forkmann Abstract An e cient incubation and inoculation system for white rust was estab- lished using plantlets of chrysanthemum growing in vitro . The internal conditions of a culture vessel (plant box) were maintained at a humidity of 90–100% and an optimum temperature of 20–25 ± C, which are suita- ble conditions to germinate teliospores and basidiospores of the patho- gen. Telia were maintained continuously on plants in the plant box and were used as an inoculum for infection experiments throughout the year, allowing di erences in susceptibility to white rust among chry- santhemum cultivars to be detected. Susceptibility to white rust in the plant-box evaluation showed a good correlation with the rating of spor- ulation on plants grown in a greenhouse. The method described here is a simple, space-saving inoculation system to evaluate the susceptibility of chrysanthemums to white rust. Key words: Dendranthema grandiflorum Puccinia horiana rust susceptibility — inoculation Chrysanthemum is a major cut flower worldwide, and its many characteristics have been improved through conventional breeding programmes. White rust, Puccinia horiana P. Hen- nings, is the most serious fungal disease in chrysanthemums, as it is widespread and causes severe economic damage by redu- cing the flower quality. This disease peaks in the production fields from spring to early summer, and in the autumn in Japan (Yamaguchi 1981, Morita 1988). Although the disease has been e ectively controlled by oxycarboxin since 1972, isolates of P . horiana tolerant to the fungicide have been discovered (Abiko et al. 1975) and have spread in the production fields (Iijima 1976). Although De Jong and Rademaker (1986) sug- gested that the resistance of chrysanthemums to white rust is usually controlled by a single dominant gene, only a few culti- vars show resistance to this disease in Japan (Yamaguchi 1981). Since white rust is an obligate parasite, telia need to be maintained on plants as inocula for inoculation tests. Field trials require considerable land and time in order to complete evaluations. Yamaguchi (1981) reported an improved protocol for selecting strains of chrysanthemum resistant to white rust
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