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Evaluation of Tomato Cultivars for Susceptibility to Rhizoctonia Damping-off Danésha Seth and Bonnie H. Ownley Interpretive Summary Ten tomato cultivars that are grown commercially in East Tennessee were evaluated for susceptibility to damping-off caused by Rhizoctonia solani. The cultivars included ‘Carolina Gold’, ‘Celebrity’, ‘Hybrid 882’, ‘Mountain Belle’, ‘Mountain Delight’, ‘Mountain Fresh’, ‘Mountain Pride’, ‘Mountain Spring’, ‘Mountain Supreme’, and ‘Sunpride’. The cultivars ‘Hybrid 882’ and ‘Mountain Belle’ had significantly higher percent seedling survival and lower disease ratings in potting mix infested with Rhizoctonia solani than any of the cultivars tested. In contrast, ‘Celebrity’ consistently had the lowest survival rates and highest disease ratings. Introduction Damping-off of seedlings is the most common disease caused by the fungal pathogen Rhizoctonia solani. Planting disease-resistant or less susceptible cultivars is a cost-effective method of lessening the impact of R. solani, however there is no information available on the susceptibility of most commercial tomato cultivars to Rhizoctonia damping-off. The objective of this study was to evaluate 10 commercial tomato cultivars for susceptibility to damping-off caused by R. solani. Materials and Methods Inoculum of R. solani was produced on 3% cornmeal sand (9 g cornmeal and 300 g quartz sand) (CMS) substrate. The inoculum was incubated at 28°C for 12 days prior to addition into planting medium. Seeds of ten tomato cultivars (‘Carolina Gold’, ‘Celebrity’, ‘Hybrid 882’, ‘Mountain Belle’, ‘Mountain Delight’, ‘Mountain Fresh’, ‘Mountain Pride’, ‘Mountain Spring’, ‘Mountain Supreme’, and ‘Sunpride’) were planted in either Pro-Mix potting medium with no amendment (control) or amended with CMS inoculum of R. solani at 4% weight/weight. Pots were placed in a growth chamber at 28ºC and received 65 ml of deionized water once every two to three days. The experiment was designed as a 2 ´ 10 factorial in a randomized complete block with 2 levels of R. solani inoculum and 10 tomato cultivars. There were 5 observations (seedlings) per replicate and 5 replicates of each treatment. Emergence data were recorded at 5, 10, and 19 days after planting (DAP). At 25 DAP, plants were evaluated for disease on a scale of 1 to 4 where 1 = no disease/healthy seedling; 2 = diseased seedling; 3 = post-emergence damped-off/dead seedling; and 4 = pre-emergence damped-off/dead seedling. Results and Discussion Effect of inoculum level on seedling survival and disease rating. The effect of inoculum level on percent survival of tomato seedlings was significant at 10 and 19 DAP, and on disease rating at 25 DAP (Table 1). As expected, the uninfested control had significantly higher survival than the plants exposed to CMS inoculum of R. solani. The disease rating was significantly lower for plants with 0% Rhizoctonia inoculum than with 4% (Table 1). The low level of disease in the mix without R. solani was probably due to low levels of other pathogens, such as Pythium spp., that occur naturally in peat-based potting medium. Table 1. Effect of inoculum level on percent survival of tomato seedlings at 5, 10, and 19 days after planting (DAP), and on disease rating at 25 DAP. Rhizoctonia solani was added before planting.
a Values include all cultivars.b Disease rating was measured on a scale of 1 to 4 with 1 = no disease/healthy seedling, 2 = diseased seedling, 3 = post-emergence damped-off/dead seedling, and 4 = pre-emergence damped-off/dead seedling.c Within each column, values followed by the same letter or no letter are not significantly different according to a F-LSD at P = 0.05.Effect of cultivar on seedling survival and disease rating. There were significant differences between cultivars in percent survival of seedlings (Table 2). ‘Mountain Belle’ had the highest survival rates at 5, 10, and 19 DAP. However, at 10 DAP, the percent survival for ‘Hybrid 882’ and ‘Mountain Fresh’ were not statistically different from ‘Mountain Belle’. At 19 DAP ‘Mountain Belle’ and ‘Hybrid 882’ had the highest survival rates, while ‘Celebrity’ had the lowest survival. At 25 DAP, the cultivars with the lowest disease rating were ‘Hybrid 882’, ‘Mountain Belle’, ‘Mountain Delight’, and ‘Mountain Fresh’, while ‘Celebrity’ had the highest disease rating (Table 2). Table 2. Effect of cultivar on percent survival of tomato seedlings at 5, 10, and 19 days after planting (DAP), and on disease rating at 25 DAP. Rhizoctonia solani was added before planting.
a Disease rating was measured on a scale of 1 to 4 where 1 = no disease/healthy seedling, 2 = diseased seedling, 3 = post-emergence damped-off/dead seedling, and 4 = pre-emergence damped-off/dead seedling.b Values include plants in mix with and without R. solani.c Within each column, values followed by the same letter are not significantly different according to a F-LSD at P = 0.05.
Effect of inoculum level and cultivar on seedling survival. The interaction of inoculum level and cultivar had a significant effect on seedling survival at 19 DAP (Table 3). There were few differences between cultivars in the uninfested mix. Survival of ‘Carolina Gold’, ‘Hybrid 882’, ‘Mountain Belle’, ‘Mountain Delight’, ‘Mountain Fresh’, ‘Mountain Pride’, ‘Mountain Supreme’, and ‘Sunpride’ were all above 76%, and not statistically different. ‘Celebrity’ and ‘Mountain Spring’ had the lowest survival in uninfested mix with 72 and 68%, respectively. With the R. solani-infested potting mix, the cultivars with the highest survival were ‘Mountain Belle’ and ‘Hybrid 882’ with 88 and 72%, respectively. ‘Celebrity’ had the lowest survival with 12%. Table 3. Effect of inoculum level and cultivar on percent survival of tomato seedlings at 19 days after planting (DAP). Rhizoctonia solani was added before planting.
a Within each column, values followed by the same letter are not significantly different according to a F-LSD at P = 0.05.Effect of the interaction between inoculum level and cultivar on disease rating. The interaction of inoculum level and cultivar was significant for disease rating at 25 DAP (Table 4). ‘Celebrity’ had the highest disease rating in the uninfested mix due to indigenous populations of pathogens in the peat mix. In the R. solani-infested mix ‘Carolina Gold’, ‘Hybrid 882’, and ‘Mountain Belle’ had the lowest disease rating, while ‘Celebrity’ had the highest. Table 4. Effect of inoculum level and cultivar on disease ratinga of tomato seedlings at 25 days after planting (DAP). Rhizoctonia solani was added before planting.
a Disease rating was measured on a scale of 1 to 4 where 1 = no disease/healthy seedling; 2 = diseased seedling; 3 = post-emergence damped-off/dead seedling; and 4 = pre-emergence damped-off/dead seedling.b Values followed by the same letter are not significantly different according to a F-LSD at P = 0.10.Genetic resistance to various fungal pathogens such as Verticillium dahliae, Fusarium oxysporum f. sp. lycopersici, and Alternaria solani, is known for most of these cultivars, however, there was no information available on their susceptibility to R. solani. Although none of the cultivars could be considered resistant to R. solani, there were significant differences in the degree of susceptibility. The cultivar ‘Celebrity’ was the most susceptible to Rhizoctonia damping-off. In contrast, ‘Mountain Belle’ and ‘Hybrid 882’ were the least susceptible, suggesting that these would be good choices in environments with high disease pressure from R. solani. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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