Bio-control of the soil-borne pathogen Rhizoctonia solani of radish (Raphanus sativus L.) by Trichoderma species

The soil-borne fungus Rhizoctonia solani is an important pathogen of Brassicae crops worldwide, including red vegetable radish (Raphanus sativus). However, the impact of R. solani on New Zealand radish production has not been evaluated. This project examined the effects of the pathogen on red radish production, from seedling emergence and establishment through to final crop yield. R. solani infections occurred on different plant parts, causing seed rot, brownish lesions on foliage, damping off, stunted stems and root rot. The damage caused by R. solani caused reduction in seedling emergence and plant growth. The potential of New Zealand strains of different species of the bio-control fungus Trichoderma for controlling R. solani was investigated, both in vitro and in vivo. Strains of Trichoderma (T. atroviride, T. asperellum, T. hamatum, T. harzianum, T. spirale, T. polysporum, T. viride and T. virens) were obtained from the Bio-Protection Research Centre collection and tested against the pathogen in glasshouse studies. The four most effective Trichoderma strains (LU132: T. atroviride, LU785: T. hamatum, LU1358: T. polysporum and LU1347: T. harzianum) were formulated into seed coatings. The disease control performance of the seed coatings was compared with that of thiram fungicide seed treatment, currently used for radish, using soil naturally infected with R. solani. The four seed-treatment applications of Trichoderma strains in glasshouse experiments significantly increased the fresh shoot weights and total leaf areas per pot, as compared to the R. solani control. In the field experiment, the radish yield from the untreated control was 3.9 t/ha for Red Round and 4.6 t/ha for Fresh Breakfast, around half the yield of 7 – 10 t/ha normally obtained commercially. Yield for the thiram seed treatment did not differ from the control. However, compared to the untreated control, the LU785 seed treatment increased yield by 96% for both varieties, while LU132 and LU1358 also significantly increased yield (by 83% and 60% respectively) in French Breakfast. Trichoderma seed treatment would be beneficial for radish production in New Zealand.