Screening tobacco germplasm for resistance to diseases affecting transplant production

Abstract

Rhizoctonia solani causes stem rot and target spot of greenhouse-produced tobacco seedlings. No fungicides are registered for control of these diseases, so sanitation is the primary disease management strategy. Seedling resistance to R. solani has not been characterized in current tobacco germplasm. The objective of this study was to screen seedlings of a diverse array of accessions, including several classes of tobacco cultivars and related Nicotiana species for resistance to a stem rot (AG-4) and a target spot isolate (AG-3) of R. solani. Further studies were conducted to determine if the resistance identified is heritable. Experiments were conducted in environmentally controlled growth chambers at the NCSU phytotron. Tobacco seedlings were grown in polystyrene trays floating on a nutrient solution to replicate greenhouse growth conditions. Approximately two weeks after germination, rice grains colonized by R. solani were placed on the surface of the growth medium to infest the medium. Symptoms, including death, stem lesions, and target spot lesions, were observed for 42 days after infesting the soil for stem rot and 56 days for target spot. Data were analyzed using a GLM procedure in SAS (SAS Institute, Cary, NC). Significant differences were observed among the accessions in level of resistance to stem rot and target spot. Disease incidence ranged from 12.5 to 100% for stem rot and 6.2 to 97.9% for target spot. This wide range of disease incidence observed among accessions for both diseases indicates that useful levels of resistance may exist to both diseases and may be useful in future breeding efforts.