Da. Neher et al., RELATIONSHIPS AMONG PHYTOPHTHORA ROOT-ROT DEVELOPMENT, P-PARASITICA POPULATIONS IN SOIL, AND YIELD OF TOMATOES UNDER COMMERCIAL FIELD CONDITIONS, Plant disease, 77(11), 1993, pp. 1106-1111
In 1989, 1990, and 1991, 6-m-long row segments of tomato cultivar FM62
03 were planted adjacent to 10 other cultivars in 12 commercial fields
(within 28 km of Davis, California) with histories of Phytophthora ro
ot rot. Populations of Phytophthora parasitica at planting ranged from
0 to 3.7 cfu/g of dry soil as determined by dilution plating, and 2-1
00% of tomato leaf disks used as bait in a soil assay were colonized.
Populations increased and fluctuated during the growing season. Aboveg
round symptoms of disease developed at similar phenological stages, as
sociated with the setting and maturation of fruit, in all cultivars, a
nd the final disease incidence and severity ranged from zero to the ma
ximum possible. Harvestable fruit yield decreased linearly with increa
sed symptom severity for all cultivars and years. Final disease severi
ty was correlated positively with pathogen populations detected by bai
ting at planting and with increasing soil clay content, and negatively
with soil sand content and time after planting at which symptoms firs
t became visible. There were no clear associations between pathogen po
pulations and soil temperature or moisture. The results suggest that t
here is little difference among processing tomato cultivars in toleran
ce or yield potential under given levels of disease pressure.