Arbuscular mycorrhizal fungi (AMF) actively colonize plant roots and thus enhance plant growth through different mechanisms. In the present study, trifoliate orange (Poncirus trifoliata) seedlings inoculated with Diversispora versiformis were subjected to 0 and 0.2 mmol/L sodium nitroprusside (SNP, a nitric oxide donor) treatments. After eight weeks, exogenous SNP considerably increased root mycorrhizal colonization by 25%, showing a positive stimulating effect of NO on mycorrhizal formation. Mycorrhizal inoculation significantly increased plant growth performance (height, stem diameter, leaf number and shoot and root dry weight) and root traits (length, projected area, surface area, volume and number of 2nd and 3rd order lateral roots) than non-mycorrhizal treatment and NO (exogenous SNP treatment) heavily strengthened the mycorrhizal effects. Moreover, NO and mycorrhization induced more fine root (0-0.5 cm) formation. There was an opposite changed trend in root sucrose and leaf and root glucose contents by SNP in AMF versus non-AMF seedlings. All these results implied that NO plays important roles in mycorrhizal formation and development and also accelerates mycorrhizal effects on plant growth and root development of trifoliate orange.
China is one of the largest citrus producers in Asia, where Phytophthora parasitica infection has become the major
threat in sustaining long term citrus production. The proposed study examined the effects of P. parasitica on Citrus junos,
C. limon, C. tangerina and Poncirus trifoliata to evaluate the resisted rootstock to Phytophthora root rot. P. parasitica
infection notably decreased plant growth, root morphology and activities of pathogenesis-related proteins (PRs) in
C. limon and C. tangerina. Root β-1,3-glucanase, chitinase and phenylalanine ammonialyase activities significantly
increased in C. junos and P. trifoliata after infection with P. parasitica. P. parasitica infection notably decreased root
salicylic acid concentrations in C. limon, C. tangerina and P. trifoliata, while increasing it in C. junos. An opposite
trend was observed in root jasmonic acid levels after infection with P. parasitica, relative to root salicylic acid. Root
nitric oxide and calmodulin concentrations were significantly increased in P. parasitica-infected C. junos, C. tangerina
and P. trifoliata, while C. limon exhibited a decrease. These results demonstrated that citrus species like C. junos and P.
trifoliata displayed a much higher resistance to Phytophthora-induced root rot, and C. limon and C. tangerina showed
a comparatively lower degree of resistance.