PHYTOPHTHORA PARASITICA INOCULATION AND INTENSITY OF VESICULAR‐ARBUSCULAR MYCORRHIZAE IN CITRUS

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Abstract
SUMMARY: Shoot weights, root weights, and percentages of healthy roots of mycorrhizal (Glomus fasciculatus) sweet orange inoculated with Phytophthora parasitica (20 or 50 chlamydospores g‐1 soil) were greater than those of non‐mycorrhizal seedlings at either inoculum density. However, the growth response to mycorrhizal infection was reduced 23 and 58% by inoculation with 20 and 50 chlamydospores per g soil, respectively. Mycorrhizal infection was not reduced by P. parasitica at 20 chlamydospores per g soil, but was reduced 72% in seedlings inoculated with 50 chlamydospores per g soil. The latter also reduced the phosphorus content of the leaves. Tests with seven mycorrhizal fungi on two citrus rootstocks showed that different VA infections might confer variable tolerance or resistance to P. parasitica. Two fungi, Glomus mosseae and Gigaspora margarita, not isolated from nor as nutritionally efficient as others on citrus, conferred tolerance or resistance.