Influence of planting seed tubers with gangrene(Phoma foveata) and of neighbouring healthy, diseased and missing plants on the yield and size of potatoes

SUMMARYPotato seed tubers infected or not infected with gangrene (Phoma foveata) were planted at Rothatnsted in 1987 to measure the effect of the disease and of neighbouring plants on yield. The experimental design was constructed so that the effect on growth of six adjacent plants (two nearest neighbours in each direction within rows and one nearest neighbour in each direction across rows) could be estimated for each plant. Total yield, ware (> 150 g) yield and tuber number from individual plants were affected most by the disease but also, in decreasing importance, by the two plants on either side within the same row (first neighbours), the two plants adjacent to the first neighbours (second neighbours) and the two adjacent plants in the rows on either side. Yield and tuber numbers increased as the different combinations of neighbouring plants contained increasing proportions of plants from diseased seed and missing plants; plants compensated for decreasing competition. Tuber size distributions showed that numbers of ware tubers decreased with increasing competition whereas numbers of small tubers were less affected. The fitted model was used to predict yields from crops planted with different proportions of diseased or missing seed tubers.

The effect of disinfectants on fungal diseases of potato and vegetables

Treatments of one and ten minutes were too short for all disinfectants against fungi in peat and plant debris. The best effect was achieved with a treatment of 90 min. Sodium hypochlorite (NaOCl) was the most effective and Korsolin and Virkon S were the least effective in the control of Fusarium culmorum and F. oxysporum. Virkon S (2%) was the most effective against Mycocentrospora acerina and Phoma foveata. Soaking for 15 min and 60 min in a disinfection suspension eradicated Botrytis cinerea and P. foveata totally from the contaminated plastic pots. Fusarium spp. were the most difficult fungi to disinfect and these were best controlled with formaline, lobac P, Menno-Ter-forte and sodium hypochlorite. lobac P, formaline, Menno-Ter-forte, Taloset and Virkon S were the most effective disinfectants against club rot (Plasmodiophora hrassicae). Washing under running water was not sufficient to eradicate club rot. Against Rhizoctonia -induced damping off of cauliflower the most effective disinfectants were formaline and Virkon S.

The effect of disinfectants on fungi in pure culture and on different surface materials

The effect of eight disinfectants was tested on 11 fungi. The concentrations recommended by the manufacturers were mostly used in the present trials. Five and 15 min treatment times were too short for most preparations. The best efficacy was achieved at 60 min treatment lime. In pure cultures, all disinfectants tested were most effective against Pythium sp. Overall, the most effective preparation was Desinfektol EL which was effective against all fungi tested at 5 min treatment time. Wood surfaces were more difficult to disinfest than metal and plastic surfaces. Rhizoctonia solani and Verticillium dahliae were highly susceptible only to Desinfektol EL, and NaOCl controlled Pythium sp. and Botrytis cinerea. None of the preparations controlled completely the other test fungi. On metal surfaces the most effective disinfectants were Desinfektol EL and NaOCl; moderately effective were lobac P and Menno-Ter-forte. Korsolin was the least effective preparation. Verticillium dahliae and Phomopsis sderotioides were difficult to kill. The easiest fungi to disinfest were Pythium sp., Rhizoctonia solani, B. cinerea, Fusarium avenaceum, F. culmorum, F. oxysporum, Mycocentrospora acerina and Phoma foveata. Fungi grown on plastic surfaces were best controlled with Desinfektol EL. Also NaOCl, Menno-Ter-forte and lobac P were effective. Korsolin was the least effective preparation. The easiest fungi to eradicate were Pythium sp. and R. solani. The most difficult fungi were V. dahliae and P. sderotioides. Both peat and clay deteriorated the efficacy of the disinfectants except for Desinfektol EL.