Strawberry Cultivar Screen for 

 Tolerance to Black Root Rot 

 Disease Complex 



David Marchant, Daniel R. Cooley, Sonia G. Schloeman, and 



William J. Manning 



Department of Plant Pathology, University of Massachusetts 



Black root rot is a disease complex of strawberry 

 that reduces vigor of the root system, resulting in 

 decreased productivity and longevity of a straw- 

 berry planting. Disease pressure can reach levels 

 where new plantings can be lost totally. Common 

 symptoms are blackening of the structural roots and 

 death of feeder roots. The disease complex does not 

 have a specific cause, but usually results from inter- 

 action of pathogenic fungi, root-lesion nematodes, 

 and stressful environmental conditions. Binucleate 

 Rhizoctonia spp. have been demonstrated as com- 

 mon causal fungi, as well as the nematode Praty- 

 lenchus penetrans (Husain and McKeen, 1963; 



Martin, 1988; Townshend, 1962). The disease may 

 be confused with red stele, a disease caused by the 

 fungus Phytophthora. Black root rot lesions on 

 roots are typically brownish to black in color, and 

 they destroy the cortex, or outer layers, of the root. 

 While early red stele may blacken root tips, fully de- 

 veloped red stele has the typical brick red stele in the 

 center of infected roots. Red stele generally occurs 

 on wet sites, while black root rot may be less likely on 

 a wet site. Cultivar sensitivity for red stele is well- 

 understood; however, little work has been done on 

 cultivar variation in sensitivity to black root rot. 

 In 1990, a cultivar screening test for resistance 



20 



Fruit Notes, Winter, 1991 



